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Unread 01-05-2016, 03:15 PM
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Default Re: Vorshlag Budget TT Build: Project DANGER ZONE

Project Update for January 5th, 2015: Its been a couple of months since I touched base on the progress of Project #DangerZone, our 1992 Corvette race car, and a lot of little things have happened - both to the car and to the NASA base classing rules for 1992-96 Corvettes. We've made some updates to the C4 to hopefully make it lighter (pre-ballast), run cooler, and more importantly - be more reliable once it returns to track use later this month. The C4 is also looking like my only primary race car for 2016, so we're getting a bit more serious with prep on this car and might add a few other racing groups to run the car in. There's only 3 weeks until the next NASA race we want to make in this car (NASA @ MSR-Houston event Jan 23-24) plus a test day at MSR-Cresson the weekend before (Jan 16th at MSR-C). I'm only going to cover the work completed up until now then catch up on the finish work before these two race dates in the next update.


As some of you might know we've started a BMW E46 330Ci build for NASA TTD class. That project has gobbled up some time and we switched chassis before we even began major race prep on the first car (325iC), which slowed us down a bit, but it was the right move going from the 325 to a 330 (the latter of which was classed better and makes a lot more power). You can read up on that car here, which we've named Project #JackDaniels. I explain the name in that thread.

Normally in December of each year, NASA will release an updated rule set for Performance Touring, Super Touring, and Time Trial classes - all 3 of these groups use essentially the same set of rules. PTB-PTF wheel to wheel classes equate to TTB-TTF and ST1/2/3/U equate to TT1/2/3/U. Sometimes the rules aren't published until after the first of the year but this time the 2016 NASA TT rules came out on time, with nearly 8 weeks before our January 2016 event.

The C4 listings above are what we built this car around, and those haven't changed in many years (we know because we have been eyeing this car for TTC for 4+ years). But due to how well Dave Schotz did at NASA Nationals West in his PTC/TTC C4, and how much we riled up a few folks with our forum build thread (even though it really only completed one race weekend), we were expecting either a points penalty (*), class change (TTB?) and/or minimum weight change (increase) to these C4 base classes. So here are the 2016 changes...

All changes from the previous edition of the rules this year are shown in blue. As you can see the minimum weights for 3 of the C4 models were changed, all higher, including our 1992 LT1 base model. We have to add 57 pounds to our weight or else take points for weight loss, which gets expensive. As you may know we had maxed out this build on points from the beginning. Somehow I never really covered that in this thread...

This post on our E46 TTD build thread explained in great detail how we came up with the classing, tire size/compound, chose modifiers and found rules exploits for both the TTD car and this TTC car. I won't repeat what I wrote there in total but if you care to learn some of our secrets, please go here and check it out.

Here is a quick summary of our TTC class build for this 1992 Corvette, based on the old 2015 rules. After we saw the base classing (TTC*) and weights we looked at the Power-to-Weight (P-to-W) ratio assigned to the class (12:1). The * cost us 7 of the 19 class points we had to spend, so we have 12 to play with to stay in TTC. Then we looked at the base tire assigned to the class (255mm). Going up in size costs points, down in sizes nets points back. From there we looked for modifiers to the P-to-W ratio... and found a big bonus (+0.8 ) if we ran a small 245mm or smaller DOT tire (see Appendix B in the rules). 1 point was also gained back because that's 10mm below the TTC class starting tire size of 255mm.

This modifier effectively moved the P-to-W from 12.0:1 to 11.2:1. Luckily the stock LT1 motor could still hit that revised P-to-W limit without any power modifications. This meant we didn't have to burn class points on exhaust or headers or camshaft swaps or intake mods to max out P-to-W. We spent ALL of our remaining points on suspension changes (springs at +3 points) and tire compound (R7, +10 points), plus our point gained back for 245s (-1) and it worked out to the 12 point mod limit for TTC with maxed out power limit.

Let's show those P-to-W calcs "the NASA way" for our TTC Corvette:
  • Weight must be at or above the listed minimum classing weight of 3203 pounds, from the 2015 rules
  • That 3203 number is also just above the minimum "competition weight" modifier numbers, which start at 3200 pounds
  • We chose a 245mm width DOT legal tire (+0.8 P-to-W bonus)
  • The stock engine made 284 whp peak (highest of 3 pulls)
  • 3203 lbs / 284 whp = 11.28:1 (P-to-W) + 0.8 for (245 tire modifier) = 12.08:1

TTC Class "minimum" adjusted P-to-W is 12.0:1, which this car is just a hair over. That's what you want to do - aim for the P-to-W limit and find any modifiers you can to help that ratio along the way. Avoid modifiers that hurt, then use your points to run the best tire compound/width and fix any suspension issues, and add aero if you have any points left. Again, this is more detailed in the E46 TTD thread, linked above.

