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We are racing at the SCCA Regional race this weekend at Laguna Seca (Weathertech raceway) weather looks to be great. car has been through a lot of maintenance since my shock blow out at Sears point during the race, so this will be the final shake down before the SCCA National Championship Runnoffs. ( new shocks, tune up, with new cap and rotor, oil change, and new spark plugs)
there is a chance i might do one more weekend , but we will see. ill have new tires for the event as well and they might even be REAL slicks (like Yok Advans) since the GT2 class the 928 is classed in now, doesnt have the DOT limit on it. Also, the GT2-ST class i was going for, didnt ever really happen due to the lack of the VTS from WCGT . Eitherway, you dont get anything more than an (*) after your car for placing in the field. no real benefit.........so, its not going to be in the front of the pack, but if i can be in the top 15-20 that will be pretty cool based on the quality of the 40 car field planned for the race.
The race went great . the car felt new, but the old rear tires are still an issue. times were average but the car never felt squirrly diring the race as it has as of late. had a great grid made up of lambos, porsches bmws vets , nascar, and many others. a ton of fun with the BMW for the win over him (a pro prepared car ) so that was fun, and took 3rd in GT2 class out of about 10.. 9th overall out of about 25 cars.
Here are some pics
video soon
the grid
a monster NSX look to this car winning the runoffs
new shock but worried about the size of the new bump stop
The race went great . the car felt new, but the old rear tires are still an issue. times were average but the car never felt squirrly diring the race as it has as of late.
new shock but worried about the size of the new bump stop
Make you wonder what the actual spring rate is, for the next couple of inches?
This is a "classic" Porsche weekend racer problem (early 911's, 964's, and 993's are famous for this problem.) Standard length shocks in a significantly lowered car. The bump stop becomes the most significant part of the spring rate, with any tiny amount of travel.....the size of the actual spring is moot. (As soon as the bump stock compresses, significantly, the spring rate goes very high and that end of the car will "wash" away.....Travel induced snap understeer or oversteer, depending on which end of the car hits first.) To allow the shock and the regular spring to do their job, in a 928, you need about two inches of shock travel, before the bump stop adds in any additional rate.
Koni used to make a large variety of bump stops, that could be used to tune what impact the bump stop has on the spring rate when it actually hits..
The only real solution is to buy shorter shocks or raise the car.
Semi-retired, as of Feb 1, 2023.
The days of free technical advice are over.
Free consultations will no longer be available.
Will still be in the shop, isolated and exclusively working on project cars, developmental work and products, engines and transmissions.
Have fun with your 928's people!
Make you wonder what the actual spring rate is, for the next couple of inches?
This is a "classic" Porsche weekend racer problem (early 911's, 964's, and 993's are famous for this problem.) Standard length shocks in a significantly lowered car. The bump stop becomes the most significant part of the spring rate, with any tiny amount of travel.....the size of the actual spring is moot. (As soon as the bump stock compresses, significantly, the spring rate goes very high and that end of the car will "wash" away.....Travel induced snap understeer or oversteer, depending on which end of the car hits first.) To allow the shock and the regular spring to do their job, in a 928, you need about two inches of shock travel, before the bump stop adds in any additional rate.
Koni used to make a large variety of bump stops, that could be used to tune what impact the bump stop has on the spring rate when it actually hits..
The only real solution is to buy shorter shocks or raise the car.
it was a bit pushy, considering i had new tires on the front and used tires on the rear from the NSX after ACS a few months ago. however, if you dont get a snap, (as the body compressed the spring and it all of the sudden "stops" when it bottoms or progressively hits that bumpstop) the you are left with a rigid situation, where you wouldn't think it would effect a constant radius turn that goes on for a few seconds.
as far as travel goes, i do seem to have about 4
" of wheel travel, and i think i equated that to about 1-2" of shock travel. these bump stops are quite a bit larger than the ones that came on the shock originally, so maybe if i have enough travel, i just need to cut say, half the bump stop ? But i think the real answer is clear.. these shocks have no business being on the car. i need much shorter shock bodies. below is a pic of the example of how much actual travel the wheel makes And below that, is a pic of the rear shocks that use the same bump stops after being rebuilt as well. they are MUCH larger so im thinking cutting them to size might be warranted.
You need to check the rear shocks when installed, to see how close the bump stops are.
The 964 "American Cup" cars were terrible to drive, on long high speed sweeping corners, because the rear bump stops would hit before the fronts. The rear spring rate would way up and the rear end would rotate. In a 911, this is really tough to "fix" if you are already at full throttle.
The idea is to hit the bump stocks on quicker, tighter corners, where increased spring rate is desirable. You generally will need to "tune" the bump stops, so that one end of the car doesn't get a whole bunch of additional rate all at once.
