Timeslip diagnosis... need help with launches...
 

Went to test and tune today, got in 6 runs. I'm really not doing well with the launch as my 60' times and resultant ET's show. My trap speeds seem to indicate that there is a lot of room for improvment:

# 60' 1/8 ET 1/8 MPH 1/4 ET 1/4 MPH
1 2.614 9.779 76.190 14.703 101.824
2 2.552 9.508 80.237 14.325 103.593
3 2.590 9.688 79.034 14.549 102.729
4 2.566 9.705 79.014 14.540 103.241
5 2.685 9.784 79.185 14.766 90.681
6 2.312 9.427 78.340 14.318 101.973

I coasted through the last 100' or so on run 5 after missing the last shift.

Relevant mods are DP, M2 Intake, Efini Y-Pipe, ACT Street/Strip Clutch, and Nitto 555R Drag Radials (245/50 R16). I run the stock ECU and try to keep the boost at 10lbs but sometimes see a bit more. I started out with 22 PSI in the tires and went down to 20 PSI. I was shifting at about 7500 RPM's and lauching from 2.5K to 3.5K. I started low with the launch but it was bogging bad so I increased the launch RPM's a bit until I started getting wheel hop. Any advice would be greatly appreciated. TIA!

Man oh man...damn. 14.3 on a modded FD. Alright well, hmm. You have drag radials and a good clutch. Mmm. How are you launching? Dropping or slipping the clutch? I think your car is capable of around 13 flat. Do you have good rear shocks?

103.5 mph is a very very low 13. Did you heat the tires up good?

I'd try slipping the clutch real quick at about 3200 rpm.

What size of tires and boost pressure are you running? Not to mention, what kinda of weather conditions was it like? CJ

try to launch at a higher rpm, like 4000. If you launch at a low rpm, thats when you get the wheel hop. If you launch to high you will spin the tires. Just go out a find a happy medium. Good luck

The way I got the best time out of my 87t2 was keep at 4000rpm let the clutch out gradually while gradually leaning in on the gas. this gave me a constant slow chirping all the way through 1st. My time got way qwicker by launching like this.

Have fun
stock 87t2 14.9 possible clogging cat.

Thanks for the help. I posted a similar question a while back (https://www.rx7club.com/forum/showth...threadid=65103) and got some of the same advice. I wasn't dropping the clutch, but I was letting off it very quickly, I think I just need a lot more practice, but I'm worried that there may be a problem with the rear suspension. Everything in the suspension is stock. The tires are 245/50 16's on stock FD rims (16x8) with 22-20 psi air pressure, running 10PSI boost with occasional spikes to 12 at the transition. The track is at sea level, and temps were 60-65.

yo i got a 60ft time of 1.960 with street tires and bad ones at that.You just have to warm your tires up really good man and ride the clutch as you accelerate. Try luanching at 5500 - 5000 rpms that worked for me. Good luck man.

my best 60 ft with mp,dp, cb running 12 psi was a 2.0 launching at 5500-6000ish with a 13.9 at 102 at 3600ft but that was with my enkei rpo1s 18x9.5 with 265/35-18 nittos 555 at 22psi, o i also had rb drop springs.
but you are definetly losing it at the 60 ft or i should say launch, try launching at a higher rpm, that should help you some

Uh, no it's not - not on drag radials.&nbsp 103-104mph would only net a mid 13 second pass.

Are you running 300# of stereo equipment in the car???


-Ted

Where were you running, Riverhead?

The car weighs 3000 lb's with 1/4 tank of gas and me in it according to the scales at Englistown.

Riverhead is a dirt oval, I was at LI Motorsports Park in Westhampton. www.limotorsportspark.com

I need some help too! Check this out. Hers my dyno #s from 3 weeks ago 396 RWHP @ 6400 rpm and 331 ft-lbs of torque. I told the guy doing the pulls to let off at any sign off knock (which he did around 6500-6800) I have the J&S set kind of sensitive, but most of the time I dont show any knock around 7k but I did on the dyno. Anyways I did a add a little full to WOT settings to be safe after the pulls. I should be in the 420-430 RWHP range around 7500 rpm I feel. So check out my time slips and tell me whats up!

R/T .462 .709
60' 2.101 2.068
330 5.992 6.192
1/8 8.992 9.287
mph 85.36 84.88
1000 11.526 11.791
1/4 13.622 13.884
mph 108.22 105.00

Now on the 2nd one listed I blew a coupler of my I/C around 3/4 of the track.
Now this is on bald 255/40/17 A520s
Also due to tire spin I cant floor it til i get in 3rd (even in 3rd i get some tire spin at times)
Also if im spinning in 2nd I miss 3rd every time which= 14.00s, so I have to baby it.
but still with all the mods I should be running much better times. On the previous motor I ran a 13.024 @ 113 or 117 I cant remember, and i was mad then.
Now Im P!SSED!! Whats the deal here! Im far from a great driver but still.

I'm not a professional drag racer by any means but I've been to the strip on 6 or 7 different occasions, with a TII and a FD.

Both cars have ACT street/strip clutches and both like to be launched around 4500rpm. What I do is slip the clutch ever so slightly while getting into the throttle until the car is moving fast enough for the revs to be at 4500-5000 rpm with the clutch out. This is hard on the clutch but I don't slip it excessively, that would waste it quickly.

