3.55 or 3.73

Rdchallenger · October 23, 2020, 01:00:03 PM

As I'm getting closer to getting paint and such on the car I'm thinking of gearing... I'll have a 340 4 barrel with a slightly larger than stock cam. 904 Auto trans...I honestly can't decide between 3.55 or 3.73 any suggestions of experience would be great.

chargerdon · October 23, 2020, 01:19:13 PM

The 3.73 gears will provide faster acceleration than the 3.55's no doubt. And 4.11 will provide more acceleration than 3.73.

It all depends on your application, and your wheels/tires. If your still running the stock 14's for wheels, then 3.73 will be quite a bit much for freeway cruising. Check your choices with the Gear/tire selector at: https://www.e-bodies.org/resources/rpm-speed-gear-tire-size-calculator/

Plug in the 3.55 and 15" tires/wheels and you will see that at 70 MPH you will be turning 3000 RPM. If only running 14" wheels/tires then you would be at 3300 RPM. For me even that is too high for any length of a drive.

This calculator doesn't have a 3.73 option but 3.91 gears would be turning 3500 with 15" wheels and a whopping 3700 RPM with 14" wheels.

At any rate plug in the tires you think you will end up with and let it do the math for you to decide.

GoodysGotaCuda · October 23, 2020, 01:28:26 PM

I would run 3.55 without an overdrive.

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7212Mopar · October 23, 2020, 01:30:57 PM

I think CP said before it also depends on your camshaft size and tire size, how much freeway driving and if you compete on the tracks. Lower rear ratio works best if you have overdrive trans.

I am running a 727 on a stroked 340 and I choose to keep the rear at 3.23. About 3000 RPM at 70 mph on the freeway with 275/40/17 rear tires at 25.7" tall. No problem getting the car moving at any speed. RPM goes up with the lower gears. Here in NCal, if you drive at 65 mph (speed limit) at the right lane, you have people constantly passing you on the freeway. Just don't feel right with a muscle car.

dodj · October 23, 2020, 01:52:26 PM

3.23 if you envision a reasonable amount of freeway, 3.73 or higher if you stay mostly on the city streets. 3.55 will do neither very well.

Cuda Cody · October 23, 2020, 02:58:40 PM

I personally like the 3.55 a lot. The 3.23 are great for driving a lot, but the 3.73 and 4.11 put more revs in my engines than I want.

Rdchallenger · October 23, 2020, 06:06:52 PM

Quote from: dodj on October 23, 2020, 01:52:26 PM
3.23 if you envision a reasonable amount of freeway, 3.73 or higher if you stay mostly on the city streets. 3.55 will do neither very well.

Wouldn't that be a happy medium then? Haha

Rdchallenger · October 23, 2020, 06:09:07 PM

I've had 3.55 in my head for the longest time... Running 15 inch wheels with (normal) sized master crafts

, but for some reason I recently got 3.73 in my head. I live in a rural area with lots of mountains and interstate.

JonH · October 23, 2020, 06:41:53 PM

In all honesty, not a heck of a lot of difference between the 2. I have run both. YOU need to decide how the car will be used and what the end game is. If you are looking to cruise, go with a 3.23 or even numerically lower gear set. If you are looking for tire smoking acceleration, then 3.73 or higher numerical gear set is the way to go. I currently run 3.55, but that fits what I want to do with the car. Good acceleration, but long trips would be annoying. If you are set on one or the other, either will work well, but consider how the car will be used and you may realize that neither is right....JMO

nsmall · October 23, 2020, 08:15:09 PM

Quote from: Rdchallenger on October 23, 2020, 06:09:07 PM
I've had 3.55 in my head for the longest time... Running 15 inch wheels with (normal) sized master crafts , but for some reason I recently got 3.73 in my head. I live in a rural area with lots of mountains and interstate.

Rural + Interstate= 3.23 or 3.55

RUNCHARGER · October 23, 2020, 08:45:47 PM

For any highway driving at all a 3.55 I think. The 340 can take the 3.73 alright but the 3.55 will be happier, only about 6 or 7% difference though.

kawahonda · October 24, 2020, 12:27:11 AM

Very happy with 3.73 with occasional highway.

These cars were never designed for the interstate. Why even consider that a target?

Try riding in Idaho freeways where 75 MPH is the posted speed limit (which means 80-85 MPH). Even 3.55s will be hurting with any size tire...

3.73 was a real change over 3.23, so it made the most sense for me. What is your driving habits? What is your gearing? You have to consider everything.

Small blocks have no issue cruising at 3200 for good periods of time. In-fact, it's very quiet at that RPM when are moving 65 MPH..

dodj · October 24, 2020, 08:20:12 AM

Quote from: Rdchallenger on October 23, 2020, 06:06:52 PM
Quote from: dodj on October 23, 2020, 01:52:26 PM
3.23 if you envision a reasonable amount of freeway, 3.73 or higher if you stay mostly on the city streets. 3.55 will do neither very well.

Wouldn't that be a happy medium then? Haha

I guess so

I consider the 355's like an all season tire, good enough for most stuff. Does not excel at anything.
I have 3.23's cuz I like cruising more now than the stop light grand prix. If I was staying in city limits, I'd have 3.73 or 3.91's.

But like has been said earlier. You need to decide how you intend to use your car. Nothing changes a car's personality like gearing will.

Ebody Edgar · October 24, 2020, 08:30:44 AM

a better choice is 3.23 with 26" tall tires and a 3000 stall converter
that is 70 mph at 3000 rpm

Rdchallenger · October 26, 2020, 02:17:06 PM

It is mostly interstate where I live, of course with this car I'll probably take the scenic routes and enjoy the view. I just always assumed the 340 enjoyed and really came into its own at the higher RPMs. The most interstate driving this will probably get it the 3 hour drive to Carlisle when done.