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Discussion Starter #1
Hi all,

I am rebuilding my diff and going from a stock 3.08 to a 3.36. It is a '70 stock big block(454/390) with an M20.

Other than the spedo driven gear and the higher RPM's at cruise, are there other things that I need to take into consideration?

Is a 3.36/M20 a good combination? It a more of a pleasure ride...no track or racing.

TIA,

Paul
 

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Hi all,

I am rebuilding my diff and going from a stock 3.08 to a 3.36. It is a '70 stock big block(454/390) with an M20.

Other than the spedo driven gear and the higher RPM's at cruise, are there other things that I need to take into consideration?

Is a 3.36/M20 a good combination? It a more of a pleasure ride...no track or racing.

TIA,

Paul
Personally I would stay with the 3.08. With that said, what sways me to that conclution is your pleasure ride and no racing statement. The M20 has a very low first gear of 2.52 you multiply that with the 3.08 rear which gives you a first gear final ratio of 7.7616 which is not shabby, while you retain your higher ratio for the highway. Besides you have a ton of torque in the BB, no need to increase it with gears! :cheers:

Just my .02. :thumbsup:

(I know a lot of guys are going to bash me on this so take it for what is is worth! :laughing: )
 

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I agree with Rjent, but for different reasons. The change from 3.08 to 3.36 is not going to be all that dramatic. If it was to a 3.50 or 3.73 or 3.91, then it would really be a major difference. To me, not worth the expense to change to 3.36 with the limited performance you would gain.

Dep
 

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Discussion Starter #5
Well it looks like you 2 are in agreement.

One other thing that I am considering is the housing...it is original (as is most of the rest of the car). The tank sticker also says 3.08 on it.

So since there is limited performance gain I am thinking I might keep it original 3.08.

Thanks
 

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Well it looks like you 2 are in agreement.

One other thing that I am considering is the housing...it is original (as is most of the rest of the car). The tank sticker also says 3.08 on it.

So since there is limited performance gain I am thinking I might keep it original 3.08.

Thanks
With $13.50 in gas, stick with the "freeway flyers." As stated above, unless your going 3.73, why bother at all?
 

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The trade off from 308 to 336 is not much but it wll give a little more grunt with the BB. The cruise RPM is not much more - not enough to warrant any MPG concerns with a part time driver.

I switched from 308 to 336 in my SB auto. TQ is no where near a BB but I still liked the switch. Since this is your first rebuild and setting up used gears can be a pain at times the extra money spent on new gears is worth it in my opinion. Everything else is new so start with a fresh set of gears. Since that would be my approach the selection from 308 to 336 is not a concern. I have set up a few 336's for BB cars and M-20's and the guys loved them. Comes down to your call, I found Toms 336's setup better then the 308's also- I don't know why?:thumbsup:
 

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Discussion Starter #8
With $13.50 in gas, stick with the "freeway flyers." As stated above, unless your going 3.73, why bother at all?
Well I am rebuilding the dif and there is no price difference between the 2 gears. I don't want to lose my "decent" gas mileage since I like to cruise. I thought going up to 3.36 would give a little better performance in first gear and only bump up the cruising RPM's a little.

Waht would 3.73 do for a big block with an M20? Would it turn my freeway flyer into an out of breath gas hog?
 

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I setup a 373 for DIP51 "over there" and he loves it. He has a BB crate motor with 500 HP?? You will be around 3400 RPM @70mph I don't think you would like it for your driving style but street driving through the gears would be much different then with your 308's! you will want to put your foot into it a lot. Tire cost may overcome gas prices!!:rolling:
 

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Discussion Starter #11
Well, 3.73 doesn't sound like it would fit me:smack With my driving style...my tires may outlive me:laughing:


Yesterday I was moments away from ordering the 3.36's. Then I thought I'd check it out here to see if I have my bases covered. With little impact in gas mileage due to my driving style(today when she is running, I go through a tank in a weekend), the only drawback is that the gears won't match the housing stamping...but who is going to know but me?


Going to sleep on it one more night.
 

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Discussion Starter #12
I setup a 373 for DIP51 "over there" and he loves it. He has a BB crate motor with 500 HP?? You will be around 3400 RPM @70mph I don't think you would like it for your driving style but street driving through the gears would be much different then with your 308's! you will want to put your foot into it a lot. Tire cost may overcome gas prices!!:rolling:

When I put a post up over there, DIP51 enthusiastically suggested that I go with 373's:laughing: Damn, 500hp in a torque monster, that thing must be a beast!
 

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OK, i'ts certain NOT a vette, but my 4400 lbs empty work van....318 auto TF999, the thing came with a 294 rear, me switch to 321 ratio was a HUGE improvement in that truck's ability to get up and move, and with those tall tires it's not so awful bad on the freeway long as I stay below 70-75 or less...

I have 336 in my '72 vette with a mild build SBC, and O/drive auto...I find it's a perfect blend....2400 at 80, cruise nicely, plenty of pickup even though I do not have a BBC....supposedly 425 ft lbs tq......plenty to move a vette...with that BB, I think a 308 is a good choice, and I would stick with it....

keep in mind, I come from the Pontiac school of thought, all torque down LO....engine died at 5 grand....but GOD help you off the throttle....550 ft lbs at dead idle....273 was my gear choice....

BTW, I NEVER owned a RWD vechicle of ANY TYPE without POSI....NOT ONE....EVER...
 

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Discussion Starter #14
OK, i'ts certain NOT a vette, but my 4400 lbs empty work van....318 auto TF999, the thing came with a 294 rear, me switch to 321 ratio was a HUGE improvement in that truck's ability to get up and move, and with those tall tires it's not so awful bad on the freeway long as I stay below 70-75 or less...

I have 336 in my '72 vette with a mild build SBC, and O/drive auto...I find it's a perfect blend....2400 at 80, cruise nicely, plenty of pickup even though I do not have a BBC....supposedly 425 ft lbs tq......plenty to move a vette...with that BB, I think a 308 is a good choice, and I would stick with it....

keep in mind, I come from the Pontiac school of thought, all torque down LO....engine died at 5 grand....but GOD help you off the throttle....550 ft lbs at dead idle....273 was my gear choice....

BTW, I NEVER owned a RWD vechicle of ANY TYPE without POSI....NOT ONE....EVER...
It suppsedly has 500 ftlbstq (flywheel?)at about 3400 if I remember correctly...and it plants your arse squarely in the seat when you kick it.
 

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I have a 3.73 in my 2004 Silverado 1/2 ton truck. Engine is a 325 with 4 speed auto. Mileage averages 18 around town and a little better on the highway. RPM is quite bearable. But it is an auto with different gearing. Oh yeah...I can smoke the tires pretty easily and it does have posi. :D

Dep
 

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I have a 3.73 in my 2004 Silverado 1/2 ton truck. Engine is a 325 with 4 speed auto. Mileage averages 18 around town and a little better on the highway. RPM is quite bearable. But it is an auto with different gearing. Oh yeah...I can smoke the tires pretty easily and it does have posi. :D

Dep
It has overdrive.
 

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I have a 3.73 in my 2004 Silverado 1/2 ton truck. Engine is a 325 with 4 speed auto. Mileage averages 18 around town and a little better on the highway. RPM is quite bearable. But it is an auto with different gearing. Oh yeah...I can smoke the tires pretty easily and it does have posi. :D

Dep
Hell, any 4 cyl with auto can smoke the tires in a PICKUP.....and they said C1 Vettes were taill assed light.....:laughing: :laughing: :rolling: :nuts:
 

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Discussion Starter #20
Thx guys for the input......and the answer is

3.36

ordered them today:cheers:
 
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