Final drive calculator

[Astro]

Hey guys,

How can I accurately calculate my rpms and final drive?

I want to gear my truck, but want to make sure I put in the right gears and not sacrifice top much too end. Want to see what my rpms would be like around 75 mph.

I have 35's, a 4L80, and 3.73s at the moment and was thinking of swapping to 4.56.

Thoughts and advice?

 

[Caman96]

Google a final drive calculator.

 

[Sean Buick 76]

Engine RPM / Engine Speed Calculator

Crawlpedia's RPM and Engine Speed Calculator will find your engine RPM at any speed given your transmission ratio, ring and pinion gear ratios, and vehicle speed.

www.crawlpedia.com

The 4L80E 4th gear ratio is listed on here as well.

You would be at 2400 rpm at 75 MPH with the 4.56 and 2200 rpm with a 4.10 gear.

 

[Astro]

Thanks guys.

I wonder if I should stick to 4.10s. i want to be able to go on long trips with the truck. 2400 rpm isn't too high, I guess. What do you guys think?

On the other hand, If I wanted to go with a bigger tire in the future, 4.10's would put me right back where I started.

 

[L31MaxExpress]

My 383 loves it when it turns 2,000-2,500 rpm. When I tow a heavier tralier it is in 3rd gear @ 2,850 rpm @ 75 mph.

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[L31MaxExpress]

The 1987 G20 will also cruise 80 mph all day long with its L31 I built. TH400, 3.08 gear and P275/60R15 rear tire that is ~28" tall. It was still knocking on 17 mpg when I checked the mileage. It is actually the perfect case for lean cruise. The engine is not under any real load at that speed. I wish the 87 G20 had come with the available 2.73 gear actually though.

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[Cadillacmak]

Hey guys,

How can I accurately calculate my rpms and final drive?

I want to gear my truck, but want to make sure I put in the right gears and not sacrifice top much too end. Want to see what my rpms would be like around 75 mph.

I have 35's, a 4L80, and 3.73s at the moment and was thinking of swapping to 4.56.

Thoughts and advice?

Here is one that I built. You can leave it set up for your truck and not have to keep going to a website. Don't change the green cells