I would like your advice on why my car initially hooks up and then just after the initial hook up I spin my rear tires.

I have brand new ET Streets (26 x 11.5) and my best 60' time has been 1.731 and that is with a launch from about 1500 RPM and then florring it. If I try to load up the torque converter to say 2500 RPM or more, the car's front end comes up and then the tires spin (resulting in a 2.0 sec 60' time).

I'm wondering if the torque converter is locking up too quickly (it's a 9.5" Street edge with a 2800 stall converter) or whether it's the tires that are unloading or whether it's something else.

I feel that I should be able to run a better 60' time than what I am currently running but because of the tire spin, I'm not able to run a better time. My race weight is 3550 lbs.


The Mustang chasis dyno results for my combination are 296 rwhp @ 6088 RPM and 404 ft lbs @ 3200 RPM.

My best 1/4 mile pass has been 12.495 @ 108.98 (at sea level).

Do you think that I should be able to run a faster time than what I am currently running with the combination I have?

Some additional information about my car is in my signature and any help would be greatly appreciated.

 

That sounds like a decent time, if anything you should get your converter re stalled to 3500 or so

 

Tire pressure?

Check your pinion angle. It should be angled down in relation to the driveshaft 2-3*

Do you have LCARB? If so the LCA should be parallel with the ground. Normally the LCA should be angled down slightly at the front but with the torque arm suspension, angled up at the front also works.

Stock or adjustable rear shocks? If adjustable, stiffen them up.

It sounds like you're hitting the tires hard then they unload. This is normally a suspension problem.

What's the advertised duration of the camshaft?

 

hmm... maybe not enough stall for that cam....

 

Yeah - I think a higher stall coverter will work much better!

 

My tire pressue is 16.5 psi.

Pinion angle is -3 degrees relative to the driveshaft.

The specs on the cam are as follows:
249 I/256 E @ 0.050", .520" I/ .536" E at 108 LSA.

Do you think I should run a higher stall with that above cam?

I'm not sure what LCARB is - can you clarify?

The rear shocks are Competition Engineering adj shocks and they are currently set to 50/50. What setting should I change it to? Should I set it to the 30/70 setting?


BTW, I have Lakewood drag struts up front (90/10) and I also have air bags in the rear suspension where the driver side is set to 10 psi and the passenger side is set to 35 psi.

 

LCARB = Lower Control Arm Relocation Bracket... The cam I'm running is 248 @ .050 with .525 lift on intake/exhaust and a 4,000 was recommended for my setup. Loosen that converter up and mess with your suspension a bit then you should be doing better. Wouldn't hurt to try the other shock setting in the rear just to see what it does. Tire pressure, I had problems spinning a bit at 16.5 psi with my slicks but seemed to work better at 14-15 psi. 28x9 hoosier slick.

 

I think the cam is a little big for the 9.5 to 1 compression, which is probably bleeding off cylinder pressure at low engine speeds (torque) , which is probably causing the converter to tighten up the stall speed. 2800 is too tight for that cam. 3600 would fit the bill nice and still drive around the street with good manners.

 

Have a friend take a vid of car launching, you will learn alot.
I had similiar problem, mine was the short jegster tq arm was lifting rear of car so hard, that it would full extend shocks then unload tires. I solved that by lowering the car.. Bottoming out will do same thing, or hitting airbags to hard, also tire wadding-up will deffinetly do it, after a while sidewall gets to worn, tire beging running over itself.. I have a pic of my car doing rhis really dab somewhere.. A stiff sidewall tire solved that.. (Common with heavy cars leaving hard) - hoosier says anything over 3200 lbs is heavy.

 

Yes I have the LCARB and my LCA's are currently installed in the lower of the two holes. I will need to check to see if the LCA's are parallel to the ground (like Stephen said).

Since there is little time left in my drag racing season, I will try playing around with the rear suspension shock setting and also with tire pressure.

How low can I go with the tire pressure on a 3550 lb car with my ET Streets?
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I have spoken to the manufacturer of the converter and they indicated the same thing that you have said - increase the stall to about 3500. I just wanted to check with you guys to make sure that you agree and also to see if there was anything else that I could do in the meantime.

 

I will see if I can get a friend to take a video of my launch. Do you think I have too much air in my airbags (I currently have 35 psi in the passenger side and 10 in the drivers side)?

 

I would say probably, but really depend on how your car reacts. with stock TQ arm I used to run airbags with no pressure - 1-2 lbs. Also don't count out track prep, my track is famous for prepping about a 2-3' sq., so you will initially stick then spin once out of. A video will really help, up close, keep jogging pause when watching and see whats happening.

 

Was the MFG of the converter TCS up in VC, BC? If so, I deal with steve a lot. They got some real neat parts.

Mike.

