Corner balance on race prepped 928
07-02-2008, 03:05 AM
#1
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Thread Starter
Corner balance on race prepped 928
John Davis took his 928 racer over to Ken Osage's tonight to have it corner balanced.
We got it up on the scales and this was the initial reading:
(Sorry for the crappy phone pic)
794/853
858/605
Notice how "light" the passenger rear is. Is this typical? I don't know how much fuel John had in the tank, but he did say he had as much as he thought he would typically carry in a race.
Any other racer's come up with this kind of variance in the RR corner?
His front corners were within an eighth of an inch of each other for ride height.
The rears I think were within half an inch.
Both sway bars were unbolted.
What do y'all think?
We got it up on the scales and this was the initial reading:
(Sorry for the crappy phone pic)
794/853
858/605
Notice how "light" the passenger rear is. Is this typical? I don't know how much fuel John had in the tank, but he did say he had as much as he thought he would typically carry in a race.
Any other racer's come up with this kind of variance in the RR corner?
His front corners were within an eighth of an inch of each other for ride height.
The rears I think were within half an inch.
Both sway bars were unbolted.
What do y'all think?
07-02-2008, 08:37 AM
#2
Drifting
is this with him in the car? the weight is being carried by the left rear and front right as if on a four cornered stool two legs on a diagonal were longer and the other two shorter. these two should be ajusted down or the other two ajusted up.
07-02-2008, 08:49 AM
#3
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Car is sitting on the Left rear and right front.
I'ld start by winding the adjuster on the left rear down a bit (as if decreasing that corners rider height) and the same on the right front. But if the front ride height is as low he wants it don't do the right front, wind the left front up to increase the ride height (and corner weight).
I haven't read it anywhere to my knowledge but it stands to reason that given the 928s inability to settle quickly after adjusting suspension, you should probably unbolt the sway bars then drive the car to settle the suspension before corner balancing. Similarly when the corners are balanced (remember that when the fronts are equal and the rears are equal changing both fronts the same amount shouldn't change the corner balance) the sway bars should just bolt straight back on with no need to force the 2nd side into place - If this is the case then the swaybar is bent or the springs are unequal stiffnes - good for oval racing or very fat drivers but not much else.
I'ld start by winding the adjuster on the left rear down a bit (as if decreasing that corners rider height) and the same on the right front. But if the front ride height is as low he wants it don't do the right front, wind the left front up to increase the ride height (and corner weight).
I haven't read it anywhere to my knowledge but it stands to reason that given the 928s inability to settle quickly after adjusting suspension, you should probably unbolt the sway bars then drive the car to settle the suspension before corner balancing. Similarly when the corners are balanced (remember that when the fronts are equal and the rears are equal changing both fronts the same amount shouldn't change the corner balance) the sway bars should just bolt straight back on with no need to force the 2nd side into place - If this is the case then the swaybar is bent or the springs are unequal stiffnes - good for oval racing or very fat drivers but not much else.
07-02-2008, 09:32 AM
#4
Drifting
So when I was volunteering at tech for the Porsche Clash at Watkins a couple of years ago. All we were doing was pushing cars up on the scales and writing down weights and names. In the morning we had a lull so I rolled my car up on them. 3414lbs. Right front corner was 900 lbs (heaviest corner) and left rear was 750lbs (lightest corner). I had all of the floor mats and standard stuff in the car. The only change was the H-pipes, RMB and no spare tire. I was not in the car.
07-02-2008, 10:30 AM
#5
Rennlist Member
Thread Starter
The weight was with Ken's wife in the car. I don't recall the weight of the car empty, but it was in the 2900's. The car was driven over with the front bar disconnected, but I think the rear was disconnected on sight. I had to leave before they did any adjustments, but they did pull the battery and moved it from the stock position to the rear passenger area to get more weight over the light corner. Suprisingly, it had little or no affect.
I'll get an update today to see if they got the corners to balance out, but I thought it was peculiar that the one corner was so light compared to the others, and was curious if this was typical when our cars are stripped for racing.
I'll get an update today to see if they got the corners to balance out, but I thought it was peculiar that the one corner was so light compared to the others, and was curious if this was typical when our cars are stripped for racing.
07-02-2008, 10:47 AM
#6
Rennlist Member
Thread Starter
Just checked my email, from Ken last night:
Adam,
The scales were off a bit, not too much.
