C6 wide gear ratio - Ford Truck Enthusiasts Forums


C6 wide gear ratio

Old 09-02-2004, 11:57 AM
1978Crew is offline
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C6 wide gear ratio

How can I tell if I have the standard or wide gear ratio in my C6? How difficult is it to replace the standard with the wide gear ratio? What would that modification cost?
Old 09-03-2004, 02:16 AM
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The wide ratio kit sells for $300-350. Summit Racing is one place that sells it. It involves complete tear-down of the transmission, so it wouldn't be cost-effective to have them put into a trans that you were not otherwise planning to rebuild.

You likely have the standard gears in your C6 since that's all they came with from the factory and my guess is very few people do the swap. If you want, you can test for trans ratio by accurately recording the engine rpms and vehicle speed in each gear and use your axle ratio and tire size in the following formula to find the gear ratio. Stock C6 ratios are 2.46, 1.46, 1.00. The low ratios, depending on the kit, are around 2.74, 1.55, 1.00. Your speed and rpm recordings would have to be pretty accurate to tell the difference in 2nd gear. I would try it with 1st gear instead.

AxleRatio x TransRatio = (RPM x TireDiameter) / (MPH x 336).

You can divide out AxleRatio to get just TransRatio if you want, but the equation will work fine the way it is too.

None of this takes into account the rpm increase due to torque converter slip in the C6 trans though.... Torque converter slip is not a known constant rpm either, it can vary from about 200-400 rpms. Not knowing that information will throw off the calculation, but you can still find vehicle speed % change from gear to gear at a constant engine rpm and should be able to tell which gearset the % change matches.

Last edited by SoCalDesertRider; 09-03-2004 at 02:28 AM.
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