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#1
03-07-2012, 01:14 AM
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M20 wide box
My original M21 needs a rebuild so we swapped it out for an M20 box. The M20 along with the 4.56's made that little 302 wake right up. Nothing like a set of gears in a SB Chevy! The old saying goes with a sb Chevy "you can keep the hood closed cause the performance is under the trunk."
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#3
03-07-2012, 02:21 AM
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Re: M20 wide box
Sammy,
Did your Z come from the factory w those gears? You must be enjoying the balmy wx that we are getting over here in Ohio. [img]<<GRAEMLIN_URL>>/  [/img]
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Sam...  
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#4
03-07-2012, 02:49 AM
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Re: M20 wide box
I'm glad to hear that that combo is making you happy Sammy 'cause that's gonna be my setup in a few months (I hope). I have to see how the intake change works, then swap out the 780 for the 850. After that the 4.56's go in. (One thing at a time)
Kurt [img]<<GRAEMLIN_URL>>/ [/img]
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 1969 SS396 Post Sedan Delivered to Van-T Topeka KS MCACN Day2 Concourse Gold Award 1965 VW El Lobo Dune Buggy built in the mid 70’s for the Iowa Shriners 1968 Schwinn Orange Krate 1969 Schwinn Pea Picker 1968 Schwinn 5-Speed 1970 Schwinn 3-Speed Deluxe 1972 Schwinn 10-Speed Continental 1973 Schwinn 5-Speed Suburban All Original Paint Bikes
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#5
03-07-2012, 03:26 AM
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Re: M20 wide box
yep, one thing at a time Kurt. I would put the 56's in before the carb swap. You will want to run that gear no matter what carb you have on that chevelle. Don't go to big on the carb. 85% efficiency on a smaller carb is better than 60% efficiency on a big carb IMO. Remember the Stock eliminator boys are running 780's with vacuum secondaries on their 396's and running in the nines. MacNeish is running low 10.40's with the 780 also on his 302.
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#6
03-07-2012, 04:36 AM
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Re: M20 wide box
I'm smelling what you're cooking Sammy. I just know that the motor likes fuel at high rpm. The reason I say that is when we had it on the dyno the 800 DP wasn't enough for it at 6200. If it doesn't help I'll put the 780 back on. Ya don't know if ya don't try.:-)
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1969 SS396 Post Sedan Delivered to Van-T Topeka KS MCACN Day2 Concourse Gold Award 1965 VW El Lobo Dune Buggy built in the mid 70’s for the Iowa Shriners 1968 Schwinn Orange Krate 1969 Schwinn Pea Picker 1968 Schwinn 5-Speed 1970 Schwinn 3-Speed Deluxe 1972 Schwinn 10-Speed Continental 1973 Schwinn 5-Speed Suburban All Original Paint Bikes
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#8
03-07-2012, 02:13 PM
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Re: M20 wide box
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: [email protected]</div><div class="ubbcode-body">My original M21 needs a rebuild so we swapped it out for an M20 box. The M20 along with the 4.56's made that little 302 wake right up. Nothing like a set of gears in a SB Chevy! The old saying goes with a sb Chevy "you can keep the hood closed cause the performance is under the trunk." </div></div>
I thought you Italians kept everything "in the trunk" [img]<<GRAEMLIN_URL>>/hmmm.gif[/img]
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02 Berger 380hp #95 Lots of L78 Novas Join National Nostalgic Nova! 70 Orange Cooler 69 Camaro
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#10
03-07-2012, 04:02 PM
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Re: M20 wide box
I don't think M21s have any place in a street car these days. The ratio "spread" from 1-2, 2-3 is exactly the same on an M20 vs M21. M20 just has a wider ratio spread on the 3-4. Seems to me that M20s are a more practical choice if you are not racing and can afford the greater 3-4 rpm drop.
You can run a taller axle and still have the same "feel" in 1-2-3 gears. A 3.31 gear behind a M20 will have the exact same final drive ratio in 1st, 2nd, 3rd as a M21 with a 3.79 gear (3.73 if you want to talk about "real" ratios).
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