86 GLHS High Speed/High Power Control Problem?

[jonnyb]

OK, this one is stumping me.

My built up 86 GLHS had a really bad wandering problem last year under full throttle/full boost on the highway. Basically, the car handled OK until you floored it on the highway and full boost kicked in - then it was hang on for dear life because the car would want to float all over the highway. It felt like the car was hydroplaning on dry pavement!

So I sent out the Koni's to Koni for a rebuild and also went through and checked all suspension pieces on the car (all poly bushings, oversized sway bars, new ball joints, new wheel bearings, new rack - almost everything on the car has less than a thousand miles). Everything checked out OK and I installed the rebuilt shocks/struts and got an alignment yesterday. I had it aligned fairly aggressively with about 5/8 neg camber and zero toe up front and 1/8 neg camber and 1/16 total toe in on the back. Since it's a pain, the back actually wasn't adjusted and the rear passenger side actually had almost 1/4 neg camber, but I wouldn't think that 1/8 more of neg camber on that side would cause a problem (someone please correct me if I'm wrong).

I took the car out for a ride and it handled great through the twisties on the backroads and there was no torque steer when doing some quick 1/2/3 gear blasts, but when I took it up on the highway - same thing - the car felt like I was riding in ice when I hit full boost in 4th.

Like I said, I don't see anything loose and I've pretty much replaced everything on the suspension so I'm stumped. I've searched through a bunch of threads on this site and I've found lots of advice on bump steer and torque steer, but none of those really seem like they are what is going on with my car.

Help - I need to be able to drive this car like it deserves to be driven! Is it possible that having near 400 whp is just too much for an L-body to keep under control?

Jon

[GLHNSLHT2]

How are the motor mounts? Do you have the block off plate removed from the hood vent? Might want to try an S10 air dam to keep more air out from under the car (see Reeves GLH). Does it have a LSD? One other thing is you might want to add end links to the sway bar if you haven't already, the stock setup will bind and not allow the control arms to move freely. But then so does the stub strut a-arm setup as well, but ever little bit will help. Like this:

[jonnyb]

How are the motor mounts?

Poly front and pass side mounts, new stock style drivers side mount and new rear mount, so I would have to think the motor mounts are OK. I was thinking maybe I should go solid poly on the back mount though. Is it possible that the motor is twisting back under full boost and causing my alignment to go out of whack?

Do you have the block off plate removed from the hood vent?

Nope - the block of plate is still installed.

Does it have a LSD?

Yup - it has a quaife diff in a 523/568 hybrid tranny.

One other thing is you might want to add end links to the sway bar if you haven't already

I have a 1 1/4 bar with end links on the front already.

[T-Bohn]

John

is it worse in lower gears at the same speed? If yes torque steer maybe.
Are the A arms solidly bolted in proper torque etc. causing the toe to change?

Something else messing with the toe

K frame cracked cause a flex? Floor pan it mounts onto?

gene

[OmniLuvr]

^def check the kframe closely and kframe mounts on the chassis (the front ones, they bend and crack), both have failed on me. you think its scary now, wait til the kframe or the mounts break

[shadow88]

I find alignment settings have a lot to do with how well any high powered car handles. You didn't mention caster settings either and there could be an issue there. I found negative toe in the front greatly improves touque steer, and how touchy any car is. My settings are as follows. BFG g-force tires 205-50r15 at 34 psi

Front
caster - 1.53 left --- 1.25 right
camber - negative .21 left --- negative .43 right
Toe - negative .07 left ---negative .07 right.

I make close to the same power you do and I find this is more controlable. It's tough to put 400 hp through the front wheels and it may never be easy or feel perfect, but I found my setting tolerable. It does wander a little under full tilt, but that's almost always when there's lots of room to do so.

[zin]

Here's a thought, you mentioned the front toe is set to 0*, when a FWD car is under a load/accelerating, it will try to pull the front wheels toward the center-line of the car, rotating around the axis of whatever will allow it some give, typically the control arms or the knuckles. This is why they often have some positive toe, because it will tend to be pulled to 0* or slightly toe-in. With 400whp, and who knows how much torque, this problem would be even greater...

The thing that might exclude this as the culprit, is that you only seem to see it at high speed, that sounds like too much air getting under the hood causing lift, kinda like the Buick T-type turbos would do. The fix there, and possibly here too, is to prevent the air from going under the car (the air damn previously mentioned) and/or extracting that air, either via Trans-Am/GNX style fender vents or ??? I'm not sure if removing the drip pan would do the trick, it might help, but I'm not so sure it's in a low pressure area, being so close to the windshield, which creates a high pressure area (the reason cowl induction works!).

The LSD could be trying to shift torque from wheel to wheel, but that would always be there and more prevalent at lower speeds, or so I would think...

Given the suspension work you've done, and the fact you only see it at high speed, it sounds like you'll be doing some Aero work very soon!

Hope this helps!

Mike

[jonnyb]

Thanks for all the replies.

