[joedls]

Originally Posted by 94cobra69ss396

Can you run a 28 inch tire with 3.73 gears and tell me what mph you show for 6000rpm?

Also know that a Slick will grow as you go sown the track. So if we use a 26 inch slick it will act like a taller tire further down.

Without allowing for any growth and/or variances in the tire, a 28" tire with 3.73 gears will be running ~134 MPH @ 6000 RPM in fourth gear.

[BRUTAL64]

Originally Posted by Vettezuki

I have to go for a few hours, I'll run this later. But yes, the tire changes in diameter is where the real world differences in speed as a function of gearing changes.

Just for shits. WEIGHT can limit the rpms the engine is able to turn.


What ever could be MORE important than Motorgen??????????




Hey, I just noticed I have OVER 1000 posts on this site. Damn, what the hell would I have to say that takes that many posts???????

[Vettezuki]

Originally Posted by BRUTAL64

Just for shits. WEIGHT can limit the rpms the engine is able to turn.


What ever could be MORE important than Motorgen??????????

Absolutely.

My implicit assumption was that given our power to weight ratio, the engine would have sufficient power to rapidly reach redline given either a 3.55 or 3.73 axle. I was isolating a single variable in the system. There is basically no cost difference with either axle, but there plausibly could be a few mph and/or couple tenths penalty one way or the other. My hypothesis would be that with the power to weight we're likely to have, the "slightly" taller rear axle, would result in faster ET and Trap in the 1/4. However, it is possible that while the top potential speed is lower with the shorter gear, it may reach that top speed faster enough to result in a faster ET. To model this properly we'd be changing from simple arithmetic to real math. I'm looking for accumulated experience.

Anyway, this is getting to the kinda splitting hair territory, but I enjoy that, so you have to endure it.

[Vettezuki]

Originally Posted by BRUTAL64

. . . .

What ever could be MORE important than Motorgen??????????

. . . .

Making the scratch that allows me to underwrite this project is pretty important.

[Vettezuki]

Originally Posted by joedls

Without allowing for any growth and/or variances in the tire, a 28" tire with 3.73 gears will be running ~134 MPH @ 6000 RPM in fourth gear.

A tiny bit slower, but close enough.

6,000rpm (shift/redline)
Wide Ratio Top Loader
3.73 Axle
275/60x15 Tire

If we have enough power to turn this gearing (my guess is around 500 BHP with this much weight, very rough) and make it stick for a wicked 60', and click off clean shifts, this would be a consistent low mid 10 second pass.

[BRUTAL64]

Originally Posted by Vettezuki

Anyway, this is getting to the kinda splitting hair territory, but I enjoy that, so you have to endure it.

You mean endure it....like a tooth ache????

[joedls]

Originally Posted by Vettezuki

A tiny bit slower, but close enough.

6,000rpm (shift/redline)
Wide Ratio Top Loader
3.73 Axle
275/60x15 Tire

[/IMG]

Since we're being nitpicky, your math is a little off. Here's how I calculated it.

MPH= ((RPM/(rear gear ratio*trans gear ratio))*60)/tire revs per mile

RPM = 6000
Rear Gear = 3.73
Trans gear ratio = 1
Tire revs per mile = 720.49
MPH = 133.95708

Thus my earlier posting that it would be ~134 MPH.

[Vettezuki]

Originally Posted by joedls

Since we're being nitpicky, your math is a little off. Here's how I calculated it.

MPH= ((RPM/(rear gear ratio*trans gear ratio))*60)/tire revs per mile

RPM = 6000
Rear Gear = 3.73
Trans gear ratio = 1
Tire revs per mile = 720.49
MPH = 133.95708

Thus my earlier posting that it would be ~134 MPH.

My sheet does three things a little differently. It calculates circumference exactly on input tire size. A 275/60x15 is slightly less than 28 inches. Additionally for reasons I can't remember and forgot were in there it has built in corrections altering the revs per mile and revs through the transmission. Hence the reduction from your completely accurate pure calculation. I can alter my sheet to remove these built-in corrections and we'll come out to the same numbers exactly. But this would be a totally idealized, perfect circumference, no slop kinda situation. I suspect my sheet may model reality a little more closely, but I certainly can't give you the logical proof for the constants that are used. There, aren't you glad you asked?

[BRUTAL64]

Originally Posted by Vettezuki

Making the scratch that allows me to underwrite this project is pretty important.

"If" I wanted to donate a buck or two how would SOMEONE do this???

[joedls]

Originally Posted by Vettezuki

My sheet does three things a little differently. It calculates circumference exactly on input tire size. A 275/60x15 is slightly less than 28 inches. Additionally for reasons I can't remember and forgot were in there it has built in corrections altering the revs per mile and revs through the transmission. Hence the reduction from your completely accurate pure calculation. I can alter my sheet to remove these built-in corrections and we'll come out to the same numbers exactly. But this would be a totally idealized, perfect circumference, no slop kinda situation. I suspect my sheet may model reality a little more closely, but I certainly can't give you the logical proof for the constants that are used. There, aren't you glad you asked?

So how many tire revs per mile does your sheet calculate? Because I calculated the revs per mile using the exact circumference of what a 275-60-15 tire should be. I don't allow for any variances and frankly I don't know how your spreadsheet could do that accurately, considering different variances between tire, tranny, and rear-end manufacturers.

Here is my calculation.

(((275/25.4)*.6)*2)+15 = 27.992125 (Tire diameter)

27.992125 * 3.1416 = 87.940059 (Tire circumference in inches)

87.940059/12 = 7.3283382 (Tire circumference in feet)

5280/7.3283382 = 720.49076 (tire revolutions per mile)