3.73 Posi

Pharozen · Feb 26, 2017

I've been doing a little reading on reviews for the 3.73 posi, and I read a lot of negative reviews regarding highway usage...
Can someone give me the details on why this gear isn't recommended on the freeway for fuel efficiency. Would an Over-drive transmission help?

This is the combination I've been working on for over 4 years: 350 Rocket, 2004r trans, 2500 stall, 3.73 posi.

Ribbedroof · Feb 26, 2017

GM thought it was good enough for their performance model G bodies with OD transmissions, I don't see why people are so worked up about it. If their primary concern is fuel economy, why are they involved with old cars?

UNGN · Feb 26, 2017

It depends where you live. When GM put 3.73's in 4 speed cars, the speed limit was only 55 mph.

In Texas, 70 mph gets you run over in the slow lane (I know this because I set my Cruise at 70 mph every morning and stay as far right as I can get). Highway traffic is really 75 mph, and cruising at 75 mph with 3.73's gears, even with OD, gets old. 3.42 is is a much better choice in Texas. If you live somewhere where 60-65mph is the norm, 3.73's will probably be fine.

Kwik_Cutty88 · Feb 26, 2017

I run 3.73's with a 700R4 and a 28" tire. My car sees plenty of street duty, IIRC 60-65 mph is about 2100 with the converter unlocked, 1900-2000 with it locked.

Pharozen · Mar 4, 2017

Kwik_Cutty88 said:
I run 3.73's with a 700R4 and a 28" tire. My car sees plenty of street duty, IIRC 60-65 mph is about 2100 with the converter unlocked, 1900-2000 with it locked.

What does the tire size has to do with this set up? Better gas efficiency?

Texas82GP · Mar 4, 2017

The taller the tire, the numerically lower or conceptually higher the final gear ratio is. In other words given the same rear axle ratio, taller tires will make the rear axle ratio seem like a higher gear (numerically lower).

mobileaudio25 · Mar 4, 2017

I run 3.73 in a th350 on the highway and I don't like it much. Screaming going down the road and sucking down gas my 350 is modified. I'd do anything to go back and do a 200R4... I also have a custom built 2800 stall converter

ssn696 · Mar 4, 2017

Funny story. In Hawaii 22 years ago, I pulled the carpet and pad out of my wagon. When I put in 3.73s behind the TH350, my feet would get uncomfortably hot in flipflops cruising up H1 at 65 MPH...

I just pulled 2.56 gears out of my current wagon axle. 41/16. If you take 3.73 and multiply by 0.67 overdrive (200-4R), you get 2.50. So, if you can swing for an overdrive transmission and 3.73s, you get acceleration and fuel economy. Want 4000 RPM? Drop it into third...

KYMalibu · Mar 4, 2017

UNGN said:
It depends where you live. When GM put 3.73's in 4 speed cars, the speed limit was only 55 mph.

In Texas, 70 mph gets you run over in the slow lane (I know this because I set my Cruise at 70 mph every morning and stay as far right as I can get). Highway traffic is really 75 mph, and cruising at 75 mph with 3.73's gears, even with OD, gets old. 3.42 is is a much better choice in Texas. If you live somewhere where 60-65mph is the norm, 3.73's will probably be fine.[/QUOT

ssn696 said:
Funny story. In Hawaii 22 years ago, I pulled the carpet and pad out of my wagon. When I put in 3.73s behind the TH350, my feet would get uncomfortably hot in flipflops cruising up H1 at 65 MPH...

I just pulled 2.56 gears out of my current wagon axle. 41/16. If you take 3.73 and multiply by 0.67 overdrive (200-4R), you get 2.50. So, if you can swing for an overdrive transmission and 3.73s, you get acceleration and fuel economy. Want 4000 RPM? Drop it into third...

Forget highway , If using for cruise ins and busting a mustang light to light . Perfect

KYMalibu · Mar 4, 2017

Shane Campbell said:
Forget highway , If using for cruise ins and busting a mustang light to light . Perfect

4 SPD 3.73 don't need first gear much that's another story. But yes very fun. Long trip trailer.

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3.73 Posi

Pharozen

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Ribbedroof

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UNGN

Comic Book Super Hero

Kwik_Cutty88

Royal Smart Person

Pharozen

Greasemonkey

Texas82GP

Just-a-worm

mobileaudio25

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ssn696

Living in the Past

KYMalibu

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KYMalibu

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