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SCCA Time Trials - Rules Suggestions from Vorshlag

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  • SCCA Time Trials - Rules Suggestions from Vorshlag

    SCCA TT Letter Post # 1: In this forum topic we will address the brand new ruleset that was released last week for the new SCCA National Time Trial series. We will point out what works best in the NASA TT rules and why. We will also point out what we like better about the proposed SCCA TT series and rules. This is not meant as a mean spirited attack on either series - the both have their pluses and minuses - but more of a look at where the Time Trial scene is in 2018.

    We built this car initially for SCCA STX class, but had much better success in NASA, Optima and GTA time trial classes

    We at Vorshlag have been racing in NASA Time Trials since 2006, SCCA Club Trials since 2014, Global Time Attack since 2012, and Optima series Time Trial events since 2011. We have also been racing in SCCA Solo since the late 1980s, and have run with many other groups in timed competition events across the country.

    At Vorshlag we are building about a dozen cars at any given time for NASA and/or SCCA competition use, including 4 shop owned cars

    We design and build suspension components that cover dozens of car models and also build race cars in our shop (above). We are not in the pocket of any racing group, are not restricted to one car type/marquee, do not harbor blind product brand loyalties, and do no limit ourselves to one form of racing over another... we just do as many Time Trial and autocross events we can find. All of this combined gives us a unique perspective.

    To us, the addition of a National SCCA Time Trial series only adds to the opportunities for us (and our customers) to race! Our hope is that the SCCA TT Board (and maybe NASA people, too) read our suggestions herein, reach out for any follow up questions, and that some of you reading this will also write similar letters to the SCCA TT Board email address above.

    We have tried to build some of our cars around both SCCA autocross and NASA TT class rules - which can be difficult

    Why do we care? Well it starts in our own back yard. The Texas Region SCCA Club Trials series (this north Texas SCCA region has 950+ members) has been running their time trial events for the last 4 years, and it has grown tremendously. Just in the North Texas area they have 7 stand-alone Club Trials events scheduled for 2018. They use SCCA autocross prep rules, grouped into 8 classes with some modifiers, which do not always port over well to a road course. They were one of the first SCCA regions to host a series of timed road course TT event with results, and lots of autocrossers jumped into this series to get their first taste of a road course with times. Many were hooked, including a lot of our HPDE customers here at Vorshlag. Competition breeds better customers: faster drivers need more of our parts to stay ahead of the competition, so we welcomed it. We have competed with Club Trials here every year since they started.

    Some of the 37 Club Trials competitors at the Texas Region SCCA event May 7, 2017

    The growth within the NASA series of HPDE/TT/W2W events did not go unnoticed by others. Due to what looks like dwindling numbers in SCCA Road Racing (nee "Club Racing") and some success with their "Track Night in America" events (their lower cost HPDE series run on weeknights, with little to no instruction), the SCCA added their new TT series in January 2018 at the National level.


    In mid January 2018 the SCCA announced their own National TT Championship and in February they announced the rules outline for the National TT Series linked above.

    This was an ambitious first stab at a series of 17 Time Trial classes spread over 4 "levels", and it had some brilliant changes that we liked - namely two entire categories of classes that are built around 200 treadwear tires (more on that below). I was excited enough by their pitch at an SCCA awards banquet in February that I went out and bought a brand new car to build for this series. I'm putting some skin in the game with some regional Club Trials sponsorship, too. (we already sponsor Texas Region SCCA autocross events as well as the NASA NOLA Time Trial series)

    But the new, undeveloped, SCCA TT ruleset also has some admitted flaws that they know need to be addressed before the trial period ends in the next few weeks and the TT Board locks down the rules for 2018. Instead of writing detailed private emails to a board of 4-5 people, we instead decided to post it here on our forum and then send the link to the new SCCA TT Board.

    SCCA TT Board: <- send your constructive rules comments here


    SCCA announced their first TT Championship scheduled for September 28-30th, 2018, at NCM. It will be a stand-alone event separate from SCCA's Road Racing Nationals (aka: Runoffs).

    One of two TT Grids at NASA Nationals, Miller Motorsport Park, 2013

    NASA held its first National Championship in 2006 but has never had a separate Time Trial Championship. Instead NASA runs TT and W2W groups on the same Championship race weekend. The SCCA seems to want to keep their W2W Road Race and Time Trial weekends and championships separate. This is neither good nor bad, just different. Financially it might be smarter to combine them (to save costs on track rental, emergency crews, and corner workers), but that's their business. I suspect there is substantial push back from the old school SCCA Club Racers - they want all the track time, no sharing of weekends with HPDE and Time Trial customers.

    NASA runs HPDE cars (left) in their own run groups, Time Trial cars in another, and W2W in their own race groups at the same track

    The issue with keeping HPDE + TT and W2W racing separate is that it could limit growth within an organization, with no obvious "feeder series". NASA Texas regularly has more TT competitors in a race weekend than all of the entrants in a local SCCA Club Race event, plus NASA has paying customers in HPDE and W2W too. NASA has used their established ladder series of HPDE, Time Trial, and W2W amateur racing series to grow - this ladder is unique in club level motorsports in this country, if not the world. They run all 3 types of activities at the same track on the same weekends. It seems a bit hectic with 3-4 HPDE groups, one TT group, and 2-4 W2W race groups, but it works.

