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Discussion Starter #1 (Edited)
I'm in the market for a new 4-speed, and am thinking of going with an Autogear 4-speed unit. Intended application is probably 25/75 street/strip, with an emphasis on the strip. I am having some trouble coming up with the correct gear ratios that I should be putting in the tranny to get me down the line the fastest. I have heard to keep the final drive ratio around 10 (for first gear?), but am unsure how this relationship continues throughout shifting. Here are my specs:

- 383 SBC
- AFR 210 Comp. Ported Heads (~11:1 Static C/R)
- Solid Roller, 258/[email protected]", .668" on 1.6's
- GM 8.5 Big 10 Bolt with Yukon 4.11 Gears/Detroit Locker with 28 spline axles
- 255/60-15 MT ET Streets
- '72 Nova, ~3400 lbs. (guessing here)

With my 4.11's and my 27" tall tire, I can come up with an optimal first gear ratio of around 2.6 or so. It's a putz under 3000 RPM (all relative, of course), but really hauls the mail after that. I figure I'm setup to run atleast a high 10 second 1/4 mile.

I am looking at a Tex Racing 4-speed unit as well, and it has a 2.88 first gear. Would I really be leaving that much on the table by going close to 12 FDR in first? How would I calculate the optimum gear ratios for my car? Should I go wide ratio? Close ratio? I know I need to keep the RPM drop where I will make my power, and that also depends on shift points, which I don't know yet. I can see myself shifting around 7000 though.

On another note, is it possible to beef up a stocker Super T-10 (nickel gears, etc.) and have it live at the strip? It's hard to justify spending $2k on a new transmission, but I do understand that I may just have to pony up the $$ to live, but was curious if anybody had any success with running a Super T10 at my power level.

Thanks for any help.
 

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With 4:11s and a 27 inch tire, The 2.56 with even gear splits or 2:20 first should work.
 

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When you say even gear splits, are you implying a close ratio gearset?
No, Autogear as an M22 gearset with a 2.56 first and gears 1 - 4 are evenly split. Factory M20s have a 2.52 first with gears 1 thru 3 being closely spaced and a steep drop in 4th. I've never been a fan of close gear spacing if your engin has a broad power band. Pick the first gear that will get you launched and evenly space the rest. The factory M20 spacing is fine on a lower powered car that needs to get to 85 MPH quickly.
 

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If it were my car, I'd run the 2.20 first gear and switch to a 4.56 rear gear, if you're more worried about your ET. Remember that a stick car can use a little more gear because it dosen't have the torque mulitplication that an automatic sees thru the convertor. This will put you at 7400 thru the traps if you can hit 130mph. And if you're using a regular slick, don't forget that it will grow slightly at speed, so the rpm may loweer a little thru the traps, as long as you don't have a slipping clutch. Also, the close ratio will be a little quicker. It's not much, but they can be a little more consistant than a wide ratio as well.
 

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Discussion Starter #6
No, Autogear as an M22 gearset with a 2.56 first and gears 1 - 4 are evenly split. Factory M20s have a 2.52 first with gears 1 thru 3 being closely spaced and a steep drop in 4th. I've never been a fan of close gear spacing if your engin has a broad power band. Pick the first gear that will get you launched and evenly space the rest. The factory M20 spacing is fine on a lower powered car that needs to get to 85 MPH quickly.
Ah, ok. I figured you were talking about an even drop in gear ratio. I figured close ratio was implied. Have you run an Autogear M22 before? That was what was recommended to me by one of their techs I talked to. Thanks for the info on the even gear drops, it helps alot. It was just too much math to think about in my head all at once, :devil:

If it were my car, I'd run the 2.20 first gear and switch to a 4.56 rear gear, if you're more worried about your ET. Remember that a stick car can use a little more gear because it dosen't have the torque mulitplication that an automatic sees thru the convertor. This will put you at 7400 thru the traps if you can hit 130mph. And if you're using a regular slick, don't forget that it will grow slightly at speed, so the rpm may loweer a little thru the traps, as long as you don't have a slipping clutch. Also, the close ratio will be a little quicker. It's not much, but they can be a little more consistant than a wide ratio as well.
yea, I thought about 4.56's as well, but I will be driving this on the street, and that is just too high for that. I'm hoping for a 125-130 MPH trap speed, but who knows. I'm concerned about the trans holding up though. Any experience with an Autogear unit?
 

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What's too high about 4.56's? I run them on the street all the time, usually with 28" tires, but that would be like you running a 4.30 gear, which is another option for you.
 

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Discussion Starter #8
What's too high about 4.56's? I run them on the street all the time, usually with 28" tires, but that would be like you running a 4.30 gear, which is another option for you.
Basically due to not having an overdrive. Going ~50 @ 3000 RPM (speedo doesn't work) when I am actually street driving is a little intimidating, but I'm not against a gear change, it's just what I have in there currently. If I can get it without having to change out gears that's fine.

Am I really leaving that much on the table? Does having a closer ratio gearset, with regards to 4.56's and a 2.20 first, provide a noticeable benefit? I need to find a damn calculator.
 

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http://files.me.com/oddie/riq3it

Here's a gear calculator I used to compare the M20 I have with the new Autogear M22Z. This equates with a 3:08 rear to be the same as a 4:56 rear in the first two gears and then it evens out to an M20 in 3rd and 4th. So this may be a good compromise - it is for me since I have 3:08 rear.
 

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Ah, ok. I figured you were talking about an even drop in gear ratio. I figured close ratio was implied. Have you run an Autogear M22 before? That was what was recommended to me by one of their techs I talked to. Thanks for the info on the even gear drops, it helps alot. It was just too much math to think about in my head all at once, :devil:
I've run M20 and M21. I prefer the M20 unless you have a 4.56 or so. I"ve never driven the aftermarket gear sets. The 2.66 first in my T-56 with even gear splits is perfect for my 3.73.
 
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