Need Help choosing a transmission

[bzblaine]

I have a 1970 C10 SWB. I'm trying to decide what tranny to put behind my 468 BBC. We are thinking it will be right around 550 HP/TQ. I currently have a TH400 for it. The problem is this will be a daily driven/ 3 days a week truck. I don't really ever plan on taking it to the track. My concern is that there is no overdrive. I'm not concerned about MPG. I'm worried about the health of my engine as I assume it would be running high RPMS at 75-80 MPH. I am aware of the Gear Vendors or a 4L80E. The problem is budget, I simply cant afford Gear Vendors right now and the 80E is computer controlled. I have about $1000 to spend plus whatever I get for my TH400. I also heard the 700R4 can handle right around that kind of power if built for it. I'm still in the learning process, so my apologies for my lack of knowledge. Any Ideas would be much appreciated. Let me know if you have any questions. Thanks!

[steelhorse]

A well built 700r4 will work but you may need to up your budget a few hundred.

[Bigdav160]

The 700R4 and lots of torque do not mix. It beats them up.

Stick with the TH400. A big block can turn 6000rpm all day

[bzblaine]

Originally Posted by Bigdav160

The 700R4 and lots of torque do not mix. It beats them up.

Stick with the TH400. A big block can turn 6000rpm all day

That's great news. That's really the only thing I'm worried about. I plan on making trips to Austin from San Antonio often (140 miles round trip). I just want to make sure that's not going to kill my engine cruising at 65 - 90 MPH. I appreciate both of your responses. Thank you.

[Mike C]

A TH200 4R can be built to take the power and has a better gear split than the TH700R4. Along with 3.73 gear will be a beast out of the hole and on the highway.

The 4L80E can be built to take big power but factor in the $$$ of the electronic controller and it gets pricey.

Hot Rod drag week cars mostly run TH400 with Gear Vendors overdrive on the back. No electronics to deal with.

Running a non-lockup converter and a TH200 4R is my plan behind my 427 I'm building for my short step. I'm guesstimating 450hp and 550tq. Most likely I buy from Bowtie Overdrives but other vendors are out there. I even found one that had lifetime refreshes for $550. Something to consider.

[jeh]

I know for a fact a "stockish" 700r4 will not hold up behind a 550-600 hp big block. Mine lasted 515 miles!!! If you want to spend about $2k some are supposed to hold up?

[El Dorado Jim]

I would stick with your bulletproof 400, they are awesome, change to a higher gear rear end if you want the engine to run lower rpm's.....would be cheap, pick up one for a few hundred bucks.... and like others have said, the 700R4 wouldn't hold up, I have checked into that for my '73 Suburban with 454,with t-400, I have a 4x4 so am keeping my 4:10 gears but going with a gear vendor, very expensive,but I bought a used one and now have to buy the adaptor and install it.....thought about the 4l80E but way too expensive!!!!

[kehstr]

Originally Posted by Bigdav160

The 700R4 and lots of torque do not mix. It beats them up.

Stick with the TH400. A big block can turn 6000rpm all day

That's true with a stock 700r4, but a build 700r4 will hold up to it all day long, as long as you don't race it, haul a bunch of weight, or beat on it really hard. But if you are not concerned about gas mileage, i would just stick with the th400, they are quite a bit stronger in the stock form.

[brad_man_72]

The only way to stay under a grand is a rear end swap with highway gears. Keep te th400

[kwmech]

Originally Posted by kehstr

That's true with a stock 700r4, but a built 700r4 will hold up to it all day long,

With a built 468? Not race it,..., Yeah, I don't think so. I broke 2 BUILT 700s in my suburban with a stock TBI 350 with mild towing, 4.56 gears and 31'' tall tires. In my opinion the 700 should never have been put into a truck, just like the crap 10 bolt rear end

You have to use the HP or it will go to waste, the only thing that will live behind that engine is either a built T400 or a built 4L80 with coolers

[bzblaine]

Originally Posted by kwmech

With a built 468? Not race it,..., Yeah, I don't think so. I broke 2 BUILT 700s in my suburban with a stock TBI 350 with mild towing, 4.56 gears and 31'' tall tires. In my opinion the 700 should never have been put into a truck, just like the crap 10 bolt rear end

You have to use the HP or it will go to waste, the only thing that will live behind that engine is either a built T400 or a built 4L80 with coolers

Believe me when I say it will be raced. I just wont be going to a track. I know a couple closed roads. :P

[bzblaine]

The biggest concern is the life of the engine. I expected to get 4-6 MPG. Which I'm ok with. I'm not building it for the gas mileage. I was worried about cuising at 4000-4500 rpms for an extended period of time (3-4 hours). But if the engine will be fine with it, I will be too .

[my67c20]

So here is some numbers to consider. For every inch in diameter your tire grows you gain 2 mph at a given rpm. For every inch your tire grows you reduce your rpm by 100 at a given speed. An overdrive transmission will reduce your rpm by 600. Changing rear gears to 3.42 drops rpm by 250, and 3.08 by another 250. Assuming these are available for your axle. Estimate gears to cost 1k per axle, or tires 1k per vehicle, or transmission 2k per vehicle, best bet is to go the tire route. Might be a dog off the line. So for my 2 cents, i would go with the TH400, and change tires, at least on the rear. Might be able to find some taller tires on the cheap, and at least see if this is the right direction.

[kehstr]

Originally Posted by bzblaine

Believe me when I say it will be raced. I just wont be going to a track. I know a couple closed roads. :P

That's how any truck or car should be used!!!

[kwmech]

Originally Posted by bzblaine

The biggest concern is the life of the engine. I expected to get 4-6 MPG. Which I'm ok with. I'm not building it for the gas mileage. I was worried about cuising at 4000-4500 rpms for an extended period of time (3-4 hours). But if the engine will be fine with it, I will be too .

At that rpm all you're gonna be doing is shoving a ton of fuel through it. My big block, 3.73 gears and 265/75-16 (31'' tall) spins about 2600 on the freeway at...I think....60mph (speedo needs repair and calibration) I do have overdrive which pulls it down to about 2200

[57taskforce]

Originally Posted by kwmech

With a built 468? Not race it,..., Yeah, I don't think so. I broke 2 BUILT 700s in my suburban with a stock TBI 350 with mild towing, 4.56 gears and 31'' tall tires. In my opinion the 700 should never have been put into a truck, just like the crap 10 bolt rear end

Yes sir I agree! Keep the 400, why waste cash on a 700r that's eventually gonna grenade. I've got one in my 3100 and I really don't like it. I ran it because it's what I had to work with but I know the big tires I've got will kill it soon enough.
Why would you ever want to build big power and limit your application of it? I'd drop the rear gear down to 3.42 or 3.08, with that kind of torque I don't think it would be much of a dog off the line and would still be decent on the highway. However I agree as well that higher sustained rpms aren't gonna hurt your motor much.