    The owner of this white Mustang ran in NASA HPDE for 3 years, but was "scouted" and encouraged to move up by a Race Director

    The advantage of running your HPDE drivers at the same event as your TT and W2W racers (like NASA does) is that your HPDE beginners are exposed to W2W racers. HPDE and TT makes for an on-site pool of future talent that Race Directors can scout from. This cross-pollination of HPDE folks with racers does lead to a progression of drivers from HPDE -> TT -> W2W. This helps the HPDE drivers grow, with instructors mostly picked from the TT racers, and it moves people up the ladder. Which in turn grows the events and NASA membership. Our NASA Texas region didn't exist before the early 2000s and now has track events with 200+ participants regularly over 6-8 events per season. Just a data point to consider for the long term.


    We want the SCCA to make a successful TT series, hopefully by looking at what we are pointing out that has worked well in NASA TT. We also hope that NASA takes note of some of the better SCCA ideas and mimics them in their series as well (200 treadwear classes).

    We have built most of our cars around SCCA and NASA rules and "crossed over" for many years (EVO X: SCCA STU and NASA TTB)

    How could both series grow? Wouldn't the success of one TT series diminish the other? The reality is that most folks are not "loyal" to one series or club. It's common that once a car is prepped, the owner will take it to multiple series if the rules/classes are close enough. We have done it with cars built to SCCA rules that we also run in NASA Time Trial. BMWCCA has racers that run crossover classes with NASA (GTS is close to some CCA classes). PCA has some Spec series that NASA recognizes (Spec 944, Spec Boxtser), and the most famous of them all...

    Spec Miata runs in both SCCA and NASA with only minor differences (mostly tires). Lots of crossover potential!

    Spec Miata is the biggest example, and with only minior changes a SM racer can run in SCCA and NASA. This is how we have seen fields of 60-80+ Spec Miatas at events - they are drawing racers from two clubs. We feel that the closer that SCCA's and NASA's TT rules become, the easier it is for TT drivers to participate in both, encouraging more crossover participation.

    NASA TT comp license - $10 to renew each year, but it allows me to run with other TT groups

    We also hope that the two clubs recognize each others' TT licensing. NASA has a rigorous series of driver check rides to move up from their HPDE1-HPDE4, that have to be done by NASA Instructors. When they ask for a TT Check ride this is done by the TT Director, Chief Instructor, or TT driver they designate - then they can be checked off for their Time Trial license. Texas Region SCCA Club Trials series has recognized NASA TT licenses, and I have used my NASA TT comp license to move directly into GTA, into "Red" groups with HPDE clubs I have never run with, etc. I hope the National SCCA Time Trials series reciprocates.

    There is another crossover potential that BOTH the SCCA and NASA need to wake up and recognize - the amazing growth of 200 treadwear endurance road racing. A number of years ago racers started by building and racing $500 crap cans in Lemons, but with some commonality in rules a massive number of series and race teams have popped up. This spread to Chumpcar (now ChampCar), WRL, AER and more.

    These competing Endurance series have started to somewhat merge and stabilize their rules, so a team that builds for WRL can also run Champcar and the others. The theory of "A rising tide lifts all boats" applies to these series just like NASA and SCCA Time Trial could both grow with more attractive rule sets and some commonality/crossover.

    (Oh and by the way - NASA and SCCA both need to get off their butts and create a 200 treadwear endurance road racing series that is in-line with the others!)

    continued below
    Terry Fair -
    2018 GT / S550 Dev + 2013 FR-S / 86 Dev + 2011 GT / S197 Dev + C4 Corvette Dev
    EVO X Dev + 2007 Z06 / C6 Dev + BMW E46 Dev + C5 Corvette Dev

  • #2
    Re: SCCA Time Trials - Rules Suggestions from Vorshlag

    SCCA TT Letter Post # 2:

    NASA and SCCA have had different classing philosophies in both their autocross and Time Trail rules. Boiled down, SCCA classes on preparation level, and NASA classes almost exclusively on measured performance (power & weight). With the original NASA points system, you could focus on correcting the unique issues your car may have, or add more performance and jump up a class. With the SCCA, you have to do all the prep your class allows, and none of it that it doesn't. A good example of an issue with the SCCA rules would be an otherwise bone stock car with a cam swap. That would put it in one of their highest level classes. With NASA it would barely nudge it up the prep ladder.

    In this post we will look at NASA TT rules then start into a rules analysis by looking at some of the fundamental ways SCCA is trying to differentiate their 4 levels of TT levels and the 17 (for now) individual classes. We hope this review is welcomed by various racers as well as the SCCA and NASA staff members. All opinions written below are our's here at Vorshlag, but we talk to hundreds of racers every month who follow our various SCCA and NASA racing exploits and/or buy parts for these series. We share all of our shop race car builds to hopefully share lessons we have learned and to get people excited about autocross, time trial, and road racing in general. The more people that do these events is the more potential customers we have, of course.


    As a quick overview we wanted to show the NASA Time Trial classing theories and a basic outline of their rules. NASA Super Touring and Performance Touring W2W series have classes (ST/PT) that often run in the same race group. These 9 classes are made up of 3 different sets of rules (STU-ST4, ST5, and PTD-PTF), which can be a bit confusing. These 9 classes all crossover to identical NASA TT classes (so that W2W racers can jump into TT within NASA with no changes), but the TT classes do not have the W2W safety requirements.

