Something aint right here. Went to the track again saturday and had pretty much the same results from last week. Best I managed was, again, 12.2 @ 114. The engine seems to be running fine. The gauge shows I am making full boost, I am not spinning or losing much traction at all. Got a few 1.8x 60 foots saturday, so I know its not traction. But my MPH is simply not there. I am pretty sure I should be pulling upwards of 120+ MPH and I KNOW it should be in the 11's easily. If the MPH was greater, I'd credit it to bad driving or traction, but since it is not, I know it is not the driver. Like I said, engine seems to be running fine- no misfiring, or hesitation, no smoke out the tailpipes when going down the track, etc. So I'm thinking its gotta be something downstream of the powertrain. I'm guessing its the clutch, but it does not feel like it is slipping any. I’ve done a couple highway runs where I floor it from 70 in 5th gear, and RPM’s don’t climb any higher than what the speedo goes. It boggs it down, so this makes me wonder if it is really even the clutch at all… This is so frustrating to be making the power I am at the wheels and not be able to put it down at the strip

Heres 2 timeslips from last Saturday, and the Friday 1 week before:

____10/29/05__11/5/05
60'___1.951_____1.852
330'__5.266_____5.206
1/8___7.970_____7.947
MPH__91.56_____90.30
1000'_10.295____10.295
1/4___12.253___12.274
MPH__115.29____114.22
Temp__~63°_____~75°

Another interesting bit of info my tuner noticed:

Chad, here is your first pull vs your last pull when we tuned plotted against time in seconds instead of against rpm. On the first pull the recording started at 2100 rpm and ended at 6050 On the last pull it started at 2600 rpm and ended at 6150. The last pull took over 2 seconds LESS time than the first. Now a car will spin up faster making more power, but a slipping clutch will let it spin up faster too.



A few things point towards the clutch, but I still am not sure. I would think I’d at least have some form of clue as to it going south like a smell or some noticeable slip, but nothing… I’m stumped. Any help or suggestions would be appreciated to help me get this problem straightened out

 

ya, i remember when i had heads/cam and dynoed around 425 rwhp and 408 tq here in az, Best I could scrounge up was a 12.9 at 112, but that was because my master and slave cylinder was fucked up and couldnt engage properly or get a decent launch better then 2.0 60 ft.

Hows your altitude/DA?

what are other people with similiar power in your area running?

 

There is a guy here making 415 rwhp and getting the damn near the same ET as I am, and trapping at 117ish. DA on last friday was 900ish if I recall correctly.

 

Was the car tuned/checked out on the street? There is a chance you might be getting KR on the street which will bring HP way down.

 

We did some data logging on the street and weren't getting any KR...

 

If you look at your graph you can see a problem. -Where it dips in hp/tq and the graph get wavy.That is indicating something.Could be a COT ,timing ,belt slip, ect.

 

That is very minimal on the graph. I don't think it would cause me to lose out on 6+ MPH and at least .5 in the quarter mile at the track. Plus, I can see I am getting full boost when going down the 1/4...

 

I can't believe that noone out there has any idea of what could be going on. I'd hate to pull the trigger and get a twin disk clutch only to find out that wasn't the problem

 

I'm kinda new to racing performance but from a mechanic point of view you might have a catalyst restriction. That could be the cause of the bogging down. I have test drove many cars with resticted catalytic converters and they all seem to lack top end speeds on top of poor performance. You might want to try a exhaust back pressure test.

 

your mph is indicating that your making about 400 hp to the wheels. What is your timing at? What is your air/ fuel at?
It sounds like your tune is off. Have you looked at your plugs?

I don't think its your clutch you would know by smelling it, or if the pedal went down to the ground.

Get a data log on the street for wide open throttle, that should tell you exactly what's going on.

We did that with my car and although I don't have dyno numbers, my car feels like it picked up 30-40 hp easy.

 

not sure if you have cats but I'd run an open exhaust and see if your car picks up, that is a good suggestion by the firechicken.

 

datalog at the track to really know what is going on.

i bet you find your tune was fine on the dynojet and not fine on the street.

if you retune try to find a load bearing dyno like a dynapak, mustang, dyno dynamics, etc...

dynojets are not that good for tuning.

 

now lets keep in mind that all though you are a very good driver Chad, that guy is amazing and has a huge ***** to boot.

but like iv said before i think that the combo of sticky tires+ sticky track+ stock rearend+450rwtq and hp= death for stock clutch.
try making a pass or 2 on street tires and see how much your MPH goes up

 

Thanks for the replies guys. I do not have cats- as stated in my sig. So that isn't the problem. I guess I need to log it on the street & at the track and see if that shows anything unusual. Tyler- I also thought about doing a pass on street tires and seeing what happens. Maybe I will if I get a chance this saturday.

 

450+ HP and a stock clutch?? My stock clutch will slip after 1 pass, even on the street, and my CAR is STOCK also...

 

I have a turbo on my car and it dynoed 413 hp at 4 psi and 467 hp at 7 psi. I took it to the track and was having problems with not being able to even get it in the 12's at 4 psi. We ran an autotap on one of my runs and found out that at 5K rpms there was a 3rd degree knocking in my motor that was retarding the timing. Have you had a computer hooked up to that thing to see what it's doing at higher RPM's? Have you checked your a/f ratio? Mine was also running rich at 5K too.

 

We fine tuned it on the dyno. I thought it was loaded, but not sure now that it is mentioned. a/f is around 11.8ish and 20° timing.

 

It was just an idea. I found out the other day that my spark plug have too big of a gap in them and are too warm for my car. The ones I have are great for a NA car but since mine's FI, they aren't very good. So that's another part of my problem.

 

I got brand new NGK TR6's when I installed it not 700 miles ago. I gapped them all to .035

 

Amazing the stock clutch is holding up but the Z06 clutches in the 01-02s will hold up until it slips bad once - then its over. It held my 425rwhp head/cam car for a while, then I smoked it once doing a burnout and it was never the same.

Anyhow, you need to log it, all it takes is something banging somewhere to get 5 degrees of KR on the top of high gear and there goes your mph. Overall your ET really doesnt look that bad if you are not really driving it hard, you have to do a little beating if you want to be quick at your power level. I would definately put headers on the car (I dont see any in your sig), any long tube, and you will pick up a bunch under the curve. My old 2000z28 with a P1SC @ 7psi picked up only 20rwhp peak going from stock manifolds/no cats to long tubes but picked up 5mph+ in the 1/4.

For reference, back in 2000 my stock weight '00 z28 @ 430rwhp ran 11.80s @ 115mph with the stock manifolds @ 7psi, it was really falling off on the top end but had a decent 60' because of the auto. Doing nothing but swapping a set of FLP headers and a quick retune (went from 436 to 459rwhp) and the car ran 11.30s @ 120-121mph which was pretty good at the time so sometimes little things make a big difference.

Just keep trying, get your 60' down, start logging and I'm sure you will get what you want - going to need a clutch if you really push it at the track, then a rear end... It never ends

Also 20 degrees of timing is very little for 6-7psi, you can usually get away with 24-25 pretty easy on 93 if you are running 11.5:1 or so a/f. Also make sure at lower RPM/low boost the timing is near stock and ramps down as the boost comes up.