Have RB20, want RB25

[atticus]

Hey everyone I have a 90 s13 with a RB20 in it, everything works, p/s, guages, but I have lost compression in two cylinders maybe 3. I have 3 options rebuild it, another rb20, or rb25. I have a chance to get an automatic rb25 for cheap. Will this work? Will everything plug up the same? Do I need to have a special motor mount kit? Can I use my RB20 transmission? Thanks for all your help.

[Joe]

well if you get a auto RB25 you are at the least gonna need to get eithre a R33 crossmember or a mount kit from mckinney. the RB20 does not use the same mounts at the 25. the wiring harness' are different. your gonna need one for a RB25 along with the ECU. the transmission and driveshaft will work.

[Eikon]

I think you would be best to get the 25 transmission... have you seen the difference in size? The 20 transmission is tiny in comparison.

i think you will need a custom driveshaft as well

[dekand]

well he could use the rb20 transmission, and try to source an rb25 transmission in the meantime, if it breaks, put the rb25 transmission on.

[BoostFab]

you can transfer your flywheel and clutch over to the automatic motor

[Joe]

you can transfer your flywheel and clutch over to the automatic motor

DO NOT FORGET TO REMOVE THE AUTOMATIC PILOT BUSHING.

trust me, i speak from experience.

and a RB20 transmission works fine with a 25, just dont expect it to hold 500whp. you will only need a driveshaft if you get a 25 trans. im using a rb20 trans and have no problems. they are just as strong as a KA trans (nearly identical) and the KA trans has supported into the 400 range reliabily.

[lyon23]

well if you get a auto RB25 you are at the least gonna need to get eithre a R33 crossmember or a mount kit from mckinney. the RB20 does not use the same mounts at the 25. the wiring harness' are different. your gonna need one for a RB25 along with the ECU. the transmission and driveshaft will work.

so the rb20 xmember is not the same as the 25 and a 25 CAN NOT be mounted where a 20 was installed with its original xmember? If so good to know... I might be in the same boat and trying to just get the 25 motorset.