    We compiled these 3 rule sets to show the 2018 NASA TT rule outlines below:

    TTU - Unlimited. No minimum weight, no max power. Just about anything goes!
    TT1 - Adjusted Power-to-Weight ratio of 6:1 or higher, no penalty for aero
    TT2 - Adjusted P-to-W ratio of 8:1 or higher, no penalty for aero
    TT3 - Adjusted P-to-W ratio of 10:1 or higher, penalties for non-stock aero
    TT4 - Adjusted P-to-W ratio of 12:1 or higher, penalties for non-stock aero + additional aero and tire restrictions
    TT5 - Adjusted P-to-W ratio of 14:1 or higher, penalties for non-stock aero + additional aero, suspension, and tire restrictions
    TTD - Modification Points based classed, aero & tire width by points, P-to-W ratio 14.25:1
    TTE - Modification Points based classed, aero & tire width by points, P-to-W ratio 16.50:1
    TTF - Modification Points based classed, aero & tire width by points, P-to-W ratio 19.50:1

    Left: Our TTC classed 92 Corvette set a few records. Right: Our TTD classed BMW 330 set a number of track records, too

    Up until few years ago there were fewer NASA "Number" and more "Letter" TT classes. The TT-Letter classes were more for dual purpose/lower prep builds that had a defined minimum weight for any given car. These classes let the racer spend classing "points" on mods that could juggle between suspension, engine, aero, braking, tire width, or tire compound upgrades as needed to address deficiencies in their choice of car.

    The "Bench racing" aspect of NASA TT-Letter classes was pretty fun and we built a number of shop and customer cars around TTA, TTB, TTC, TTD and TTE classes. The problem with "Letter" classes turned out to be chassis inequalities - some cars had a more favorable "base class" and a lower assigned minimum weight, and others had more points to play with. Sometimes a car got a "dyno reclass" that allowed a total ringer to be built. I am kind of glad these points-based classes are going away, because of these inequalities, but I'm not sure the new TT4 or TT5 classes are radically better (there are some unique restrictions in those two classes).

    Left: Our former EVO X we built for TTA set some records. Right: Our TT3 Mustang set a LOT of records

    TT-Letter classes have been dying slowly since 2013. That year the TT3 class was added in place of TTA, and we jumped in with our 2011 Mustang GT. The new "non-stock aero" penalties were first floated here. Gone were the "points" system at this P-to-W level - you no longer had to choose mods, and instead you could max out your P-to-W and suspension / tire performance. We ran our car "heavy", with ballast, to get a competition weight "bonus". This in turn let us run more power for the class.

    We took the "aero penalty" and maxed out the splitter and rear wing, then gradually moved from 315mm Kumho V710s in that first year up to 335mm front / 345mm rear Hoosier A7s in 2014. We set 14 different track records in TT3 with this strategy.

    The NASA TTB class (left) went away in 2017 to make way for TT4 (right), using the same P-to-W ratio

    In 2017 the TT4 class emerged to replace TTB, and it had even more aero restrictions for a TT-Number class - certain things were not allowed, even if you chose the "aero penalty". Canards, diffusers, and flat bottoms were banned, splitters were very limited, as were some other tire aspects (no more Hoosier "A" compounds). These TT4 aero rules were tightened up again for 2018. I'm not sure this was a step forward or backwards for the same P-to-W class, but "it is what it is".

    2018 saw TT5 class debut and the death of TTC, and again - some cars got slower moving from TTC to TT5 with the growing list of odd penalties and restrictions. They even have tire measuring fixtures now? No longer can we just look at the number on the sidewall. This is now my least favorite TT class concept so far, and I hope it goes away or changes greatly. TT5 sure feels like a step backwards for NASA, unfortunately.


    There are many things that attracted me, as an engineer and racer, to NASA Time Trial and Wheel to Wheel (W2W) competition classes back when I joined NASA and got my TT license in 2006. At the time I had been running PCA "Drivers Education" events (HPDE) since 1988, and had already been an SCCA member and autocrosser for the same 18 years. I was somewhat frustrated with what I felt like were imbalanced SCCA classes that overly favored certain car types - mainly super light ones. The rules always seemed to be 10-20 years behind the aftermarket and customer base, too.

    At this NASA event at ECR in 2008 we brought three Vorshlag shop cars built around NASA TT rules

    I always seemed to be racing in a variety of cars that sometimes didn't fit well into an SCCA class (see some of that variety above - an EVO X that was too heavy for the fixed tire limit of 245mm in STU, an E30 that was the wrong car for STS, and an E36 LS1 that was classed into X Prepared with cars that weighed 1000 pounds less, etc), and I wanted a little more freedom to play with tire widths, engine swaps, aero additions, and chassis weights.

    NASA was the perfect place for these freedoms - without SCCA's hundreds of pages of restrictions on engine mods, brake system changes, aero rules written in the 1960s, or obsessions with stock interior components. The SCCA categories also had a non-linear path upwards, where a certain mod might be allowed in a lower class but then not allowed in a higher one. It hasn't changed a whole lot since then, but there have been some improvements, namely with the introduction of the Street Touring and CAM categories. But now there are what seem to be 100+ classes.

