[Todd Buttrick]

I was speaking with a FFR owner who doesn't get on-line here and asked if I could ask you IRS gurus a question. His car is pushing about 575-600HP from a BB 514. His ride comes alive at about 4K rpm and when it hits that magic number it sends the car into an barley controllable surge to the right. He described a situation where he was headed out on three lanes of highway when he put his foot into the car darted right over two lanes before he could get it under control. Scary stuff. He is assuming the cause is the torque of the motor is planting the right rear and lifting the left rear and sending the car off right. Anybody else with this set-up have similar experiences? Recommendations?

Thanks

 

[Frank n Sons]

Todd - I'm no suspension genius but 3070 would do the same thing in 2nd. While it was fun, the neighbors got tired of replacing mailboxes. I think your reasoning is correct. We changed the spring heights in the rear to counteract the "drift" and it is almost 100% straight down the road now.

The real people to ask would be like John Phillips or Inman or Kartman.

Frank.

 

[Todd Buttrick]

Frank,

Did you change out the springs to a different rate or just change the ride height with the existing springs?

 

[johnh]

Frank - I thought you had a live axle rear?

The two work differently, the live axle rotates under acceleration torque and this cause the left-right traction imbalance. The IRS pumpkin is bolted to the frame and there is no lateral rotation.

This sounds more like a diff problem (and a loud pedal control problem - but we all have that).

 

[Brentt]

I have a BB with IRS in #2283 and have never experienced this problem. Even at the drag strip, there was no tendancy to swerve. My guess would be the alignment.

 

[Richard Oben]

I am with Brent. (we built his car). I think alignment or probably the Diff is not in good contition. The trac loc is not working. Not sure either of these is the problem but it is where I would start looking. My car was by no means a monster (12.56 in the 1/4) but I never saw any of the problems you are seeing. It would shuffle a little under hard acceleration but nothing unexpected. Cheers Richard.

 

[Wayne Presley]

I would also guess the alignment, you could also be getting some deflection from the rubber spindle bushings. Vintage Performance has urethane replacement bushings or you can replace them with spherical bushings like Allison Hines did on her car for a 0 slop.

 

[Frank n Sons]

John - whoops - your right, I missed the IRS part. We do not have IRS, so I guess we had similar results from different problem. The mailboxes did not know the difference. For the record though, we did not change springs, just ride height and adjusted the autowelds some. Works great now for straight ahead work (read - stop light racing) but Adam doesn't like it, says he has push or pull or oversteer or understeer or some other terms that I could care less about. I guess i know what he's doing when he takes the beastie out for a ride.

Frank.

 

[David Borden]

Agreed with the above posts. alignment and deflection in the spindle bushings...

David

 

[Ophitoxaemia]

another possibility is when the suspension loads under acceleration, one side (or both) of the rear suspension is bottoming. this will create a lot of instantaneous rear roll stiffness and funky handling. whats the ride height set at?

-james

PS borden's IRS car with 500+ hp goes straight

[ September 09, 2002, 01:27 PM: Message edited by: Ophitoxaemia ]

 

[2FAST4U]

It's not horsepower, but torque that moves the car.

Keith