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73-87 Chevy _ GMC Trucks => Engine/Drivetrain => Topic started by: BADAZ chevy guy on April 02, 2014, 06:03:02 pm

Title: 3.07 gears?
Post by: BADAZ chevy guy on April 02, 2014, 06:03:02 pm

3.07 gears behind an M40 transmission. Thoughts... Good, Bad, Pro's, Con's?

Title: Re: 3.07 gears?
Post by: zieg85 on April 02, 2014, 06:06:05 pm

whats a M40?

Title: Re: 3.07 gears?
Post by: BADAZ chevy guy on April 02, 2014, 06:23:01 pm

Sorry. M40 is a Turbo 400.

Title: Re: 3.07 gears?
Post by: zieg85 on April 02, 2014, 06:33:30 pm

Fine, that is a decent all around gear.  You will get all kinds of opinions and it really depends on your type of driving and engine/tire set up.  3.07 is highway friendly but may lack take off power when pulling a trailer and you have tall tires.  Is your engine stock?

Title: Re: 3.07 gears?
Post by: VileZambonie on April 02, 2014, 07:04:13 pm

Need more details....

Title: Re: 3.07 gears?
Post by: BADAZ chevy guy on April 02, 2014, 08:33:57 pm

I haven't decided what I'm going to do with the the engine. I want low to mid range tork, so the cam will be pretty much stock. I'll probably drop a couple of Vortec heads on top. Definitely balance the motor. I'm looking more towards efficiency (And turning heads) then racing. This is going to be a daily, around town, driver.

Title: Re: 3.07 gears?
Post by: zieg85 on April 02, 2014, 08:44:16 pm

That gear choice should be good IMO

Title: Re: 3.07 gears?
Post by: VileZambonie on April 03, 2014, 08:08:01 am

What year make model? What size tires?

Title: Re: 3.07 gears?
Post by: BADAZ chevy guy on April 03, 2014, 09:58:11 am

1977 C10 Heavy half ton. Not sure what tire size I'm going with yet. That's later in the build.

Title: Re: 3.07 gears?
Post by: VileZambonie on April 03, 2014, 04:10:27 pm

Well that's a big factor in selecting a final drive ratio

Title: Re: 3.07 gears?
Post by: BADAZ chevy guy on April 03, 2014, 07:53:08 pm

Very true, VileZambonie. Looking at some of the pics posted here, and other forums, I'm thinkin' I'll stay pretty much with the stock height 15" tires and just go wider. Say, 7" wide front and 10" wide rear.

Title: Re: 3.07 gears?
Post by: BADAZ chevy guy on April 05, 2014, 07:34:30 pm

I'ne also read that a slightly higher RPM stall convertor will help getting off the line a bit quicker. Any thoughts?

Title: Re: 3.07 gears?
Post by: rich weyand on April 06, 2014, 12:26:39 am

I have 3.43:1 gears on a K10 with 31" tires, which comes out same as 3.21:1 on original size 29" tires, close to what you're talking about.  It's not a race car, but with a torquey engine it works out alright.  I never use all the pedal I have getting rolling, so if it had more, I wouldn't use that either.  As it is, it's perfect for my around-town daily driver.

A higher stall torque converter does stress the transmission more, but slightly higher shouldn't be much more.  I stayed with the stock, which I think is 1500 rpm or thereabouts.  Note that you will have smoother around-town driving with the original stall speed.  Lucky you, with a C truck, you can change the stall converter pretty easily, so you can always change it back if you don't like it.  It's just a little more involved on a K truck!  ("Lessee, is it easier to pull the engine, or the transfer case and transmission...?")