    Virtually all of the LS V8 swapped cars we build are classed poorly in SCCA but easily classed in NASA

    NASA has 9 classes and you can always find a place to race. Want to swap an LS into your car for NASA TT? Fine - just dyno it, run across the scales, and there's a "TT-Number" class for you. Want to run non-DOT racing slicks? There's a modifier for that in most classes. How about adding a big wing or splitter? There's a modifier for that - aero additions are allowed in every class. Want to gut the interior, add a real cage, and lightweight racing seats? Not only do they allow it in every class, NASA encourages these safety upgrades (in TT where it is optional). Just weigh the car, pass tech, get your dyno sheet, and fill out a classing form that is mostly power-to-weight based.

    Virtually all NASA classes allow aero modifications, but often with a penalty to some major factor

    I have spent the last 12 years racing cars in NASA Time Trials, maximizing the Power-to-Weight limits of every car we have built for that series. In many cases we had to juggle aero additions against tire width changes, weight reductions against power additions, suspension upgrades against "class points" (which is sadly going away). It was a fun technical challenge and a delicate balancing act between "this vs that", with plenty of testing to prove out theories.

    Now I don't want to paint NASA as some perfect racing organization. There are still politics at play and rules stability has recently been fleeting. Our TT4 preparations made late in the 2017 season on the red BMW shown above were legal for ONE event, then they re-wrote the rules for 2018, after this new class' very first year, to exclude our wing placement, endplate size, and splitter length/measuring plane. And our wheels became illegal. So yes, NASA can be frustrating and the rules somewhat of a moving target, but this barrage of changes to TT4 after only one year was the exception, not the rule.


    Fly weight Miatas and Hondas seemed to have a dozen SCCA autocross classes they can dominate, but the heavier end of the sports car spectrum was often classed with some super light sports cars, and in autocross the Tire-to-Weight ratio is super critical, moreso than power-to-weight ratio (but that was still important). Even the lamest little subcompact car has a better Tire-to-Weight ratio than most 3000+ pound sports cars, and when you class them together the "slower" cars tend to do exceptionally well, until you allow for massive tire width additions or significant weight reductions.

    The SCCA Solo has had a half-hearted attempt at balancing classes by weight and in some higher categories (Street Modified, Prepared and Modified) they actually weigh cars - usually without the driver, which to me is a flaw (one driver might be 100 pounds racing in the same weight car as a 300 pound driver). Some of the new proposed SCCA TT classes DO finally factor in weights with drivers, so that is a step in the right direction.

    All NASA TT cars have this "weight and power" declaration decal on the side, for all competitors and tech officials to see

    Every NASA W2W and TT class other than "unlimited" has a weight check, often several times during an event - always with the driver on board. In a given TT weekend I might be asked to roll across the scales a half dozen times, which I am happy to do. It's impossible to add ballast as you go from a hot track to the tech shed for weighing - as right when we come off off track we are pointed straight to scales. If you weigh under your declared class minimum your times are thrown out for all sessions run since the previous good weigh-in. It happens from Regionals to Nationals, all classes, and its a great thing.

    to be continued...
    Last edited by Fair!; 09-21-2018, 12:39 PM.
    Terry Fair -
    2018 GT / S550 Dev + 2013 FR-S / 86 Dev + 2011 GT / S197 Dev + C4 Corvette Dev
    EVO X Dev + 2007 Z06 / C6 Dev + BMW E46 Dev + C5 Corvette Dev


    • #3
      Re: SCCA Time Trials - Rules Suggestions from Vorshlag

      SCCA TT Letter Post # 3: The SCCA TT board is rolling out their new rules package with 4 levels or categories of classes. Within the first 3 levels there are 5 classes each, and these are mostly broken down by power and weight. The measured weight of a car is easy to understand and verify, and for once the SCCA is doing actual car weighing with drivers in all of these classes - a huge step in the right direction!

      But how they measure horsepower, or actually how they infer power, is flawed. In this segment we will talk about the problems with using engine displacement as an indicator of actual horsepower.


      One of the biggest issues we can see within the 2018 SCCA TT rules are the "displacement to weight" formulas used in Level 1 to Level 3. Using the published displacement is an easy way to try to class cars, but it is ineffective and outdated. We will first try to explain with a few examples, then delve into some engine design history and technical explanations. If you fall asleep on paragraph 5, its OK.

      One misleading measure of "engine superiority" used by magazine writers and 12 year old boys is "Horsepower per liter" ratios. This tells you how efficient a given engine is, in some ways. HP-per-liter was something that the car mag writers used to write on and on about in the 1990s and 2000s, so much so that people fell in love with smaller displacement engines even when their actual performance was not all that thrilling. This is how we got the Fast and Furious franchise...

      This Ford 4.6L DOHC V8 makes 50% more power than the 5.0L OHV "302" Ford on the right

      These hp-per-liter ratios vary wildly among older engines vs modern ones, smaller vs larger displacements, just in Naturally Aspirated form (no power adders). A 1987 Mustang LX with a 5.0L OHV V8 made 215 hp in stock form. This pales in comparison to the 5.0L DOHC direct injected 12:1 compression V8 in the 2018 Mustang GT that makes 460 hp. Time and engineering advances have wreaked havoc on older hp-to-displacement formulas for many car models, when you compare old vs new.

      Left: The 1987-93 Mustang 5.0L is rated at 215 hp / tests at 180 whp. Right: 2018 Mustang 5.0L makes 460 hp / tests at 420 whp

      Even within the market, model year, and with the same total power numbers, these ratios vary. The 2018 Camaro SS makes 455 hp with 6.2L V8, compared to the 5.0L V8 in 2018 Mustang making 460 hp. This is skewed because GM GenV LT1 V8 engine has a single camshaft with 2 valves per cylinder vs 4 camshafts with cam phasing and 4 valves per cylinder in the Coyote 5.0L V8. They both have direct injection, similar compression ratios (11.5:1 for LT1), and similar engine weights... but if you look at "hp-per-liter" number the Coyote is a clear winner.

