I know this has been the rollercoaster of the year, at least for me. I finally decided to break down and try the RWD conversion because of the weight potential, and greatly improved turn in. I then found out how much more top end the car had, it was great. Well I got to try every aspect of that out this weekend at the track.

Since my last real run at BMP I've lost apprximately 174 lbs from the car. (RWD, Battery, Straight Pipes, Decklid, Race Seats) I was also running on new versions of the same scrubs I ran in October. So you can imagine how I watered at the mouth of the potential for the weekend.

Well to make a long story short, I got schooled in Power understeer vs Mid corner push. The later of which similar to what was causing the RSR's to get spanked in ALMS last year. I had noticed a severe increase in bumpsteer once the drivetrain was out, so I had the front lowered accordingly and my corner weights were in good shape. But the 70lbs of front ballast was a dear price to pay. The camber settings were identical. And other than two specific areas, the car was just "as good" as it was before, which was dissapointing in itself, and much worse in two specific sweeping turns where the mid corner push was attrocious.

I ended up 1.1 seconds slower and that was ***** to the wall driving, probably over driving by the end of the weekend. And only two seconds faster than on bald sport cups with the only difference other than tires being the rwd conversion in March. The track conditions were HOOOOOTTTTTT!!!!! But most people were able to run at, or above their best times.

For anything other than some good runs at the track, I love it, other than the bouncy front end. Drag racing, 1/4 mile, 60-130, occasional mexico runs (which I may try all of the above before I switch back)

So IMO, the best actual idea (which I'm not going to do) if you are going to track with a RWD TT, is to keep the front diff in the car. Most of the speed increase comes from the lack of drag from the front drivetrain anyways, 70 lbs doesnt make much difference on it's own. (considering a full 200 lbs passenger may only be worth a carlength or two from 60-130). That or you need to add a GT2 suspension, or buy a GT2.

Or, stay on tracks with little elevation changes, or very slippery or off camber turns. At least if you want to go fast.

So back to AWD I go. For good.

 

Dez,

Great write-up and I'm glad you've found what works best for you.

I'm curious about one thing though; regardless of which tire I'm running (r-compounds or drag radials) my car oversteers before it will understeer (which I love). What do you think is the main difference between our setups that causes this?

I'm running RWD (no front diff), JIC Cross lowered to GT2 specs and corner balanced with moderately negative camber. I run 235/40/18 Nitto NT01's up front at 38 psi cold.

Thoughts?

 

Easy, power at the wheels. You have much more power than I do, and even those that have equal or less are running street tires, and on the street, which isnt nearly as sticky as a track covered with race rubber. I can make my car oversteer if I wanted to fairly easily, but also remember, I'm running full silcks which will have more traction than even your DOT R-comps, and after several laps in 100* + temps, you heat soak and it's harder to spin the tires. And my goal is to keep rear wheel spin at a minimum, so I'm going right at the limit of that.

Also when you are pushing the limits of handling (which you can drive hard on the street, but no where near as hard as on the track) you find out where the deficiences are. The turn in is extra crisp, but when you are trying to get the car rotated through a decreasing radius sweeping turn and get to a certain point the input becomes numb. It does it in AWD too, just not as bad as the front wheels turning in the direction you want to go and with power to them is enough to rotate the car some. I even tried lifting mid corner to get some rotation and it didnt respond.

The encouraging thing was that I got the car WAY out of whack and it was very easy to correct.

 

I'd like to see what Tom has to say when he tries it this weekend (I think) at Sebring. Sebring is flat so he may not notice much of a difference, but I'd be willing to bet I'd have been 2 seconds or more faster had I stayed AWD.

It may be that it just needs more developement in this format and will work better, but there is no doubt at all that the 70 lbs hurts a lot. I thought about taking the rear bumper support out to balance it some, but I'm just going to go back to what I know works instead of chasing my tail here.

I really wish someone would design something that gives a HUGE amount of front DF. That would do the trick.

 

I did pick up 3 mph on the straights though so the straight line speed is definitely improved. Barber doesnt even have any real straights, even with as much power as I have I could only get 127 mph before, now I'm getting 130.

Though I did gain about 20 whp from the huge gash in my DV Y fitting and DV's so some of it is from there. That was done after my last Time Trial there, but before I switched and the car is definitely faster in a straight line.