I'm pretty sure the K-frame is good and I even had extra welds added before powder coating it and adding all new bushings so it shouldn't be flexing. Maybe something loosened up on it though. I haven't checked the k-frame to frame bolts yet to see if they are tight, nor have I checked the rack to k-frame bolts so it's possible something loosened up since I put it together last year. So I guess I'll put some wrenches on those and see what happens.

However, the floor pans in the car were pretty rotted, so I'm wondering if maybe that even though I replaced them, the body was structurally weakened and it's flexing from the torque.

Since the car blows through 1st and second so quick at WOT, I can't really feel if it's floating in those gears so I don't know how to narrow down whether it's a torque or a wind issue. I get a little more time to feel for it in third, but I don't want to sit there and rev the thing out and spin a bearing trying to figure this out...LOL!

[GLHNSLHT2]

I find alignment settings have a lot to do with how well any high powered car handles. You didn't mention caster settings either and there could be an issue there. I found negative toe in the front greatly improves touque steer, and how touchy any car is. My settings are as follows. BFG g-force tires 205-50r15 at 34 psi

Front
caster - 1.53 left --- 1.25 right
camber - negative .21 left --- negative .43 right
Toe - negative .07 left ---negative .07 right.

I'd be telling my alignment guy to go back and get the camber a hell of a lot closer side to side than that.

Here's a thought, you mentioned the front toe is set to 0*, when a FWD car is under a load/accelerating, it will try to pull the front wheels toward the center-line of the car, rotating around the axis of whatever will allow it some give, typically the control arms or the knuckles. This is why they often have some positive toe, because it will tend to be pulled to 0* or slightly toe-in. With 400whp, and who knows how much torque, this problem would be even greater...

The thing that might exclude this as the culprit, is that you only seem to see it at high speed, that sounds like too much air getting under the hood causing lift, kinda like the Buick T-type turbos would do. The fix there, and possibly here too, is to prevent the air from going under the car (the air damn previously mentioned) and/or extracting that air, either via Trans-Am/GNX style fender vents or ??? I'm not sure if removing the drip pan would do the trick, it might help, but I'm not so sure it's in a low pressure area, being so close to the windshield, which creates a high pressure area (the reason cowl induction works!).

The LSD could be trying to shift torque from wheel to wheel, but that would always be there and more prevalent at lower speeds, or so I would think...

Given the suspension work you've done, and the fact you only see it at high speed, it sounds like you'll be doing some Aero work very soon!

Hope this helps!

Mike

That hood vent actually blows a lot of air out stock. I've driven onto the freeway with 2" of snow on it. Once above 35 the snow starts blowing off like someone has an air gun under it. Also when driving in the rain. Notice how the water hits the windshield higher behind the vent than it does everywhere else.

[black86glhs]

I would try the solid rear mount first. Also, are the correct axles in this thing? Mine had a K-car drivers side in it and it would hunt from side to side like a rabid raccoon, under full boost, and I'm not making much more than stock(or rather wasn't....lol). It obviously was too long and it was compressed badly.

[cdavis]

I wonder if the rear is squating and the front is rising too much, causing the front toe to change.

[shackwrrr]

I wonder what "traction bars" (really just toe change prevention bars) would do on the older a-arms seeing that the neon uses the same basic design (why?) and T-bars help with them.

How is torque steer when accelerating at the edge of wheelspin in 1st/2nd? And It doesent do it just under high speed, it has to be full boost/High speed right? If so I would say then its alignment changing under boost. Aero would cause problems even under high speed cruise.

[shadow88]

[QUOTE=GLHNSLHT2;661830]I'd be telling my alignment guy to go back and get the camber a hell of a lot closer side to side than that. QUOTE]

Cross camber of .22 degrees and you would be worried? Why is that? BTW I'm the alignment guy.

[jonnyb]

I would try the solid rear mount first. Also, are the correct axles in this thing?

I have DSS axles that are made for an L-body with a 568 transmission. Long one on pass side and shorty on drivers side.

I wonder if the rear is squating and the front is rising too much, causing the front toe to change.

I doubt the rear is squating - Koni's are on full firm and it doesn't seem to move much. The front lifting, now that's a different story! It does feel like the front is lifting under heavy boost/acceleration, but that's mostly in the lower gears where I feel that.

How is torque steer when accelerating at the edge of wheelspin in 1st/2nd? And It doesent do it just under high speed, it has to be full boost/High speed right? If so I would say then its alignment changing under boost. Aero would cause problems even under high speed cruise.

Good point - I can cruise at part throttle making a couple pounds of boost and it's smooth and steady at 100 mph, so that would sort of narrow it down to a torque issue.

I'm going to head out there now and check all the bolts and see if I find anything loose. If I don't, then I'm going to turn down the boost to about 12 psi and go for a rip and see if it pulls under WOT. If it doesn't (or the pull is less), then I know it's a torque issue and something is twisting somewhere when I'm putting down the big power and I'll have to figure it out (probably start by throwing a solid rear mount on and see what happens).

Thanks again for all the suggestions.

[cordes]

I have DSS axles that are made for an L-body with a 568 transmission. Long one on pass side and shorty on drivers side.



