V1 bad hunting when coming out of power

[redline]

Hello guys,

I have been fighting this problem for quite a while. I have had the car aligned many times at different shops and always the same result. I am now running ET mickey Thompsons on the rear and they are 325's and triple 5's on the front which are 315's. It goes fairly straight while under power during a pull, but as soon as you lift off the gas the car starts swaying. If i do a pull up to 130 the sway is so bad you can't stay in one lane. I run 22psi on rear and 28 on fronts, but I have played with this a bit with no conclusive evidence. I am starting to suspect the steering box??

any thoughts?

 

[Gtstorey]

When you say aligned at different shops, have you tried different alignment settings?

Pressure is way to high in the front and probably a little high in the back.

Have you upgraded any bushings?

Have you tried adding a swaybar?

Chopping the throttle at 130mph may be enough to induce bump steer.

The overboost of the stock power steering can cause feedback issues and other problems magnify.

I've never really driven mine about 100mph and it does exhibit a little of those tendencies of sway on decel. But it was a lot worse before I messed with the list above. At some point these a light, short wheel base kit cars and I don't expect the stability of something like my Camaro SS.

I don't know if going that big on tires might cause an issue?

 

[redline]

well I was trapping in the 130's before and not having problems so something changed. I will try lowering the air pressure and see if I can find a antisway bar. maybe ZZP? I do have the upgraded bushings. I have always tried to go to the settings that Adam and Lonny suggest.

 

[Gtstorey]

Stock base swaybar and ss endlinks from rockauto.

Try reducing toe and camber and possibly increasing castor.

 

[redline]

Will do, you have a recommendation on settings?

 

[Gtstorey]

Ross has posted some that I shot for on mine, but I did it at home so I'm sure how close I am to his numbers.

 

[redline]

not sure who Ross is, would you by chance have the numbers or know where I can look them up?

 

[Rttoys]

Agree on getting tire pressure down. Somewhere around 18-20 all the way around.

What are you setting the alignment at? We have found -.5 to -.8* camber on the front, works very well. Rear camber around -1.5* seems to be the norm.

If you do a rear sway bar, get a dorman “comfort ride” bar and SS links, as stated already. Dorman 927-109. This would be last on my list though. Tp and alignment needs to addressed first

 

[Gtstorey]

More Information for SKP SK927109 (rockauto.com)

 

[Rttoys]

Buy toe plates and angle gages, then do your own alignments. You can mess with all the settings you want and not have to “pay” for an alignment all the time.

 

[Gtstorey]

Ross is a user on here. Use the search function for "alignment" and his name in the username.

 

[redline]

parts ordered. thanks for all the help.

I have toe plates and and an angle gauge. I have tried to get it to the specs that Lonny said. I started doubting myself when the problem didn't go away. I will realign myself and install the swaybar, hopefully that gets me there. what do you guys recommend on tire pressure?

 

[redline]

sorry Rttoys I missed your first post about pressure. I will try those setting as well.

 

[JBINTX]

Just another thought besides the list offered above. Have you corner balanced your suspension?

With only 600 lb front and 1000 lbs rear, it follows your tire pressures would be higher in the rear.

Other than Justin Reed, not many have pushed Goblins over 100 mph consistently. Most of the suspension discussions revolve around much lower speeds seen at autoX at tighter tracks. So, not a lot of data points on Goblin handling over 100 mph or fine tuning it there.

 

[Desert Sasqwatch]

Another aspect to remember; under acceleration the rear suspension will squat and the front suspension will lift. When letting off the opposite is true with the rear lifting and the front diving. The rear suspension toe angle will change between the 2 making the rear end geometry change with a significant affect on handling. Also true for the front If there is any bumpsteer causing toe angle changes too. You could be going from a nominal front and rear toe under acceleration and quickly go to a squirrelly geometry under deceleration. Something to check.

 

[comegetjoe]

You could be going from a nominal front and rear toe under acceleration and quickly go to a squirrelly geometry under deceleration. Something to check.

How does one take this into account while getting an alignment?

 

[Desert Sasqwatch]

By checking for bumpsteer on both the front and rear suspension and making changes to the front steering/rear toe links to minimize this condition. A-arm angles, height of the steering rod end links, front steering arm (on the hub upright) and steering rack/toe rack height can all be adjusted to gain an ideal geometry. This is the first step. Afterward the front and rear of the car can be lifted slightly with a jack or weighted down to simulate the front and rear squat/lift to see if any camber and toe changes go in the wrong direction - basically you want to avoid toe out.

 

[Rttoys]

How does one take this into account while getting an alignment?

Lots of measuring, beer drinking, thinking, searching, luck, guessing. Sometimes physics.


the rear toe moves roughly 1/8” from center, when cycled up and down. If you set your rear ride height with the tie rods level, then set toe at 1/4” overall, or 1/8” toe in each side. As the rear suspension cycles up and down, it’ll only move you back to 0 toe. I found 1/8” total toe in on the rear seems to work best. I would say 1/8 to 1/4 rear toe in being fine.

 

[redline]

Another aspect to remember; under acceleration the rear suspension will squat and the front suspension will lift. When letting off the opposite is true with the rear lifting and the front diving. The rear suspension toe angle will change between the 2 making the rear end geometry change with a significant affect on handling. Also true for the front If there is any bumpsteer causing toe angle changes too. You could be going from a nominal front and rear toe under acceleration and quickly go to a squirrelly geometry under deceleration. Something to check.

that is what it feels like is happening. but I have ran this level of power for years and it has only been about the last year that the squirrelly has started happening. now I have changed tires, so maybe that is a factor too?

 

[redline]

Lots of measuring, beer drinking, thinking, searching, luck, guessing. Sometimes physics.


the rear toe moves roughly 1/8” from center, when cycled up and down. If you set your rear ride height with the tie rods level, then set toe at 1/4” overall, or 1/8” toe in each side. As the rear suspension cycles up and down, it’ll only move you back to 0 toe. I found 1/8” total toe in on the rear seems to work best. I would say 1/8 to 1/4 rear toe in being fine.

I have not tried going out to 1/4. I may try that as well. My new parts came in so lots of things to try!