I have a 396 bored 60 over. I'm using a comp cams 286 magnum cam in it. My transmission is a M-20 wide ratio 2.56 first gear. I currently have a 12 bolt posi housing 3.31 gears. I was going to change them to either 3.73s or 4.10s. What can I expect from this gear change using the wide ratio trans vs. a M-21 close ratio? The car is going to be used for street strip use.

The wide ratio trans was designed so that the first 3 gears with a 3.55 rear end was the same as a close ratio with 4.11s. The only problem with a wide ratio is the horrible 3rd to 4th spread alot of small blocks won't pull it. Most big blocks actually like it because of there wide torque band.

Thanks for the info. I understand what your saying but if you could elaborate a little more it would help me a lot. With the wide ratio and 4.10s would I have a hard time getting traction? Would I have to start off in second gear? Or is this an absurd combination (4.10s w/a M-20) and if i'm going to use 4.10s I should replace the tranny w/a M-21?


<BLOCKQUOTE>quote:</font><HR>Originally posted by oger:
The wide ratio trans was designed so that the first 3 gears with a 3.55 rear end was the same as a close ratio with 4.11s. The only problem with a wide ratio is the horrible 3rd to 4th spread alot of small blocks won't pull it. Most big blocks actually like it because of there wide torque band.

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If you are going to be driving it on the street you would be better off with the wide ratio and 3.55 gears so you can still drive at highway speeds without spinning your engine too tight. Keep it drivable, you'll have more fun.

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'69 RS/SS396 pro street
427/4spd/9"

thanks bgh, any idea what kind of performance improvements can be expected from changing gears from 3.31s to 3.55s? Is it worth the work? will the difference be felt? and would a gear change of that small of an increase have any effect on my 1/4 mile times?

I don't think that small of a change will make a big difference. I don't think I'd go to the 4.10s though. The 3.73 may be all right if you are not going to be traveling much.

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'69 RS/SS396 pro street
427/4spd/9"

4.10's are a PITA - my (stock) Z/28 came with the optional 4.10, and it finally drove me nuts on the highway (3800 at 70); swapped it out last Fall for a 3.55, now much more civilized (3200 at 70). With your big-block, unless you're going to live at the strip, leave the rear gear as it is - you've got plenty of torque to pull it, unlike the little 302 in the Z.

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JohnZ
'69 Z28 Fathom Green