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Hi, jeepstroker!…Can’t think of any manual 2 or 3-speed that will handle 800 horsepower.  (An Atlas II transfer case, by itself, would be a 2-speed that could handle this torque.)  For 800 horsepower, racers use a racing version of the Powerglide 2-speed automatic transmission.  Advance Adapters might be able to configure an adapter for the 4.0L Jeep engine to a Powerglide or the GM Turbo 350 or 400 3-speed automatics, which can be rebuilt and upgraded to handle this high horsepower.  Manual transmissions that can handle the torque you describe typically use a 4-speed, 5-speed or 6-speed “truck” type platform. 

 

Also, Jeep used the Chrysler 727A automatic, a three speed.  This same transmission design was also used behind Dodge/Plymouth 426 hemi muscle car engines and in Dodge class A motor homes.  You could adapt a 727 Torqueflite from a late 1980s to 1991Grand Wagoneer to the Jeep engine.  The AMC 360 V-8 is the same bellhousing pattern as your 4.0L.  A racing build 727 Torqueflite could handle 800 horsepower.  You will also need a transfer case that can handle this torque is you are running 4WD and low range.  The Advance Adapters Atlas II, well tested in 4x4 truck and Ultra4 racing, can handle this kind of torque.

 

If you still want a manual transmission, you need an NV4500 or NV5600 truck transmission for this kind of torque and horsepower…See NV4500 adapters to the 4.0L engine at Advance Adapters:  www.advanceadapters.comAny passenger car or light duty/compact truck or Jeep XJ Cherokee/Wrangler transmission will not handle this horsepower.  Advance Adapters can supply the adapters and likely a rebuilt NV4500 transmission.  There will be driveshaft length changes needed.

 

Moses

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Jeepstroker...The 3-speed manual transmissions offered for light duty trucks through the 1970s were replaced in the 1980s with the four- and  five-speed light duty overdrive transmissions (T5 Warner, Aisin AX4, AX5 and AX15 and others).  These became the base transmission offerings to meet emissions requirements and fuel efficiency. 

 

In the 3-speed era, the most rugged transmissions were the T85 and T89 Borg Warner units and the Chrysler/New Process 3-speeds used in big engine muscle cars.  None of these transmissions were designed to handle 800 horsepower.  I will note that the T85 and T89, or the Chrysler muscle car units could handle an honest 400-425 horsepower.

 

From 1957 onward through the muscle car era, the "high performance" transmissions were always four-speed units like the Borg-Warner T10, the "Rock Crusher", the Saginaw GM and Muncie units and the Chrysler New Process transmissions.  These were all-synchromesh on forward gears and designed for drag racing and even track use in the Corvette or Trans Am cars.  The T10, in particular, was a popular swap into Jeep CJ 4x4s used for sand drags or hill climb competition with engines to 300 horsepower or so.

 

I believe that for 800 horsepower and a manual transmission, you need a heavy-duty truck transmission, one designed for the bigger Ram 2500/3500 with a Cummins diesel engine or even a medium-duty truck.  Shafts, bearings, gear size and tooth contact area, the overall stamina for the kind of torque you describe requires the use of an NV4500 or NV5600 transmission. 

 

In fact, there are many XJ Cherokee models with the NV4500 behind a modified 4.0L engines.  Advance Adapters can furnish adapters for this transmission to the stroker 4.0L engines you build.  In my Jeep CJ Rebuilder's Manual (Bentley Publishers), I feature an NV4500 in a CJ-7 Jeep with a Dana 300 transfer case.  I also  used this transmission in a Toyota Land Cruiser FJ40 with a 350-plus horsepower 383 Chevrolet stroker V-8, the 4x4 is featured in my Toyota Truck & Land Cruiser Owner's Bible.  I used a fresh Toyota transfer case behind it.  For 800 horsepower, I would use an Advance Adapters' Atlas II transfer case.

 

In my view, there was never a 3-speed manual transmission built to handle torque and horsepower in the 800 HP range.  Even WWII GMC "deuce-and-a-half" 4x4 trucks built from 1942 forward used the GM SM420 four-speed with compound low gear.  This SM420, by the way, has been a very popular Jeep 4x4 retrofit transmission since the 1950s, usually attached to a Chevy V-8 engine conversion or at least a V-6 transplant.  Jeep used the BW T98A truck four-speed in many '50s to 1971 models, replaced by the T18 four-speed option in the '70s.  Four-speed truck transmissions were always more rugged than the base 3-speed offerings, including the Jeep CJ's BW T90, T86, T14 or T15.  And none of these truck four-speeds are as strong as an NV4500 or NV5600.

 

Is there a reason why you would not consider the NV4500 5-speed transmission, a conversion that many have done with the XJ Cherokee, Jeep CJ and the Wranglers?  Why the need for a three-speed manual transmission?  Again, a more rugged three speed automatic transmission (GM Turbo 400, Chrysler 727A Torqueflite or a Ford C-6) could be built to barely withstand this kind of horsepower.

 

Moses

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Rocket Doctor...I hadn't considered Lenco.  They have been building custom drag racing transmissions for a long time.  Trick stuff, including CO2 powered shifters...

 

This may be what jeepstroker needs...Thanks much for sharing the link!  Trust you had a fun Thanksgiving with the family.

 

Moses

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