3.55's, 3.73's Or 4.10's???

jimberg · 03-18-2001, 11:21 AM

I thought you might like some further reasoning as to why 4.10s are too much.

Let's say that your RPMs will be good to 5000 as you suspect, the last gear ratio of a C4 is 1.00, and you have 28" slicks.

Since the tranny is turning as fast as the engine, just divide your engine RPMs by differential ratio. 5000/4.10 approximately = 1219.51. Now take your tire height and multiply it by PI. 28 * 3.14 = 87.92. Multiply this result by the previous result and you get the number of inches per minute you will be going at 5000 RPMs. 1219.51 * 87.92 = 107219.3192. Multiply that by 60 and then divide by 63360 for MPH. ( 107219.3192 * 60 ) / 63360 approximately = 102 MPH.

That's it. You'll be losing steam at 102 MPH. High gear ratios are either for weak engines that need a boost in torque or for strong engines that can put out high RPMs. Even with 3.55s you'll be losing steam at 118 MPH.

Come to think of it, you either want to do something so you have power through 6000-7000 rpms, go with maybe 3.27s or 3.08s, or use really tall tires.

------------------
351W 89 Mustang GT Convertible

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03-18-2001, 11:21 AM	#1
jimberg Registered Member Join Date: Oct 1998 Location: Rogers, MN Posts: 2,089	I thought you might like some further reasoning as to why 4.10s are too much. Let's say that your RPMs will be good to 5000 as you suspect, the last gear ratio of a C4 is 1.00, and you have 28" slicks. Since the tranny is turning as fast as the engine, just divide your engine RPMs by differential ratio. 5000/4.10 approximately = 1219.51. Now take your tire height and multiply it by PI. 28 * 3.14 = 87.92. Multiply this result by the previous result and you get the number of inches per minute you will be going at 5000 RPMs. 1219.51 * 87.92 = 107219.3192. Multiply that by 60 and then divide by 63360 for MPH. ( 107219.3192 * 60 ) / 63360 approximately = 102 MPH. That's it. You'll be losing steam at 102 MPH. High gear ratios are either for weak engines that need a boost in torque or for strong engines that can put out high RPMs. Even with 3.55s you'll be losing steam at 118 MPH. Come to think of it, you either want to do something so you have power through 6000-7000 rpms, go with maybe 3.27s or 3.08s, or use really tall tires. ------------------ 351W 89 Mustang GT Convertible