M20 or M21
GM was thinking of avoiding Warranty issues. M21 is stronger then an M20 due to internal stresses of the trans. The gears are pushing each other away trying to split the case.
I don’t believe Pontiac ever put an M20 behind a 455. When they switched back to T10’s in 75, they always used 2.43 first gear on the 400’s. I’m guessing for the same reason.
Sent from my iPhone using Tapatalk
__________________
1979 Firebird Trans Am 301/4spd (Now 428)
1977 Firebird Formula 400/Auto
2007 Grand Prix GXP 5.3L
Last edited by 74Grandville; 12-01-2021 at 08:06 PM.
|