John Speake

You rpm figures stack up pretty well with the 30mph/100rpm gearing of your car. That confirms the speed OK.

You can fit a switch on the octane loop if you want, but the stock timing is very conservative so I don't thinkl you need it. I could give you a chip which would make the car accelerate a little quicker above 180 :-)

RKD in OKC

Here is pic from 1996 and 199mph

mickster

I've read it offers greater downforce-but I'm no engineer and you can't always trust what you read!!

Jim Devine

Do what you can to keep the air from getting under the car. Take a look at the NASCAR cars. At
Bonneville, some classes are required to have roof
rails about 3/4" high.

IcemanG17

The white car did 209-210 in 1999....Tim and Cheryl with Cheryl driving did 209.9 on the GPS...but I think the traps were a touch lower....

George should break 200 this year......Todd's boosted monster in green bay could theoretically go pretty fast with 675whp...or around 800hp it should do about 225

http://www.rbracing-rsr.com/aerohpcalc.html

Pcplod

WOW! That's a fine of over $900,000!! Too rich for my blood!! (Of course, I can't afford his car either!!)

Roy928tt

Congratulations Brett, impressive drive, ***** of steel. The old 4.7 seems to be made of stern stuff as well, thats a lot of punishment for a stock car.

Again congratulations, it has taken single minded determination on your part to achieve this, well done.

Cheers Roy

Brett928S2

Hi Roy

Many thanks, its appreciated especially from you....

Doing something "different" always seems harder for some strange reason but the satisfaction is greater...

All the best Brett

Maleficio

Brett,
What kind of oils are you running?

danglerb

So, running a little late for work that morning?

Rick Carter

6100 6200 RPM with your tire size and gearing for 208 MPH.

mickster

He probably just had to go to the toilet...

rawky

Good god, how fast has he really gone?!

89FrontPorsche

You need to do something to counteract the natural tendency of the shape of the car to produce lift. Bernoulli's prinicple is involved here and when air travels over the top of a wing, the air underneath flows in a straight line. The air over the top must travel faster to meet the air at the bottom and therefore creates a low-pressure area. This is why a wing works and why your car, or most any car with nice, flowing shape like the 928 has, needs something to push the car down onto the ground, which is why you felt it "go light" at higher speeds which also results in less traction, among other things.

An S4 spoiler would be helpful, even going so far as to put some additional negative pitch to it. That means putting some angular shims between the wing and the car. Through-drill them so you can experiment.

The downside is that there has to be a compromise between downforce and aerodynamic drag. Too much wing angle and it robs the car of the ability to go faster. You probably already know this.

Additionally, the rear isn't the only thing to worry about. The front of the car is lifting up too and affecting steering. The speeds you were traveling at are higher than what it takes to get a multi-ton airliner off the ground. Most airliners rotate the nose high at around 150 knots which is about 172 mph. There is no doubt your car is creating lift but the spoilers are having some effect. I would not go much faster than 150 mph in a spoiler-less 928. Those Porsche engineers knew what they were doing. The spoilers on your car are designed to be "satisfactory" to the factory design speed limits of the car.

Naturally you are exceeding those with the nitrous and thus, entering into race-car territory.

A more aggressive front spoiler to generate front-end downforce is needed as well as more downward "lift" at the rear. But the more downforce, the more aerodynamic drag at high speeds so it's an art as much as a science. But in clinical terms, it's called "induced drag" or drag due to lift.

Some people, and myself included, have taken model cars, put them in a homemade wind tunnel and experimented with the model on a kitchen scale to see how much downforce I could make. Those scales are available at cooking shops and are usually not too expensive.

Then, to make it even more interesting, I had gone so far as to put two scales side-by-side to see what happened front vs. rear.

It was all an academic exercise while attending an aeronautical college years ago. I got a "B". Was really angry for all the effort I had expended. Internet didn't exist yet and all my data was actual, calculated and charted.

The drag part of it is a little harder. You have to take a string and put the car on its wheels and I found they needed bearings...so it started getting involved but..with the air moving at a constant rate, I could use the string, run through small pullies and attached to the scale, would pull it down a certain amount.

Naturally, the larger and more aggressive spoilers I tried, the more drag.

It's not something everyone enjoys doing but since it was an exercise for a paper, I thought it all very enlightening.

You have entered into the world of aerodynamics, sir. Not the goofy, kid-racer with funky colors on the cars with fart exhausts type of wings, either. Serious stuff. Many F-1 racers typically blast down the straights at 2225 mph+ often limited by either the length of the straightaway or by regulation. But aerodynamics plays a HUGE part in it.

http://en.wikipedia.org/wiki/Formula_One_car

Be careful, m'lad. You are in dangerous territory. I wish you well and success. But do so in one-piece, please.

Brett928S2

Hi

I run Silkolene 15/50 full synthetic and fully synthetic auto fluid as well...

All the best Brett