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Chevy TH2004R Transmission Build - Stout & Small

You Can Build A TH2004R To Handle 400-800 Horsepower

By Doug Marion, Photography by Doug Marion

Back in the '80s, General Motors introduced the Turbo 200 automatic overdrive transmission. Despite its use in the mighty Turbo V6 Buick, its failures in earlier applications gave it a bad reputation. It was considered a weakling, not capable of performance intentions.

It can sure be termed "smaller" when compared to a 4L80E AOD and that's because it is. From this moment on, forget everything you ever read about the TH2004R of old-and remember everything here on out. This transmission could very well benefit you.

The California Performance Transmission Company is the latest venture by the legendary Art Carr, who has been been building high-performance automatic trannys for longer than many Super Chevy readers have been alive. His slightly reworked TH2004R transmissions can handle anywhere from 250-400 horsepower. We have a 360-horse, 355-powered '70 Monte Carlo with a TH350 and it was in desperate need of an overdrive automatic transmission to combat today's high fuel costs. Another benefit of the C.P.T. 2004R is the installation is straight-forward and (we believe) affordable.

First of all, the 2004R is the same length as the Powerglide and TH350 transmissions. It also has the same dimension output shaft and uses the same TV cable and transmission coolant lines. We therefore consider it a "drop in" with one exception: The transmission's rear crossmember must be moved back 6.5-inches. Many frames are already drilled or dimpled for this because this is the approximate distance between a PG/TH350 and GM's numerous other transmission rear crossmember location.

A 2004R is therefore easier to install than a 700R4 and has a slightly better Overdrive ratio (0.67 vs. 0.70). The 2004R's First-gear ratio is 2.74 while the 700's is 3.06. Rumor has it that the 2004R First-gear ratio is stronger. Second-gear ratio comparo is 1.57 versus 1.62. Third-gear ratios are both 1.00:1. For comparison, the Turbo 350's First- and Second-gear ratios are 2.52:1 and 1.52:1. With a better First-gear ratio and an Overdrive, it's like having your cake and eating it too.

Extreme Duty Upgrade-800 Horsepower Capable
From working on Buick Turbo V6 2004R transmissions beginning 20-plus years ago, Carr took aim at what modifications the transmission needed for these cars to run as quick as the high 7-second range in the quarter-mile. Some of the internal modifications include extra clutches in Third and Fourth gears, a larger Second-gear billet aluminum servo, heavy-duty Second-gear band, a 10-vane pump kit, a hardened steel stator, and a heavy-duty, heat-treated intermediate shaft and drum assembly and a custom-calibrated torque converter.

Art Carr does not believe in using a lock-up torque converter in any aftermarket-engineered, high-performance application. None is used in the California Performance Transmission 2004R. The approximate rpm different is about 200 rpm. But the driveability problematical factor is immense, especially if you have a lot of horsepower or a medium duration camshaft of 270 degrees duration or more. Due to camshaft overlap, drivability below 2,000 rpm is poor. So a lock-up torque converter is a no-no.

Mileage with a big cam will generally be lousy too. Overall drivability will be even worse. A V8 engine with a smooth-idle cam with high idle-vacuum would also have poor drivability as the lock-up design feature would continually be locking and unlocking at cruise-speed depending on road angle and throttle position. Many, including this writer, believe it's not worth the hassle.

Art Carr's California Performance Transmissions sells its transmissions like Burger King sells its food-any way you want it. The basic 250-horse-capable 2004R transmission begins at about $1,600 without extras, plus shipping. A 400-horsepower version begins at $1,799 without any extras (plus shipping). The 800 horsepower-capable 2004R's pricing begins at $2,400. All Extreme Duty 2004R internal components are available individually. A complete transmission parts kit, part number 11251 (less friction band) is $295. Visit the CPT website for more product and pricing information.

Author's Note:
California Performance Transmissions is the only company Art Carr is affiliated with. He sold his original company, Art Carr Transmissions, in 1997, only to see it move to Abilene, Texas, as well as Northridge, California. He is not part of either company.

SOURCES
California Performance Transmissions
Huntington Beach
CA
8-00/-278-2277
cpttransmission.com
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By Doug Marion
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