6-speed launch help - Wheelslip graph
 

I have a 440 rwhp, 6 speed GTO and I'm looking for some launch help. This is all the relevant track information

-Dead 26x10.5x16 MT ET Streets (Bias ply) @ 14 psi cold (could not go lower due to lanewalk)
-Street tires up front
-Healthy white smoke burnout
-Clutch dump off the limiter
-3.46 rear gear (equal to 3.90 on an F-body trans)
-Double adjustable rear shocks (setup slightly backwards, had high compression, and low rebound damping instead of the other way around)

ET, MPH and 60' are shown in graph.
http://i693.photobucket.com/albums/v...aunchRun10.png

As you can see, there is enough traction to bring the RPM's down, but I wouldn't call this a bog necessarily as this pretty much brings me to peak engine torque for the entire trip through the first 60'.
I have had heard multiple people say its either too much spin, or not enough spin (I find the latter hard to believe). What do you guys with 1.5 60's see?

The only idea's I have:
1) Set up shocks correctly (low compression damping, high rebound damping) to get weight on the tire as quickly as possible.
2) Buy bias-ply skinnies so that I can try running lower rear tire pressures without fear of dying.
3) Buy new slicks (perhaps stiff sidewall for a heavy car). Maybe 15" rims?
4) I would think gears MIGHT help, but until I get more traction, I would think it would be counterproductive.

Would appreciate any comments.

Are you still running the IRS rear or have you swapped to a solid rear axle? If you're still IRS then the suspension/shock settings are going to be quite a bit different than what most of us are used to with a solid rear axle setup. Don't most of the GTO's tend to squat in the rear on the launches?

I'd like to see some video of the launch if you have one.

Mike

how did you get this, is that all hptuners. thats really cool

Too much wheelspin. Try not hitting the tires so hard - launch below 6k. The attached 5k launch is with a 125-shot. I have 26x11.5 ET Streets at 17.5 psi. My recollection is that MT recommends not running ET Streets below 16 psi.

+1 what software are you useing?

Yeah, still the IRS so the settings will be a bit different. Rear end squat's hard on launch. We don't get a nice advantageous torque reaction loading the tire in addition to the weight transfer. I don't currently have video (though I ordered a slow-motion camera that should be here this week, so I will have some interesting video's in the near future).



Yup, all HP tuners. Very handy.

Thanks for the comments/graph. You're graph is very interesting as it looks like you are barely spinning the tire. Even at 4,000 RPM launches I was seeing significant spin, so this tells me that new slicks should be my first priority. This would also explain why no psi I ran really helped significantly.

Have you tried equal compression/rebound? My car hooks and launches straight with non-adjustable Bilstein shocks. Course, its an F-body. :D

i havnt looked info like this before to see what that is to a vid and whats really going on watching the car at the line.

but it looks like up to almost 2sec. is tirespin and that might be alot. but i don;t know how bad it really is. i can see at the end when it gets closer the the real mph is might not be a big deal, but this is the 1st time with this info to use. and i would think the rpm wouldn't stay that linar in 2sec, of wheel spin, to how it climbs normally when to car stars moving along. i would think there would be a climb more, no.

do you have a 2step or using the stock limiter. :angel:
a and what tps are you at for the launch and for the tire spin. it might be your only at 60-80' /percent/ for the lunch, and pedaling it with the wheel spin:confused: that might be why the rpms look like that, or are you wot. but i havnt seen this data before to know what i'm looking at really. lol

if you can, get tps too. you dont really need to see 3rd and 4th if your getting the car down the track thu the gears good. and you could see whats going on better with the lines in just the 1st 4-5 secs, i might be asking for to much lol


sorry for my worse them normal spelling and grammer, i dont have a shift key and some other keys are not working. i can't do cap. colons, questeion marks, but just periods .

New ET Drags, I bet can still solve a lot. Even with the IRS they will either hook or break the diff/axles trying. I like the graph and the Wheel spin is certainly evident.

Gearing may not be a bad thing, as you can lower the RPM of the launch and that may actually TAME the car down but when it comes to TQ Multiplcation you can be at the same spot HP/TQ wise but just a lower rpm. The race weight of the car has a big factor on the launch as well.

6 Speed racing is crazy enough to begin with, and its hard to find good advice as most drivers only know how Auto cars react, adding to the fact the IRS allows for only so much makes it really bananas.

I suspect you need more things to stiffen that IRS up to allow it to load the tires properly. IMO of course.

Haha, I hate you guys.
Haha, no problem on the grammar, I understand. Yeah, there is a good amount of tirespin up to 2 seconds. It is crazy how the RPM comes down and stays there. I assure, I'm not keeping it there with the throttle. This launch consisted of "Wait for the first yellow, put right foot on the floor, when I hear the 7k rev-limiter, sidestep the clutch". Looking at the log, I have TPS maxed everywhere during the run except the first data point or two (about 0.1 second).

It is interesting that I'm getting so much spin, but it's not blowing the tire away. It's like the engine torque just matched what the tires were providing

Thanks for the input. I agree on the assertion that new tires should be a first step. On a sidenote, I noticed that the coilovers came with very soft springs (so much so that they bottom out going over bumps on the interstate), so new stiffer springs are also on my to do list.

From the above graph from Gary Z, it appears as if I should see no where near that amount of wheelslip on launch (his graph is almost pure hook). I bought the ET streets used with 50 passes on them, and have probably put 20 additional passes on myself along with 10,000 street miles - lol. The sidewalls are cracked, and the two grooves down the tire are now almost completely gone. So yeah, I will be ordering new slicks this week and seeing where that gets me.

So, given that this is a heavy car (~3600 race weight w/ driver), should I be ordering stiff wall slicks? I think I remember reading this somewhere. I'm just confused because everyone always says to go with a slick on a 6-speed due to the soft sidewall. It seems odd to want a stiffer sidewall slick - unless too much sidewall deformation is a bad thing.

I am no IRS Guru, this would be a good post for the GTo or Vette Section. I would PM JL-Ws6. I know he is on vacation and is far better at specing out tires then me.

I do know the ET Drag construction has a inherent "give" to them which will make a immediate difference. I would call M/T just incase to get their opinion as well as checking other IRS specific sections

Here's the thing about a drag slick compared to a drag radial. When a slick starts to spin, it still has a lot of traction and will keep gripping hard even though it's spinning (your graph shows this fact). Now a drag radial, once it starts to spin, it loses most of it's traction. For a clutch/stick car to work properly, whether it's an IRS or solid axle, it needs to have a certain amount of tire spin (or wheel speed) off the line to keep the rpm's up in the powerband. If it dead-hooked, it would bring the rpm's down too far and bog every time. The trick is to find that happy medium between traction and wheel speed. It can be very tricky for a clutch/stick car to achieve this with all the given variables such as: changing track conditions, changing temps, tire pressures, shock settings etc.... I hope that all made sense.... :)

Mike

Bias ply also absorbs alot of the shock of a 6k+ launch by giving a little cushion to the drive train by wrinkling the sidewalls of the tires.

Knee jerk at 6K. Also I would invest in some drag bags.

How can you log wheelspin in HPTuners?

Holy hell is this old.

Old??? Same cars, even same HPTuners version :)

old or not, this is a good question.

yepp, would love to see that in HPT. Too bad FSAE_Junkie doesn't want to share :)

He doesn't 'log wheelspin', he logs rear and front wheel speed sensors separately and then compares them (graphically or numerically). When they don't agree, it's spinning.

OK, but how did he get wheel speed sensors in HPTuners?