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Discussion Starter #1
Anyone know what the gear ratios are for a 67 C4 ?
I am trying to calculate rpm/trap speed to find out what ring and pinion gear ratio to get. Thanks.
 

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If that's all you want, this is an easy question... Answer: 1:1. That's because in high gear, any non-overdrive trans has a 1:1 direct coupling. We'll ignore transmission or coverter slippage at this point.

To calculate theoretical top speed, you need to know tire diameter, gear ratio and engine rpm. You will have to pick a target rpm to figure things out. Let's say your engine has a theoretical redline (rpm limit) of 6000rpm. Lets say you have a 3.00:1 rear gear set. That means that the axles will be turning 2000rpm. With a tire diameter of 26", that means your tire circumference is 81.3". At 2000rpm, you'll cover 162600 inches in one minure. divide by 12 to get feet = 13550. divide by 5280 to get miles = 2.566 and multiply by 60 to get miles per hour = 154.

Now this is all theoretical. At speeds greater than 40mph, you have aerodynamic drag of the car body to deal with. Well, it is a factor below 40mph, but a small one. the faster you go, there is a marked increase in aerodynamic drag.

I have calculated several theoretical top end speeds with a rev limit of 6000rpm and a 26" tire diameter.

rear end ratio speed
3.00 154
3.50 132
3.70 125
3.91 118
4.11 112
4.30 107

Your rate of accelleration is all determined by horsepower and torque of the engine.

Hope this helps you

Milo
 

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Discussion Starter #3
Thanks CJ. I am not concerned with top speed, but trap speed at the track. Here is a good calculator that does all of the math for you.
http://www.corral.net/tech/gearcalc.html

I get you on the 1:1 at 3rd gear. I will just select 4th on a manual. (the calc only has manual trans)

How does the C4 differ in first gear compared to a FMX or AOD?
Are they all about the same?
 

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This is from memory.

C-4 C-6
1st 2.46 to 1 1st 2.46 to 1
2nd 1.46 to 1 2nd 1.46 to 1
3rd 1.00 to 1 3rd 1.00 to 1

R 2.20 to 1 R 2.175 to 1

I think most Ford Automatics have these ratio's.
 

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Actual gear ratios

The C4 & C6 ratios were listed correctly except for some special cases.

The C6 could be had with a low-gear set (2.74-ish.... 1.54-ish).

The AOD & FMX have the same ratios, again excluding the AOD low gear set, which are 2.40/1.40/1.0

The AOD-E comes with the lower ratio gears (model dependant).
 
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