The car feels a bit floaty over about 140. It doesn't feel like its hugging the road... kinda like it's about to take off. Trying to manuver the car above 130-140 is downright scary sometimes! Im trying to figure out how to fix the problem.

Part of the problem is that there is about 3/8" of play in the steering, and a slight speed wobble over 120. Ive been told to have the wheels "road force balanced" to reduce that annoying wobble.

What can I do to address this issue? The car is currently running stock alignment on 250# front/back spring rates. Tire pressure is set at 36.

More downforce?
Higher spring rates?
Manual steering?
????

 

Where in the world do you go over 140? I went 140 on the Indian reservation once where I could see there was no traffic for miles and it felt rock solid but that was in a straight line. You might want to consider moving to Germany if you're planning on making a habit of it

 

Of course this was a professional driver on a closed course... But please lets not let this trhead drift that direction...

 

Assuming stock batwing, engine pans, and rear wing, make sure the ride height provides a rake front to rear, ie. the front is a little lower than the rear. 1.5° is what I've heard is the correct angle the door line should be at. You may need to raise or lower the front to rear angle to get the correct rake at those higher speeds depending on how your suspension compresses. If it feels like the front is getting light, lower it or raise the rear.

Road force balancing is a good thing, you can also have the tire/wheels balanced for higher speeds. Most shops balance for 80 mph.

If you are unsure about tire pressures, make a run then stop and check the temps across the tire to make sure the temps are even across the tire. Most modern radial tires require 3 psi to make much difference in how the tire performs.

 

I am buying an AIR splitter this month. I may modify that to make it a bit more effective as well.

I see what you are saying about the rake. Like a venturi effect? creates lower pressure at the rear... reduces downforce without any drag. Nice.

Has anyone done any other mods to support speeds of 160+ on a stock bodied car? Yes there are other things to be considered at that speed, but knowledge is helpful.

Aero guru's, feel free to comment.

 

Also, How much downforce is the TRS adjustable wing capable of? anyone have specs on that, or real world experience? That might be something else I can look into.

 

DId you fix your leaks yet?

 

In the turbo? no. Its been put off till the 8th because they shipment was delayed and parts won't be here till monday. Im taking the 8th-17th off work just to do all that stuff. Also going to be installing my 3" exhaust from turbo back.

Im going to be going to the dyno after each and every mod I do and posting it here for everyone to see. After the exhaust is a back to back comparison between a stock intercooler and one with the SFR end tank mod.

 

Seriously, do the rake thing before any modifications. The era of your car's aerodynamic design was one of high speed handling. These cars were designed to aerodynamically fly on the road at higher speeds. ie. the 928 is an excellent example. That was why Porsche added the rear under bumper wing on the Turbos. I say era because I was sorely disappointed in my 2001 Boxster S handling at high speed. It was designed to have less drag so higher speeds could be reached with less power. The big trade off was handling. The boxster was so twitchy above 130 I would not drive it above 140 period.

When I had my 88 Turbo S, I made several high speed road trips in various states of suspension upgrades. When the front was even the slightest bit high it made the car get wondery above 100.

Alignment and front toe makes a huge difference too. The front toe needs to be less than zero for higher speed stability even though zero or a little positive is considered within spec.

 

very interesting i would be looking foward to your findings.

I would worry take it as one project at a time instead of trying to do it all at once type thing. GOOD LUCK

 

Thanks, that is just the kinda of info I was looking for!

Speaking of the rear spoiler, what do you think about moving the exhaust and making it one solid piece all the way across. Also dropping it about 1/2 inch. Might not be as pleasing to the eye, but whatever.
I really would like to lower the front, but I dont have the height adjustable konis. It is lower all around 1" I think.

I know the air splitter itself might not create a whole lot of downforce, but the reduction of air traveling under the car from the front will help to add to the effect that the "rake" you ar talking about creates, no?

 

Don't worry, I'm not going to let myself get overwhelmed like I did with the last car.

I was also wondering... If I wrecked this car at say.... 160 - what are my chances of survival? assuming I dont hit any objects like big trees or other vehicles. Just a loss of control/rollover situation

Original seatbelts, no airbags etc. Just something I have wondered about in the past.

This is becoming a multi-faceted thread....

 

death most likely is my guess. if you hit any soft soil, ditches, or bumps the car would most likely flip and roll. at 100+ it would roll many times too. But I have no idea how damaged the roof would be...

 

Roll cage should be a given if you are going to routinely reaching those speeds on a street car. The extra 50-70 lbs will be WELL worth it...not that it would save you pending the wreck situation, but it would be one less thing to have to worry about(ie: roof caving in)

 

I dont know how much the 944 bolt in rollbar's would actually help in a rollover, but they atleast allow you to have some freedom to use harnesses. Without airbags, that would be nice. Only thing is there is no effective way to run a substrap with stock seats it seems, so then 4 point are the only option, and I hate the way those feel.... oh well.

Back to how to make my car feel better at high speeds.