Gears -- 3.08 vs 3.70
Thread Starter
Instructor
Joined: Jul 2007
Posts: 108
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Gears -- 3.08 vs 3.70
Hey all -- My '68 runs a stock close ratio Muncie and 3.70 rearend. I love the low end grunt, but tired of the hi-rev highway cruising.
I'd appreciate any thoughts on swapping out the rear gears with a set of 336's or possibly even 308's.
Will I notice the loss of low end thrust much? Will the 65 mph cruise be much more relaxed? And roughly how much $$ to have this swap done?
Oh, background info... engine is a mildly modified L36 427 (bored/stroked to 463, street/strip cam, Edelbrock performer rpm heads, stock manifolds, and magnaflows).
Thanks in advance--
I'd appreciate any thoughts on swapping out the rear gears with a set of 336's or possibly even 308's.
Will I notice the loss of low end thrust much? Will the 65 mph cruise be much more relaxed? And roughly how much $$ to have this swap done?
Oh, background info... engine is a mildly modified L36 427 (bored/stroked to 463, street/strip cam, Edelbrock performer rpm heads, stock manifolds, and magnaflows).
Thanks in advance--
Drifting
Joined: Apr 2006
Posts: 1,911
Likes: 2
From: gold coast queensland
Hey all -- My '68 runs a stock close ratio Muncie and 3.70 rearend. I love the low end grunt, but tired of the hi-rev highway cruising.
I'd appreciate any thoughts on swapping out the rear gears with a set of 336's or possibly even 308's.
Will I notice the loss of low end thrust much? yes you will, with 3.08 say goodbye to hard launches, it will be gone. Will the 65 mph cruise be much more relaxed? for the hiway it will be purring along and become a real nice cruiser on the open road . it will prob sit on about 2200 rpm at 60mph. And roughly how much $$ to have this swap done? very little . a shop would put them in for a few hundred and the gears im guessing would only be a couple hundred as well.
Oh, background info... engine is a mildly modified L36 427 (bored/stroked to 463, street/strip cam, Edelbrock performer rpm heads, stock manifolds, and magnaflows).
Thanks in advance--
I'd appreciate any thoughts on swapping out the rear gears with a set of 336's or possibly even 308's.
Will I notice the loss of low end thrust much? yes you will, with 3.08 say goodbye to hard launches, it will be gone. Will the 65 mph cruise be much more relaxed? for the hiway it will be purring along and become a real nice cruiser on the open road . it will prob sit on about 2200 rpm at 60mph. And roughly how much $$ to have this swap done? very little . a shop would put them in for a few hundred and the gears im guessing would only be a couple hundred as well.
Oh, background info... engine is a mildly modified L36 427 (bored/stroked to 463, street/strip cam, Edelbrock performer rpm heads, stock manifolds, and magnaflows).
Thanks in advance--
Intermediate
Joined: Mar 2010
Posts: 46
Likes: 0
From: Saginaw Mi
Personally, my 454 with 308 is fine. BBC have a ton of torque and will get you moving w/o a problem. You will notice a difference on take off but if you're tired of the highway buzz swap to 336/308, your motor will thank you for it. Probably close to 500 rpm diff at 70 mph.
Le Mans Master
Joined: May 2003
Posts: 8,877
Likes: 3,556
From: Fernandina Beach FL
2023 Restomod of the Year finalist
2020 C3 of the Year Winner - Modified
With 255/60-15" tires- or about 27" diameter-
The 3.08 rear will be about 2500RPM...@ 65MPH
The 3.70 should be about 3000RPM.
So about 500 difference as DW5555 said...
There's a lot of tire/ratio/speed calc out there-
http://wildcatent.freeyellow.com/zookmods/calc.htm
My 71' LS5 came from the factory w/ a 3.08- I don't think you'll have any problems.
Richard
The 3.08 rear will be about 2500RPM...@ 65MPH
The 3.70 should be about 3000RPM.
So about 500 difference as DW5555 said...
There's a lot of tire/ratio/speed calc out there-
http://wildcatent.freeyellow.com/zookmods/calc.htm
My 71' LS5 came from the factory w/ a 3.08- I don't think you'll have any problems.