      This false displacement based formula ends up giving a lower competition weight to the 5.0L Mustang than the 6.2L Camaro. And it also lumps the latest generation Corvettes in the same class as virtually all Mustangs and Camaros (we will look at that in an extended "Examples" post, below).

      Displacement is a poor indicator of horsepower. MEASURING ACTUAL HORSEPOWER (via a chassis dyno) is the the best "indicator" of horsepower.


      For decades European and Japanese countries used engine displacement as a means to tax car owners - the higher the engine displacement, the higher the tax on a given car. This led car makers in many of these countries to cater to smaller displacement engines as well as turbo- and super-charging smaller engines to make more power. It was a tax work-around.

      Different racing organizations often try to use engine displacement as a restriction to limit horsepower, and displacement does correlate to one thing in a Naturally Aspirated engine: maximum engine torque. But not necessarily power.

      There are formulas that are easy to calculate that show the absolute maximum torque per cubic inch that is possible. At our engine shop HPR, engine builder Erik Koenig has explained this to me many times. Pump gas street type engines have a theoretical max of 1.25 to 1.35 ft-lbs per cubic inch. There aren't any ways to "trick" an engine beyond this number without a power adder. Race fuel all-out dry sump NA engines can touch 1.5 to 1.6 ft-lbs per cubic inch.

      Erik can look at a dyno chart, see the torque values, and tell you pretty close what the displacement is - or if it is "down a cylinder" when the displacement and cylinder count is known. This is something that many tuners with dynos sometimes miss, but when they call him about an engine he has built that is having tuning trouble, and they tell him the torque values - he can quickly tell if one cylinder is not contributing. This in turn reminds the tuner to check the spark, fuel and compression on that cylinder. It's a basic fact of naturally aspirated engines - displacement and torque are directly correlated. Not causation, but correlation.

      Horsepower is work over time, and that is effected by RPM. So HP number is not tied to displacement. You can take two engines with the same displacement and the same maximum torque - then make changes to intake runner length, camshaft numbers, cylinder port shape/size, valve size, and other RPM maximizing tricks on one of those and raise the power level significantly. If you have two engines that make a peak of 300 ft-lbs of torque, one could make 250 hp and the other makes 500. Its all part of an this equation:

      HP = (Torque x RPM) / 5252

      This is what OEM engine designers and aftermarket engine builders for NA engines are doing: taking the maximum torque number, then playing with RPM tricks to maximize horsepower. This is something the auto makers have gotten better at over the years using CFD in the intake tract, new engine theory in combustion chamber design, new piston/oiling/bearing materials, moved from 2 to 4 valves per cylinder to increase valve area, tweaked valve timing on the fly with variable cam phasing, and upped compression ratios from 8:1 in the 1980s to 12:1 in modern direct injected engines.

      Compression ratio is another trick engine builders use to add horsepower - for every "point" increased in this ratio you make about 4% more power. Those 4% adders can go up for every point, and an engine built for modern racing fuels can run as high as 16:1 compression - nearly double what the average stock engine ran for compression in the 1980s. This is great, if you can afford $20/gallon 116 octane fuel and only run at race tracks with a large supply on hand, but not so useful for street or dual purpose cars.

      Now we have cheap Ethanol. What is sold as a "renewable and green" replacement for gasoline is really a boosted octane mix of Ethanol and Gasoline. E85 is ~85% Ethanol and available at Wal-Mart and many other gas stations across the country. E90 and E100 is also available from racing fuel suppliers. This fuel has less energy per ounce so to make the same power you have to use more of it. It is a "cheaper" way to gain octane, but only adds more power when the compression ratio (or boost) is there to take advantage of the slower burn front of these higher octane fuels. So you see some NA engines with high compression converting to E85, but mostly it benefits turbo and supercharged engines - where "boost is cheap".


      Lets talk about power adders for a moment. These tend to come in 3 flavors: Nitrous Oxide injection, Turbocharging and Supercharging. The first of these (N02) is a chemical that brings extra Oxygen to the combustion process. This is injected along with additional fuel to trick the engine into thinking it is bigger, but it is fairly dangerous (lean outs, backfires... and a massive accelerant / explosive in car fires) and Nitrous is almost universally banned in all autocross or road course use.

      Boosted engines make an engine act like a larger displacement engine, but with with less reliability, more complexity, and more heat management problems.

      Turbo- and supercharging has become more common from the OEMs over the past 20 years, and they are increasingly using this trick to add power to smaller displacement engines - originally for tax reasons, but lately for emissions and bragging reasons. Smaller disparagement boosted engines are not better for the environment, just easier to trick government emissions and fuel mileage tests with (see: automotive diesel emissions scandals of late). The actual, real world fuel mileage is just as bad as engines twice their size, sometimes worse.

      "Boosted" engines come with some level of risk, even when engineered into the whole car by the OEMs. The heat load on the engine is higher, and bigger/more coolers need to be used to shed that waste heat - intercoolers, oil coolers, larger radiators, etc (which adds complexity and weight). These tend to "heat soak" with road course use, too. Once the coolers and fluids and metal get hot they take hours too cool down again, so they run hotter and hotter the longer you run them. The increased cylinder pressure from boost makes octane requirements go up and knock detection and spark control much more critical as well.

