How strong are the stock auto transmissions?? I am in the process of putting a built 13b in an offroad vehicle and an auto trans works better than a 5 speed because of the torque converter slipping making it climb hills better.

 

not very powerful due to the age of wear on most of them. mine slipped when I had full intake/exhaust and efan. no PS or AC belts.

 

Indeed... All the years of high revs apparently wore the crud out of mine.. It shifted very slowly, had to gas off-gas on to shift faster. Never completely failed though..

 

the s1-3 rx7 will have a jatco 3n71b and the s4 is jatco 4n71b
they can be modded to be very strong

cars i tooled on-
s4t stock 4n71b --slipped around 300 rwhp
s2 rx7 ( custom s2 rx7 vert with 9 inch ), modded 3n71b, high stall and manual shift 350-400 rwhp no issues


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the 3n71b is used in aus on the VL commodore of old
( type of chev fitted with a nissan rb30 turbo engine )
and modded versions of these have been in the 7 second zone

it is known as the KEAS modified box ,,you should be able to google it
and although paul keas doesnt do them anymore, there is a shop that continues to use his methods
( you can go mild to wild,, manualised shift and hi stalls, big shafts and much more )


the 4n71b can also be moddified to take a lot more,, but not as much as the 3n version

 

https://www.rx7club.com/race-car-tec...e-body-881364/

The above link shows pictures of a newer than 1974 valve body, 4- speed. It is definately different than the one I have. (see attached)

I have been reading about former shift kits and all the info is for the more modern 4 speed. I am trying to figure just where to enlarge the separator plate holes for 1-2nd gear change and 2-3 gear change.

I have the shims and heavy spring placed for the pressure regulation.

Has anyone been there with this old style transmission?

The green mark shown is where the 2nd gear shift hole is enlarged. This is the only hole that matches the 4 speed diagram.

The red marks near the green ones are for 3rd gear. the solid dot is where the diagram appears to show and the red circle nearby is where there is a logical hole to enlarge.

The other red marks are near the pressure regulator. This is also where the old plate differs greatly from the newer type. The red dot there makes no sense to me and the red circle is an existing hole to enlarge.

It seems that shift kits are no longer made for these. I would sure appreciate some help here.