stump_breaker Posted May 21, 2007 Report Share Posted May 21, 2007 In another post you said you have 4.30 gears in a Cobra and still were doing 140ish in the car. How tightly wound is the engine and what are you rpm's at 70 mph? I've been thinking about a gear swap to 4.10's. Link to comment Share on other sites More sharing options...
sexybackshelby Posted May 21, 2007 Report Share Posted May 21, 2007 My wife was driving the cobra ? Link to comment Share on other sites More sharing options...
stump_breaker Posted May 21, 2007 Author Report Share Posted May 21, 2007 My wife was driving the cobra ? I know you said your wife was driving. You have never driven it? That's ok anyway. I got the answer I was looking for earlier today. Link to comment Share on other sites More sharing options...
ShelbyGT/SC Posted May 21, 2007 Report Share Posted May 21, 2007 I know you said your wife was driving. You have never driven it? That's ok anyway. I got the answer I was looking for earlier today. Stump, can you post the answer for the rest of us? Thx Link to comment Share on other sites More sharing options...
stump_breaker Posted May 21, 2007 Author Report Share Posted May 21, 2007 Stump, can you post the answer for the rest of us? With 4.10 gears and the OD gear (5th) in the tranny being a .62, RPM's at 70 with 27" tires should be about 2215 +/-. with 28" tires = 2135 +/- with 29" tires = 2062 +/- Final drive ratio would be approx (.62 x 4.10) = 2.54 I don't have the car with me and can't remember the tire size..... The #'s with 4.30 gears 27" = 2322 +/- 28" = 2239 +/- 29" = 2162 +/- Final drive ratio = (.62 x 4.30) = 2.66 IMO 4.30 would work nicely in this car giving a good launch and with the .62 OD gear still get decent mileage. Our cars currently have a 2.20 final drive gear which IMO is way to high for a sports car although it does give it great top end speed. At launch with 4.30 with first gear having a 3.37 ratio it would be like having a 14.49 geared rearend vs. the 11.96 we have now. That is quite an improvement. I had 4.10's in my Dodge truck with an auto and OD gear was .70 (I think) and 30" tires. RPM's at 70 was 2500 on the nose and it really woke the truck up. It started with 3.92 and average mileage never moved from the 17 MPG mark (as long as I was not driving that is) with either set of gears although 4.10's did improve city mileage. If my #'s are off, I'm sure someone will tell me. EDIT 1.0 - WHOOPS, it's actually a .62 OD gear so the RPM's will go down slightly. I corrected it all. I didn't think something looked right. Remember RPM's are estimates. It could be 100-200 more. The calculators are never perfect. Link to comment Share on other sites More sharing options...
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