Prepping for track weekend at Motorsport Park Hastings

[flickery8]

In less than 2 weeks I will be off to my next track day, and can't wait! But, nothing has changed since last time out regarding my uneasiness at 100+ mph. I haven't had a chance to measure my bump steer, but I do have the ffr kit installed. Last year I was hitting speeds of 130+ with much more confidence. Last month (after getting car aligned) when accelerating in the straights the car felt "unplanted", I've described it as feeling like you are running on ice. It feels very light as if it doesn't have down pressure. I had an experienced track passenger once last track day who said he felt like the car was always on the edge of having the rear end come around (though I don't know if he was referring to the straights). My current alignment is:

1/8" total toe front and 1/8" total toe rear (that is 0.22 front and 0.30 rear with my size tires).

Caster is at 3.1 and 2.7 degrees.

Front camber is -0.6 and -0.2

Rear camber is -0.6 and -0.5.

Last year my alignment was at:
Left front
Camber -0.5
Caster 3
Toe .08

Right front
Camber 0.5
Caster 3.4
Toe 0.2

Left rear
Camber -0.6
Toe -0.3

Right rear
-0.5 camber
0.12 toe

I am not sure what to address to gain the straight line stability. My thoughts are:

1) close off some off the rear hatch air intake (see pics at facebook.com/FastGTM ) This is great for cooling engine bay, but may be lifting the car up.

2) add front splitter. I am guessing I will break it first time I use it, these cars sit so low.

3) close off some of the front grille (and hope I don't over heat)

4) of course getting a wing could help, but I am looking for something I can do in the next ten days.

Any other ideas?
Thanks

[eseethal]

I really cannot imagine that you got an aerodynamic problem - especially with the speed in the region of 100 mph). IMHO blocking off some intakes will not cure your problem - just create other (heat) problems.
Your front camber left/right is quite different - I would prefer to have this symmetrical.
Also (and most important) your rear toe numbers are off - that is really dangerous and scary. You must have rear left/right toe symmetrical (toe in)! Your left rear toe is actually toe out, your right is toe in! This cannot be good :-)



Eugen

[kabacj]

(and most important) your rear toe numbers are off - that is really dangerous and scary. You must have rear left/right toe symmetrical (toe in)! Your left rear toe is actually toe out, your right is toe in! This cannot be good :-)



Eugen

I agree

I'm 100% sure your stability issues are due to your rear wheel alignment.

I would take the car to be aligned. Then mark the camber adjusters to ensure they don't move or swap the cam adjusters with plates that lock the adjustment in place.


If you have rear toe out the car is very unstable. Toe in and you are golden. I had a loose rear camber adjuster and when it moved it changed the rear toe on my car. The car transformed from rock solid to very nervous.

Proper alignment is critical for any GTM traveling over 80mph.

Hope that helps
John

[flickery8]

I agree

I'm 100% sure your stability issues are due to your rear wheel alignment.

I would take the car to be aligned. Then mark the camber adjusters to ensure they don't move or swap the cam adjusters with plates that lock the adjustment in place.


If you have rear toe out the car is very unstable. Toe in and you are golden. I had a loose rear camber adjuster and when it moved it changed the rear toe on my car. The car transformed from rock solid to very nervous.

Proper alignment is critical for any GTM traveling over 80mph.

Hope that helps
John

OK, my first post was maybe not very clear. I currently have
LF toe in 1/16" RF toe in 1/16" (total toe is 0.22 degrees front)
LR toe in 1/16" RR toe in 1/16" (total toe is 0.30 degrees rear)


I posted my old alignment for reference, but I think that is what you guys are seeing? Or are you saying this toe setting is wrong?

Caster is at LF 3.1 and RF 2.7 degrees.

Front camber is LF -0.6 and RF -0.2 (I don't think I can improve this without different upper control arms, I sacrificed camber for caster)

Rear camber is -0.6 and -0.5.

Ride height started at 4 1/4" front and 4 3/4" rear. Once we set the corners weights it got weird. The car sits higher on one side than the other, I can measure later how much.

Total car weight with full tanks = 2,812 includes 200lbs added to driver seat.
Front left = 609lbs
Front right = 537lbs
Rear left = 843lbs
Right Rear = 823lbs

Tires are Nitto Invvo:
Front 245/35/ZR19 93w
Rear 345/25/ZR20-100Y

I have 20X13.5 asanti af121 wheels with 8" back spacing on the back and 19x9 with 7" backspacing on the front.

I do have Crash's shim kit installed.

Not sure where to look next to figure out how to get more stability at higher speeds. As I mentioned, with my crappy alignment I was doing 130+ and it felt stable. I guess it could be related to bump steer if the straight is really bumpy, but I have the bump steer kit installed per the manual (just never measured it). The early kits included the bumpsteer kit.

I really appreciate the help!

[kabacj]

Just for the sake of double checking I would rig up or borrow a set of toe plates and verify the toe settings. Those are critical.

The rear toe setting transforms the car.

If you are looking for straight line stability caster and a lower steering rate on the rack will help.

The stock manual rack was chosen to give good slow speed and highway speed steering effort. Once you are going 130 it's a little too much. Swapping in a power rack will both allow you to add caster (makes steering firmer then you would like with a manual rack) and control how much boost you have.

