The 1947 - Present Chevrolet & GMC Truck Message Board Network - View Single Post - 454 Dually with 4.56 rear diff, what auto trans to use

**kwmech** · 02-02-2022, 01:30 PM

A gear swap from 4.56 to 4.10 will yield you a 10.1% difference in RPM. So spinning the BB at highway speed of say 2800 will drop you to 2520. An overdrive swap to a 4l80e (25% reduction) will give you about 2100 rpm or effectively drop your rear diff ratio to 3.42. Low 2000s in rpm for a big block is the sweet spot for cruising.

02-02-2022, 01:30 PM	#16
kwmech Senior Member Join Date: Mar 2003 Location: Colfax-California Posts: 8,396	Re: 454 Dually with 4.56 rear diff, what auto trans to use A gear swap from 4.56 to 4.10 will yield you a 10.1% difference in RPM. So spinning the BB at highway speed of say 2800 will drop you to 2520. An overdrive swap to a 4l80e (25% reduction) will give you about 2100 rpm or effectively drop your rear diff ratio to 3.42. Low 2000s in rpm for a big block is the sweet spot for cruising.