Appropriate rear gear ratio for my set up?

[mmanship]

I have a 64 Impala SS with QC block 340 hp 409 with a Comp Thumper cam. I have open 10 bolt diff with 3:36 gear and Muncie M21. I am running 27" tires out back. The 3:36 is going to be changed as it takes too much effort to go from dead stop. I have an Auburn posi unit ready to go in. I do not know if I should get 3:55 or 3:70 gear. I do drive the car and do not race. Right now, at 68-70 mph I am turning right at 3000 rpm. I'd like to keep the RPMs around there somewhere close at 65-68 mph. Is there a 3:62 gear!!! Ha.
So, 3:55s or 3:70s ?? Thanks

 

[Don Jacks]

Niether,get rid of that sorry-@@ed cam! You'll like either the 050,or the 0951 cam from Show cars much better.

 

[Phalen409]

Niether,get rid of that sorry-@@ed cam! You'll like either the 050,or the 0951 cam from Show cars much better.

Come on Don......Tell us how you really feel.................no really.........don't hold it back!!!!!

 

[blkblk63ss]

Niether,get rid of that sorry-@@ed cam! You'll like either the 050,or the 0951 cam from Show cars much better.

Just what I was thinking. I had a 64 409 340 Stock cam with 3:36 and it certainly had no trouble getting started!!!

 

[Don Jacks]

Come on Don......Tell us how you really feel.................no really.........don't hold it back!!!!!

Just calling it the way that I see it.

 

[mmanship]

I'm changing rear gears. Just needed opinion based on what my current setup is. I usually get pretty good feedback here that's all.

 

[LMBRJQ 60]

If you are doing the same MPH as current 3000 rpm then with
3.55 you will be doing 3171 RPM
3.70 you will be doing 3303 RPM

If you are changing rear gears and that is your only option then you only need to ask what RPM will you be doing with the two options
The way i read it was you were looking for more off the mark performance but wanting to keep your RPM the same and you were looking at opinions
Option one is cam choice
I think the guys read it the same

Sorry if the cam change comment offended but that is what the best option would be
But this is only my opinion

Steve

 

[mmanship]

Thanks for all the input. Since I had found a brand new in the box Auburn posi unit for $123.00, I thought I might just change the gearing while we were in there working. The cam sucks. Sounds good. But is an awful cam. I know that. I might go back to my stock one someday.

 

[Carmine]

Just what I was thinking. I had a 64 409 340 Stock cam with 3:36 and it certainly had no trouble getting started!!!

Ditto. My '62 came with a 3.70 posi and T-10 transmission. I'm assuming it's a close ratio. My car is just street driven and I didn't like the 3.70's. I put in a 3.36 gear and never looked back. A great cruising gear and no problem getting started. My cam is one level above being stock, Carmine.

 

[models916]

Make sure the posi is for the 55-64 ten bolt and not the later version of the 10 bolt. The Thumper cam is for sound and not power. Lots of loss in those cams. Look for the power curve for that cam and keep the cruising RPM within it. I would think 4:11.