 

I run a very simular set up to yours. No LCRB's, stock torque arm thou. 16-17PSI
The converter should be 3600-4000rpm stall but your converter will not cause the tires to unload on launch.
If anything, a converter that is a little shy on stall speed, will make it easier to hook the car.
Cam should be in on 102 to 104C/L and spark timing should be locked out for max hit on the converter on launch.
The LCRB's in the lowest location hole + the air bages combined may be causing too much lift or over reaction. Get someone to watch the car on launch, side , other side, rear Let the air out or move the lower control arm up on the bracket.
When the tires unload after initially loading, does the front end fall down?
Is one tire only or both tires loosing traction? is the front end twisting on launch?
Try swapping the tires,right to left side.
Is the engine laying down after inital launch? Fuel slosh?

As said before, track condition counts for a lot. What happens on the street.
3.70's is not a lot of gear for that combo. Should be trapping close to 7000rpm.
4.30 4.56 ish.

Post all of the info from say 4-5 good time slips to see how the car is progressing down the track.

 

No it was Andre at Edge Racing Converters.

 

I will try making changes to the airbag pressue as well as the LCARB setting and rear shock settings the next time I get out (Sept 26th).

I believe that the car is twisting on launch (that is why I increased the airbag pressure on the passenger side).

The car is not laying down after initial launch.

Here are the results of the last 4 runs.

1st run - shifting at 6000 RPM & tire pressure at 18.0 psi
1.781 60'/5.220/8.062 @ 86.65/10.514/12.595 @ 108.26

2nd run - shifting at 6200 RPM & tire pressure at 18.0 psi
1.767/5.178/7.998 @ 87.48/10.428/12.495 @ 108.98

3rd run - shifting at 6500 RPM & tire pressure at 16.5 psi
1.731/5.175/8.015 @ 87.06/10.447/12.509 @ 109.42

4th run - shifting at 6400 RPM & tire pressure at 16.5 psi
2.025/5.479/8.304 @ 87.3/10.732/12.794 @ 109.27

Note on the 4th run, this is where I tried launching at a higher RPM (i.e. approx 2500 RPM) and this is where I encountered tire spin after the initial bite.

I`m currently shifting at 6500 RPM and crossing the finish line at approx 6000 RPM. Based on my calculations, there is approx 14% slippage. I shift at 6500 because my peak power is at 6088 RPM and I found that I got my highest MPH when shifting at 6500.

 

Did you take off the front sway bar? They will limit the front end travel.

What kinda front shocks and springs are you running?

 

Yes the front sway bar has been removed. The front has Lakewood 90/10 struts with stock springs.

 

You really want to run as much pressure as you can while still hooking up with the heavy car. In the past I've gone to 10 psi but the car walks in the tires quite a bit. So I've been sticking with 13-15 psi hot. Best 60 foot I've done was I think a 1.46 with the 210 shot out of the hole, that's with the tires set at 15 psi. But then, every track and car are different so you'll just have to play with it.

 

I don't see anything in particular in your timeslips to indicake a problem. other than the car is under geared.
It's doing whats supposed to do down the track.
But based on your best 1/8th mile MPH, your car is cappable of trapping at 111 MPH. You are just not using all the power band of the motor at the end.
The fact that your best shift point is 6500rpm indicates that you should be trapping at a rpm somewhat higher than that. 7000rpm ish.
When the car is geared right to rpm right and the end of the track, the converter will show less slippage. Converter coupling efficientcy tends to improve the further up in rpm away from the stall speed.
The higher combined gear ratio will help plant the tires and launch the car, improving your 60ft times, ET and MPH.

Once the car is geared right you'll most likely find the best ET occures by short shifting 1-2 (say 6000ish) and winding it out on the 2-3 shift (6500-6800rpm)
then with the correct rear gear ratio, you'll trap at around 6800+/- at 110+mph and et a little quicker.
Althou you certainly could benefit from a 4000 stall converter, your present converter will work much better with more rear gear ratio.

Need to know the effective diameter of your rear tires when loaded to suggest a new rear gear ratio.

If the car front end is twisting on launch, try reinstalling the front sway bar.
Once the gear ratio is increased, the thing will have no problem raising the front end against the small resistance of the sway bar.

 

More rear gear will make the stall speed problem worse and to the tighter side.

 

The converter stal speed is not the problem. He has a chassis/tire setup problem.
The converter stall speed at the track will not change by changing the gear ratio. It will act exactly the same at the track on slicks on launch.
More (or less) engine torque will change the converter function on launch, but not a gear change. The converter is not causing the car to loose traction.

 

Rear gear will change the stall speed, you just don't know that it will. A gear change in either direction (3.73 to 4.10 for example will bring down the stall speed aproxx 150 rpm and the other way 4.10 to 3.73 will raise the stall) I suppose vehicle weight has nothing to do with it either.

He has a few issues..
1. I agree, there probably is a chassis/ tire chassis problem

2. The cam is too big for the engine compression ratio, killing the engine torque down low. The stall speed needs to come up to make up for the saggy low speed torque.

 

I've been away from my computer for a few days thanks for the replies.

I think converterguy has summed up my issues. I will see what I can do to correct the chasis/tire issue and later on this year I will sent the converter off for an adjustment to stall speed.