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Discussion Starter #1
I have an '82 chevy K20 currently set up with a turbo 400 trans & i believe 4:56 gears. Great pulling power but my 6.5 revs fairly high @ 60mph, I am wondering what the best way to do at least 65 mph with lower engine rpm.

The truck originally had the 700r4 / 6.2 combination - would I benefit more from finding and installing the OD trans or swapping diffs with 3:73's? I have a line on 3:73 frt & rear diffs with 8 bolt floating axles. I will prob do more highway driving than serious pulling.

Thanks for your help.
 

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You could look for a used Gear Vendors O/D unit that would bring your TH400 final drive ratio down to 3.55 in 3rd-over(.78 x 4.56=3.55), or you can do as you say and install the O/D tranny for a final drive of 3.42(.70 x 4.56=3.42). Either way is gonna be better highway gears than just the 3.73 rear end. I think the best setup might be a 4L60 AND the 3.73. The 4L60 has a deeper first gear than the TH400 (3.06 compared to 2.88) so you would still have good off-the-line pulling power and you would gain an O/D (.70) in addition to your 3.73 with a final drive ratio of 2.61 (good highway gearing).
JP
 

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Discussion Starter #3
Thanks for the ideas JP - I likely will do the trans & the gearing as you suggest. Would you go any higher than 3.73's? or is that possible with a 14 bolt rear?
 

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Umm don't know about higher gears than a 3.73 for the 14 bolt rear, but that doesn't mean they aren't out there. To tell ya the truth, I don't think I'd go higher than the 3.73's anyway. The 3.73's will be a good compromise between pullin' and mileage. Then if you do add an O/D tranny it'll be that much better. Try to stay away from junkyard 700r4 trannys, they had lots of problems, but if it's built right and you don't beat on it to hard it'll do. I'd look at a 4L60E or 4L80E. Both are gonna need a stand-alone controller but they are available. The 4L60E may even need a good shift kit...I mean if it's out you might as well fix it up right. Last but not least, tall narrow tires will also help RPM's, like a 235/85/16, but it's marginal in the looks department. Good luck and post what you decide to do.
JP
 

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Discussion Starter #6
Thanks for the advice JP - I will probably go with the 3:73's, 3:21 may be a little tall although I am curious how they would work with my current T400 trans.... hmmm. I will post when my project is complete.

Thanks again.
 

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You could run a non-electronic 4L80 found in '88 to 93. Same great old TH400 trans with the OD and no real elecronics.
 

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You could run a non-electronic 4L80 found in '88 to 93. Same great old TH400 trans with the OD and no real elecronics.
That would be a good choice, but I seem to remember readin' in one of the car mags that they are pretty scarce. That's because all the drag car guys snatched them up back when the Pro-Street era was in it's hey-day. Mountain motors for the street, need a trans that would hold up, and could crusie with the O/D, etc. etc. But if you can find one that would be the ticket.
JP
 

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Only tranny I'd put in it.........NV4500 :ro)
 

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What size tire is on the truck? 37's would work well with that gear, and 35's would lower RPM's significantly compared to 31-33" tires if that is where you are at. 4.10 and 35" BFG on my Jimmy turn ~2500 rpm at 65 mph.
 

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I was doing some lookin' on the internet and decided to check out Art Carr transmissions. He got real popular when he was able to build the 200r4 to withstand the rigors of drag racing behind the 84-87 Buick Regal T-Types. Some of these cars are making well over 1000hp and as much torque. Anyways, I checked out his website and he also does the 700r4. Talk about simple, just buy one of these and put it in and never worry about it again. You could add a taller tire and not even mess with the gear swap. If nothing else, it's another option.
Art Carr---> http://www.artcarr.com/
JP
 

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Be very careful of Artcarr these days. Heartbeat hauler is correct in everything he said about Art Carr from years past Art carr the man sold the business and the name a few years back. I have heard of a few bad dealings with them as well as had bad dealings within my family since Art carr the Man left.
Art carr the man started a new tranny shop and I think it is called California Performance transmission.

Would go with the tranny idea whether it is a 700r4 or one of the new types.
 

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Be very careful of Artcarr these days. Heartbeat hauler is correct in everything he said about Art Carr from years past Art carr the man sold the business and the name a few years back. I have heard of a few bad dealings with them as well as had bad dealings within my family since Art carr the Man left.
Art carr the man started a new tranny shop and I think it is called California Performance transmission.

Would go with the tranny idea whether it is a 700r4 or one of the new types.
Wow! That is some good info. I would definitely want my trans from Art himself, rather than someone that bought a name and did not maintain the philosophy. I did check this out, but the website does not mention Art Carr, however, that could be an arrangement of the previous sale of his company. Anyways, here is the other site. Here ---> http://transmissioncenter.net/competition.htm
JP
 

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Discussion Starter #14
What size tire is on the truck? 37's would work well with that gear, and 35's would lower RPM's significantly compared to 31-33" tires if that is where you are at. 4.10 and 35" BFG on my Jimmy turn ~2500 rpm at 65 mph.
Yes, I have thought about the larger size tire options and may go taller at later - right now I have next to new 235/85r/16's. I would rather spend the money on an OD trans than tires at this point.

I have a 700r4 / NP241 combination lined up for the first stage. We'll have to see what happens from there. I like JP's idea of the OD / 3:73 combination.

Thanks for all the great suggestions.:cool:
 

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I believe that the 700r4 has the same gear ratios as the 4L60E, which means even though you drop down to the 3.73's from 4.56, you will gain back a bit more pulling grunt with the 700r4's 3.06 first gear compared to the TH400's 2.88....not a lot, but some is better than none. :D
JP
 
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