Original tranny or m21 ?

[sparky]

Hi guys

I went to transmission shop today to se if they had car ready ( hehe and to hurry them along ) and when i got there we took side plate off Of my original muncie 4 speed and there was metal shavings in it ( reason i took it was a knocking noise coming from tranny ) Anyways i called a Guy i know of and he told me he had another tranny ( 450.00 for it ) When i got there it looks like it is a m21 tranny ....# on it was P0b10b I think that is muncie 1970 model made in sept 69 and the b at the end is for close ratio ( I think ) I got the shop checking it out and they said the can have it in monday for me ( looks to be in good shape ) All the part #s on it match mine except that mine is a wide ratio m20 i know.

My question is even tho i am going to get mine rebuilt and back. should i go with the close ratio m21 tranny ....Will i get better performance from it...My motor is a 350/350 that is pulling 383 horspower ( had it checked out and motor has never been into before ) friend of mine owns a motor rebuilding shop and he has a machine that he put it on that Checks the engine and runs it without it being in car ( had this done before i put it in just in case motor had to be rebuilt it checked out fine ) tells you Cyl. pressure ( mine checked out 175 per with a minus of 5 pnds give or take per cyl. it also tells you how much horsepower engine is pulling and he can check his motors with that. I also added headers ( not stock on car )

Hope i am building this right lol......my 1st vette ....we went from ground up naked frame Replaced all bushings and if i didnt replace it i had it redone all the way thru car except motor which was fine..also do headers ad power ??....sorry again for all the questions but you guys seem to know just about everything about vettes hehe and your a great source of info :BOW anyways thanks again All.....oh ya another pic of front of car....Man she is pretty

Sparky

 

[Stingray6974]

Hi Sparky,
The m20 and m21 are identical except the m21 is close ratio with a 2.20 first gear. No performance gains but it will be a little harder to get going from a dead stop. What part of Texas are you in? If you need a second opinion on your trans I can check it out for you.

Mike

 

[JohnZ]

M20 vs. M21 is a matter of personal preference; it will launch harder with the M20 due to the lower first gear, but has a much wider gap (rpm drop) between 3rd and 4th than the M21. The M21 has a higher first gear, but has evenly-spaced ratios (rpm drops) going into 2nd, 3rd, and 4th that makes a nicer-driving road car. Just depends what you want; other than ratios, the transmissions are identical.

 

[sparky]

Hi mike

I live right outside tyler about 75 miles from dallas. I think ill go with the m21 sounds like it is what i need for road driving. Wife and i are going to plan a trip (road trip ) after i get all the bugs worked out. Maybe we can bring it by to show to ya

Thanks john... it's the road driving i am interested in so sounds like m21 might do for me. I was curious too what makes the 350/350 pull 383 HP Or what did chevy do to engine to get to that HP and since i added headers the guy i bought them from said that they add about 8% more HP is that true? If so it means the 350 i have has about 410 Hp now ?

Thanks guys