Richard
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Instructor
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Le Mans Master
Joined: May 2006
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From: League City Tx
I think the 3.08 will be fine with your big block...unless you are trying to extract every last tenth at the strip...you will be happy with the 3.08s.... If you are a "spirited" driver, go to 3.36s but the highway cruise won't be as nice....
FWIW... I have 3.08s in mine. My car is an Auto and I have a stall converter so it skews my RPMs some but.... At 70 mph(gps verified), I turn 2950rpms, 75mph is 3150rpm, 80mph is 3300 or so.....I believe 85 mph was 3500. Very liveable... Ofcourse my converter really helps the acceleration from all speeds and my motor makes a LOT of torque....but my 60's at the strip are still decent at 1.61 on 27" tires...w/3.08 gears.
Good luck on the gear swap...3.08 or 3.36s will be fine.
Race Director
Joined: Dec 1999
Posts: 11,096
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From: Sierra Foothills CA
You just need to decide how important it is for you to pull hard off the line vs. cruising easier at speed. You will notice a difference in acceleration no doubt. Your street/strip cam could be the critical factor here because if it's near the edge for streetability your rear gear change could make throttle response a bit soft with that 2.20 first gear in your trans vs. the 2.52 that comes with the wide ratio trans. What are the specs on your cam? FYI, I went from 2.73s to 3.55s and it was night and day but that's with a TH400. However, I don't take many trips in that Vette.
Burning Brakes
Joined: Nov 2006
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2022 C3 of the Year Finalist - Modified
I changed my deff' from 4.11 to 3.36, the RPM go down by ~600RPM, but in first I tried to change only the pinion/ring and it didn't fit in the original case, I was told that the higher ratios (4.56,4.11...) had deferent cutting inside the case so I changed complete deff'.
Avner
Avner
Burning Brakes
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From: Finland
i´m slow...
Le Mans Master
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From: Las Vegas - Just stop perpetuating myths please.
Can't tell where your located.
Hey all -- My '68 runs a stock close ratio Muncie and 3.70 rearend. I love the low end grunt, but tired of the hi-rev highway cruising.
I'd appreciate any thoughts on swapping out the rear gears with a set of 336's or possibly even 308's.
Will I notice the loss of low end thrust much? Will the 65 mph cruise be much more relaxed? And roughly how much $$ to have this swap done?
Oh, background info... engine is a mildly modified L36 427 (bored/stroked to 463, street/strip cam, Edelbrock performer rpm heads, stock manifolds, and magnaflows).
Thanks in advance--
I'd appreciate any thoughts on swapping out the rear gears with a set of 336's or possibly even 308's.
Will I notice the loss of low end thrust much? Will the 65 mph cruise be much more relaxed? And roughly how much $$ to have this swap done?
Oh, background info... engine is a mildly modified L36 427 (bored/stroked to 463, street/strip cam, Edelbrock performer rpm heads, stock manifolds, and magnaflows).
Thanks in advance--
BTW do you have an extra close ratio muncie for sale?
cardo0
Burning Brakes
Joined: Mar 2006
Posts: 915
Likes: 2
From: Lima, OH -- 69 L71 427/435hp
Another option, is an overdrive/wide-ratio kit for your Muncie. I have 4.56/4.88 gears in mine and it brought it up to a 3.91 final drive ratio.
I bought mine from www.autogear.net.
The wide ratio kit for 3.70's is ~$700-800.
It wasn't too hard to change the gears either.
I bought mine from www.autogear.net.
The wide ratio kit for 3.70's is ~$700-800.
It wasn't too hard to change the gears either.
Team Owner
Joined: Jul 2008
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From: In limbo
St. Jude Donor '13-'15, '17 thru '22
Yeah, I think your close ratio is where the issue is. I have a 454 with a 3.08 and the wide ratio. I have no trouble smoking the tires in first, screeching in second and chirping in third, even though I have never gone out of my way to do this. 65 mph cruise is at 2600 rpm, so that isn't bad. I wouldn't go so far as to say I "like" my 3.08, but it is plenty fine for street driving, which is what I use the car for 100% of the time. If I got into drag racing, I am sure I would change the rear, but for street driving, it is fine.