      GM, Ford, and Chrysler took a page from the "small engine boost" book and created supercharged V8s for their ZL1/ZR1/C7 Z06 (abive), GT500, and Hellcat vehicles. We have seen these used on a road course, and to put it nicely, its pretty much a sh!t show. The C7 Z06 was so bad about overheating (many driver's can put them into dangerous temperatures IN ONE LAP) that driver's have had to resort to class action lawsuits and buy backs. What works in boosted LMP and F1 boosted engines does not correlate to production 600+ hp engines in sub $100K cars.

      For the most part, boosted engines are not used in serious road course use without big changes on the entire cooling system and chassis. Sure, some folks run a turbo VW Golf (above) or Focus ST on track for fun without major problems, but others are not so lucky. The real problems begin when people start running these cars in higher ambient temps, or with higher than stock boost levels. Aftermarket boosted engines are even less reliable. None of the boosted engines work as reliably as naturally aspirated engines that make the same power levels. Ever. To encourage their use by biasing the rules to favor boosted engines is just a bad idea, in our view.

      To account for the added power of boosted engines (supercharged or turbocharged) the SCCA loves to use a 1.4 displacement adder or multiplier (depending on the class), which is based on something the FIA abandoned around 1970. The problem that the FIA figured out was that these types of "displacement equalizer formulas" tended to push people toward smaller boosted engines instead of away from them. Why? It was easier to make more total power in a small displacement engine by turning up the boost pressure than with a larger displacement engine even in 1970, based on these old formulas. And at the levels where cost no longer matter (F1) they could overlook the reliability and cost issues. Boost pressures (and power) rise considerably faster than the "fixed" adder/multiplier penalty can compensate for. This is how we see 2.0L EVO engines make 500 whp, but they don't last long on track like this.

      Using a direct power measurement (dyno testing) makes this "boosted bias" go away completely. People can still build time bomb boost buggies if they want, but you aren't giving up a huge advantage if you stick with NA engine in the same class. It works well and there is a good mix of boosted and NA engines in NASA Time Trial, with fewer boosted cars built every year

      Why should we care? Well even in SCCA TT's limited prep Level 1 and Level 2 TT classes people will start to play with boost if they have a factory turbocharger. Adding boost, even illegally, is too easy and beneficial to ignore. Without direct dyno testing, "boosted" engines are impossible to police (just ask the SCCA's SPEC and STAC committees about policing boost). Without any threat of on-sight dyno checks (occasionally done at NASA Regionals, done a LOT at NASA Nationals) the temptation to increase boost is too great, and modern EFI engines can compensate and respond very well to it. I've seen it, I've done it when legal, it works. It always comes with a price in reliability, but if you are gaining a big advantage over your competitors, people will do it.

      If one of your class competitors is accelerating away from you on track too quickly, drop some paper and ask for a dyno check!


      This is something fundamental that NASA grasped in in the 1990s and is what attracted a lot of people to this organization's racing classes. All W2W and Time Trial classes within NASA have a Power-to-Weight ratio limit, which are based on actual car weights taken (with driver) and horsepower measurements taken directly at the wheels with a chassis dyno. Direct measurements that show the actual power of the engine, which in turn helps dictate where the car ends up in classing (or determines legality within a claimed class).

      Chassis dynos became commonplace in the 1990s and there are thousands of them across the country, with most major cities hosting multiple dynos. Supplied with built in weather stations and industry standard SAE calculations, the raw horsepower measurements can be corrected for factors such as air pressure (elevation), ambient temperature, and humidity. Not only are chassis dynos great for tuning, they are the ultimate lie detector. Combine measured power with the measured weight and now you have the ultimate classing factor: Power-to-Weight.

      This direct measurement of P-to-W ratio for classing also reduces the need for dozens of pages of rules restrictions in many if not all racing classes. This is a simple factor that even pre-teens who read car magazines (or their online equivalent) can understand. Lighter and more powerful cars WILL go faster on a road course. In the Autocross world that the SCCA has its most participation in, power is less of a factor but weight is important. For a road course horsepower is hugely important, and not worth "interpolating" or guesstimating around just engine displacement. It needs to be measured.

      More soon!
      Last edited by Fair!; 03-06-2018, 02:52 PM.
      Terry Fair -
      2018 GT / S550 Dev + 2013 FR-S / 86 Dev + 2011 GT / S197 Dev + C4 Corvette Dev
      EVO X Dev + 2007 Z06 / C6 Dev + BMW E46 Dev + C5 Corvette Dev


      • #4
        Re: SCCA Time Trials - Rules Suggestions from Vorshlag

        So interesting timing...but my division- Midwest division, is starting its on TT series this year, with simpler and possibly more sensible (?) rules.


        The long and short of it, without getting too in depth-

        -Many other organizations' licenses are accepted
        -It's power/weight based, not displacement/weight based
        -mods are pretty open
        -Impactful mods give a power/weight hit-
        - Tire width and compound
        - Shocks
        - Aero
        - Exotic or heavily modified brake systems
        - Engines

        There are some kind of weird things concerning engine mods when you can't get a dyno sheet (?) and some possibly misguided shock rules, but...for the most part I think this set is solid, and quite a bit more solid than the national rules. Hopefully they'll notice and edit- I suppose we wait and see! My letter is written.


