Hi Everyone,

Finally got my crate motor 290hp/350 it is good now after some warranty issues fixed. I put an Edelbrock performer manifold and Thurder Series 650cfm. Oh my does it use a lot of gas. more than 3/4 tank to beach and back. (I got to fix this????) Now I need a new auto tranny. My 39 year old 2 spd. powerglide is toast and has been leaking excessively, pretty powerless and winding etc. So, I need some help as I am clueless on this issue. Turbo 350 or 400.? Pro/Con change outs necessary etc. Do I need to change out the standard 10 bolt rear end. It is a daily driver (my baby) but I want power to go with my engine (otherwards what a waste, right?)

So, what do you think? Thanks for your help!

since you got a lower hp engine. i would go with a 350 tranny. a 400 trans is heavier. need new crossmember. yolk and driveshaft. unless you planning on adding like another 200 more hp or more i would stick with a 350. which you drive everyday use a stock torque converter. it is around 1400 stall you will be fine with it. a higher stall you will suffer gas mileage with it.

Wendy,

I had a power glide in my 68 Convertible and am in the middle of changing it out for a 2004R. I have 3.73s in the rear and really wanted the overdrive the 2004R provides. The TH350 and TH400 are good trannys too but their highest gear is a 1.0 ratio where a 2004R is a .63 to one. A 700R4 is another one to look at. It has an over drive also, but not quite as low as a 2004R. Just depends on what you want. Recommend you search the threads for more info. There is a lot of discussion on this subject within the site with a bunch of good info. Many talk about what you need to do the swaps, etc. If you decide you want to go to a 2004R, I can point you in the direction I went to get one. You should not need to change the rear end. Your 10 bolt will work just fine. You might consider changing the gears to get the most out of your engine. If you decide to do that, highly recommend you change it to a posi. All of this you can do with the 10 bolt. Just some thoughts.

Good luck.
Brian

The 350 route is a bolt in, except linkage and shifter. Definitely the cheapest route: same crossmember, driveshaft, and I even used the same cooler lines. Your 10 bolt will be fine with the combo you mention. Piece of cake!

Enjoy!

Well, I'm a noob here so take it for what ots worth, or isn't...

The 400 trans will suck up a lot of your power and a 350 to handle the power can be had.
An overdrive would be nice depending on the rear gears, if built ok.
The auto will keep the 10 bolt happy.

You might spend some time dialing in (tuning) the carb, timing, etc.

More info on the current milage could help...

More info on the rear gearing could help deciding if its better to use the 350 trans or an overdrive. A low numerical gear in back such as a 3.07 may be happier with the 350 trans.

Yeah, but the only way he is going to gain fuel mileage is with an overdrive tranny. The 350 and 400 both have a final drive ratio of 1:1.

Like Brian said, you have to use an overdrive tranny. If you keep a tranny with a 1:1 final drive, then she will have to change the rear gears and then it would lose take off power. With an overdrive, she can have the best of both worlds. Keep the rear gears and go with an overdrive.

Wendy, I know how you feel. I have a Powerglide with 4.10 rear gears. At 55mph I am turning 3112rpm. I am going with the T-56 6 speed. It has the overdrive and it's a manual. I get bored while driving an automatic. So bored that I find myself having trouble staying awake sometimes. I drive my car EVERYDAY and in ALL WEATHER CONDITIONS so I have to have a tranny that keeps me interested.

The bad gas mileage might have been from the trans slipping, carb or timing not set optimum, etc. The TH350 route is a direct bolt-in like has been previously said and you should still be able to get 15-20 mpg with your combination, depending on driving style. I think your motor will lug with an OD trans and stock gears and probably get no better gas mileage for the increased conversion cost. That's my vote for what it's worth. Let's us know how it works out.

3.08 or 3.36 axle gears go good with TH-350. 3.73 might be better with 200-4R. 3.55 axle gear might go either way, depending on highway use, tire size, horse power. Even 2.73 gear would feel faster off the line with TH-350 (than the PG). Have fun.