I have been looking into the 6 speed conversion. It looks like there are several 1st gear ratio options, but it boils down top a 2.80 +/- first gear.

It appears that the stock 4 speed in 72 is a 2.20 1st gear (3.70 rear). Is the factory 1st gear too deep? Why would the aftermarkets go to a 2.80? How useful is this first gear with a 3.70 rear? How are the gear splits in the Richmond 6 speed? Are they Great/good/average for the street?

 

Those muncie gears imo are too tall.

2.66 first in mine with 4.11 and 26 in tire, love it.

When you get above 3.00 it gets a little tractor like feel to it.

 

Installed a Richmond 6 spd a couple of months back,link to write up.http://forums.corvetteforum.com/c3-t...am-change.html I have a 3.08 rear and it's just about perfect.Gear spreads are great with no large RPM drop offs. 1st gear start offs are a blast! You can get the trans with a different gear set to match your rear gears,maybe a 2.70 1st gear X your 3.70=9.99 ideal start off ratio.Mine is 3.27 1st X 3.08 rear=10.07 start off ratio.Richmond part # 7021626ED would be the trans with the 2.77 1st and .67 6 gear OD.This was my most expensive mod to date but wouldn't hesitate to do it again! The 6spd gives me more gears to play with and when I hit the open road shift into 6th the motor is just cruising.Simply wonderful!! Aloha's

 

Not if you have the power - this is 565 ft lbs though a M21 with 3.08 overtaking at approximately 40 mph
http://i160.photobucket.com/albums/t..._DSC4315-1.jpg

 

The rule of thumb is to have a first gear final drive ratio as close to 10:1 as possible.
2.8 X 3.7 gets you to 10.36:1
You can get a T56 with the first gear of 2.66 which would be 9.84:1

 

Can you give some background on that rule of thumb?

I would tend to think it all depends on the particulars of the cam, motor build specifics and where you want your final gear rpm to be.

 

that makes sense to me. On our inlines we say between 10 and 11. We really need gearing to help these little engines

 

Oops. Misread and consequently miswrote above. In any case, I would think the rule of thumb was created for gear combinations with, say a four-speed trans in mind. When you add trans gears, you add steps to get from your initial drive ratio to final drive.

Your power band and subsequently, your ideal shift points are certainly something to consider as well. I have the ROD 6-speed with a 3.28 first/0.76 6th and 3.70 rear and am also very happy with it.

In doing your planning, set up an Excel spread sheet to do the math. Put the different trans gear combinations in different columns to see how your final drive ratio combinations look side-by-side.

To show the advantage of this 6-speed, also add a column to show the final drive ratios of the Muncie 4-speed.

 

Side note,I live were stop lights are on steep hills(volcanic island).The 3.27 1st gear makes starting out a breeze very little clutch slippage! However on the flats you do shift out of first gear rather quickly, the 6spd ROD with the extra gear handles this very nicely.If you go over that 10:1 ratio you will shift out of first gear even quicker.I know a guy with a 700r4 and 4.56 rear gear,nice burnouts but useless for everyday driving.3.06 1st gear 700r4 X 4.56 rear gear =13.9 not ideal.I have a 350 L48,now a big block with lots of low end torque may warrant a different combo than what I am using it all depends on what your running.With the right trans & gear choice you be smiling ear to ear when your rowing thru the gears. Good Luck on your swap....

 

At all depends on your motor combo HP and tire size, whether it's strictly Street or you would like to make few good passes at the track once in a while. Give us some more info and whether you're looking for nice cruiser or a spicy Hot Rod combo?

 

This is the first "bent" motor I have ever had, so to me it has horsepower coming out its ears.

I am looking for a highway cruiser. I have never been to the drags so it likely wont happen. If I do anything to up the horsepower it would be something like headers, HEI, TPI or 3 deuces - pretty mild stuff. Might bump the tire size up just for looks. (Kind of a wimp, arent I???)

 

I prefer the 2.66 1st

 

I agree with I88rocket !
2.66 1st with 370 in the rear should work nice for you and still have some pretty good spice on it of the start, should also work nice in heavier traffic where you wouldn't have to be jumping on the clutch to often.
Had few different combination's in my 69, BB 427 that had 562 HP with Muncy 4-Speed 2.20 1st 336 rear gears with 28'' tire, switched to Richmond 5-Speed 3.27 1st gear and that combo worked real good. Stepped up with a different motor and trans combo to 572 ci 819.5 HP and G-Force custom built hard core t-56 6spd with 2.98 1st and Tom's diffs complete setup with 456 rear gear. With this setup first gear was useful, with 456 in rear I was not happy with it so I switched to 370's in rear. That setup with 370's was working out pretty good but with big cam if in heavier traffic I got tired of having to keep jumping on the clutch, so I switch gears again in the rear to 411's. That combo was working out pretty good and I was happy with it, no problems if in heavier traffic. Recently switched to custom built automatic transmission 4L80E with manual valve body and engine brake ( no electronics) 2.10 1st, 1.40 2nd , 1/1 3rd, .75 overdrive and 411s in rear with converter stalling at 3200rpm and I just love it. This combo is set up for Street - Strip and I can't wait to
go and try it out. I will post how it does on track.
-Paja

 

Dont overlook a nice 5 spd either.
Honestly, unless you cruise at high speeds youll hardly use 6th on that T56. One day id like to get a lower OD gear so it only drops a few hundred rpm. BBC or smaller cammed car would pull it ok but was borderline with the last motor (large sr cam).
never really go much over 65 hwy so leaving it in 5th with a slight buzz to the motor it seems happier but as said above all depends on the motor/gear combo. Great tranny though youll love it.

 

I have the Richmond 6 speed with 2.77 1st gear and .62 6th gear, driving a 4.10 rear gear. This gives me a overall 1st gear of 11.357 and a 6th gear of 2.54. This setup seems to be about right for my street driven car with a 383 small block. Awesome 1st gear and good highway cruise in 6th.