I do need to know how to get the CV races back in the hub, it took forever to get them out, I bet they dont go in too easily either.

 

Two questions Heavy:

Did you get upgraded wastegates yet?

Why not try to keep going with RWD and add some front end camber? and play with toe...?

BTW 3 MPH is pretty huge. Butt dyno was right on.

 

On my way to Sebring this weekend and I will also report as far as track impressions. I will have a full corner balance. VERY heavy springs, new front sway bar, new rear toe links, 335's in the rear and mad camber.
I am expecting at least 2 seconds faster (and that's alot)
also I am running a Guard LSD with 50/80 lock up which I am expecting big things from.
also I plan on some Pro instruction so someone more track savy then me can give me their input on how the car drives vs me just to be fair to the set up.
my set up is very similar to Scott's with the above.

 

What are your hot tire pressures? 38 psi cold seems too high. I start mine around 29 to reach about 40 psi hot. I'm also using the same size NT01 up front.

 

Nice write up Dez. I had been playing with the idea of going rwd. Not so sure now.

I also look forward to Toms' review.

 

IMO Heavychevy you have not tried enough. It took me a good month of testing before I got my car setup right for RWD driving.

Weight balance at standstill and front/rear ratio has little if anything to do, while you are driving the mass transfer offsets by far any differences you might have vs a stock setup. The problem is in the car setup. You can make your car to push or pull as much as you want, if you are feeling understeer at all it means your car is not well setup.

If you are feeling bump steer, it means your car is not well setup either, could be hardware or geometry..none of these should be there.

With the right suspension bits, LSD and alignment setup you will be faster than 4WD I have no doubt, except under rain maybe. But at least you tried and now you don't have any "what ifs" to worry about.

If Tom can be faster at the track from is first go with 2wd it will mean that the advantages are huge, or that he did everything right from the first time! It takes a lot of time and effort to get a 2wd conversion setup to work, and a lot of tweaking! FR/Rr weight bias is almost irrelevant.

 

Ya, I solved the problem by getting a gt3...haha...Dez...you should be at that point too...haha (we gotta move up to the next driving level man!)

 

Nice description, but my opinion is to start from begining with an gt2, you can't go wrong with it.

 

Dez it's a great write up and impression, but now you must get it sorted out and TWEAK.. No one gets it perfect the first time, hell even 2nd or 3rd. I am still tweaking my setups in my GT2, just added toe links and several other components and will see what I need to do by the end of the month!

Good luck with the setup , I wanna run at Road Atlanta sometime this summer too, any good 3 day events?

 

What front wheel carriers are you all using? Are they original TT or GT3/GT2 type? I don't think you are going to maximise(minimise?) potential handling gain of going 2 w/d without doing something about the fundamental disadvantage of TT wheel carriers.interested to hear experiences .

 

I didnt have to develope the AWD for it to be fast (er). I just added negative camber and went. And anything I develope on the RWD platform with be just as effective on the AWD, unless I change the geometry completely at which point I'd rather buy a GT2 than trying to make one. I'm going to work with what I have until I get to it's limits, then move up. I'm already running mucho negative camber in the front 2.9 and 2.4 rear. Granted on some tracks the RWD may be beneficial, I bet I could hit 175-177 @ Road Atlanta now, but I dont want to, too hard and too heavy to stop that.

The front end bounces around far too much in the front as well. You cant just ignore 70 lbs of ballast being taken out of the car. In fact when I still run faster times with the 50 lbs or so of difference with a full tank than I do with less weight at 1/4 tank. So now with the AWD out and lower amounts of fuel I've lost 120 lbs from the front of the car. Unacceptable for turning. The ballast makes that much difference especially on tight circuits. I felt the same feeling in a 997 GT3, more so than a TT, but still less than what I'm getting now. It's 911 character to have that

Also the rear diff does not like RWD and cornering. While taking the AWD out takes some drivetrain loss off, it adds stress to the rear components. I would not track RWD unless I had done everything that Tom has done, otherwise it's a time bomb. Frankly having to build all of this stuff is not what I want. I want the car as close to factory as possible. So I know it's the driver and not the car. Right now I have essentially an X-50 with ECU, Exhaust, Coilovers, some minor weight loss and a rear sway (safety mods, but they dont really help). When I feel I am beyond the capabilities of the car I will throw some stuff at it or move up. But I havent gotten there yet.