Wide Ratio vs. Close Ratio - Team Camaro Tech
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post #1 of 13 (permalink) Old Sep 13th, 02, 11:33 AM Thread Starter
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Dave
 
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I'm looking at swapping my Th350 auto for an M20 4 speed.
What's the diference between a Wide Ratio and Close ratio?



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post #2 of 13 (permalink) Old Sep 13th, 02, 12:16 PM
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the close ratio will probably set you back a couple hundred dollars more than the wide ratio.

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post #3 of 13 (permalink) Old Sep 13th, 02, 12:22 PM
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Yeah, the close ratio has a taller 1st gear, and the others are closer together.

They work well with an engine that has a narrow power band, if you have enough rear gear to get the car moving.



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[This message has been edited by ZZ430DropTop67RS (edited 09-13-2002).]
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post #4 of 13 (permalink) Old Sep 13th, 02, 12:22 PM
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The close ratio has gear sets closer to each other, and because of that a higher first gear, I believe it was about 2.20:1; where the wide ratio is spread a little farther, with a few different first gears, but the most common one is 2.52:1;

If you are going to be doing drag racing, most motor combo's work better with the wide ratio, as far as it will give you lower et's. The close ratios are great for road racing and are kind of fun to drive since the rpm's stay up there a little more as you shift. But, there is nothing wrong with either one.

-Dan
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post #5 of 13 (permalink) Old Sep 13th, 02, 03:52 PM
SY1
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A lot of guys will run the wide ratio to get away with a little less rear end gear and off the line a little quicker.
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post #6 of 13 (permalink) Old Sep 13th, 02, 08:45 PM Thread Starter
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Sorry I didn't add this info to start with, but I have a 383 Stroker ~ TH350 ~ 3.08 12 bolt posi. Lots of torque >20mph but will hardly break the tires loose from take off.
I won't spend much time at the track, just to play with on the backstreets and an occaisional trip down the HIGHWAY, so I need something streetable and yet capable of a burnout when I need it.
As is, I get about 11 mpg (no tach yet, so I don't know WHERE I am on rpm's) but it sounds like my rpm's are up there tooling down the interstate at 70 mph...

I'm corresponding with a guy who has the m20 who wants to go AUTO (possible swap) but his 69 is a big block. Any differences to worry about if it comes out of a big block car?

I think the gears are 1st: 2.56 2nd: 1.91 3rd: 1.48 4th: 1.00

Should I be looking for something in a 5 speed with this motor and the hunt for less rpm's on the highway?

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post #7 of 13 (permalink) Old Sep 13th, 02, 08:49 PM Thread Starter
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The number on back of the tranny is 3857584. I'm not sure how/where to decode this...

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post #8 of 13 (permalink) Old Sep 14th, 02, 07:00 PM
SY1
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Dave
 
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Kwik,
I'd run the M20 from reading your posts about what you hope to achieve with your combo. The lower first gear will allow you to use less rear end gearing, get you moving a little quicker off the line. The 3.08s aren't doing you any favors though. I'd never run a gear that numerically low in a street car, but many guys do especially if they're looking at highway use too. Don't go with a light flywheel or you'll have the same problem launching the thing. Not enough mass to keep things turning to break the wheels loose. If you have a choice go with the 14" flywheel and matching 11" clutch, this will give you a little extra weight (inertia) to help keep the power up and the wheels loose off the line. Remember though a heavy flywheel is just robbing power once you're going down the road, so be careful not to go too heavy.

[This message has been edited by SY1 (edited 09-14-2002).]
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post #9 of 13 (permalink) Old Sep 15th, 02, 02:22 AM
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KWIK 69,

The number you posted is the casting number for the tailhousing.

Here is a link for decoding.
http://www.4speeds.com/muncie2.htm

I agree, with a 3.08 rear, you need an M20 (wide ratio).

Good Luck,
Joe

[This message has been edited by Turbo_Jet (edited 09-15-2002).]
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post #10 of 13 (permalink) Old Sep 15th, 02, 03:48 AM
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If you look at how the factory decided which tranny to specify as "standard" you will see an overall pattern. The engines that had lots of low end torque and wider power bands like base engine 396's got wide ratio trannys and the higher HP engines with narrower power bands got close ratio tranys, generaly as standard. It depends on how you built the engine. If you have a narrow high RPM power band, run the close ratio. If you have the wider RPM power band, run the wide ratio tranny. Either one will work.

-Mark.
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post #11 of 13 (permalink) Old Sep 15th, 02, 08:59 AM
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Be careful on which m20 you get. The gear ratio of 2.56 if I remember correctly is the number for the pre-67 tranny. This tranny used the 7/8" pin. Most people say it is much weaker than the 67+ with a 1" pin. I believe the 67+ should have a 2.52 1st. Check http://www.muncie4speed.com for more info as stated before.
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post #12 of 13 (permalink) Old Sep 15th, 02, 08:36 PM
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I could have swore that I read somwhere that if a FirstGen came with a 3.73 or numerically highier rear-end, then it would have been equipted with the M-21 or the M-22 (both 2.20-1.64-1.28-1.00) to help tame the high gears. And the numerically lower gears got the M-20 (2.52-1.88-1.46-1.00) to help with acceleration.

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post #13 of 13 (permalink) Old Sep 16th, 02, 02:44 PM
 
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Jim,

No, that was the Z- cars if I recall right..


Kwik,

My SS/RS is stock with 3.31's and I say this b/c the Salesman that went through the option list explained the difference in gear ratios to me.

I just said, heck, stock 3.31's should be fine, good power, not like the automatic ratio's and a lot better gas mileage then the performance ratio's, plus faster, (but not quicker), on top end..

Btw, you might run a short wide tire to help keep you at a true 3.08 rearend ratio! I say this b/c my 406 didn't do all that good at smoking my great big old-fashioned L-60's b/c I think the effective gear ratio of my 3.31's was more like the 3.08's.

I did use ta love rolling her out of the hole and hazing the big suckers through first gear, (M-20)!!!

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