Gear ratios - The 1947 - Present Chevrolet & GMC Truck Message Board Network

**AussieinNC** · 07-06-2024, 11:30 AM

Here is a link to an online calculator, using trans type, rear gear ratio and tire height...makes it simple

https://www.blocklayer.com/rpm-gear

Using your 3.08 gears, I get around 1590 rpm and 70 mph.....engine better have some deep torque curve for this to work ok....

Leave the 4.11 gears in it for a decent driver....

Ziegelsteinfaust · 07-24-2024, 04:04 AM

Update.

I just did a 1000 mile trip with 31" tires, 2500 rpm stall converter, and close to 800 pounds in the bed. Along with a roof top cargo carrier mounted above the bed height. While I had a head or heavy cross wind nearly every time I hit the highway. It was still better on mpg then the 4.88's did.

The only downside was the converter. As it flashes to high for that kind of load.

Today I had to put new tires on since my 285/65r17 were to wide for the new rear axle. 235/60r16 front and 255/60r17 rear. They stretched perfectly to my rims, and look better then I hoped.

So the rear tires are considerably lighter then the old ones, and measured height is 28.5 inches. The truck now feels more then fast enough empty for a DD, and well it did handle the old tires with weight good enough. Atleast for a temporary fix.

Unfortunately my fuel pump died this morning, and I only drove with the new tires for 10 miles.

Will do another update when I fix the pump this weekend.

Ziegelsteinfaust · 08-20-2024, 03:02 PM

New update.

After I swapped in the new motor I have driven it for about 150 miles now. It has plenty of power for normal driving, and doesn't feel stretched to accelerate the truck. Even with a engine in back. Also I know have a 1800 rpm stall converter vs the old 2500 version.

Old motor 10-1 gen2 LT1 with a Corvette cam, 1.6 roller rockers, and 1992 vintage AFR 195 heads. That I believe are the cnc version.

New motor. 10-1 gen2 LT1 with a B-body cam, factory steel 1.5 rockers, and factory aluminum heads. This was a Caprice engine I got with a carb intake for a price I could not pass up. So all I did was regasket the engine, and use the factory aluminum heads instead of B body iron heads. For safety with california gas as I run a quadrajet. Honestly I believe below 3000 rpm at part throttle to accelerate. This engine puts out atleast 25lbft more torque below 2500 rpm. After that it just doesn't carry, but who cares. This is a driver for my dad.

So if your building a similar truck and engine. 3.08's are fine if you want a driver or minor work horse.

07-06-2024, 11:30 AM	#1
AussieinNC Moderator Join Date: Jun 2017 Location: Cherryville, NC Posts: 2,204	Re: Gear ratios Here is a link to an online calculator, using trans type, rear gear ratio and tire height...makes it simple https://www.blocklayer.com/rpm-gear Using your 3.08 gears, I get around 1590 rpm and 70 mph.....engine better have some deep torque curve for this to work ok.... Leave the 4.11 gears in it for a decent driver.... __________________ Family and country before all others... 2006 Chevy Silverado (Daily Driver) 2012 Chevy Equinox Last edited by AussieinNC; 07-06-2024 at 11:36 AM.

07-24-2024, 04:04 AM	#2
Ziegelsteinfaust Registered User Join Date: Dec 2012 Location: Temple City Posts: 3,623	Re: Gear ratios Update. I just did a 1000 mile trip with 31" tires, 2500 rpm stall converter, and close to 800 pounds in the bed. Along with a roof top cargo carrier mounted above the bed height. While I had a head or heavy cross wind nearly every time I hit the highway. It was still better on mpg then the 4.88's did. The only downside was the converter. As it flashes to high for that kind of load. Today I had to put new tires on since my 285/65r17 were to wide for the new rear axle. 235/60r16 front and 255/60r17 rear. They stretched perfectly to my rims, and look better then I hoped. So the rear tires are considerably lighter then the old ones, and measured height is 28.5 inches. The truck now feels more then fast enough empty for a DD, and well it did handle the old tires with weight good enough. Atleast for a temporary fix. Unfortunately my fuel pump died this morning, and I only drove with the new tires for 10 miles. Will do another update when I fix the pump this weekend.

08-20-2024, 03:02 PM	#3
Ziegelsteinfaust Registered User Join Date: Dec 2012 Location: Temple City Posts: 3,623	Re: Gear ratios New update. After I swapped in the new motor I have driven it for about 150 miles now. It has plenty of power for normal driving, and doesn't feel stretched to accelerate the truck. Even with a engine in back. Also I know have a 1800 rpm stall converter vs the old 2500 version. Old motor 10-1 gen2 LT1 with a Corvette cam, 1.6 roller rockers, and 1992 vintage AFR 195 heads. That I believe are the cnc version. New motor. 10-1 gen2 LT1 with a B-body cam, factory steel 1.5 rockers, and factory aluminum heads. This was a Caprice engine I got with a carb intake for a price I could not pass up. So all I did was regasket the engine, and use the factory aluminum heads instead of B body iron heads. For safety with california gas as I run a quadrajet. Honestly I believe below 3000 rpm at part throttle to accelerate. This engine puts out atleast 25lbft more torque below 2500 rpm. After that it just doesn't carry, but who cares. This is a driver for my dad. So if your building a similar truck and engine. 3.08's are fine if you want a driver or minor work horse.



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