So that was our TTC strategy for this C4. Now we have to recalculate for the higher 2016 minimum weight bumps, which honestly aren't that bad and are not unexpected. I have to agree with these changes, even if I don't like them. This will mean we have to run even more ballast on the same 245mm tires, which worries me. We haven't dyno'd the fresh LT1 motor but I'm also worried it might make too much power, even at this higher weight (and with the 11.2:1 P-to-W ratio we can now make 291 whp). Even with it only running briefly due to the ECM issues it felt STRONG - and yes, it was a 100% legal engine rebuild. We shall see soon enough.

Sadly our E46 TTD build gained a 7 point penalty with the 2016 rules, which I'm not at all happy about. Really borks the planned build. So of the very few changes made in 2016 both of our TT-Letter builds were impacted. I'm just that lucky, I guess.


Meanwhile in last two months, before we got the new 2016 rules, we have been working on some reliability mods to the C4. Of the 2 race weekends we ran this car I never managed to make more than 2 laps in a row. So the stock Z51 brakes haven't been pushed hard enough to overheat, but I'm worried they will be taxed once we get the car on track without a leaking or smoking engine. Why worry? Well because I'm a Left Foot Brake fanatic (learned in my autocross background) and I tend to abuse the crap out of brakes.

With an R7 tire compound I don't have to get my best laps in on lap 1 or 2 like we did on the A7s in TT3 last year, so yea... brakes might become an issue. So one day when we had the C4 up in the air for harness removal (see below), I asked Olof to pull apart the front brakes on one corner for a better look. We had built brake backing plates with cooling ducts for a C4 before and he kept the templates we used that time, so this shouldn't be a whole lot of work.

After he made a flat plate that fit around the hub we discussed where to route the hoses, what sizes to go with, and what shape for the duct at the backing plate. We decided to use 3" oval tube for the inlet, aimed at the hub and inside the rotor face. He built these 2-piece backing plates below.

With only a 13" rotor there wasn't room for a 4" duct, and with the track performance of this car a 3" cooling hose should be enough. Now there's also lower piece to this backing plate added to help seal off the hub section so that the incoming air goes where we want it to. It also allows for a bit of a heat shield from a ball joint that is very near the inside rotor face, shown below.

The spacing from the backing plate to the rotor face (shown in the picture above right) is what we try to stick with, which allows a decent seal to the incoming air but shouldn't ever rub. The goal is to turn the rotor into a centrifugal air pump, with the incoming air forced into the hub area inside the rotor and the curved vanes of the rotor pulling air through the rotor and out radially. This can increase effective braking during a session considerably, as well as extend brake pad and rotor life substantially.

As you can see above left, even the oval shaped 3" duct doesn't put the incoming air completely inside the rotor face, but its as close as we can get without nearly flattening the oval shape. Another thing that we did while the hubs were off was install extended length 3.25" ARP wheel studs. We couldn't find a bullet nosed ARP stud any longer than the itty-bitty stock studs, so we'll just have to start each lug by hand with this fully threaded ARP (it's not like we're doing fast pit stops). The reason why I wanted long wheel studs will make itself known in my next post.

While doing the front stud install we would normally swap in new hubs at the same time, for other cars. But for the C4 we kept the original front hubs - they were still low mileage, still felt tight, and the aftermarket options are total CRAP for this chassis. The only good aftermarket replacement hub for this car worth using is a racing hub made by HPE that costs $699 per corner, and I'm not sure if their solution is even TTC legal, so we'll keep the stockers on there for as long as we can. Brake cooling aimed at the hubs tends to extend their lifespan quite a bit on track, too.

Backing plates are only 1/3rd of the brake cooling solution - you also need INLET ducting at the front of the car and then brake hoses to join them. After looking at the front end of this C4 I wanted Olof to "keep it simple". Why? Well we're likely replacing the bumper cover later in the 2016 season since the stock cover is pretty beat up. We had discussed about re-purposing the turn signals, adding NACA ducts in the old headlight doors, or even NACA ducts under the front bumper... but I wanted to keep it very simple. "Just make a 3 inch round tube and a flange", which is exactly what he did.

Remember - this might not be the permanent inlet duct solution, just a quick one for now. The inlet ducts were relatively easy to make and I had a specific place I wanted them placed. The front of the C4 has a LOT of "front overhang" (see above) where the nose pokes out about a foot in front of the factory front lower air dam (the air dam feeds air to the radiator). All of the radiator cooling is drawn in from under the giant overhang, but there is still some dead space on both sides of the radiator inlet that goes unused...

continued below
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