If you have 6.17:1 rear gears, and run the GV overdrive designed to fit a Muncie, which has 0.78:1 overdrive, your car will behave like it has 4.81:1 rear gears, when it is top gear, with the overdrive engaged. If it has 5.38:1 rear gears, that number will be 4.17:1. Yes, your axles, carrier, ring and pinion, and drive shaft will all be still turning at the same RPM. Given the same road speed, and no other changes, your engine RPM's will drop, substantially. If you have 5.38's, you will probably like it enough to drive it more that just a little more! If you post your tire diameter, I can lay out all the numbers for you.
No apologize, I often dwell in the realm of rabbit rabbit trails and derailment. [emoji1303]. Sent from my iPhone using The H.A.M.B. mobile app
Sorry, at first glance I thought you were asking about my buddy’s jr stocker and why he ran an OD trans in a race car. I see what you were saying now. Disregard my response [emoji3] Sent from my iPhone using The H.A.M.B. mobile app
The current slicks are 33 inch Goodyear’s but they are too old and will need to be replaced. I’m going to try and get the tallest tire I can without going to wide. Probably a 30 or 31 inch. Sent from my iPhone using The H.A.M.B. mobile app
I'm looking at overdrive for my 39 Plymouth coupe with some of the newer transmissions they use a lower 1st gear so you need to put that into your figures. You can make or break it with the wrong gearing.
Current operation: 33" tire. 1:1 top gear. 5.38:1 or 6.17:1 final drive. RPM at 65: 4083(6.17) or 3561(5.38) If you have a tach, you can verify your rear end ratio! Potential future tires: 32" tire. 1:1 top gear. 5.38:1 or 6.17:1 final drive. RPM at 65: 4211(6.17) or 3672(5.38) 31" tire. 1:1 top gear. 5.38:1 or 6.17:1 final drive. RPM at 65: 4347(6.17) or 3790(5.38) With a GV 0.78 overdrive: Current tire: 33" tire. 0.78:1 top gear. 5.38:1 or 6.17:1 final drive. RPM at 65: 3185(6.17) or 2777(5.38) Potential future tires: 32" tire. 0.78:1 top gear. 5.38:1 or 6.17:1 final drive. RPM at 65: 3285(6.17) or 2864(5.38) 31" tire. 0.78:1 top gear. 5.38:1 or 6.17:1 final drive. RPM at 65: 3391(6.17) or 2956(5.38) I highly recommend a GV overdrive, should you have the means. They are impossibly stout. I know guys running them in tow rigs, with modified turbodiesels, in the >1000lb-ft range. Ain't nobody complainin'. Buy a second set of wheels, and some drag radials. Get out to cruise night!
5.38’s. GV OD and 31 inch tires would put me right where a stock 57’ Chevy would be with 3.70’s or close to 3.55’s with no OD. That would work. Thanks!! I appreciate the help. [emoji1303] Sent from my iPhone using The H.A.M.B. mobile app
1/2" stroked 265/283 cranks with 4" bore was indeed 352" and some were done almost immediately by Howard Johanson. 3-1/2" Chev cranks are available from Scat. Now it's just finding a 4" bore SBC.
The Jalopy Journal
