442fanatic

Hey All,

Well have finally fixed the gremlin on the reman quadrajet that was hampering the choke from kicking in upon foot feed before cold start. They don't have a good shim in place on the linkage that connects to that choke tube shaft... Without it, the linkage slipped out of the whole.

Now was able to get the choke re set so that it starts releasing quickly upon start in the warmer conditions like I want and how it was, it won't be run in winter.

Past few tanks I have calculated mileage from 7.75 to 8.75... 3:42 rear end and posi.

For those with 455 s what mileage are you getting with them with a lower gear ratio like this?

Fun71

FYI, a friend in college back in the 80s had a 77 Cutlass with a 350 and it got around 10 mpg.

My experience with my 1970 Supreme 350 was that the in-town mileage didn't change when switching from the original 2.56 rear to a 3.55 rear. My theory was the trans shifted through the gears faster so it got into third gear sooner, plus there was less load on the engine at part throttle.

olds 307 and 403

That mileage blows but is probably typical. I was disappointed with 19 mpg imperial with 70, considering OD and 2.78 gears. Probably 15 will be it with the TH350 going back in. Our 75 Cutlass with a 350 and tall gears could get 20 imperial highway. Our 81 Delta 88 with a 307/250C and 2.41 gears got a best of 32 mpg, usually mid high 20's highway.

442fanatic

I got up to near 10 mpg recently. The engine has less than 2000 miles on it sense rebuild, restoration, and such. Still breaking in. I know it won't get any higher such as it was when I had the 2:92 gear behind the original olds 350.
I am considering changing the rear ratio. However it is fun to get out on the county hard tops and just punch it. With tight gas budget, and the ever changing fuel prices... Take it out for the closer car shows and runs around locally.
Gear vendors over drive is pretty high cost.

I need to look into how one can hook up a 700r4 and how the O.D. works, heard there was a vacuum modification that would control the OD kicking in...

Fun71

Well, I don't think that's too bad at all. I have a 350 and I typically get about 8 mpg. That's due to the way I drive, which is WOT blasts from every stop light.

don71

I've averaged 11mpg with my 455 for years with a 2.56. The best ever I achieved was 15mpg on two consecutive fill ups...long distance.

About six years ago, I swapped the rear gear to 3.23. My average has dropped to 9.5mpg. This is with the same 3spd. th400. There were times I got better mileage, but the average is what it is. I don't do long trips anymore.

Don't let fuel consumption and mileage keep you from enjoying your classic car. Its still a good tool to know regardless.

olds 307 and 403

I wouldn't put a 700R4 or even a 2004R in unless they had many upgrades. The 2004R actually bolts to your 455, has the same mount location and may be close for length, just might need a different yoke and has better gear ratios. The most durable option is the 4L80E with a controller. They are the TH400 with OD. Only minor mods are needed for big power.

442fanatic

Good to know about the mileage in the 2:56.

When the car had its original olds 350 and gear ratio 2:92 I think it was, I would get 17 mpg regularly. Then though they had 89 non ethanol.

I am enjoying the car, but fuel budget can restrict it and other "to do list" things. I work in a service job in agriculture and getting into our longer hour season...

Working today and rain foiled going to a good car show in Guthrie Center Iowa...

442fanatic

Looking at the gear vendor's overdrive. Looks like a good deal if one had $2700 + to spend.
Looking for installation videos for the 70s era cars. If another support is needed. How it is controlled. The info on their website talks more about later model cars with existing electronics.