Rear Gear reccommendations

oj · May 30, 2012, 08:20:13 AM

I'm finishing a '66 Chevelle and need input for rear gear. The car has 9" ford rear with tremec 6spd, 28" tall rear tire, 632 engine with 750-850lbs torque from 3500rpm up.
With all that motor i am thinking the first couple gears in the tranny will be about useless, i am also thinking that i don't want to be anywhere around when this thing is in 6th at about 5K rpm.
What do you guys think for the gear ratio?
Thanks, oj

phat rat · May 30, 2012, 10:56:53 AM

What are your plans as far as driving? Local only or distance? By distance I mean putting some real miles on it in a day. 200-500mi +

Charlie Chops 1940 · May 30, 2012, 11:48:53 AM

Not anywhere near enough information. I've never had anywhere near 632 inches with that kind of ponies. Normally aspirated, one carb or two, fuel injected, estimated idle speed, etc.? If it has turbos or other centifical power adders the approach would probably be different too. What does your engine builder think about where the sweet spot might be?

Generally your gonna want 2300-2500 at 70 mph. Is the Tremec OD in 5th and 6th?

Read Glens thread about his recent big horsepower Chevy II build.

Charlie

oj · May 31, 2012, 08:47:29 AM

Well, a little more info:
It has a single dominator, naturally asperated, i imagine it'll idle 800ish if they do a good job on the headers and the tremec is overdrive both in 5th and 6th.
With the 396 motor it would cruise 12-1400rpm at about 65mph, the 396 was about as gutless a bigblock as i have driven but it must've had some torque.
Sweetspot? Where this thing will want to run at? depending on the headers i would imagine you are about right 2500-2800ish but that just scares me silly to set this car up to run at that kind of rpm with this much torque, somebody will get hurt.
I am thinking 1st and 2nd will be near useless with the rear gearing that it now has.

Dusty · May 31, 2012, 09:42:31 AM

Is this an April Fools Joke left over posting?

?

phat rat · May 31, 2012, 10:31:53 AM

Quote from: "Dusty"Is this an April Fools Joke left over posting??

Starting to wonder

oj · May 31, 2012, 10:54:49 AM

Nope, this be the real deal.
It is Blueprint Engines# PS6320CTC, ser# 290016

phat rat · May 31, 2012, 01:23:21 PM

Holy S%@t Batman.

Charlie Chops 1940 · May 31, 2012, 01:48:39 PM

There are a number of calculators for gearing, engine speed and vehicle speed available by Google search. I believe I would want to run that engine in cruise at aroung 2300-2400. You just need to pick whether you want to do it in 5th or 6th.

If you set it up to cruise 70 in 5th then you alway have 6th for the BIG numbers.

Charlie

Mikej · May 31, 2012, 01:50:50 PM

Is the trans and rear gear the same as you are using now? If so the rpm's and speed will be the same as you have now. What ratio do you have presently?

oj · May 31, 2012, 02:00:37 PM

I don't have the tremecs' gear specs, i presume they are nearly the same as the muncie.
I expect without a rear gear change the motor will not be loaded properly and it'll be like pedaling a 10spd bike in 1st gear - its' legs will go like crazy but it won't go anywhere because there won't be a load on the engine.
Think of when you did a dyno test, the motor can't make power until they put a load on it. When they do you hear the motor respond, give a grunt to get its' shoulders squared away and then you throw the rpm to it.

Mikej · May 31, 2012, 03:17:37 PM

So you have a Munice 4 sp, but you don't know your rearends gear ratio but it go 65 mph at just off idle with the 396. Does this about sum it up?

oj · May 31, 2012, 04:11:05 PM

Quote from: "Mikej"So you have a Munice 4 sp, but you don't know your rearends gear ratio but it go 65 mph at just off idle with the 396. Does this about sum it up?

Forget it, sorry i asked the question.

Mikej · May 31, 2012, 04:38:06 PM

oj, don't want to be a butt but to help you we do need a little more info then you have given. There are calculators you can put in different numbers so you can see the different effects for tire size, rpm and rear end ratio.

teal32 · May 31, 2012, 05:03:29 PM

Try this site: http://www.project33.com/tiresize.cfm to calculate RPMs.

Here is what they say about their calculator...

"I hope some of you will find this RPM-finder useful. Just take the tire height information you learn above and use the drop-down menus below to calculate your RPM's for a desired speed. Keep in mind these figures will get you close but are not exact. Only OEM automatic transmissions are listed (manual transmissions have too many variables) and the differential ratio menu contains most of the common ratios. Hope you find this useful. Let me know if there's anything else I can program to make your project easier. The answer will appear above the form."

Hope this helps.