Who has the formula to calculate top speed??? I used to have it but can't find it.

I have already gone 181 MPH in my car, with more RPM to go. But I wanted to determine what my car is "capable" of.

Stock tire size
Stock Diff (3.42)
Stock tranny(5th= 0.84)
7200 RPM rev-limit

Cd & power are obviously NOT an issue.

Thx guys.

 

Darth,
7200 rpm would equal 194.9MPH with the variables you specified.
That’s ignoring any possible tire growth and assuming you’ve got enough power at those rpms

Hope this helps :cool:

 

Vetter,
I don't have the calculation but I do have a Physics minor an I would bet you take your peak RPM (7200) divide by 5th gear ratio (0.84) divide again by the diff ratio (3.42).

This should give you 2506.27 RPM of the tire at redline in 5th. I'm not sure the profile on your tire but I know it's an 18" wheel and a 295mm wide. For now I'll assume it's a 35 series tire(295-35-18). We need the diameter so this is the formula: (295mm) * (0.35) * (2) / (25.4) + 18" = 26.13"
To get the circumference: 26.13" * 3.14159 = 82.09"
(conversion factor is 25.4mm/In)

Now we have the distance in inches the car travels for every full rotation of the tire. 82.09" / 12 = 6.84 feet per revolution. At 2506.27 RPM of the rear tire at redline in fifth gear the velocity of the car will be 17,144.87 feet per minute. 17,144.87 / 5,280 (5280ft/mile) = 3.25 miles per minute. 3.25 * 60 (60 minutes in 1 hour) gives you 194.82 mph at 7200 rpm in 5th assuming I got the tire size correct did my math properly and have some clue of what I'm talking about.

If I have the tire size wrong let me know because that will throw things way off. Man you can tell I have some free time. :lol:


[Modified by 96VIPERGTS, 7:15 AM 11/15/2001]


[Modified by 96VIPERGTS, 7:22 AM 11/15/2001]

 

EUG- THX, do you have the formula? So I can play with the #'s? Like if I change to a 3.73.
your # is ironic. Off the top of my head, I thought it would be about 194. But I wanted to confirm it.

 

GTS-THX The tires are actually 295/35/18's

 

Vetter,
I just edited my original post with the corrected tire profile and came up 194 also. Making that kind of power would 6th be an option or is is too long?

 

I just figured it out using the 295/35 & it came out to 194.828 MPH

Just about what I thought & what EUG said. :smash:

 

You must have sent your response right before I did. hehehe

I'm not sure if it'd pull in 6th with the 3.42, But it might with a 3.73 with me spraying the GAS !! :eek: :eek: :cool:

 

Just Kidding!

 

My guess is 185mph, maybe. You need more ponies to hit 194. (We played with these numbers in figuring what my top speed would be and we were in the 190s with 600hp and an increase in the rev limiter).

 

Your spinning that motor to 7200 with a stock crank? :eek:

 

DArth -

I have a simple EXCEL spreadsheet which does the same calcs VIPER did in his post. You can plug in whatever gear/tire/rpm parameters you want and it computes MPH.

I'll be happy to e-mail it to you if you want.

 

here you go:

http://www.vetteguru.com/misc/topspeed.zip

 

Here is a good calculator:
http://www.f-body.org/gears/

You can look at swapping in a M6 tranny for your M12 if you want to pull 5th to 200MPH with your 3.42's. Either that or I would look at getting some 3.15 or even 2.73 gears for the top end runs.

The engine is under a very high load at that speed in 5th gear and you really don't want to wind the RPM's out that much if possible. Use your calculations to try and gear the car to hit your desired speed at around 6-6.2K. That way when you're out testing the car with a radar you have not only a higher margin of safety but can pick up a few more RPM's if you're not hitting the speed you want.

-Jeremy

 

I've got another nice calculator, created by Kent Schock, a forum member. I don't know how to post it, but, you can contact Kent, or I can email it to you. It's in *.xls format and it specifically for the C5 trans. i.e.: M6, M12, and A4.
Just enter your tire size, R.E. ratio and RPM redline. It calculates RPM at speeds upto redline. It's a nice chart. Thanks Kent.

My email: mcmlxiii@eudoramail.com


[Modified by 2KFRC5, 9:55 AM 11/15/2001]

 

sounds like the spreadsheet link i posted above.

 

I downloaded that also. It's different from Kent's. They're both nice and obtained the same conclusions, just differently.

[B]Don[?b]

 

Let me throw in my O2. It was stated the cd and power are not an issue. I would disagree. As speed doubles, drag quadruples. This exponential increase becomes harder and harder to overcome. Meaning it takes twice as much power to get half as much gain at those speeds. This is even more of an issue for you frc guys, as your cd is not the .29 of the coupe. I'm no engineer, but STAGED is. Let me see if I can get him in here...

Greg
:cool:

 

I know my spreadsheet takes into account Cd and Frontal area, and I am sure the others do to. So just run the numbers and see the HP needed at speed.

arguement over... :cheers:

 

I don't know about HP being a factor for Darth getting to 190+. He makes more power than a STOCK Viper, 911 Turbo, or Ferrari 360 Modena, and they all go 190+. I don't think he'll have a problem, but I haven't looked at his dyno to see how much his hp drops off at those high revs. The FRC still has decent aerodynamics with a CD of 0.31 or 0.32. Better than a Viper GTS which has 0.34, I believe.