A
Anonymous
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How much of a gas mileage improvement do you guys think I can expect from swapping out the original powerglide 2 speed for a 4 speed TH700R4 in my 3500lb 67 biscayne sedan?? (driving habits pretty mellow)
Huge! I can't think of a better swap in any car, anywhere. Wait, a T5 in a 3-speed 200 Mustang could be close!
The stock Iron Glider has a tall first gear, and a tall diff ratio. The use of a proper modern THM 700R4 will make a huge differnece on take off. The older 2004R is a similar kind of transmission and is lighter and has a less savage first gear. They are getting older. The 307 Olds, Buick V6's and lots of other GM cars used it, but you need a SBC bell pattern, so a THM 700 is a better option.
The THM 700 first gear is a savage 3.06:1 rather than shallow 1.73.
2nd on the THM is first on the Power Glide.
3rd THM is top on the Power glide.
Over drive is an absolute moonshot!
The easy going 250 has a very smooth and tranquile quality about it in stock form. I spent 18 months behind the similar Toyota Landcruiser 4.2, and it was much smoother than my Falcon 250. I've read a bunch of drive reports, and the 'Biscuit' sort of dies with the Powerglide, but will be smooth and economical with the THM 700.
Find all Chevytown's posts, and read. There is some important back-up switching and lock-up clutch in over drive to sort. The block pattern is straight SBC. The stock flywheel may have to be replaced for the last THM 350 250 six form the 76 on 250 Chevy Caprice.
It'll make the car! You should be running the 3.55:1 diff at the very least. With the overdive on, its like its running a set of 2.4:1 gears. The take off form the lights will be roughly twice as rapid.
The stock Iron Glider has a tall first gear, and a tall diff ratio. The use of a proper modern THM 700R4 will make a huge differnece on take off. The older 2004R is a similar kind of transmission and is lighter and has a less savage first gear. They are getting older. The 307 Olds, Buick V6's and lots of other GM cars used it, but you need a SBC bell pattern, so a THM 700 is a better option.
The THM 700 first gear is a savage 3.06:1 rather than shallow 1.73.
2nd on the THM is first on the Power Glide.
3rd THM is top on the Power glide.
Over drive is an absolute moonshot!
The easy going 250 has a very smooth and tranquile quality about it in stock form. I spent 18 months behind the similar Toyota Landcruiser 4.2, and it was much smoother than my Falcon 250. I've read a bunch of drive reports, and the 'Biscuit' sort of dies with the Powerglide, but will be smooth and economical with the THM 700.
Find all Chevytown's posts, and read. There is some important back-up switching and lock-up clutch in over drive to sort. The block pattern is straight SBC. The stock flywheel may have to be replaced for the last THM 350 250 six form the 76 on 250 Chevy Caprice.
It'll make the car! You should be running the 3.55:1 diff at the very least. With the overdive on, its like its running a set of 2.4:1 gears. The take off form the lights will be roughly twice as rapid.