This weekend at Thunderhill I experienced significant hopping of the car in the rear end. I initially attributed it to lack of an LSD and my inexperience with V710 tire pressures. And this is probably a contributing factor. But another thing I experienced on the old buttometer was that the car felt and sounded liked it was coming to a hard stop (i.e. metal to metal) under suspension compression in the rear. And the sound was coming from the shock towers.

My current thought is that I have the car set too low. I may have been bottoming out the shocks under compression, particularly in Turn 3 where the off camber and application of power without a limited slip plays hell on the car's handling. I'm thinking of raising the car an inch to an inch and a half all the way around. It's currently corner balanced, so if I turn each corner an equal number of turns on the coil overs, it should be relatively close. If I get it to where the hop is reduced or at least the "clunking" goes away, it's probably a good thing for the shocks and for getting the power to the ground.

What do you guys think?

Thanks,

Bill P.

Low is gud
You will benefit from low CG 90% of the time, while the suspension fix idea seems to be during 10-20% of the time. I would inspect for stress and blown bump stops, change it if you might brake stuff. Low is good!

Bill, I am not convinced that Lucille is too low.

Can a racecar be too low

I still think the car is too stiff, unlike Rich, who thinks the car needs to be stiffer. I know your times got better after playing with the suspension in the PM but I am not convinced it was due to the tweeks but your improved lines and pushing harder, plus gettting into the groove of the track and the car.

Before you start changing the ride height I would explore loosening the shocks and the sway bars. my 2 cents worth.

I understand your concern about the suspension bottoming....I have that same concern...with the "Puttputt".

Have you checked to see if you can see any actual evidence of suspension bottoming?

I keep thinking about GT3 cup cars. In Europe they use very stiff springs and bars because the tracks are extremely smooth. In the US they change to softer springs and shock settings because the tracks here are much bumpier.

I suggest you leave the ride height alone and experiment with a softer setup overall. It can't hurt and that way you don't change anything that can't be put back exactly as before without the need of an alignment or new corner balance.

After riding in and driving Lucille several times, my vote would be to try to soften things up and then see how she reacts.
easy enough to undo if you don't like the results.

Bet she is fine on Laguna

It would help if you had a little more data other than from the bottom meter. If you are bottoming out it should be more apparent when you have a passenger.
I can understand Dan's concern about getting too stiff. My car and my driving have gone through a lot of changes in the last 3 years. One thing nagging me in the back of my head is 2 years ago I thought my car was very neutral and predictable. I now consider my car skittish. Is it because I'm turning faster times and am pushing the edge or is it because I've stiffened the car up to where it's like driving a block of wood? I wish I had the answer for both of us.
I'm figuring I need some test and tune days at a track without an event taking place where I can make changes, go out and see how it feels. You might need to do the same.

I'm not so sure that Lucille can be softened up much more. I ran the morning 2 clicks from softest and the bars in the "middle" ground of setup. Rich drove this setup and got into the 10's. He suggested I stiffen car based on the fact that other drivers said my front wheels are coming off the ground under acceleration in corners and the car was porpoising and jumping as we got faster. I stiffend the shocks in the afternoon to (2) clicls from stiffest and put the swaybars at full stiff front and rear. I ran the car in the 11's, but I wasn't too comfortable with the setup. It felt like the front was in bind and rear was dancing all over in turns (you'd probably like the tail now!). The car became much more of a throttle steerer.

I checked the Spec Boxster org website and the pictures of the shop prepared cars show them to be off the ground a good 1 to 2 inches higher than Lucille. I called Michael Essa at Tech Trix Motorsports who is building several of the Spec Boxsters and currently is driving a car himself and he said the PSS9's aren't necessarily the best shock, particulary in the rear. He says the rear stroke is shorter compared to the front ones and that since the bump stop is internal to the shock, you can't do much with it. He started low as well, and ended up raising the car up 1.5 inches to maximize the cars suspension capability.

I'm probably going to burn 2 days at Thunderhill with NCRC on April 28th and 29th to test the car. Doris will be with me and I'll have her drive as well. So we'll get several hours in the car.

I remember when my 914-6 was slammed and I raised it to work the suspension. And Fritz wasn't a bottom scraper either. I'll just take my collar wrenches with me to Thill next month and go full soft, full stiff and then raise and lower the car. If I get rid of the clunking, I can corner balance it again or maybe buy those scales I've been eyeing....

Bill P.

Hi Andy,

I've kinda had a change in my driving as well. My 914-6 was much stiffer and looser than my 911. My 911 had 350/550 springs on it and felt fine. The Spec Box has a 450/500 combo but is heavier, yet bounces. The bouncing occurs as you push the car in off camber or fast transitions. It doesn't bounce on slow speed turns or banked turns. And I was getting the bottoming out feel with 1 or 2 passengers.

