I am working through a set up that I am happy with for my car. 68 camaro, new Chevy zz454 crate, summit racing ignition, Holley 750 dp, m20 4 speed, 10 bolt 355 open diff. I am not getting the pull that I want out of the car. 1st gear is just ok, 2nd is pretty flat, 3rd and 4th are just ok. Until I am ready to put some much bigger horsepower in it, I am ok with maybe changing the gears and going to a posi. I have been told a 10 bolt can take 650 hp, and I am not there.

The reason for my post is advice. I don’t do much highway driving at all, so I am not too worried about going to a 373 or even a 411 if it will give me a little more low end power. DISCLAIMER: I am not a master mechanic... I can handle general stuff, but if you’could “dumb it down” a little for me, that would be great. I guess what I am looking for is a moderate fix until I have time to really get serious. Your thoughts and input are very much appreciated,

 

gearing is about your only option unless you want to get into the engine
I have no clue what the hp of your engine is.
I have a 68 with the M20, 3:55 gear in a 12 bolt posi. behind a sb 540/515 torque engine
when I drop the hammer the passenger cant grab the dash in 1st or 2nd

 

I don't know about a 10 bolt taking 650 hp who told you that? Especially with a posi, sounds like a recipe for disaster to me.
That 454 makes a lot of torque and a 10 bolt with a posi could very well break on a hard launch.
I'd suggest trying to find a 12 bolt rear for it if not a 9" ford set up for a Camaro.
12 bolts aren't real hard to come by, a little scarce compared to back in the day but look around they turn up here and there and most likely will already have a posi and maybe lower gears.
You don't want to end up like this guy, granted probably big HP there and on slicks but that 10 bolt with lower gears and a posi could do the same thing to your street car.

 

Thank you for the reply! the ZZ is rated at 469 HP and 519 torque. I suppose I should bite the bullet and go to a 12 bolt posi. It just don't quite understand why 2nd gear seems so much more flat. I hate the open differential. I know the posi will be much better. you and I have the same trans and rear end....you have some more HP, but it sounds like your car performs way different. That is where i get tripped up. I will say that my motor is not quite broken in yet, so I really have not gotten in to the higher RPM range when I get in to it.

 

I definitely don't want to end up like that guy! I will probably go the 12 bolt posi direction....I just want to make sure I have the right gear when I do. 355s were highly recommended, but perhaps it isn't aggressive enough for what I am looking for? The ZZ454 has some good HP and torque out of the box, but I just feel like i am losing it somewhere.

 

you are noticing the "wide" gear ratio of the M 20. 2.52 to 1.88 vs the M21 2.20-1.64

Your 10 bolt peg leg would work better with a posi and 3:73. You said Fwy driving is not your thing so the 3:73's will be good. With your 2.52 first 4:11's would be a very quick first gear so 3:73 would get you a longer pull in 1st

With this said you are pushing the envelope with the TQ the 454 on a 10 bolt, especially if you do hook with a posi. Rolling starts will very much help prolong the 10 bolt. 12 bolt or Ford 9" would be ideal

 

thank you for the reply! I checked the timing yesterday, and it was off a bit....when the new motor was put in, I think my mechanic set the timing a little mild for the break in. Anyway, it made all the difference in the world! The car came with an old Saginaw that was worn out....I found a great deal on the rebuilt M20 I have now....would have preferred a closer ratio, but couldn't pass it up. I am going to continue to dial the tune in, but will for sure upgrade to a posi....hoping I can find a good deal on a 12 bolt.

 

I had a Super T-10 four speed in my old '69 behind a 427,not sure how the gearing compares to the M20 but I think it was also more wide ratio than the M21 and probably similar to your M20.
At any rate I had a 12 bolt posi with 3:90 gears, seemed like a good gear set for daily street use and not as bad on the freeway as say a set of 4:10s.
I liked them a lot but I didn't do much freeway distance driving and it was so long ago premium gas was only a buck a gallon. lol
I plan on putting 3:90's in my '01 SS in place of the 3:42's it came with, of course it's a six speed so she'll still have pretty long legs.
I don't do much freeway driving anyway and with the 3:42's I need to be doing 65mph or better to use 6th gear at all.
It'll still be like having a close ratio 4 speed with two overdrives and maybe I can use 6th gear once in a while out on the country roads near home.
(I live out in the sticks)