        • #5
          Updated thoughts on National SCCA Time Trial Classing and Rules - July 26, 2022 - So it has been another four years since we wrote the appeals to logic above. It fell on deaf ears and they went ahead with their original ideas about Time Trial rules based on categories and classing versus measurements and logic.

          My thoughts have changed on NASA vs SCCA Time Trial over the last 4 years since SCCA rolled out their new National series. While I still respect the "actual weight and actual power" measurements of NASA TT, the SCCA's 4 categories with 3 of those restricted to 200TW tires makes a huge differences in spending, and you can actually be competitive on "street tires" in those classes (Sport, Tuner, and Max) while picking the prep level that you want to run for your car.

          I will be honest, I kind of ignored the National SCCA Time Trial series for that four years. Largely because I sold my last Time Trial eligible car in August of 2019, got busy with work at the shop, and we were delayed in finishing our next two Time Trials cars. But in April of 2021 we bought this little base model 2006 Corvette, which has a modest LS2 and the narrow bodywork. We were only able to work on this intermittently in 2021 and spent time chasing some factory ABS issues until about a year later. Then we tackled some suspension, wheel and tire, and other upgrades - and the thing finally got pretty quick.

          After being out of the Time Trial game for nearly 3 years I was missing some form of Motorsports competition. Sure, I'd done a few autocrosses in 2020, 2021, and even a couple in early 2022. Below are two events I won this year. But the limited amount of seat time in these parking lot events wasn't "scratching that itch", even with some solid wins. What I really needed was some road course competition, and the most affordable road course events I have found over the last 30 years are Time Trials.

          If you have followed my social media and forum posts for a while you would know that over the past 15 years I have trended away from autocross (which I started in 1987) and towards Time Trial events (I did my first TT events with NASA in 2006 and other groups as far back as 1991). While I will always be an autocrosser at heart, and will continue to compete there, for business reasons and my personal driving skill set (or lack thereof) I think my time is better spent doing Time Trial.

          My "go to" TT series NASA has over the last 15 years become much more focused around Hoosier DOT tires as the the basis for all TT classes, from TT1 to TT6, and showing up on 200 TW street tires will get you relegated to "class filler". I did two seasons of events with NASA Texas (2018 and 2019) in my '18 Mustang GT (below left) on 200 Treadwear street tires on Day 1 and would switch to Hoosier A7 and R7 tires on Day 2 of a NASA weekend.

          The difference in times was always around a second per lap, but I noted that without aero or gutting the car to get on the edge of the Power-to-Weight ratio, it was largely uncompetitive in NASA. On the other hand, from 2012-15 we ran our 2011 Mustang GT (above right) in NASA TT on the max width Hoosier A7s, with full tilt aero, and at the edge of the power-to-weight ratio - and dominated TT3 class - racking up dozens of wins and setting 16 class track records. So from my first hand experience, NASA TT is really geared towards the super serious, not dual purpose street/track cars like our current C6.

          And while NASA has tried to offer parity with some sort of "tire equivalency" with modest power-to-weight modifiers for TT in 2022, it is virtually impossible to do this right. The breadth of grip levels within "200TW" tires is huge, and the difference between 200TW and R7s is also significant. We have seen 1.15g on the R-S4 and 1.30g on A052s, both marked and classed as 200TW tires. Hoosier R7s and A7s tend to make closer to 1.4g grip sans aero, which is another big step up. NASA has seen unintended secondary effects from their "tire modifiers" in TT that added even more class instability and cost.

          I'm not willing to play "The Hoosier Game" at the moment, especially with a legit street legal car like this C6 - which I have promised my wife and crew at Vorshlag that we will NOT do the following to: cut it up, add aero to, gut the interior, add a cage, or swap the engine. This C6 was supposed to be an easy "tweener" track car build, to allow Amy and me to have some fun track time while our REAL cars are being built: her '13 FRS and my '15 Mustang. It has already gone past the "easy" but it is still streetable with a full interior, functional emissions, cold air conditioning, roll up windows, and yet monster improvements in suspension, brakes, and more.

          The sad truth was that the lap times in this little C6 were pretty uninspiring on the 275mm R-S4 200TW tires, and the bone stock 360 whp engine was a little underwhelming as well. So after we tackled the troublesome ABS issue and got the MCS coilovers on, I started looking at places to race this in Time Trial. Looking at the power and weight of the car (3320 pounds with driver + 360 whp) it was pretty much doomed in NASA TT classing - just like my 2018 Mustang, it was it was stuck DEAD in between their TT2 and TT3 classes...

          Each NASA TT class has a strict power-to-weight ratio you have to build towards - TT3 is 10:1 while TT2 is 8:1. Like the 2018 GT, this C6 was stuck almost exactly at 9:1, right in between two classes. I spent 2 years trying to get around that limitation in the red Mustang, jumping between TT2 and TT3, and was largely unsuccessful and frustrated. I found once again that to be competitive in NASA TT you have to CUT ON THE CAR to fit max width tires, GUT the interior to get the weight closer to the P-to-W limit, add REAL AERO that wrecks the streetability, and of course RUN HOOSIERS in widths that will cost $500-600 per corner.

