4bt to T-56?

4

4bt bowtie

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Apr 8, 2011
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I am planning to put a 4bt in to my 1990 Chevy s10 4WD. I am looking to get roughly 350- 400hp out of the engine which, as a general rule of thumb, should land me in the 700-800 ftlb of torque range. I plan on doing an SFA swap in the truck and I am thinking of using a T-56 transmisson coupled to a divorced NP208 t-case.

My reasons for using a T-56 are thus:

-better gear ratios than an NV5600 and G-56

- The extra overdrive will allow me to run a lower spool (thinking 4.11:1 with a 33 or 35 inch tire)and still run highway speeds at a near perfect 1700 rpm.

-considered using a ZF-6 but from what I've seen the parts are considerably more expensive and the T-56 would shift faster which would be nice at the drag strip.

-I know a stock T-56 will come apart very quickly behind that kind of power but I have seen a few rebuild kits for around $1400.00 that claim to put the torque rating over 600 ftlbs. I have seen used T-56's go for around $400 so in total I would be in roughly $2500 by the time the plumbing and installation is all said and done.

Any opinions and info on this would be greatly appreciated. If anyone has any better ideas I would love to hear them. :thankyou2:
 
they break pretty easily behind a LS2 gasser at about half the torque. they seem pretty light duty to put behind a diesel in my opinion.
ed
 
I think there is a reason they didn't put the T-56 in trucks...just sayin.
 
How do the ZF transmissions compare to the NV4500 as far as longevity? I have heard people swear by the ZF 5 speed but I know the NV4500 is cheap and easy to find.
 
just for your info on the 1700 cruising rpm.... id recomend running the 4bt at wround 1800 to 1900 if you plan on running 70 or so crusing sped a lot. 1700 the 4bt dosnt pull to well and the rattle will tear up those little overdrive gears. At least my 4bt did. It got better mpg and felt smoother and ran better at 1900 than it did at 1650(where my cruising rpm used to be.)

in my hounest opinion the 6bt does great cruising at 1500 to 1700 but the 4bt does not.
 
Thanks for the info. I was basing the 1700 rpm off of the peak torque. According to a fuel consumption chart I found for the 4bt it theoretically consumes the least amount of fuel at 1700 but of course that is in a controlled dyno room not in the real world. As we all know, lab results and real world rarely coincide perfectly.$.02
 
If you actually are gonna end up with as much power as you say , you are definately gonna need to raise your cruising rpm!
 
the more i think about it in all hounesty i dont think that even a built t56 will handle the 4bt tourque pulses down lower in the rpms(under 2000) i think it will destroy the gears fast and as you might be saving a little money up front going with the t56 i dont think it will be worth the hassel of rebuilding every few months... i think if it were me and i wanted to go with a manual 6 speed i would just use a nv5600. but if you plan on racing with it a lot at the strip i would be saving my money for a auto and be money ahead in the long run becasue i think that even a nv5600 when drag raced will need to be rebuilt quite often...
 
Auto is the easiest if you wanna go faster than 13s everytime. Trust us on that one.
 
I agree that the T-56 is probably not the best way to go. I was looking at the T-56 because of the two overdrive gears. Yes, the NV5600 and ZF 6 are six speed transmissions but they do not have a double overdrive. They have an extra gear before direct drive to make towing easier. I will probably go with the tried and true NV4500. This truck is not going to be a drag truck, it is a daily driver that will see occasional track time. I would prefer to keep with a manual trans for ultiamte longevity. I have known some people swear by the ZF5 transmission, any opinions on it versus the NV4500?
 
I thought about that, but then I would have to get a standalone computer to run it and the cheapest standalone I’ve seen is close to $800. I still would prefer to run a manual trans.
 
Does anyone know of a good link to go to in order to find the physical dimension of an NV4500 and ZF-5? A friend of mine (who has more experience with the NV4500) thinks that I would never be able to fit the NV4500 in my S10 without some serious tunnel surgery. I’m fairly certain a ZF-5 will fit with a small body lift because I have seen it done on a late 90’s Ranger.

:ft:
 
Personally, I prefer shifting the gears. That and if I keep it a stick the wife can't drive it. :lolly: But all joking aside, what would I have to do and how much money would I have to put in to an NV4500 in order to make it handle 700ft lbs reliably?
 
a new one with a 1 3/8 input will handle it reliably. you just cant speed shift it or lay into the fuel before the gear is 100% engaged... 700 isnt much for that trans just make dam sure each gear is engaged before stepping into it.
 
I know I'm kind of beating a dead horse here, but other than fixing the 5th gear issue that I have heard about, what would I need to do in order to make sure that when I mash the trottle off road I will not have to worry about destroying my trans?
 
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