YoungGunLs1

Hey guys,

Well my dad has recently decided he wants to put a 4 speed over drive automatic transmission into our 70 chevelle that we have basically built from the ground up and he wants to make it a little more modernized, allow us to run a bigger stall converter that actually locks up, and make driving the car affordable with gas prices.

Currently we have a TH400 transmission and I was wondering what is a good tranny to go with? The car is making about 415 fwhp and 500 fwtq, so would a 4l60e auto tranny be a good choice for our car? or is there something different that we should try or is better? I think I may look at some of my chevy hi performance magazines to see what other guys have used in there cars, but I thought I would ask you guys on here to see what you all thought?

We haven't done much research yet, he just read an article in a magazine and told me it will be fairly easy to do and so that is why I am looking for any info or opinions. Thanks guys!

Strahley

iTrader: (4)

Since the tranny is already in there, why not look into a gear vendors unit? That would probably be about the same price that a good 4L60 would cost, and with the obvious superior strength of your th400

YoungGunLs1

ya I had read about something like that. Is there a website I can go to to look at that so i can show my dad exactly what it is? Thanks!

Strahley

iTrader: (4)

http://www.gearvendors.com/

There you go! They are a bit pricey though. I've seen some on ebay for about half the price that are supposedly rebuilt units. I always throw around the idea of picking one up for myself from there

YoungGunLs1

Thanks man! ill keep my eye on ebay as well...

If we did however stick with just putting a different transmission into the car, what is the best one to go with?

I was also just thinking, a 4l60e is computer controlled correct? If that is the case than that most likely wont work right? So then what transmission would work?

Any more opinions would be great!

Strahley

iTrader: (4)

Yeah that's the problem I think you guys would run into, all the computer controlling. That and the 4L60E isn't exactly the strongest thing out there. I would suggest the 4L80E instead. I hear you can hook a manual valve body up to that tranny

Outside of that, you could look into a 700r4, but probably would want one that's beefed up vs any stock one

8a8mfh

iTrader: (3)

I'd go with a 4L80E with a full manual valve body and vacuum modulation, thats standard to get it to run in all gears with no computer. Even though you have to upshift and downshift it.

Or get a stand alone computer that will shift it automatically.

Lason

iTrader: (1)

Why would you run a vacuum modulator on a manual valve body tranny? If its a manual valvebody then it wont auto shift anyway, hence what the modulator does. Right?

8a8mfh

iTrader: (3)

No, the 4L80E is 100% electronic controlled. Get rid of the electronics and what controls line pressure----nothing. So you need to have it vacuum modulated.

chris718

visit my website for comprehensive overdrive transmission listings.you can select treansmission type based on power outout.we make 2004r 700r4 and 4l60es for high power torque and vehicle weight and custom machine all failiure prone on our in house cnc maching centers. www.ckperformance.com

YoungGunLs1

well after doing some reading and some thinking my dad decided he wants to go with a 700r4 tranny for our car.

I do have another question however.

MY QUESTION is, how much power will we gain/loose to the wheels by switching from a TH400 to a 700r4?

My dad has an article on a late 60's GTO that had both its engine dynoed as well as a chassis dyno after the engine was put in. They had the same setup as we do in our chevelle (TH400, 12 bolt, 3.42's, a/c) and the engine dyno gave around 515 hp, and then when dynoed to the wheels it put down just about 325 rwhp. I don't remember the numbers exactly but it ended up being between 30-35% drivetrain and engine accessory loss from the engine dyno numbers..which I thought was insane...the car then ran a 12.5 @ 108 at the track. We figured with the same setup we are losing a good deal of power through the engine accesories and drivetrain and are just curious if we will gain anything back by switchin to the 700r4...

Thanks!

SmokingWS6

iTrader: (1)

BBC or SBC, I'd say a 700r4(4l60) behind a big block would be put under a lot of stress. I'd also go with a full manual valve body 4l80, or perhaps an electronic controller for a 4L80E.

Has he thought about a 6speed conversion? I know there's a few companies around that'll make adaptor plates to fit T56's to non LS/LT motors.

YoungGunLs1

He has thought about going to a manual transmission on the car but the conversion from auto to manual is to expensive and not something he wants to do on this car right now. He plans on swapping a manual tranny into our next chevelle if it doesnt already have one.

It is a 454 BBC btw...

And his muscle car magazine has a whole write up saying that when rebuilt the 700r4 is capable of handling 600 ft lbs of torque...our car is putting out less than 500 so he isnt worried...plus we dont drive the car much, nor race it so if it doesnt hold up then we will have to look into something else.

Thanks for the help!