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Unread 11-17-2010, 04:57 PM
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Fair! Fair! is offline
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Default Re: Vorshlag 2011 Mustang GT 5.0 - auto-x/track build

Project Update for Nov 17, 2010: We've had a huge amount of responses (some that I've replied to) on the 4 forums where I have posted this thread on so far, so some of this might look familiar on the thread you're reading. Adding the RoadRaceAutoX.com forum was a big boost in ideas/questions (thanks guys).

Autocross and Time Trial Classing - We've had a lot of folks question my sanity on the decision to run STX for SCCA Solo classing. Not sure what this class is? Read the STX rules here on Jason Rhode's STX blog page. Speaking of that...

http://www.rhoadescamaro.com/build/

Go read that blog and see another racer who's bucking the trend in STX - by using a V8 powered RWD solid axle '67 Camaro Z/28! If you thought our build was crazy, he has pretty good reasoning for his similar-yet-different V8 RWD chassis decision there. Now his 1st gen Camaro STX build, when all is said and done, will likely be 300+ pounds lighter than our 2011 GT, so he might really be onto something. And remember: he beat all the Civics in STS back in 2006 using a RWD Nissan 240SX, so don't just assume that being competitive in STX is impossible in a powerful RWD car. He's proven that winning in unconventional cars is possible, if you develop it well enough. Very cool build, mad prop's to J-Rho! We've been tossing ideas back and forth on both of our cars, and he has clued me into some great ideas already.



Also, our foray into the ST category with the S197 Mustang GT isn't unprecedented. We had a Vorshlag tester (KentK) that helped us in the development phase with our S197 camber plates and AST shocks for this chassis. Somehow Hanchey and I convinced him to try it in STU. He ran the same Enkei NT03+M 18x10.5" ET30 wheels (the rears needed more backspacing) we ran on the EVO X, and he had the STU class limit 285mm wide Dunlops, with the above mentioned AST/Vorshlag suspension. It wasn't half bad in the handful of races he ran in STU, against the Texas STU crowd here, but he didn't stick around long enough to develop it. He moved to ESP class, with big 315mm Hoosier A6 tires, where its done well Nationally - and is still doing well there. The prep level he has on the car now would have sure helped his chances in STU, way back when. So for our 2011 GT in STX... sure, its going to take a lot of testing and prep, but we think its got an outside shot at being competitive. Stock for stock, the '11 GT has +100 whp over the '05-10 GT chassis Kent used in STU, too.

For NASA Time Trial use (where we should have better luck using the proposed 450 whp we think we can make in STX legal trim) we'll use a wider wheel (18x10" or 18x10.5") and a wider tire (285mm) with something like 140-200 treadwear. The 2011 GT was just re-classed in NASA from TTC (2005-2010 GT) to TTB (2011 GT), and has a race weight of 3770. We'll have to ballast up to make that, and it will likely end up in TTA with the mods we have planned. Ugh. We'll talk more about TT prep in a later post - we won't have a track test day even planned until after at least the "Stage 2" (AST 4100) suspension and the "big" wheels are on.


Factory undertray has a flip-down trap door over the oil filter. We changed 8 qts of Mobile1 and Wix filter goodness

Wheel Testing - this has been most of what we've done with the GT the past week, other than the initial oil change @ 250 miles (the stock oiling system takes 8 qts of oil - that's kind of encouraging, actually. Went with 10W30 Mobil1 + Wix filter). I started asking about wheel options before we bought the car, back in this massive Corner-Carvers thread about the Coyote 5.0 motor/2011 GT. The beef I brought up there was the lack of wider, lightweight 18" wheels made for the S197. In my early measurements I could see that the standard GT's 18x8.5" and even the '11 Brembo GT's 19x9" (ET42) wheels were small for the size and weight of this car - and there was tons of room for wider wheels going inboard. The stock 19x9" wheels/tires are boat anchors (57.2 lbs per corner!) and the factory 255/40/19 tires are super tall, too (27.2" tall!).


Left: Stock wheel/tire is 57.2 lbs. Right: factory wheel is 19x9" ET42... that's made in China

The problem we quickly noted was that the aftermarket was pushing blingy, heavy, yet narrow wheels for the S197. Most of the Mustang drivers on the non-race forums were choosing cheap, "replica" wheels that are hideously heavy. Or Shelby GT500 wheels (18x9.5"), also very heavy. The only "real S197" direct fit wheel we found in 18x10" that wasn't a Chinese replica was the expensive BBS 18x10" shown below...


Above: The "Boss302R" 18x10" BBS wheel Rehagen sells is 20+ lbs and $637; Its used on some Continental GRAND AM S197 race cars

TireRack lists a bunch of heavy aftermarket stuff for these cars, too: 18x8, 18x8.5", 18x9.5" and a bunch of 19" rubbish - all of it heavy. I won't have a car that uses 19" race tires, no way. There's no reason to have 19" wheels on this car, period. 18"ers clear the brakes, and the tire choices are MUCH better in that diameter, so 18" it is. 19's is simply a styling move, and one I hate. Some of the reason we haven't found many wider 18" options yet, I think, is because the 2011 Brembo package is still "new" and the larger 14" Brembo front brakes are somewhat unknown - not all 18" wheels will clear the big caliper, as we found out.