          Of course you can always "aim lower" and build towards a slower class. We could have run this C6 on 275mm wide Hoosiers and either ballasted up with weight and/or detuned the 360 whp engine to make the 12:1 p-to-w ratio required to run in TT4. But I've already done too many seasons in "slow TT cars", with my E46 330Ci (in TTD and TT4) and C4 Corvette (in TTC), above. The sad fact is I just don't enjoy driving slow cars, even if they are "more competitive in class."

          So I wasn't down with making this C6 even SLOWER to fit within TT4, then running $2000/set Hoosier R7s that would wear out more quickly because they were needlessly narrow. I know we can fit 315mm tires under the stock narrow body fenders, and by damn THAT IS WHAT WE WILL RUN. And I know there is some easy power we can unlock with headers and a few bolt-on tweaks, and I want to DO THAT TOO!


          I had written the posts in 2018 about SCCA Time Trial rules and suggestions above, but I have since updated my thoughts on that series. While I was a critic in 2018 when SCCA National first rolled out their new TT series rules, they have since made some significant improvements over the last 4 years - and more pressing, my home SCCA club Region adopted the National TT rules for 2022.

          So while I had fun and success in my 2018 Mustang GT and the FRS running the regional SCCA TT (see above) for a few years with their unique Regional rules, if I wanted access to proper 200TW based TT events locally (Texas Region does 7-9 events per year - at tracks all local to me!) I would have to adapt to the National SCCA TT rules.

          So we dove into SCCA's TT rules in 2022. SCCA TT has 4 categories: Sport, Tuner, Max and Unlimited, with classes within each. The base Sport category is far too stock for my tastes or our business, Tuner was like Street Touring autocross classing (which I ran competitively in from 2004 through 2013 in many cars, including the two above), Max was pretty wide open but still 200TW based, and Unlimited was anything on Hoosiers or other mods beyond Max. Due to some wild price increases with Hoosier during the Pandemic I am going to largely stick with running 200TW tires for a bit. And while Max looks like fun (full suspension, aero, gutting, flares, cages, and virtually unlimited power upgrades), I am trying to keep this C6 a street legal car and again, not cutting / gutting / swapping engines. Maybe one or our other cars being built will run in Max.

          After weighing the 4 possible categories we picked SCCA's Tuner category for the Corvette, and the class where this narrow body C6 fits is called T2. T1 is for widebody C6 Z06 cars, and pretty much all non-supercharged narrow body C4/C5/C6/C7 cars go into T2. The T3-T6 classes are all for less powerful cars. Each class in Tuning has a Max tire width, and in T2 it is 315mm, and of course 200 TW tires. I have been doing a LOT of testing and driving on 200TW tires for the last 2 decades, so that fits. Mods allowed include common bolt-ons like headers, exhaust, cold air intake kits, seats, wheels/tires, big brake kits, and pretty unlimited suspension changes.

          Luckily almost everything we had done to the C6 was all legal for Tuner 2 class, and the rules committee was open to making some allowances if you had good arguments. Like the transverse leaf to coilover swap - it wasn't legal in Tuning until after I sent a letter and made a case for precedent from SCCA Street Touring autocross class, which had allowed this swap several years earlier. And then the TT committee made a change within about a week - that was refreshing! One limitation in Tuner is around bushings - metallic busing replacements are NOT legal - just like the Street Touring Solo classes. This influenced some decisions on our little C6, but probably for the better.


          I guess this is highly dependent on your Region, personal prep level, and class participation, but this is what it comes down to - are you having fun in a given series? And yes, the two events I have done with SCCA Time Trial this year were exceedingly fun. And the NASA events I did in 2018-19 were "less fun", because I needed to spend 3x as much to be competitive there.

          Sure, it helps that we won both of these 2022 SCCA TT events in our little C6. But the fact we could be competitive in a class with 200TW tire limits, and be fast overall for the entire group, for as little as we have spent was what was notable. I also like the fact that SCCA Time Trial events focus on HPDE and TT only, and have enough run groups to split the TT drivers into two groups, usually with 15-20 cars. Smaller groups makes for less traffic on track and fewer laps lost passing / being passed.

          At any NASA event all Time Trial entrants get crammed into one giant run group, leading to sessions with 35-50+ cars on track at once (we had 77 TT cars on track at COTA in the 2018 NASA Nationals). There is also a much broader spread of lap times from the fastest to slowest. That leads to excessive traffic, and strategies that involve Hoosier A7s and "first lap only" sessions. And then you have the W2W NASA racers that "supersize" the events to run in Time Trial as practice sessions. These "tourists" almost always ruin the sessions for a number of real TT drivers, as they are gridded out of lap time order.

          I never thought I would pick an SCCA Time Trial over NASA TT as the primary series I would build a car around, but the more I look at the rules and classes, the less expensive it seems to run competitively with in SCCA. Not having the budget burden of Hoosiers (R7 or A7) is a real game changer, and not having the hassles of annual dyno pulls & classing paperwork, average power games, juggling tire size measurement templates, and making weight after every session is a relief. So for now, yes, SCCA TT is "more fun", less expensive, and easier to do. I reserve my right to change my opinion at a later date!

          Thanks for reading...

          Last edited by Fair!; 07-26-2022, 02:44 PM.
          Terry Fair -
          2018 GT / S550 Dev + 2013 FR-S / 86 Dev + 2011 GT / S197 Dev + C4 Corvette Dev
          EVO X Dev + 2007 Z06 / C6 Dev + BMW E46 Dev + C5 Corvette Dev