Best time for my 93 R1 with DP, CB and Efini y-pipe is a 13.598@102.85. RT was 2.005 on that run. Stock wheels with 245/45/16 Kuhmos with about 20psi in the rears. I don't get wheel hop very often.

With my 87 TII I've run several 13.4's @ 104-105.5mph. Best RT was 1.982 sec. Also running Kuhmos at about 22psi.

Play with your launch technique, I don't like to just dump the clutch because it tends to promote wheel hop and is very hard on the drivetrain. Slipping it slightly keeps the tires from spinning (static coeffient of friction is always higher than kinetic) so you'll also get better '60 times if you keep your tires from spinning.

Jeff

CAL911,
Get your car redyno tuned to get real figures, but even on radials with huge ammounts of wheelspin, your mph would be way, way up on that. Should expect to see 120mph with approx 400rwhp. If the figure was right when you had it tested, it doesnt have that now.
Anthony.

I run a 1987 Turbo II that does consistent mid 13's, Centerforce DF, Nito NT-555R's, 16-18psi - I launch at 6,000RPM with slight slip of the clutch.&nbsp Car will bang out 2.0-2.1 60' times all day long.


RT has nothing to do with the 1/4-mile run itself.


This I do not agree with.&nbsp I've found spinning the rear tires slightly will give you better 60's times.&nbsp I just recently came across this graph in "Performance Handling" (Motorbooks International) that shows a Percent Slip versus Coefficient of Friction graph that clearly shows that a slightly slipping tire gives you the highest tire friction, page 23.&nbsp "High performance street radial" highest peak is around 11%, while a "Racing tire" peak is around 10%.&nbsp This blows away the keep-your-tires-from-slipping-rule out of the water in my book (no pun intended)...


-Ted

Ok, coupla things. I said RT and I meant '60 times. I think someone reading that should have known what I meant. I know that RT doesn't affect ET AND if I really was talking about a ~2 sec RT that is nothing to right home about. Right Ted? Best RT is .506 btw.

As for the tires slipping vs. not slipping. 10-11% slip isn't very much at all, dumping the clutch will get you a lot more than that which is worse, lower friction and more wheel hop. Notice you said you slip the clutch. Maybe my TII is just a little hotter than yours:), peak torque is around 5500rpm in a TII so you'd want to have the clutch hooked up before your there or idealy right at that point.

We've got the 13.4 sec runs on tape and you can see that there is a little bit of slip right off the line, but it is far from crazy wheel spin that you'd get if you told a newbie to dump the clutch at 6000rpm.

Jeff

That is a sad thing to hear about. Is your clutch slipping like mad or what. Your trap speeds are way to slow and your overall time is a good 2 seconds worse then it should be. Your 60' seems descent so you must have something wrong. List your mods.

I know my problem goes beyond this, but Im curious about weight. Is there any formula I can use to est. what would happen if I removed 100lbs, 200lbs ect.

Also I have heard people talk about some program that lets you choose a car, weight, hp ect. and it it gives you a quarter mile time. Anybody know the name of it? or where I could find it?

Im very embarrassed, pissed and discouraged. I really dont want to do this but here you go.

BTW... dyno and 1/4 mile #s are off 14-15psi of boost


You guys will have a blast with this!!!!

The general concensus i believe is that it's 7lbs = 1hp, and 100lbs is .1 in the 1/4

www.bracketracer.net has some good auto math calculators including some of the ones you mentioned. There is also a cool Excel spreadsheet here - http://www.rx7turboturbo.com/robrobinette/notes.htm

Call911, I have no idea how your car could perform as bad as it does. To crank out those dyno numbers you must be tuned descently so it's not your parts fault. I assume you have an exhaust/midpipe even though it is not listed. You have a good suspension and clutch. Is there anyone around where you live that also has an FD? If so, let them drive it and see what they think. It must be you. What about wheel hop and excessive tire spin. Do you just roast them through 3rd or something?

Yes I do have a midpipe and a Greddy SP cat back. As far as wheel hop, I do get wheel hop in the water box unless I rev it hard. The car will hop at launch unless I slip it some, which I always do. In first I might see about 10psi and shift around 6k, I dont bang 2nd hard cause I will just spin, in second I feather the gas (I have no choice cause I miss 3rd if im spinning in 2nd) I really dont bang 3rd hard just due the fact Im afraid ill miss it. Now once in third its to the floor, shift around 6500-7000 in to 4th.

I dont care how hot the tires are, there is no way I can floor it in 1st, and there is no way I can floor it in second.
Also I went today and carefully watched my boost gauge i was right around 13.5-14psi which I havnt changed in months, I turned it up to 16psi and did a pull. Big difference! but still.
My driving skills are not all that, but they are not that bad either. This is the third time taking my car to the track, but the first time I still I ran a 13 flat and I knew a lot less then. Next time I will run 16 psi and see what happens but its going to take more then that to get this car where it should be. slicks would help a lot I feel, but hell Ari runs 10s on street tires.

Your launch is what is killing you.

You should be -2.0 in your 60' times.

Get some good drag radials (BFG's), then go practice your launch.

Your top end is really good!

Put it all together, and you will be in the 12's.