I doubt the rear is squating - Koni's are on full firm and it doesn't seem to move much. The front lifting, now that's a different story! It does feel like the front is lifting under heavy boost/acceleration, but that's mostly in the lower gears where I feel that.



Good point - I can cruise at part throttle making a couple pounds of boost and it's smooth and steady at 100 mph, so that would sort of narrow it down to a torque issue.

I'm going to head out there now and check all the bolts and see if I find anything loose. If I don't, then I'm going to turn down the boost to about 12 psi and go for a rip and see if it pulls under WOT. If it doesn't (or the pull is less), then I know it's a torque issue and something is twisting somewhere when I'm putting down the big power and I'll have to figure it out (probably start by throwing a solid rear mount on and see what happens).

Thanks again for all the suggestions.

Don't forget that the Koni struts are rebound adjustable. Setting them to a more firm position doesn't stop them from compressing just the same.

[GLHNSLHT2]

[quote=shadow88;661929]

I'd be telling my alignment guy to go back and get the camber a hell of a lot closer side to side than that. QUOTE]

Cross camber of .22 degrees and you would be worried? Why is that? BTW I'm the alignment guy.

I can feel that difference when driving my car. I don't let it leave the shop with more than .1 differece side to side. It's a lazy hack not to have them at least that close.

How is torque steer when accelerating at the edge of wheelspin in 1st/2nd? And It doesent do it just under high speed, it has to be full boost/High speed right? If so I would say then its alignment changing under boost. Aero would cause problems even under high speed cruise.

Good point - I can cruise at part throttle making a couple pounds of boost and it's smooth and steady at 100 mph, so that would sort of narrow it down to a torque issue.

I'm going to head out there now and check all the bolts and see if I find anything loose. If I don't, then I'm going to turn down the boost to about 12 psi and go for a rip and see if it pulls under WOT. If it doesn't (or the pull is less), then I know it's a torque issue and something is twisting somewhere when I'm putting down the big power and I'll have to figure it out (probably start by throwing a solid rear mount on and see what happens).

Sorry I disagree with the statements above. Just because you're not feeling it with a couple lbs of boost at high speed doesn't mean it's NOT an aero problem.

Let's take an F1 car with enough d'force to put it on the ceiling if it wants at 150MPH. Wheel spin is a non-issue at high speed most of the time. Now add 300more hp and all of a sudden wheelspin at high speed is an issue.

Or a Vdub New Beetle, which basicially is like a wing and anything over 120 and it starts to leave the ground. Put your engine into it. At 100MPH with 2-5psi making what? 200hp maybe? The car is fine. Stomp on it and make 300+hp and the car doesn't have the d'force to keep the tires planted.

Understand? It's a package that you need enough d'force to plant the tires at speed. Lift happens exponentially so twice the speed means 4 times the aero forces. What might be ok under 80MPH is not ok above it.

[black86glhs]

What happens when you have someone about the same weight in the pass seat? I'm wondering if it is related to more weight on the driver's side and the high power.
You could do like BMW and add weight to each seat and align it with weight in the car to simulate people being in it. Might help.

[glhs0426]

I stopped driving mine because it was floating at boost. The car was stock. Alignment checked ok, bushings ok, etc. The core support was cracked in half at the transmission mount. The frame rails were flopping around if you found the slightest imperfection in the road when under boost.

[shadow88]

[quote=GLHNSLHT2;662034]

I can feel that difference when driving my car. I don't let it leave the shop with more than .1 differece side to side. It's a lazy hack not to have them at least that close.

A lazy hack? Buddy, sit on a fire. Well within tolerance and not noticeable.

[shackwrrr]

[quote=GLHNSLHT2;662034]

I can feel that difference when driving my car. I don't let it leave the shop with more than .1 differece side to side. It's a lazy hack not to have them at least that close.






Sorry I disagree with the statements above. Just because you're not feeling it with a couple lbs of boost at high speed doesn't mean it's NOT an aero problem.

Let's take an F1 car with enough d'force to put it on the ceiling if it wants at 150MPH. Wheel spin is a non-issue at high speed most of the time. Now add 300more hp and all of a sudden wheelspin at high speed is an issue.

Or a Vdub New Beetle, which basicially is like a wing and anything over 120 and it starts to leave the ground. Put your engine into it. At 100MPH with 2-5psi making what? 200hp maybe? The car is fine. Stomp on it and make 300+hp and the car doesn't have the d'force to keep the tires planted.

Understand? It's a package that you need enough d'force to plant the tires at speed. Lift happens exponentially so twice the speed means 4 times the aero forces. What might be ok under 80MPH is not ok above it.

I understand but it makes it easier to separate the problem. If he accelerates smooth to over 100mph at the same low boost he can see right where the problem starts if its aero related. if its alignment related the problem wont be there and shouldnt randomly start, it will also be there at slower speeds with higher boost. If its aero as you go faster and faster less throttle should be needed to cause the problem.


I replied just as I was about to go to bed I didnt think it through enough.