Best Rear Ratio for 455 w/ OD Tranny?
Thread Starter
Registered User
Joined: Feb 2008
Posts: 42
From: Austin, TX
Best Rear Ratio for 455 w/ OD Tranny?
I have converted two of my chevrolet vehicles w/ 350ci blocks and stock th350s to 700R4 OD trannys. The rear ratio that works best with the Chevy 350ci block's power band, or so i've read, is 3.73. This combination does very well with gas mileage, and sits comfortably at 2200-2300 rpms at 70-75 miles per hour.
My initial thoughts were that my '72 Cutlass w/ 455ci would also benefit from a 3.73 rear when combined with a 2004r OD tranny. It was recently suggested that the 455ci powerband is more efficient/ more in it's "operational comfort zone" at 2000 rpms or so, making a 3.42 posi rear the better mating choice. Not to mention offer me a greater top end if necessary.
So... for in town, and highway cruising which is better for the Olds' 455 w/ 2004R OD tranny? (A) a 3.73 Posi Rear, or (B) a 3.42 Posi Rear?
What are the pros and cons? I'm not looking at this from a racing application standpoint, so the steeper gearing isn't a selling point. Where will my engine's RPMs sit most comfortably, and what rear ratio will help me achieve it?
Thank you in advance for any help, or advice. Have a great day.
My initial thoughts were that my '72 Cutlass w/ 455ci would also benefit from a 3.73 rear when combined with a 2004r OD tranny. It was recently suggested that the 455ci powerband is more efficient/ more in it's "operational comfort zone" at 2000 rpms or so, making a 3.42 posi rear the better mating choice. Not to mention offer me a greater top end if necessary.
So... for in town, and highway cruising which is better for the Olds' 455 w/ 2004R OD tranny? (A) a 3.73 Posi Rear, or (B) a 3.42 Posi Rear?
What are the pros and cons? I'm not looking at this from a racing application standpoint, so the steeper gearing isn't a selling point. Where will my engine's RPMs sit most comfortably, and what rear ratio will help me achieve it?
Thank you in advance for any help, or advice. Have a great day.
Registered User
Joined: Oct 2008
Posts: 162
From: Saskatchewan Prairies Baby!
If I had to choose between those two I'd take the 3.42. IMO even that is a tad on the low side for 455. I think a 3.23 with OD would be nice.Those 455s have nothing but bottom end torque of course. My last 455 was a Pontiac...uh oh...the P word...I ran a 3.08 rear (T400)with 255/60s and it still had no problem shredding them.I don't know anything about your motor or setup but for the street/highway driving the 3.42 is the one I'd prefer.
Old(s) Fart
Joined: Mar 2007
Posts: 50,791
From: Northern VA
So... for in town, and highway cruising which is better for the Olds' 455 w/ 2004R OD tranny? (A) a 3.73 Posi Rear, or (B) a 3.42 Posi Rear?
What are the pros and cons? I'm not looking at this from a racing application standpoint, so the steeper gearing isn't a selling point. Where will my engine's RPMs sit most comfortably, and what rear ratio will help me achieve it?
What are the pros and cons? I'm not looking at this from a racing application standpoint, so the steeper gearing isn't a selling point. Where will my engine's RPMs sit most comfortably, and what rear ratio will help me achieve it?
Thread Starter
Registered User
Joined: Feb 2008
Posts: 42
From: Austin, TX
It's impossible to answer this question without knowing the tire diameter. I'll bet that the tires on your Chevy trucks are somewhat larger in diameter than the ones on your Olds, so a comparison of ratios is meaningless. Also note that the 200-4R has a different OD ratio than the 700R4, which also changes the equation.
Thread
Thread Starter
Forum
Replies
Last Post
Oldskool84
Transmission and Driveline
3
Jul 9, 2014 04:49 AM
rcdynamic88
Drivetrain/Differentials
10
Jul 9, 2010 07:00 AM