I have run my power rack without boost at all when I blew the solenoid that powered the pump. It was a shoulder work out to drive on the track but it was possible.

I would concentrate on the caster and toe as the things most likely to change things for the better.

Are you running poly bushings or stock c5? If stock you might have an issue with the toe change when the rubber bushings flex. Just a thought.

John

[Cobra 61]

A few things Your cross weight is not close to 50%. Try 3/32 toe in in the rear and 1/8 toe out in the front. try 5/16" rake since you have no wing, but keep playing with this number. The best way is to lower the front for rake and not the rear. String the car to make sure you are not crabbing, this might effect right and left turn entry. If you want to tape the front opening, tape from the bottom working up one piece at a time.

Just some random thoughts, I don't know where they came from?
Cobra 61

[flickery8]

I went to Hastings Nebraska to check out MPH for the first time earlier this month. The track was wet on Saturday morning but dried out quickly. Had a great day on Saturday. Got to know the track and knocked a couple seconds off of my lap times each session. The top speed on this track is less than those I had been to previously and I did not notice the uneasiness at high speeds. I was disappointed with my braking performance.

I am using the stock pads and vette ZO6 calipers. I have 20X13.5 wheels with 8" back spacing on the back and 19x9 with 7" backspacing on the front. I am using ATE Dot 4 fluid which I changed before this event. Rotors are drilled and slotted. I can tell the performance is not where it was previously and the brakes are getting squishy quicker than before (and I don't think it is just because I am getting faster). I plan on changing the brake fluid and getting a more neutral brake bias (currently a rear bias).

Then, Saturday night I drove the car to a restaurant to eat. We trailer the car to the event, but often leave the truck and two car trailer at the track. I got on it when leaving the lot and I was driving straight in first gear and lost traction as the tires were very cold. It didn't seem like a big deal. About 5 minutes later I heard the serpentine belt breaking in pieces. It took another 5 minutes for it to shred and start to overheat (I was hoping to get back to the track as it was very close).

Fortunately, I was able to get a belt that night and put it on in the am. The belt was VERY tight. It took two guys to pull the tensioner down and push the belt on. Started it up and the belt would work its way off in just a couple minutes. Missed the first two sessions already. Decided to get a smaller belt and bipass the pulley by the alternator that doesn't do anything but add tension. Car ran for several minutes. Drove to grid, and the shredding of the belt began. Ughh, no Sunday laps.

I did notice some stress cracking along the weld of that pulley near the alternator, but it didn't seem like enough to effect the angle of the shaft to get the belt off track when it hits the main large pulley.

So, how do I figure out if everything is lined up properly? I've read of people using a laser, but I could use some help understanding the process. I also bought a new tensioner and pulley to see if we bent it putting the belt on, but it is to deep and hits the motor. Anyone know the part # for a new tenisioner?

[kabacj]

I think the key point is that you ran the belt without issue for months but now you can't run it for a short period without it destructing. That tells me that something has changed assuming ITs the same belt i would confirm all the pulleys spin freely and you have not burnt out a bearing. My tensioner is easily loosened with one hand on the 3/8 ratchet and the other putting the belt over the top pulley. Running with too much tension is hard on the bearings. Next I would check the alignment using a few straight edges. When comparing the angle of the flat faced pulleys I think you will be able to see any misalignment. I would be suspect of anything that was cracked.

I went to Hastings Nebraska to check out MPH for the first time earlier this month. The track was wet on Saturday morning but dried out quickly. Had a great day on Saturday. Got to know the track and knocked a couple seconds off of my lap times each session. The top speed on this track is less than those I had been to previously and I did not notice the uneasiness at high speeds. I was disappointed with my braking performance.

I am using the stock pads and vette ZO6 calipers. I have 20X13.5 wheels with 8" back spacing on the back and 19x9 with 7" backspacing on the front. I am using ATE Dot 4 fluid which I changed before this event. Rotors are drilled and slotted. I can tell the performance is not where it was previously and the brakes are getting squishy quicker than before (and I don't think it is just because I am getting faster). I plan on changing the brake fluid and getting a more neutral brake bias (currently a rear bias).

Then, Saturday night I drove the car to a restaurant to eat. We trailer the car to the event, but often leave the truck and two car trailer at the track. I got on it when leaving the lot and I was driving straight in first gear and lost traction as the tires were very cold. It didn't seem like a big deal. About 5 minutes later I heard the serpentine belt breaking in pieces. It took another 5 minutes for it to shred and start to overheat (I was hoping to get back to the track as it was very close).

Fortunately, I was able to get a belt that night and put it on in the am. The belt was VERY tight. It took two guys to pull the tensioner down and push the belt on. Started it up and the belt would work its way off in just a couple minutes. Missed the first two sessions already. Decided to get a smaller belt and bipass the pulley by the alternator that doesn't do anything but add tension. Car ran for several minutes. Drove to grid, and the shredding of the belt began. Ughh, no Sunday laps.

I did notice some stress cracking along the weld of that pulley near the alternator, but it didn't seem like enough to effect the angle of the shaft to get the belt off track when it hits the main large pulley.

So, how do I figure out if everything is lined up properly? I've read of people using a laser, but I could use some help understanding the process. I also bought a new tensioner and pulley to see if we bent it putting the belt on, but it is to deep and hits the motor. Anyone know the part # for a new tenisioner?