I figured posting this here would recieve positive feedback from some who have experience with high speeds on road courses.

My siuation goes: I am in the process of researching what it would take for my Z to compete in the BBORR. Specifically the 140 mph class. I have no experience in any type of motorsports other than drag racing so forgive my ignorance.

My question is at what point or speeds does the stock suspension (reffering to the shock/spring setup) need to be modified? I want to modify my Z to handle 175 mph but run the 140 mph class. Is the stock suspension capable enough?

 

hmm your going to want a turbo :/ and fyi your already in 5 gear :/ :/ :/ coil overs (good ones) :/ :/ :/

 

I have lowering springs and have gone 165 plenty of times. Car get's a little light when you get going that fast. You might want to think about some aero parts also

 

That's very similar to a Nevada run we had on the west coast. Sorry, I've never run at sustained speeds like that but would imagine and decent set of coil-overs (setup will be most important) and a well thought out piece of aero would be invaluable. But with sustained speeds and loads like this, I wouldn't consider it until I got an oil cooler and maybe a rad.

Good luck.

 

175mph? You're gonna need more than suspension and areo.

 

Yeah...

I was assuming you had FI by your profile name, is ADMAN right in thinking there are no FI power adders?

 

Tires are the most important, make sure they are rated for a sustained 175mph.

Stock suspension will be fine if you slow for the corners. If you don't want to lose speed then upgrade the shocks, springs, etc. Avoid the cheap Chinese coil over kits.

 

One of the forum members here did that race with his turbo Z. Search and you can find his thread and then send him a PM.

I would tend to be very **** about tires for an event like that. Biggest nightmare, and most likely problem would be a tire failure at speed.

Also, if I'm not mistaken, to enter that class you have to do a fair amount of safety upgrades to the car. I'm not sure but I think at least a roll bar (maybe cage), racing harness, fire extinguisher, head restraint, etc...

I would first enter the 110 mph class to get your feet wet.

 

Thanks for the replies. I've pm'd the other guy already. Also in order to advance in BBORR you have to start in the 110 mph class.

Of course I will need aero, cooling, and tires, but right now I am focused on what the suspension can handle. I know the car can achieve 160 (stock everything) in it's current state but to sustain that speed over a long period of time. Thanks alot though.

 

I've never done one of those events, but I did run 193 miles at 117mph average speed once...Extended periods between 140-150mph, through turns, over mild crests and dips--your usual interstate fare.

I had W-rated tires (Kumho XS) on nearly stock suspension (Koni Yellows all around), and my exhaust was a single 18" bullet with a turn down right before the diff--so no diffuser-effect stock muffler, just an empty space and the rear bumper acting as a parachute. The rear end got REAL light over 152 (indicated, so closer to 148 or so, given that I was on shorter-than-stock tires). So light that I didn't want to go any faster, and I was already in "get there in time or go to jail" mode.

The suspension definitely didn't have any problems running those speeds for that long a duration, but to go faster, I'd think you might want to 1) go a bit lower (cg and aero both) and 2) go a bit stiffer on springs to resist bottoming out, and therefore 3) go with some beefy shocks that can handle those springs without pogo-ing all over the place. Last thing you want is vertical suspension oscillations at high speeds.

But I'd mostly focus on underbody aero. Getting a clean flow under the car will do more to help reduce lift (especially at the rear) without robbing speed than a wing/spoiler will. Provided you have the horsies to pull you that fast, of course. And that such work is legal within your class.

I think there's a video or photo on here somewhere of someone doing a high-speed event out west where the front or rear bumper was deforming badly under the aero load. Might want to make sure you don't use just any old aftermarket bits--they aren't all created equally.

Sure you know all this, but some confirmation never hurts, right?

 

Does anyone make a full length underbody pan that doesn't create cooling issues with everything from the engine to the diff?

 

There is one. I have it my Japanese Z modification book. Forget the name but it's expensive but I'd say for my situation would be worth it. Will post the name later but not sure what kits would work as some come standard with a diffuser.