I personally like the softer setup versus the rock hard.

Bill P.

Your trying to solve many different things at once. Start simple:

Find out if you bottoming. If you are, that is the first problem. Tie some zipties around the shock shaft and see how much travel you are using. If it's not bottoming out, your not too low (or course I can't see your suspension geometry from NH). If you are bottoming, then raise it up or put more spring in it.

Second, porpoising is caused by insuffecient shock valving. Changing effective spring rates (you did that through the sway bars) will only make it worse.

Something else to remember - If you have mongo swaybars on it you can put too much swaybar in it. This gets really hard to diagnose becuase we don't deal with it very often. Only happens with really big bars on really light cars.

Also, we need more base details of the car. Is it stock suspension design? What springs and torsion bars? Swaybar sizes? Shocks?

I was going the same place Matt was. Shock valving.
and this is stiffer in the compression dampening. If you are only adjusting rebound dampening you are exagerating the problem.

You know what sucks? I spent WEEKS learning about shocks before I bought mine. now I "think" I am an expert.

What I did learn was Next to tires, Shocks are the next best bang for the buck to make our car faster.

Thanks Matt and Joe,

I will use the zip tie method at Thunderhill next month. If I bottom, I'll raise the car incrementally.

My hardware setup is specified by the Boxster Spec Racing organization. We are mandated to use the following:

GT3 front AR bar
Tarett rear AR bar or H&R rear bar. I use the Tarett 4 position adjustable bar
PSS9 shocks all around
450lbs front / 500lbs rear Eibach linear rate 2.5 inch I.D. linear rate springs
Camber plates up front
225/45/17 Victoracers on 17x7 rims in the front (I am also tire testing 245/45/17's up front)
255/40/17 Victoracers on 17x8.5 rims in the rear (I am also tire testing 245/45/17's in the rear)

The hopping and clunking happens with either set of tires. I cannot re-valve shocks or use any other hardware components due to class rules.

I will need to look at home for the GT3 and Tarett AR bar rates. I do know that the GT3 bar on full soft is 50% stiffer than a stock 1997 Boxster AR bar.

Car weight is 2865 lbs with me in the car and 5 gallons of gas. Minimum weight with me in the car and gas is 2700lbs.

Thanks,

Bill P.

I hate rules.
is this a Spec Boxster class? Then what are them other guys running. and are they having the same issues.

I thought we were talking 914, but doesn't matter, the steps are the same. I would try and find out what other people are running for setups.

Looking the Tarrett bar size, I would start thinking your too low.

Joe - no disrespect - but weeks of shock info isn't close to being an expert. The experts around here are working on 30+ years....

Stuttgart Performance and Tech Trix Motorsports in Southern California are leading the charge in building cars for the POC Boxster Spec Series. The Stuttgart Spec Boxster was the test mule for the series and started on JRZ shocks. After deliberation mainly based on cost containment, the PSS9's were chosen as the Spec Series shocks. The Stuttgart test car, which has over 14 months of development into it, sits significantly higher than my car. The owner of Tech Trix is one of the hot shoes in the series. He recommended raising my car as well. And softening the bars. His experience is that the PSS9's have somewhat limited travel in the rear, and do not work well when the car is slammed.

I'll probably soften the car's AR bars and shocks first (along with the zip tie method) and verfiy if I'm bottoming out. If I am, I can progress to the next steps of raising the car incrementally. If I'm not bottoming out, it has to be in my AR settings in combination with the PSS9 settings. What is interesting is I have kept getting stiffer on my AR bars to the point where I am full hard on front and next to full hard on rear. The other cars in the class are running full soft in front and a medium setting in the rear.

Thanks,

Bill P.

Uh yea I know maybe I need to be clear in my "think I'm and expert" comment.

I chewed for yelling/ all caps. and I am too stupid to make italics or something flashy.

Sorry to hijack here, but....

what suspension is everyone running on their race 914's? I have stock 3.2 Carrera stuff, but I can't get it low enough, or balanced enough. I want something that I can bring the front down more and give me more flexibility on camber adjustments.

Any thoughts out there?

-Bob

RSR front struts with raised spindles.

that'll get you low!

take apart, raise spindle, weld back together:

Click to view attachment

Click to view attachment


somehow, i lost the picture of the final product, but you get the idea ...
Andy

First, Hey Andy could you post some specs on your spindle work, how much did

you move it.

Second, you probably thought of this but I was having a simular problem and

it ended up being the sway bar in the rear was set to stiff. Worth a try.

Racer Chris can raise your spindles for you. After the spindles are raised, the steering arms need to be heated and bent downward.