When it comes to GM performance automatic overdrive transmissions, most discussions center around the TH700-R4. While this four-speed auto has its merits, the TH200-4R offers equal if not greater strength with a slightly different set of ratios. In fact, longtime transmission expert Art Carr believes the TH200-4R is potentially a far better performance automatic.
Carr has been in the automatic transmission business for decades. A few years ago, he sold his original transmission business to the company in Texas that still carries his name. But Carr couldn't stay away from performance automatics for long, and he created a new company called California Performance Transmissions (CPT) located in Huntington Beach, California. This time around, Carr is focusing his attention on the TH200-4R.
Why? To begin with, if you look at our included gear-ratio chart, the TH200-4R employs a more reasonable First gear ratio, along with a slightly deeper Overdrive ratio compared to the TH700-R4. This taller First gear makes the TH200-4R slightly more durable. However, Carr is quick to point out that the TH200-4R still requires several modifications to make it capable of handling the 800 hp he claims it can withstand if properly built and maintained.
Converter ChroniclesCarr is a firm believer in reducing the size and weight of the torque converter on the way to creating the ultimate TH200-4R. Factory lockup torque converters use a large overall diameter as a way to ensure efficiency. Another advantage to a large converter is increased surface area for the internal lockup clutch. Unfortunately, a large converter pays a hefty weight penalty compared to a smaller converter.
One easy way to create additional stall speed is to use a smaller converter, such as a 10-inch versus an OEM 12-inch. Since the smaller converter is also much lighter, it allows the engine to accelerate more quickly, improving dragstrip e.t. and speed.
We followed along as CPT bolted in one of Carr's latest performance-built TH200-4R automatics in a supercharged small-block '65 El Camino. Its owner, Kris Shields, had suffered through three crippled TH700-R4s. While Shields' El Camino is more of a road car than a dragstrip hero, the trans and converter conversion was worth a solid half-second improvement in quarter-mile acceleration, not to mention making the car much more durable and fun to drive.
The CPT Extreme Duty TH200-4R with a custom-calibrated converter, TV cable, and dipstick-tube assembly bottom-lines at $2,400, so it's no budget beater. The company also offers many of the individual components from the Extreme Duty upgrade, so you can improve your trans as you go. Since few enthusiasts build their own transmissions, we're not going to detail every step and modification that CPT performs on each ultimate TH200-4R. However, we will take a look at a few of the more important upgrades so you can get an idea of the number of modifications CPT includes in each of its performance rebuilds. Check it out.
Automatic Ratios Gear Ratios Transmission 1st 2nd 3rd 4th Powerglide 1.72 1:1 - - 1.82 1:1 - - TH350 2.52 1.52 1:1 - TH400 2.48 1.48 1:1 - TH700-R4 3.06 1.63 1:1 0.70 TH200-4R 2.74 1.{{{57}}} 1:1 0.67 4L80-E 2.48 1.48 1:1 0.75Note that the TH700-R4 has a deeper First gear ratio that might appear to be better than the TH200-4Rs. The 700 was originally designed to compensate for use with small-displacement engines with minimal torque. The disadvantage to the deep First gear is the larger rpm drop between First and Second-46 percent. The TH200-4R First-to-Second gear spread is a slightly tighter 42 percent. For comparison, the TH350 experiences a 40 percent drop between First and Second gear.