Having the same bump stops, front and rear is intuitively wrong....unless the spring rate (of the actual spring) is the same front and rear. However, that is totally dependent on "when" the bump stops actually make contact.
You run your car super low....which means you give away suspension travel. What is the benefit of running the car this low?
You need to check the rear shocks when installed, to see how close the bump stops are.
The 964 "American Cup" cars were terrible to drive, on long high speed sweeping corners, because the rear bump stops would hit before the fronts. The rear spring rate would way up and the rear end would rotate. In a 911, this is really tough to "fix" if you are already at full throttle.
The idea is to hit the bump stocks on quicker, tighter corners, where increased spring rate is desirable. You generally will need to "tune" the bump stops, so that one end of the car doesn't get a whole bunch of additional rate all at once.
Having the same bump stops, front and rear is intuitively wrong....unless the spring rate (of the actual spring) is the same front and rear. However, that is totally dependent on "when" the bump stops actually make contact.
You run your car super low....which means you give away suspension travel. What is the benefit of running the car this low?
the rear spring is longer. the ride height mechanically, is much higher so there is much more travel. Ill have to see if the bump stops are ever hit, but based on the original bump stops, the rears were not touched much and the fronts were destroyed by contact and age. bump stops add about 100pounds of spring rate, per inch and i would imagine it is progressive.
yes the car is low, and the reason for that is to get the camber to the 2 degree range up front and in the rear. the main reason is to get the CG as low as possible without hitting anything on the track (and be able to get it up on a trailer). aerodynamically it is better as well with less air flowing under the car. every inch you lower the car, its like widening your car near 2" as far as its ability to develop corning forces. this is why all of the fastest of the same type cars will generally be the lowest for an advantage. you also keep the CG lower for a given weight transfer for corning and braking.all to improve both of those tasks. there is a consideration of suspension travel, but as long as it is not bottoming out abruptly, you should try and get a car to this limit. the rear has plenty of travel and the front is fine for all turns and bumps except for the corkscrew. Ive got a lot of suspension video both front and rear.
the rear spring is longer. the ride height mechanically, is much higher so there is much more travel. Ill have to see if the bump stops are ever hit, but based on the original bump stops, the rears were not touched much and the fronts were destroyed by contact and age. bump stops add about 100pounds of spring rate, per inch and i would imagine it is progressive.
yes the car is low, and the reason for that is to get the camber to the 2 degree range up front and in the rear. the main reason is to get the CG as low as possible without hitting anything on the track (and be able to get it up on a trailer). aerodynamically it is better as well with less air flowing under the car. every inch you lower the car, its like widening your car near 2" as far as its ability to develop corning forces. this is why all of the fastest of the same type cars will generally be the lowest for an advantage. you also keep the CG lower for a given weight transfer for corning and braking.all to improve both of those tasks. there is a consideration of suspension travel, but as long as it is not bottoming out abruptly, you should try and get a car to this limit. the rear has plenty of travel and the front is fine for all turns and bumps except for the corkscrew. Ive got a lot of suspension video both front and rear.
You're the one that drives it. If it works right for you, it's right.
I had success setting up the cars I worked on with enough suspension travel to make them "work" and gave up whatever aerodynamic benefits that I would have gained by lowering the car another inch or two.
I always enjoyed the track bull**** sessions where people would compare their camber settings.....with complete disregard to how low the car sat. Might as well sit around and speculate about the universe....
If someone sets their car up at 3 degrees negative and has no suspension travel left, that camber number might only be 2 degrees with the car 2" higher, but the end camber result is the same, once the car uses up the travel. The benefit would be that the higher car works better than the car on the "stops". If the person that has 2 degrees of camber, 2 inches higher was to set his camber to 3 degrees (at the higher ride height), he'd have a bunch more "end effective camber" than the guy with 3 degrees 2" lower.
You're the one that drives it. If it works right for you, it's right.
I had success setting up the cars I worked on with enough suspension travel to make them "work" and gave up whatever aerodynamic benefits that I would have gained by lowering the car another inch or two.
I always enjoyed the track bull**** sessions where people would compare their camber settings.....with complete disregard to how low the car sat. Might as well sit around and speculate about the universe....
If someone sets their car up at 3 degrees negative and has no suspension travel left, that camber number might only be 2 degrees with the car 2" higher, but the end camber result is the same, once the car uses up the travel. The benefit would be that the higher car works better than the car on the "stops". If the person that has 2 degrees of camber, 2 inches higher was to set his camber to 3 degrees (at the higher ride height), he'd have a bunch more "end effective camber" than the guy with 3 degrees 2" lower.
