What is the suggested overdrive transmission behind a 455 no more than 400hp? Looking to put 373 gears and want to still be able to drive on the highway at low rpm. Is it 200R4 or do they make a uni-bolt 700R4, or just stick with the 400 turbo? Suggestions, ideas, thoughts are appreciated.

 

200R4 has same case length as a TH350, so driveshaft could be sourced "as if' you were using a '350. Same bolt pattern on the 200=350, easy, don't need a computer to run the 200, just the specific linkage & mounting hardware to put it together.

 

If you're installing 3.73:1 , sticking with a TH400 will likely just end up revving higher and using more gas on the highway.

The 200 4R will give you a final drive ratio of .67:1. That should give you the performance you want in the lower gears and reasonable on fuel on the highway.

What do you consider low rpm? 3.73s aren't going to give you the same results as if you used 3.23 or 3.42 with a 200 4R. One of the other factors to consider is what size tire you'll be running.

 

Let me add to my question what is a good all around gear for a 400 turbo? Probably running 225/70/15 tires or close to that. I really don't know what to call a low rpm maybe under 3000. I have lost touch with rpms after having 6 gears in my truck and staying around 2000 rpm at any speed.

 

I have also been seriously kicking his question around for my 67 442. It seems one of the stronger 200r4 trannys is around 2500. bucks. The GearVendors overdrive is about 2500 bucks and rated up to 1200 HP. With it you keep your Turbo 400 or what ever Tranny you have, bolt it on in place of the tail housing and you have overdrive. It looks like a good product and their long established. Does anyone here have first hand knowledge of these units?

 

If you have a good Turbo 400 I'd go with the gear vender as they look to be the same price, you are going to have to get a new driveshaft either way.

 

The 400 transmission is one of the strongest around, but it absorbs a lot of power, a 200r4 will put more power through to the rear end, good for performance and gas mileage.


Roger.

 

I don't believe you will need a new driveshaft converting from a th400 to a 2004R. I think you only need a th350 yolk. Drive shaft is the same assuming an A-body. Also, the GV unit does not have the overdrive ratio that the 2004R has. The .67 in the 2004R would be more beneficial with a 3.73. Also, the 2004r has a higher first gear. With a 3.73, your 1st gear would only be good for pulling out a stump or burning rubber. To effectively use this trans with a motor with so much torque, I'd drop the rear axle gear down to 3.55 or 3.3.

 

I just picked up a GV and turbo 400 for 1100.00 bucks on eBay!:-) Just look there!
I'll let you know how my 455/400GV combo drives in....September LOL

 

Nice score. Last time I checked on one,
they were $3500 and change.
Was this new or gently used?

 

Used of course. The guy had it in a 1999 suburban. Rebuilt the trans and GV 2 years ago! I I got luck I guess...

 

TH400 is longer than a 2004r, a 2004r is the same length as a TH350.