Which gears

First off, It's not a Buick but I'll be in the same boat when I get my '67 going. Yall know your stuff so I came here. It's a dual quad completely rebuilt 1959 389 with headers, MSD ignition, Muncie 4 speed and I have an NOS Posi for it. SOOO....

I've been wanting the 3.64 gears from Fabcraft and when I was finally ready to order them Brad says he ran out but they plan on making more this fall. I don't want to wait that long so I'm left with 3.42 or 4.10. It's a Muncie so 4th gear is 1:1 and my tires are 26" or 27" tall. I'm going to see if I can find some wider 28" when I get the car on the road. I have an NOS posi that will be installed when I get the gears. I'm not too worried about gas mileage, It's a dual quad 389 I know the mileage won't be good. Will I be able to hook up with 4.10s? At 70 MPH there is about a 400 RPM difference between 3.64 and 4.10 (3,000ish and 3,400ish). And to add to the decision the 4.10s are about $70 cheaper and are available right now.

My builder said it should be "400 hp easy, probably more like 450" according to pontiac enthusiast they say under 350hp. Looks like all my mods only gained 35 hp over a stock tri power. So it's anywhere from 300-400 hp.

Which should I go with? Will 4.10s hook up? Will they be worth the gas mileage decrease?

 

if u are going to race the car, the 4.10 gears, but if are doing a lot of hwy driving then 3.42 gears.

 

Which Muncie 4 speed do you Have?
The M-20 wide ratio has a lower first gear that will work great with a 3.42.
The M-21 or M-22 will be okay with a 3.42, but will like a 4.11 rear better.
Personally, I don't like too much gear as it makes first gear practically useless. It sux having to shift out of first gear after the car only moves 10 feet.

 

Good point Walt. It's an M20. It's won't be a lot of highway but some. It's all highway on the way to the track and work. Thanks for the help

By the way, what is the difference in first gear ratios on the m20 vs the m21/m22?

 

M-20 has a first gear of 2.52
M-21/22 has a 2.20 ratio

To get overall ratio in first gear, multiply first gear ratio by rear end ratio.
For the M-20:
2.52 x 3.42= 8.6
2.52 x 4.11= 10.36

For the M-21/22:
2.2 x 3.42= 7.52
2.2 x 4.11= 9.04

 

That's good info, Looks like 3.64 or 3.42 will be sweet with my m20