Get my drift?
yep, you are singing my song. its not as bad as you may think because we are lucky with the 928 and the amount of camber we gain with compression. this is why i can beat on this car til the cows come home and the tire wear is amazingly even. that is the proof of camber actually working, and ive shown its NOT on the bumpstops .. well, the old ones. im worried about the new ones. here it is at sears, with the blown shocks and no bumpstops coming through turn 10 at 100mph at full tilt boogie. you can see i have a lot of movement and that movement is a TON of camber as you suggest that should never be sacrificed and I totally agree.
yep, you are singing my song. its not as bad as you may think because we are lucky with the 928 and the amount of camber we gain with compression. this is why i can beat on this car til the cows come home and the tire wear is amazingly even. that is the proof of camber actually working, and ive shown its NOT on the bumpstops .. well, the old ones. im worried about the new ones. here it is at sears, with the blown shocks and no bumpstops coming through turn 10 at 100mph at full tilt boogie. you can see i have a lot of movement and that movement is a TON of camber as you suggest that should never be sacrificed and I totally agree.
That looks amazingly good! All four corners on the ground and definitely working.
I don't know how external adjustable Konis are set-up, but on the internal adjustable ones, you need enough bump stop to keep the adjusting mechanism from being hit and destroying it.
You might want to ask the people that rebuilt them, if you can run a shorter bump stop.....and how much shorter.
BTW....I've got a few external Konis here that I'd like to get rebuilt...who did you use?
That looks amazingly good! All four corners on the ground and definitely working.
I don't know how external adjustable Konis are set-up, but on the internal adjustable ones, you need enough bump stop to keep the adjusting mechanism from being hit and destroying it.
You might want to ask the people that rebuilt them, if you can run a shorter bump stop.....and how much shorter.
BTW....I've got a few external Konis here that I'd like to get rebuilt...who did you use?
The guy that is the "greg Brown" of shocks, is located at sears point . Koni and many other brands . PSI (Performance shock Inc).
I just sent a picture to them regarding the lack of travel. i even raised the ride height up 1/2 " on the fronts. i just checked the rears, they are close too, but not as bad.. remember, i had suspension components smash the fuel pump power and ground wires in the external harness! UGGGG, ruinied my Runnoffs in 2014.... on TV sitting off track for all laps but the first 7...... anyway, im going to see if i can clip the bump stop by half, and inquire about some shorter shock bodies.
Performance Shock, Inc. (PSi)
Dealers and Service Center for all Öhlins, Koni, Penske, ZF-Sachs, Bilstein, Moton, JRZ Shocks, Hypercoil & Eibach Springs, & Goodridge Fluid Transfer Products! http://www.performanceshock.com
P: 707.938.5664
the race video.. the start few laps, and a lap or so near the end
great battle with the BMW... it broke down, near the end and the 928 ends up finishing another race!! 120plus hours on the engine and still running like a champ!!
REAR cam.. watch the 15 year old in the LAMBO pass. insane money!!!
I even caught the redline shift , right at the exhaust pipe. nice sounds!! go to 2:15 on the video
So much interesting stuff in this thread:
1) Mark, I have dreams that look just like your videos. Never gonna be me, I think, but glad someone is at it.
2) Always amazing, the things GB knows. Who knew that, in addition to everything else, he has a PhD in bump stops.
3) There is something deep about that BMW running out of gas. All that skill, all that prep, all that expense, and one totally simple and obvious detail neglected.
So much interesting stuff in this thread:
1) Mark, I have dreams that look just like your videos. Never gonna be me, I think, but glad someone is at it.
2) Always amazing, the things GB knows. Who knew that, in addition to everything else, he has a PhD in bump stops.
3) There is something deep about that BMW running out of gas. All that skill, all that prep, all that expense, and one totally simple and obvious detail neglected.
I know , HUH!! Yes, its a blast being out there is such a rare race car. I cant tell you how many people stop by and want to talk about the car and how it sounds. and yeah, about the bumpstops... i thought they were the washer equivalent to a nut and bolt.
Now the bmw running out of gas... kharma, for that opportunistic outside move at the start? I deserved it, I should have protected. And we had the exact same best lap, with most of our times being identical lap after lap. to run out of gas in a 25min race is very odd...... especially in a BMW. funny, most of the guys out there are spilling gas all over the place on the first few laps from over fill. havent figured out why everyone thinks they need to have that much gas on them!
07-25-2018, 07:03 PM
Laguna Seca Race saturday July28th 11am
weather looks to be great. car has been through a lot of maintenance since my shock blow out at Sears point during the race, so this will be the final shake down before the SCCA National Championship Runnoffs. ( new shocks, tune up, with new cap and rotor, oil change, and new spark plugs) 
