High-Performance Drive Train Upgrades

Your engine is only part of the equation. Our Tech Insider explores the world of high-performance drivetrain upgrades.

Words: Larry Shepard

For many years, I have written about engines, resto engines, rebuilt engines, up-grading engines, you name it. With so much time spent discussing engines, I have rarely covered the chassis. With all the muscle cars of the past 40-plus years, all of the Mopar high-performance engine packages (built by Chrysler) also had high-performance chassis packages. While the chassis is every bit as important to the vehicle’s overall performance as the engine, there are so many hi-tech engine parts and so much attention given to engine performance that everything else tends to be overlooked or forgotten.

With so many options in big cams, big heads, big intake systems, the drivetrain has been used to fix actual engine problems. For example, cams can easily be too big, you can have too much carburation, the ports in the heads can be too large and have no velocity, and any or all of these conditions can require more gear, and/or more converter, etc. The trick to this chassis up-grade business is to not be forced into a race-car chassis, if you actually want a street machine.

Similar to the engine, the chassis has so many options available today that I can not possibly cover them in just one article, so I’ll try to hit the highlights. I strongly suggest that you obtain a copy of Mopar’s Chassis Book (P5007160) to cover details and variations that are beyond the scope of this article. All those engine parts that increased torque and horsepower performance levels require up-grades to the chassis to match these new performance levels.

In past chassis discussions, I have started with the automatic transmission versions because they are more popular. In this article, I’ll start with the manual transmission package. In the past, many manual transmission cars were converted to automatics, but I am not going to try to restore or convert—rather just list one package. A manual transmission package is really a team, and all components in the package must work together. Start your manual transmission package with a bellhousing—production or a safety one from Lakewood. Note that there are two basic Mopar bellhousing patterns—a small-block one and a big-block version, which includes 383s, 440s and 426 HEMIs. Next is the flywheel, which bolts to the engine’s crank flange. There are two crank flanges, a 6-bolt (most wedge engines) and an 8-bolt (HEMI and race cranks). I recommend a 10 1/2" flywheel, (6-bolt) with 130-tooth ring gear and steel (P4529142). The 130-tooth ring-gear means you can use the typical gear-reduction starters like the lightweight ones (P5249644AB with the A-engine or P5007860 with the big blocks).

The clutch (pressure plate) has to bolt to the flywheel and I selected the 10 1/2" unit, so I recommend using the 11" scalloped clutch P4529141, which bolts to the 10 1/2" pattern using small-head bolts similar to those used on headers. The clutch disc fits between the pressure plate and the flywheel and is an 11" scalloped unit, which actually measures 10.95"—P4529137 (23-spline) or P4529139 (18-spline). The number of splines is dictated by the transmission’s input shaft. The transmission should be an A833 4-speed unit and it must fit into the pilot hole in the back of the bellhousing. The outside diameter of the transmission’s front bearing retainer is what pilots into the bellhousing, and there are two bolt circles (for attaching bolts related to the front bearing size) and several diameters which make for several front bearing retainers like P4529697 (available from Mopar Performance). For the A833 transmission itself, you want to use aluminum cases (main case and tailshaft). These are available new from Passon Performance (www.passonperformance.com). You can also get a Hurst shifter (04019122) and a Hurst pistol-grip lever like P4510610 (1968-1970 B-Body without console).

The automatic transmission package starts with the flexplate—6-bolt or 8-bolt. The typical converter has attaching lugs that come in two sizes—5/16" (small) and 7/16" (large). The small lugs are used on most econo (street) converters—6-bolt flexplate with small attaching bolts P4876821 or 8-bolt version P5007378. Next is the torque converter. Many production converters are in the 120K performance range while the HP engines, like the 340, the 383 Road Runner and the 426 HEMI used 145/150K converters in production packages. Today there are 166K (like P5007297AB for A727s) and 175K econo converters available for use with the HP engine packages. Some other helpful automatic transmission parts are the front clutch piston spring P2801243, the 5-to-1 kickdown lever P4529023AB, and the 1" filter spacer (aluminum) P4510054. I strongly recommend the use of a deep pan on the automatic transmission, like P3690730AB or the chrome version P4120161AB (both for A727s). There is also a cast aluminum pan P5007793AB (for A727).

Before I move on to the driveshaft, there is an aspect of both automatic and manual transmission cars that should be addressed. It relates directly to the engine, but half of the solution is in the drivetrain. This engine aspect is external balance and it is used on all 360 engines, and all 340, 400 and 440 cast crank engines. It is also used on the 1970-1972 440 HP engines including the 1970-1971 440 6-BBL and the 5.9L Magnum V8s. With external balance engines, the front face of the torque converter (flexplate itself on the Magnum engines) will have a weight (or two) added to make the whole assembly (engine and converter) balanced. The manual transmission engines are balanced by drilling two or three large holes in the front face of the flywheel. These converter weights and the templates for their location are available from Mopar Performance.

Next is the driveshaft which has a length consideration based on engine position and the wheelbase that is used in your vehicle. If you have to make a new one, use the driveshaft kit P4876886 which is a 3 1/4", 16-gauge tube with a length of 58.20", which allows you to cut it to length for your custom application. The front end of the driveshaft uses a slip-spline that fits into the rear of the transmission.

In general, there are two spline sizes and two u-joint sizes. The A727 uses a 29-spline slip-yoke and a 7290 (big) u-joint. The rear yoke fits into the rear axle (pinion shaft splines), and there are several versions—production, billet aluminum and billet chrome-moly. The 8 3/4", 10-spline yoke is P4510655 (aluminum billet).

While there are 8 1/4" and 9 3/4" rear axles, the most common and the most popular rear axle is the 8 3/4" unit. Many ratios are available. The 8 3/4" sure-grip assembly is P4876118. Remember that sure-grip assemblies use clutches to distribute the engine’s torque to each wheel and as clutches they do wear out and should be replaced every few years. Heavy-duty axle shafts are available from aftermarket companies like Moser (260-726-6689), Mark Williams (866-508-6396) and Stange (847-663-1701). There is a heavy-duty aluminum axle housing P4876445 available for the 8 3/4" unit. The rear axle’s driveshaft angle is set using angle shims like the 2-degree unit—P5153562.

One final tip: When the Chrysler production engineers developed the high-output 426 HEMI package for use with the automatic transmission, they added a supplemental transmission oil cooler in front of the radiator. So if you have a high-output engine package and a 145/166/175K torque converter, you should add an oil cooler like P4876916 in front of the standard radiator. Also remember that the standard radiator for use with an automatic transmission has a bottom tank that cools the transmission oil. This additional oil cooler would be used in addition to the standard bottom tank.