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Author: nismotony (---.cox-phxexpress.com)
Date: Nov 25, 11:43pm

Maybe this will take some stress off of Tony D to calculate everyones speed for them.
Here's how you do it.

I'll use my car as an example, everyone can plug in their own numbers for tire sizes, gear ratio, and RPM.

My car:
Tires 205/60/15
Rear Axle Gear 3.70
Top RPM 5500

Take the tire width size (205) and multiply by the tire aspect ratio (60)

205 X 60 = 12300

Divide by 100
12300/100 = 123

Multiply by 2
123 X 2 = 246

Divide by 25.4
246/25.4= 9.685

Add rim diameter to this number
9.685 + 15 = 24.685
This is your tire height

Multiply by Pi
24.685 X 3.1415= 77.54

Divide by 12
77.54/12= 6.46 This is your tire circum. in feet.

Multiply this by the Engine RPM
6.46 X 5500 = 35530

Divide this by your rear end gear ratio
35530 / 3.70 = 9603

Divide this by 88
9603/88 = 109.125MPH
This would be the top speed with a transmission ratio of 1:1 (4th gear)

If you have a 5 speed you then divide the MPH by the 5th gear ratio, lets say it's .7 ( I don't know what it is exactly in my car)

109.125 / .7 = 155.89 MPH!!
There you go, I hope this helps
 

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How difficult is it to get to 5500 rpm in 5th gear with a 3.7 rear end? Down-hill? I don't know because I've never tried, but I look forward to!
 

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As I said...

Nowhere near 180, EH?

I have an Iskendarian slide-rule that lets you do that in the ballpark real quick. I found it, and confirmed my suspicions.

BTW, all, HP comes in as a limiting factor. I seriously doubt that a N/A Z car will do much over 135 with stock HP. A turbo may be able to hit these theoretical speeds, though.
Oh, yeah, and remember many of the ZX's have a 3.90, which is even slower.

Basically what Nissan did was to gear the car to hit top speed at peak power output. This allowed best pickup with the heavier body, and gave decent MPG at the then-imposed 55MPH speed limit (divide 5500 by three and see your legal-speed rpm's!)

180 was just a bizzare and totally bogus boast of an impotent benchracer.
 

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Yup, that'll do!

I'd say that you could actually gear up and try a set of 3.36's and shoot for a 162 top end with that figure. The way I see it, I'll need somewhere in that region to hit the record at ElMirage in Production Supercharged next year....
BTW, can anybody tell me how bad that 180mph top speed claim deterioriated over thanksgiving. It seems to have been snipped before I could return, and I have some real interesting e-mails in my excite box questioning my parentage and detailing my overall physical resemblance to male genitalia! Somebody definately woke up on the wrong side of the bed and got it snipped before my return.
 

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Found it!

I just didn't look far enough back!
I have a Turbo 83 ZX FSM, but for the life of me I can't locate it right now to give you the O.D. number. I believe it's in the .74 range, though. that's the Borg tranny FS5C90somethingorother instead of the normal FS5C71B that's in everything else.

I'm planning on running the 90 as it's overdrive is higher, and the gears seem better spaced for my application. Your HP range is correct for the speed, though. Come to ElMirage or Bonneville next year. They will have a LOT of new classes with open speed classifications---ECTA has some "street" classes out in N.C., and that's always an option, too. That HP range and gearing, you should be good. The track in N.C. is one mile of concrete, out here its 1.3 miles of dry lakebed (read dirt that sometimes turns into talcum powder a foot deep during a run...)

When I find my manual, I'll post the O.D. ratio attention to Nismotony!
 
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