View Full Version : 260 to 350 conversion

07-26-2007, 06:10 PM
hay guys does anyone know if a stock turbo 350 tranny will hold up to a 350 gm motor?

im going to pull my 260 tomorow and put in a 350 just wondering how long the tranny will hold up because i wont have a new trans for about a month

07-26-2007, 06:15 PM
that tranny was mated to a 350 in quite a few applications ... what kinda weight and vehicle are we talking about ?

07-26-2007, 06:15 PM
its all gonna depend on the weight, hp,tq and what your pulling

07-26-2007, 06:18 PM
not sure how much my car wieghs but its a 79 olds cutlass salon i plan on doing some motor work to the 350 in the future aiming for like 500hp after a little while

07-26-2007, 07:32 PM
any other insight?

07-26-2007, 07:53 PM
For a bone-stock 350cid the 350 Turbo Hydramatic 3-speed auto is more than adequate. I've seen more than a few of them mated to engines making up to around 330-350hp @ the crank and held up just fine.

If you're going to be doing work to it to make it around 500hp (and that will take some real doing - don't think a few bolt-ons will get you there) you'll want to look into getting that current tranny built to hold it or possibly think about sourcing a Turbo 400.

07-26-2007, 09:06 PM
Automatic Transmission Description & Usage
THM200 - Light duty, "metric" 3 speed transmission.

THM250 - Used in small 4 cylinder cars (Vega, Sunbird, Monza) from 1973 to 1981 and some Nova/Camaro/Chevelle 6 cylinders in 1974 & 75. The 4 cylinder models have 4 large cooling holes near the torque converter, while on the "bigger cars" there are no cooling holes.

THM200-R4 - Used in GM rear wheel drive cars with the 3.8 V6, 305 & 350 Olds and 301 pontiac from 1981 to 1989. This is a 4 speed, overdrive unit.

THM350 - Medium duty 3 speed trans used from 1969 to 1989, Used in Buick, Olds, Pontiac and Chevrolet cars and Chevy & GMC light trucks until 1987. Generally used in straight and V6 and small block engines. Generally able to handle up to 400 foot pounds of torque.

THM375B - This trans is identical to the THM350, but is considered a heavier duty transmission.

THM375 - This transmission is a derivative of the THM400 sharing the external appearance of the 400. It'll be marked 375-THM on the bottom of the tailshaft housing. It's a light duty version of the THM400, has ABSOLUTELY NO RELATION to the THM375B, and was found in 1972 to 1976 full-size cars. The Turbo 375 was modified to accept the Turbo 350 driveshaft yoke.

THM400 - The THM400 was GM's Heavy-duty 3 speed transmission used from 1964 to 1990. Used on large displacement, high torque engines and engines with towing packages. Generally found in Chevy & GM trucks, cadilacs and large displacement engined, full size GM rear wheel drive cars.

THM700-R4 - 4 Speed transmission used in GM cars and light trucks with the 2.8, 3.1, 4.3, V6, Chevrolet built 305, 350 and 454 engines from 1982 to 1992.

07-26-2007, 09:07 PM
yeah they turbo 350 will only be on it for about a month after i do the motor and make my power ill be putting in a racing tranny

07-30-2007, 03:57 AM
Turbo 350 will be fine for now, but keep an eye out for a Turbo 400, as mentioned before.