V-seriesTech

iTrader: (5)

In my new downtime(car broke), I am trying to understand my setup a little bit better. I recently switched from my 47lb triple plate clutch/flywheel setup on my twin turbo car, and went to a lightweight, triple carbon 14.7lb clutch and flywheel. Now, the 47lb clutch setup, I never made it to the drag strip but, I do remember the car accelerating longer in each gear. When I DID go to drag strip with my other engine setups, I would JUST shift to 4th, and count to 1-2 and the 1/4 mile pass was over.

Now...with new lightweight setup, I am halfway through 5th gear, in the 1/4 mile. I run a ZR1 gear set(1st 2.29-2nd 1.61-3rd 1.21-4th 1.0-5th .81) , and at the time a 25.9" tall tire, and I planned to shift at 6800 but ended up shifting at 7300(so much for a rev limiter) and with a 3.42 diff gear. 4th gear at that rpm, that tire, diff gear in 4th should be 160plus mph, in 4th. I banged 5thh, and ended up going 148 in the 1/4. Now, granted the run was kinda screwed up(stalled and rolled at start), I did pick up 40plus mph on the back half nut still,...something isn't adding up.

My question is, is it possible the car is just accelerating to fast with the new, light clutch? As in NOT enough LOAD put on the turbos due to the quick revving of the vehicle? Should I go back to the heavier clutch because of this? I know I can put a TALLER tire on the vehicle and get SOME mph out of it but, this car is intended for half mile events, so I was planning on running my 18" setup for that. This new data,...throws me off on everything however.

Here is the in car video of my lightweight clutch pass. You can see on the launch, although I did blip it to slip it however it is so light, it ended up stalling at the line...so ideally this needs to be launched on a two step and go.


I just don't understand the 5th gear 1/4 mile pass. I did inspect hydraulics, throw-out, and also clutch discs for abnormal wear on contacts, everything on that end is fine. clutch was NOT slipping. I should be trapping at the top of 4th...not 5th. I have never heard a ZR1 hitting 5th in the 1/4 either.

Any thoughts from the experienced? I know when I had the 2.73 gear in the car, the amount of load generated on everything was amazing. Car worked great. I may have to go to a 3.08 or lesser of a gear if I want to run the half mile. Just doesn't add up to me.

sbcgenII

iTrader: (1)

Are you sure you have 3.42s?

gametech

iTrader: (1)

Either your math is wrong or your clutch is slipping. Wrong math could be due to bad info from your tach, or bad info about gear ratios (from tire size to trans gears to rear end gears). I'm going to vote clutch slippage. The weight of the clutch or load on the turbos has absolutely not **** to do with your trap speed not matching what your rpm vs gear ratio adds up to.

stevieturbo

Again the logs will tell all. If the clutch has been slipping it will be very obvious on the logs.

Also are you saying there were no other changes whatsoever between runs other than the clutch/flywheel ?

V-seriesTech

iTrader: (5)

The logs shows no slippage. The disc(s) are all new, no dust, and no slick spots from heat in the discs. I bought the diff straight from GM, so I don't know how it couldn't be a 3.42. I originally, immediately thought clutch when I got the timeslip, based on how straight the car went, how many gears I went through, and the actual end trap speed. I Know rpm/vs gear/vs tire height is what will make up how much MPH the car goes. Log system is a Holley Dominator, shows RPM shift points. Just soo odd. Clutch is a Tilton triple carbon. I don't think the car overpowered it but then again, I did run all of the boost.

gametech

iTrader: (1)

If you changed the diff, simply for peace of mind I would jack up the rear end, disconnect the driveshaft, and physically verify the gear ratio.
edit-- I just remembered that carbon/carbon setups need a lot of heat in them to achieve full holding capacity. I doubt that soft launch heated things up much.

sbcgenII

iTrader: (1)

It's in a C5 so not that easy. I think he is running a C6 zo6/zr1 diff and they only come in 3.42. I forgot he was running a 6060 trans and thought he might have picked up a used diff with 3.73s.

I would put my money on clutch slip. I would verify the rpm is correct with an oscope aswell since you have been having problems with the tune.

gametech

iTrader: (1)

Good point. I almost never give any thought to the torque tube/transaxle layout on the later vettes. That would definitely make my suggestion for verifying the rear gear pretty useless. Tachometer error is still possible, but I would think he would notice that much difference. Still betting on clutch slip.

stevieturbo

And again, if it was clutch slip it would stick out like Trumps wig when you look at the datalogs.

There is no way the clutch would be slipping without it being visible.