LF was 14 Lbs heavy RF was 8 Lbs light
LR was 15 Lbs heavy RR was 22 Lbs light
Actual values were with driver and fuel.
LF 800 RF 810
LR 830 RR 643
1. These were our readings after testing a few turns on the RR
2. The front ride height = within 1/16 no sway bar connection either side
3. The rear ride height = R side up ¼” over the L and no sway bar connection either side.
I will write to Dean as well as Mark Andersen,
My question is, which is the order of importance.
A). Ride Height being equal
B.) Corner weight being equal
After getting as close as possible with the springs should any further balance be achieved with the sway bar drop links
Adam,
The scales were off a bit, not too much.
LF was 14 Lbs heavy RF was 8 Lbs light
LR was 15 Lbs heavy RR was 22 Lbs light
Actual values were with driver and fuel.
LF 800 RF 810
LR 830 RR 643
1. These were our readings after testing a few turns on the RR
2. The front ride height = within 1/16 no sway bar connection either side
3. The rear ride height = R side up ¼” over the L and no sway bar connection either side.
I will write to Dean as well as Mark Andersen,
My question is, which is the order of importance.
A). Ride Height being equal
B.) Corner weight being equal
After getting as close as possible with the springs should any further balance be achieved with the sway bar drop links
07-02-2008, 12:53 PM
#7
Rennlist Member
Drop the LR and raise the RR and you will be right on the money. Its cross weights that matter most.
Right now you are at 1640 vs 1440lbs. thats bad. 200lbs cross weights. you will have to sacrafice ride hight equality to get this in check. its not hard to do. Ive done it on 4 cars. they all end up the same. why???? because all 928s are near the same
give me the ride hights and ill tell you where they need to be to get you close.
mine is at about +/- 10lbs cross weights. front to rear is the standard, 54/46%
usually, 928s are heavy on the driver side and light on the rear right. moving the battery should move the weight, unless there is some magic going on here. (or scale accuracy) you move the weight and the weight readings will move, its just the way it works.
Mk
Right now you are at 1640 vs 1440lbs. thats bad. 200lbs cross weights. you will have to sacrafice ride hight equality to get this in check. its not hard to do. Ive done it on 4 cars. they all end up the same. why???? because all 928s are near the same
give me the ride hights and ill tell you where they need to be to get you close.
mine is at about +/- 10lbs cross weights. front to rear is the standard, 54/46%
usually, 928s are heavy on the driver side and light on the rear right. moving the battery should move the weight, unless there is some magic going on here. (or scale accuracy) you move the weight and the weight readings will move, its just the way it works.
Mk
Just checked my email, from Ken last night:
Adam,
The scales were off a bit, not too much.
LF was 14 Lbs heavy RF was 8 Lbs light
LR was 15 Lbs heavy RR was 22 Lbs light
Actual values were with driver and fuel.
LF 800 RF 810
LR 830 RR 643
1. These were our readings after testing a few turns on the RR
2. The front ride height = within 1/16 no sway bar connection either side
3. The rear ride height = R side up ¼” over the L and no sway bar connection either side.
I will write to Dean as well as Mark Andersen,
My question is, which is the order of importance.
A). Ride Height being equal
B.) Corner weight being equal
After getting as close as possible with the springs should any further balance be achieved with the sway bar drop links
Adam,
The scales were off a bit, not too much.
LF was 14 Lbs heavy RF was 8 Lbs light
LR was 15 Lbs heavy RR was 22 Lbs light
Actual values were with driver and fuel.
LF 800 RF 810
LR 830 RR 643
1. These were our readings after testing a few turns on the RR
2. The front ride height = within 1/16 no sway bar connection either side
3. The rear ride height = R side up ¼” over the L and no sway bar connection either side.
I will write to Dean as well as Mark Andersen,
My question is, which is the order of importance.
A). Ride Height being equal
B.) Corner weight being equal
After getting as close as possible with the springs should any further balance be achieved with the sway bar drop links
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07-02-2008, 01:09 PM
#8
Rennlist Member
one of the many measurements was:
843 814
660 598
right rear jacked up as much as possible without looking funny (140mm) and the driver front dropped as low as it can go. 110mm
843 814
660 598
right rear jacked up as much as possible without looking funny (140mm) and the driver front dropped as low as it can go. 110mm