Where were the Enkeis, Team Dynamics, Volks, WedSports, OZs and the many other lightweight aftermarket wheel options?? Well, digging deeper we noticed that they were all out there, just not listed under the S197 Mustang. Nissan (350Z), Mitsubishi (EVO), Subaru (WRX/STI), and Honda (S2000) all use the same 5 x 4.5" bolt circle (they call it 5 x 114.3mm). And most of the aftermarket wheels use an oversized hub bore, so we can make hub-centric adapter rings to fit the Ford's 70.5mm hub bore. That's good news.



So last week I tried to fit Stuart at AST's 18x10" CCW Classics (6.75" backspacing) from his '05 GT (above, left) onto our '11, but they didn't even come close to clearing the huge front calipers. The Classics aren't known for their awesome caliper clearance, but it did have me a tick worried. Next we pulled an 18x9.5" ET20 (6" backspace) Rota "Grid" Matte Bronze wheel and 275mm tire off of Matt@Vorshlag's 350Z (above, right) to see if that cleared the brakes and fenders, but I had my doubts due to the 20mm offset... (sorry for posting this pic twice, but it is more applicable here/now)


(yes, that is photoshopped to be lowered... this is the actual pic)

That first test was pretty enlightening. The gold wheel didn't look that bad on the car, either, but that was not the point. This Rota 18x9.5" ET20 doesn't fit inside the S197 fenders, as feared; the tire was sticking out past the fenders (about 1/2" out back - see below), but it was a good reference point and let us measure the inboard clearance to the suspension. After measuring the 18x9.5" Rota on the car it looks like we could go inboard by 2.5" in back and over 2" in front... meaning an 18x11" up front and 18x12" in back could just barely fit, if you played your offsets right. With enough camber, rolled front fender lips, and a different style front swaybar end link (more on that later). It should be easy to fit an 18x10 on both ends, though. Backspacing of 7-7.5" on the front and 7.5-8.5" on back looks to be ideal for 10"+ wide wheels, from my measurements.



I then borrowed an 18x9.5" ET45 wheel (a TireRack branded Subaru-fit wheel) with a mounted Dunlop 275/35/18 tire from Paul M's '95 Impreza/STi swap project last weekend. Tested it on the GT this past Sunday and it fit much better than the same size'd wheel in ET20 we tried before (under the fenders at both ends). If I had to choose a street wheel without the need for maximum width/grip or goofy class rules that limit us to little 9" wide wheels, the 18x9.5" ET45 would be the obvious choice for the S197.

So the Subaru/Nissan 350Z fitments are what we ending up searching on, as there seemed to be many more wheel choices from companies like Enkei. Hub bore is different, but like I said, we can make a hub-centric adapter ring. I'm trying to get an 18x9" in at 18 lbs or less, so Enkei is the first obvious option we're looking at (NT03+M, RPF-1 or PF01 models). Matt found an Enkei RPF-1 in 18x9" ET35 (6.4" backspace) which might just barely fit (18.4 lbs), and they also have a PF01 (new for '09) with ET45 (6.77" backspacing) that's sub-19 lbs (the 18x8.5" shows to be "18 lbs", no weight on the 9"). The ET45 will fit inboard better, obviously (nearly identical to the stock '11 Brembo 19x9" ET42 wheel). In the 18x10" size the choices got much slimmer... the most backspacing we could find was 7" (18x10 ET3 for this bolt pattern. So we ordered one of the 18x9" ET45 in the Enkei FP01 and one 18x10 ET38 in the Enkei RPF1 yesterday from TireRack and we'll test fit them when they show up next week and report back.



We talked to the nice folks at Team Dynamics, who were willing to custom make the 5x4.5"/70.5mm hub bore in one of their 18x10 wheels in one of 3 offsets (ET40, 52 and 56 - all Porsche fitments normally in 5-130mm), all of which would fit much better ion the rear but might require a small spacer up front. Weight was the killer - 28.5 lbs for the 18x10s.

Tire height is the next issue. The stock Mustang 255/40/19 tires on the 19" wheels are a staggering 27.2" tall. The 265/35/18 we're thinking of using for STX class is only 25.3" tall, which is a huge difference (for gearing, CG height, etc). Not many choices there, as most of the ST-legal/competitive 265s are all this same size. For the street a closer match to stock is a 285/35/18 tire, which is 25.9" tall. Those probably will go on the 18x10" wheels for street/track use. For a variety of reasons (racer recommendations, price, compound, & sidewall style) we're looking at the Hankook RS-3 tire for initial testing. After being out of ST category for a year a lot has changed... we probably need to test the same sized tire in Yokohama AD08, Dunlop, Kumho XS, and Toyo R1R, if not more. I doubt many/any of these have been tested on a car this heavy, either.



Last night I worked late on SolidWorks and revised our Vorshlag S197 camber/caster plate drawings (rev 3 for all of the main parts), so we're having a short run of these made in steel. It will eventually be released as an aluminum plate, after I have time to add the "Vorshlag" logo, model engraving, hash marks, and crunch the numbers. We'll test the plates on the stock springs/suspension next week, then try it with Eibach lowering springs (I think that's going to likely become a popular and affordable S197 package - Eibach springs and Vorshlag plates). I'll rate the stock '11 GT Brembo spring rates on our Longacre spring rater, too (see this Spring Archive for similar data).

I'll stop there for now. We've got a lot more to share., and keep those suggestions, questions and ideas coming.

Thanks,

Last edited by Fair!; 11-17-2010 at 05:19 PM.
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