Hi guys, I need a bit of advice on rear end gearing. I've re-geared my Blazer and know about working out ratios etc but don't know what these cars 'like'. This is a '67 RS with a later bored 454, edelbrock Performer RPM heads, cam and airgap intake, Hooker headers and a 770cfm Street Avenger Holley. TH400, 12blt posi.I'd like the car to cruise 'comfortably' at 70 to 80 mph. When I say 'comfortably' I'm imagining 2200 to 2400 rpm (my 2 trucks have O/D trans so I'm used to lower revs). I'm assuming a healthy big block would have enough guts to still 'have fun' from the lights even if geared to cruise like that.
So my question is, what ratio would you recommend? At the moment it would appear to have 3.73s but at 'around' 40 mph (speedo out a bit) I'ts turning 2400rpm which feels so low! I know I'm not going to get it to cruise like an O/D equiped vehicle but it would be nice to get a good mix of acceleration and comfortable cruising.
Thanks for any advice.

 

you aren't going to get a cruising RPM like that with anything higher than a 2 seriesgear (and you'll have to change you carrier), somethinglike a 2:73, and you aren't going to like that off the line

do you know what you have for a stall speed on you converter?

a 3:42 gear is nice and you can still use the same carrier and depending on your tire height, you should be right around 3,000 at 70MPH. if that's not good enough go with a 3:23 and the big block will still have enough punch

 

To be honest I haven't paid much attention to stall speed but it's pretty tight. Tires are 255/60-15. 3000 rpm at cruise speed still sounds high but having said that, I don't want to kill it off the line either.

Anybody else running a big block want to give their thoughts?

Thanks!

 

I have your same tire size in back and 3:73s also with my 396. I'm taching around 3,000 at around 60 or 65MPH. if I get around to it this year, I'm putting 3:42s in myself. I am willing to sacrifice a little and not go to the 3:23

 

I like 3.36s for a good mix of moderate performance and decent mileage. But I have had a 396 325hp in a 68 convertable with no more than a 280/480 cam, TH-350, rotting 1 3/4 inch exhaust, and 2.73 in the rear. I took it to the track a couple of times that way and did a Surprisingly good 14.0 at 94 mph. That was 10 years ago, and I would recommend that you go a little steeper for adecent launch.

 

OK, thanks for the replies. I've managed to figure what axle I have now too, the previous owner put a coil sprung M 20 axle with posi in it! I'm debating now whether to regear this (they do a 3.08 for it but they're rare apparently) or whether to try and find a GM 12 blt and use that but they're pretty rare over here. The M 20 has just been fully rebuilt too. Guess I'll see if a 12 blt turns up before I can get some gears!

 

over where?

a 3:08 gear is very common and now they are actually building 12 bolt carriers again also

 

England! But I have some friends coming out later in the year for a few big swap meets, so they may be able to get me a 12blt axle. Bringing it back in another vehicle is the only viable way of getting one brought over really.

 

4:10

 

Englad huh? I guess that's why you are having difficulties then.

you must pay a premium price for a lot of the stuff you buy?