DFASTEST951

Hey Todd, I don't know what hp you were talking about to get there but I did 194mph in my car with 265/35/ZR18 wheels. It was at about 6800-6900 rpm. I have a 220mph custom speedo made and calibrated by North Hollywood Speedo. Hard to take your eyes off the road at that speed. I even tried to take a pic cause I didn't think anyone would believe me but for some reason my body didn't listen to me and when I let go with one hand to take the pic, my foot kinda lifted off the pedal and it clicked the pic at 189 and it was all blurry.

If you guys want to find out, don't speculate. quit typing, take your car out and find out by yourself. That's what I did. I'm not smart enough to calculate the ****. I just had enough ***** to find out. I think that makes me a sandwich short of a picnic but I know what my car really does. Do you?

fortysixandtwo

For those that like calculating:

For the 951 transmissions:
Final drive 3.375
Gear ratios
1st: 3.5
2nd: 2.059
3rd: 1.4
4th: 1.034
5th: 0.829

Axle RPM= engine RPM/(gear ratio*final drive ratio)

ft per tire rotation= (load diameter in ft*pi)

mph= Axle RPM*ft per tire rotation/5280)*60


I'll use my tires in the example. I have Hankook R2-S in 245/24/16.
Per Tire Rack:
O.D. is 24.6"
They also list the rotation per mile at 844. I don't trust either of these to be truely correct since the 844 number calculates out to 0.7" of tire squat, which I feel is a bit exessive. I'll use the average of the two for the ft per tire rotation value.
Now, before you go using these tire values, you must look up the demensions for your tire size, model and manufacturer . The advertised size is only a guide line.
Where:
engine RPM=1000
Fifth gear

mph=1000/(0.829*3.375)*(6.348/5280)*60 = 25.78

To get mph at engine RPM devide desired mph by the above value and multiply times 1000. You multiply by 1000 because that was the value used for the above equation. If you calculated the mph with 1 rpm this would not be needed.

So for my car to hit 200 mph
200/25.78*1000 = 7757.95 rpm

I also did not include clutch slip. I feel that you should have a clutch that can handle your engines output without slipping at a steady engine rpm.

Bri Bro

My traqmate had me at 140 MPH at 6682RPM in 4th gear with 255/40/17 tires and that is with GPS not the speedo.

tconn

I've had my speedo reading 160mph with the car still pulling
strong. 285/30/18's

Dougs951

Just for reference what was the advertised top speed for these cars? any year...

gstreev

I've tried these calculations many times and always f&*$ something up. Just go out in the simulator in 5th
gear and notice what your speed is, then double it if you are using 7000 as the max rpm. I would be surprised if this simulation shows more than 90 MPH at 3500. Then calculate the tire diameter difference from stock to correct the speedo reading.

v944god

A bit risky

CarbonRevo

One thing I have always done to find a certain speed is to do like gstreev said and cruise at 3500rpm in 5th, then double that speed and that's your 7k rpm speed theoretically.

I've had my simulated 951 with 238whp/248wtq at 163mph in 5th gear on 17's...at around 6200 revs. I believe the car does 2.5mph for every 100rpm in 5th gear. So that being said, 800 more revs would equal 20mph, which would equal 183mph when adding to 163mph.

Brian also goes to prove my point of doing roughly 148mph in 4th gear at almost 7k rpms. It hits the limiter when the speedo is JUST under the 150mph mark. Pretty impressive. Not many cars (4 cylinders), can do almost 150mph in 4th gear. A C6 Z06 does about 155-160 in 4th gear...

billthe3

Anybody have a really long vacuum chamber we can do speed tests in so we don't have to worry about wind resistance? Of course the weight from the o2 tanks to supply the engine would probably slow the car down some...

Bri Bro

Look at Clarks garage, technical information.


http://www.clarks-garage.com/tech.htm

DFASTEST951

This thread would be so much easier to read and to the point if you just go out and do it. Then report. Rent a track or something and go for it. Then post it.

THEN!!!! If you want. You can see how far your calculations were off. I think that's a waste too but I can't even add so what do I know.

I mean trying to calculate how fast your car can go is like trying to calculate how much money you'll put into your 951 before it considered well sorted and will only require oil changes until you got your money's worth. It aint gonna happen.....Unless...you...just...do it!

toddk911

Hey Joe! Its been a while! How are you??? Buying up a ton of FC's in Vegas??

Well, with those wheels/tires and right close to the 7K, I would say that top speed calculator is pretty close based on your 194mph with 100-200 rpm left.

I typed in 255/45/18 for the calculation that showed 201mph.

toddk911

And make sure you use GPS. Or perfectly calibrated speedo like yours. he he he he....."speedo".

Joe did his high speed run wearing a speedo. lol

A side note, I have been out and at least up to 100mph and my speedo was spot on with the GPS.

toddk911

I know one rennlister has been to the salt flats in his stock 951S and was close on the factory top speed; 161-163. It was on his avatar also.

And that is in salt.

Rock

Wooo Wooooo!