An Extremely Extreme GTS
#256
Bump steer.......in all the race 928's I built or was involved with, never really had an issue. Casper would bottom out in some of the high G corners with mid corner bumps and it never really upset the car? As my pace increased, I kept increasing the spring rates (especially in front) and re-valving the front shocks to compensate. I must admit Turn 8 at Thunderhill around 100mph at 1.5-6 G and bottoming out (look at avatar) is kinda freaky.....
Watching an extremely fast BMW M3 (national champion GTS3 car) he would take T8 dead flat....like a miata but SO much faster....however he is an extremely skilled driver with top of the line aero and the car is built to the limit of the rules.....he also happened to be 9 seconds per lap faster than Casper.....despite my slight power/weight advantage
Watching an extremely fast BMW M3 (national champion GTS3 car) he would take T8 dead flat....like a miata but SO much faster....however he is an extremely skilled driver with top of the line aero and the car is built to the limit of the rules.....he also happened to be 9 seconds per lap faster than Casper.....despite my slight power/weight advantage
There's a good one or two underpasses in a curve here where a lowered or totally dead suspension 928 will wiggle left and right at both ends pretty disturbingly at speed, to the point that it will induce a quick 1-2- punch of under and then oversteer as each end reacts differently, and at different times.
No car is immune to this.
#257
Bump steer.......in all the race 928's I built or was involved with, never really had an issue. Casper would bottom out in some of the high G corners with mid corner bumps and it never really upset the car? As my pace increased, I kept increasing the spring rates (especially in front) and re-valving the front shocks to compensate. I must admit Turn 8 at Thunderhill around 100mph at 1.5-6 G and bottoming out (look at avatar) is kinda freaky.....
Watching an extremely fast BMW M3 (national champion GTS3 car) he would take T8 dead flat....like a miata but SO much faster....however he is an extremely skilled driver with top of the line aero and the car is built to the limit of the rules.....he also happened to be 9 seconds per lap faster than Casper.....despite my slight power/weight advantage
Watching an extremely fast BMW M3 (national champion GTS3 car) he would take T8 dead flat....like a miata but SO much faster....however he is an extremely skilled driver with top of the line aero and the car is built to the limit of the rules.....he also happened to be 9 seconds per lap faster than Casper.....despite my slight power/weight advantage
That picture appears like the left front corner is around 75mm.
Casper had some version of an off the shelf 928 shock?
IE: Stock 928 Koni just re-valved?
#258
No.....casper has bilsteins custom valved with Heim Joints top and bottom.....they were custom made by the previous owner I believe..... I think the rest of the suspension bushings are stock
#259
Unless something was very wrong, stock shocks and associated pieces could never get that low.
BTW.....That right front suspension has over 1.0 degrees of toe out (~1/2" of toe out), at that height!
The "toe curve" on a stock 928 (173mm front ride height) is really fantastic....very little change in toe, through the operational range of the suspension. They did an exceptional job, at the stock ride heights!
And stays fairly reasonable until ~145mm ride height. (The stock shock "bump stops" are involved in the front spring rate at 145mm, so suspension compression is severely limited, below this number, on a car with stock length shocks and stock bump stops.)
Below 140mm, the toe curve gets terrible, very quickly...but by then, the stock bump stops are very involved in the front spring rate (and the cars are understeering enough (from the increased spring rate) that this height can not maintained for very long), so stock cars rarely get this low.
......However, in all fairness to Porsche, the cars were never designed to operate at ride heights or cornering heights this low
Last edited by GregBBRD; 05-09-2022 at 06:56 PM.
#260
Doc
I texted you the pictures of Caspers Heim joint suspension, its 4 pics top and bottom front-back.
I do recall putting on 1025lb springs in front plus a very high durometer bump stop on the shock shaft? Sean still says it bottoms out, but he does weigh just a smidge more than me :>
Honestly I never had an issue with rear suspension, only the front would bottom out....I did read an old post of mine that said it was set to 140mm front and 150mm rear using stock measurements.....
Whats funny is the Estate running stock shock top-bottoms had bilsteins with cut eibachs and it NEVER bottomed out in T8......it was quite low too...I guess the bump stops were working....it was only 4 seconds slower
Feel free to post the pics if you think it would help
I texted you the pictures of Caspers Heim joint suspension, its 4 pics top and bottom front-back.
I do recall putting on 1025lb springs in front plus a very high durometer bump stop on the shock shaft? Sean still says it bottoms out, but he does weigh just a smidge more than me :>
Honestly I never had an issue with rear suspension, only the front would bottom out....I did read an old post of mine that said it was set to 140mm front and 150mm rear using stock measurements.....
Whats funny is the Estate running stock shock top-bottoms had bilsteins with cut eibachs and it NEVER bottomed out in T8......it was quite low too...I guess the bump stops were working....it was only 4 seconds slower
Feel free to post the pics if you think it would help
Last edited by IcemanG17; 05-10-2022 at 07:27 PM.
#261
For those that might not have seen it on Facebook, here's some beautifully shot video compiled by David Mavro from a marathon session at Thermal this week. The slow-mo footage is part of assessing suspension motion in the various turns there.
The following 14 users liked this post by Rob Edwards:
Andrew Schauer (03-24-2024),
Bertrand Daoust (03-24-2024),
Constantine (03-24-2024),
Daniel5691 (03-25-2024),
Darklands (03-24-2024),
and 9 others liked this post.
#264
Greg, this is very cool.
To solve the transmission torque problem, why not use the C5 or C6 Z06 setup that already has a decent limited slip integrated into it and can withstand in excess of the 500 HP those cars produce in combination with your new clutch. Other than the the shift ****, looks stock enough from the inside except for that extra gear in the pattern of course. For a higher HP build, those ratios are actually quite well matched too and the carbon fiber synchros hold up and work quite well. Just curious.
To solve the transmission torque problem, why not use the C5 or C6 Z06 setup that already has a decent limited slip integrated into it and can withstand in excess of the 500 HP those cars produce in combination with your new clutch. Other than the the shift ****, looks stock enough from the inside except for that extra gear in the pattern of course. For a higher HP build, those ratios are actually quite well matched too and the carbon fiber synchros hold up and work quite well. Just curious.
OR, you could look at the selection of "paddle shift" options.
Just curious . . . .
.
Last edited by GUMBALL; 03-27-2024 at 07:43 PM.
#265
I'm not sure Greg, who put this Tilton clutch together, is on here anymore.