Yes, it's not good to bog an engine, it's good to hit the sweet spot. Sounds like your a little under 300 hp. If you're planning to bang gears constantly and drag race it may not hold up. If you drive it sensibly you'll be ok. They put 300+ through the old Saginaw peanut transmissions in the early Corvettes and they did ok.
You already have the Muncie setup in there and working,so I would leave that alone. You are a gear change away from having it right. A 3:23 or 3:42 would be a good fit for that. If you had a close-ratio M21,I would definitely go for the 3:42.
I had an M21 with 3.23, an absolute dog in first gear (7.1 overall gearing in first). I prob needed 3.42 or 3.55 (7.5 to 7.8 overall). I would recommend 8:1 minimum overall in first which means with your 2.52 first you need 3.23 or better
A fair point. Interesting that some people say these transmissions hold up behind a big block. Others say plan on breaking them. That m21 with a 3.23 rear is pretty close to what I have now. So you know what I'm dealing with. A 3.23 would be an upgrade forsure. And maybe the best compromise for around town and highway driving.
I have a 71 GS 350 4-speed and it came with an M21 and 3.08 gears. It sucked off the line. It was so close that I often went 1st to 3rd because 2nd didn't change much. I've since swapped an M20 into it and it is a lot better but I'm now looking for the M23Z gear set that has a 2.98:1 first gear. It would turn your 2.73 gears into the equivalent of 3.28:1 rear gears with a very nice cruising RPM. The trouble is those gears are hard to find right now. Nobody has stock.
That (M23Z) is what I have currently, bought it a couple years ago. With my current 3.31 rear, I have 9.86:1 in first. Should be perfect
I had a stock '70 w/3.23 & M-21 if that's m/l your starting pt. w/M20 & 2.73 - It wasn't bad. Maybe the higher HP '70 350 engine helped. Not that you're planning to race it, but the change to 3.42 was worth a couple tenths & then 3.73 a few tenths more. Being that you're dealing w/an 8.5, I'd even consider 3.55's. I drove mine w/3.73's to the Nationals (700 mi. ea. way) and it wasn't bad.
That would be the ideal solution. I took the car out this eve. First time really testing on it, after putting in a TA Performance HEI. Once the car is moving, she is a blast to drive. But the acceleration from a stop is horrible. Definitely will start looking at putting in a 3.23 – maybe the 3.42. It will be way better on the clutch, that's for sure.
