Yea I'm w/ you on that. But I'm saying, given you have more than enough hp (say you have a 500rwhp FD) on stock sized tires...what speed will you be at when 5th gear is redlined?

 

tire diameter(feet)* pi * rpm * gear ratio (tranny) * gear ratio(rear)*0.01136364 (ftm/mph)= speed


pat

 

Better check your math...

(24.8" tire = 2.066 feet diameter)

2.066 * 3.14159 * 8,000 * 0.72 * 4.10 * 0.01136364 = 1,742 mph

2.066 * 3.14159 * 8,000 / 0.72 / 4.10 * 0.01136364 = 200 mph

 

gear ratios are 1/ratio. figured everybody here would know that. sorry if i confused ya.

 

Don't worry, you didn't confuse me. Your formula was simply incorrect.

Most people would not know to use "1/0.72", because gear ratios are almost exclusively listed as decimals, not fractions.

 

oh well my bad. guess i dont know what other people know. wrote that on my way out the door to class in about 30 seconds anyway.

pat

 

So the stock gearing WILL take you to 200mph, huh?!

 

Oh, well then that must be it. You've got a quick answer for everything, huh?

Not necessarily. Even after you have enough power to overcome the losses due to air resistance, rolling resistance, and drivetrain friction at that speed, you'll still have some percentage of tire slip and other factors (including the fact that a mounted tire isn't perfectly round) that keep you from reaching your calculated maximum speed.

If you calculate the theoretical gear-limited top speed at redline for 3rd or 4th gear for your car, you can test this quickly and relatively safely. If you accelerate to redline in that gear and note your mph, you will not be traveling at the speed your calculations indicated, despite the fact that you have more than enough power to reach it. Why?

The reason is that traction is never really 100%, there are always inaccuracies in analog gauges, and you need to use the actual measured circumference of your mounted tires to increase the precision of your calculations. Bottom line, you'll always need more gear than you'll actually "use" to reach a given speed.

 

Actually, you have to think that the tire will expand at those speeds and will actually be larger...

Now Ill be running a .5 OD (t-56) and an auto rear (3.90s) so the gearing will not be a problem for me...

I just wateched the vid of the RX flipping at 210... Im a little scared....

 

To some extent. A very low profile radial tire isn't going to grow anywhere near as much as a wrinkle wall drag slick.

 

And for what its worth, I do have a few pilot licenses, so if it comes airborne, I know what to do....

lol.

 

haha.

you said you have a T56 in your car? Borg-Warner? I have wanted to do that in my fc for a long time, waiting till i kill my driveshaft and need a custom one...how hard was it to get the rx7 bellhousing on there? did you have to change the shifter hole?

 

To mark my 3,000th post, I'm officially going to begin calling you "Encyclopedia Jimlab"

 

I doubt it's connected to a rotary engine.

 

oh. well..mine will be, eventually. i checked one out...looked like it would fit without too much problem.. the bellhousing was the only complicated-looking part....my plan was to weld the front half of a fc bellhousing to the back half of a camaro one.