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SBC 350 / TH350 / 3.50:1 ???

My coupe runs a 350/350 with a 2.79 rear gear. The car weighs 2490. Back in '06 the wife and I drove it on a 2400 mile trip up through the Midwest and back through the Carolinas. It averaged about 18 mpg. I've had several TH-350's over the years in different weight and size vehicles and I love them for their reliability and simplicity. Bolt them in, hook up one vacuum line, and you're ready to go; no wiring or solenoids to mess with.:cool: They do have one quirk, however... they don't like sustained RPM's above 6800! Back in my stock car days I once had a 1981 Cutlass sportsman car with a radically built 350 Chevy engine. We ran a 6.20 rear gear on a 3/8 mile asphalt track. At the end of the straightaways, when everything was working right, the engine was turning 7200 RPM. The third or fourth time we were at the track, during pre-race hot laps, at the end of the back straight, there was a sudden violent BOOM and the car just quit pulling. After being towed to the pits we discovered that the transmission was twisted off at the bellhousing!:confused: That was bad enough, but it happened two more times! Once it threw the drive shaft out in 3 pieces and once it split the case and I spun in my own trans fluid and hit the wall.:mad: We thought we were getting faulty transmissions. Finally, an old retired transmission specialist told me that TH-350's have this odd characteristic - depending on the tolerances machined into the parts, somewhere between 6800 - 7200 RPM the front pump pressure overrides the valves and it energizes 1st, 2nd, 3rd, and Reverse all at once!:rolleyes: Something's got to give and it's generally the aluminum case. Moral of the story: a stock TH-350 is a great transmission for the street, but not so much for high RPM racing.:thumbsup:
 
My coupe runs a 350/350 with a 2.79 rear gear. The car weighs 2490. Back in '06 the wife and I drove it on a 2400 mile trip up through the Midwest and back through the Carolinas. It averaged about 18 mpg. I've had several TH-350's over the years in different weight and size vehicles and I love them for their reliability and simplicity. Bolt them in, hook up one vacuum line, and you're ready to go; no wiring or solenoids to mess with.:cool: They do have one quirk, however... they don't like sustained RPM's above 6800! Back in my stock car days I once had a 1981 Cutlass sportsman car with a radically built 350 Chevy engine. We ran a 6.20 rear gear on a 3/8 mile asphalt track. At the end of the straightaways, when everything was working right, the engine was turning 7200 RPM. The third or fourth time we were at the track, during pre-race hot laps, at the end of the back straight, there was a sudden violent BOOM and the car just quit pulling. After being towed to the pits we discovered that the transmission was twisted off at the bellhousing!:confused: That was bad enough, but it happened two more times! Once it threw the drive shaft out in 3 pieces and once it split the case and I spun in my own trans fluid and hit the wall.:mad: We thought we were getting faulty transmissions. Finally, an old retired transmission specialist told me that TH-350's have this odd characteristic - depending on the tolerances machined into the parts, somewhere between 6800 - 7200 RPM the front pump pressure overrides the valves and it energizes 1st, 2nd, 3rd, and Reverse all at once!:rolleyes: Something's got to give and it's generally the aluminum case. Moral of the story: a stock TH-350 is a great transmission for the street, but not so much for high RPM racing.:thumbsup:
I bet that was a wild ride! I had a 700 r in a s10 blazer behind a stout 283 and it split the case on the road. I never did figure out exactly why, but the case behind the bell, just in front of the selector is pretty thin material. I suspect that whoever initially swapped the v8 into it may not have properly sized the driveshaft... it too came out and was bent...
 
I bet that was a wild ride! I had a 700 r in a s10 blazer behind a stout 283 and it split the case on the road. I never did figure out exactly why, but the case behind the bell, just in front of the selector is pretty thin material. I suspect that whoever initially swapped the v8 into it may not have properly sized the driveshaft... it too came out and was bent...
I replaced it with a th350 and it was happy again.
 

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