What's The Diff?
I have a '72 Olds Cutlass fastback with a 350 Rocket backed up by a TH350. I am almost done with this project except for the rearend. I want to replace the open diff and 3.23 gears with a posi and 3.73s, but I am having a very hard time finding parts. If I use a rearend out of another GM A-body, will it be a basic bolt-on part except for the U-joint? If not, what modifications are needed? If it won't work, who has parts for the 10-bolt that's under it now?
Kansas City, MO
Any '68-'72 GM A-body rearend bolts in as a complete assembly, although a conversion U-joint may be required. However, there shouldn't be any problem finding parts for your car's existing rearend if it's the original factory-installed item: Unlike other A-bodies of the same vintage, the '71-'72 Buick Special (includes Skylark) and Olds F-85 (includes Cutlass) came with the 8.5-inch ring-gear "corporate" 10-bolt rearend. Ring-and-pinions and differential cases from many other trucks and passenger cars (including the '71-'81 Camaro/Firebird and '73-'77 A-bodies) fit, plus there's a huge selection of aftermarket parts available.
Performance With A Price
I drive a '79 Volvo 262 Bertone with a '90 Mustang H.O. 302, AOD trans, and all computer functions intact. I'm running cast-iron manifolds to 2-inch pipes to a single three-way cat. From there back, it's Volvo 1 7/8-inch pipe with a muffler from a six-cylinder Camaro. I drive the car a lot and really appreciate the quietness. What do you feel is the minimum-size exhaust that I should use, and will a freer-flowing exhaust really help my gas mileage?
Drexel Hill, PA
Up to a point, reducing exhaust restriction generally helps gas mileage. But going too large can overscavenge the engine and result in a mileage reduction. Proper exhaust size is a function of both engine output and displacement. Ford used a full 2 1/4-inch dual exhaust system on the Mustang, complete with dual cats and mufflers. Assuming the engine is stock, in theory, 2-inch dual pipes should be adequate, as indicated by the accompanying exhaust system recommendation chart courtesy of Flowmaster Mufflers. Specifically, it's the 1 7/8-inch single-pipe and weak, little, single six-cylinder muffler that's holding you back. If there's insufficient room for dual pipes and mufflers after the converter, use a single 2 1/2-inch pipe and corresponding low-restriction aftermarket muffler. The converter inlet and outlet should likewise correspond to the inlet pipe sizes.
2975 Dutton Ave.
Santa Rosa, CA 95407-7800
Ford Motorsport sells the Tremec heady-duty five-speed under PN M-7003-R58.
I have a '68 Ford Ranchero that I have been wanting to upgrade to an overdrive Tremec 3550 five-speed in place of my current four-speed Top Loader. Will it bolt to my bellhousing and allow me to use my stock clutch and linkage? I know I may have to modify the driveshaft and other things.
The Tremec five-speed uses the Top Loader trans-to-bellhousing mounting-bolt pattern, but its standard input shaft length is the same as an '83-'93 Ford V-8 T5-about 5/8-inch longer than the small-block V-8-type Top Loader. Spacer plates are available from Dark Horse Performance, McLeod Industries, and Total Performance that let you bolt a Tremec up to a stock-type Top Loader bellhousing or equivalent aftermarket scattershield. Alternatively, the correct-length (shorter) input shaft and required corresponding shorter bearing retainer is available from Tremec distributor Dark Horse Performance. Either way, the stock clutch and clutch linkage remain unaffected.