sm465+rear gear ratio=what rpms???

[treveiger]

I have a 69 c20 and have looked up rpm calculators for figuring out what rpms ill be running at driving speeds and theres a buch of different out comes for each rpm calculator so i figured id ask the people that actually run these trucks. I have a sm465 and have decided to switch it out to 5 lug and am wondering what rpms ill be running for different gear ratios and what kind of mpg ill get also. I usually cruse around town and dont hit highway speeds much but i do at least once a week go for about a 30 mile trip id like to take my truck on in the summer. Any information on this would be great.
Thanks

[raycow]

I can't understand why different online calculators should give you different answers, but I always do mine with a hand-held calculator.

The magic number is 20168. Divide your tire diameter into that to get tire revolutions per mile, and then multiply the result by your axle ratio. The number you get will be driveshaft revs per mile, which is the same as engine revs/mi if you don't have overdrive or torque comverter slip.

As an example, let's say you have 31" tires and a 4.10 rear end, so:

20168/31 = 650.6 tire revs/mi
650.6 x 4.10 = 2667

2667 engine revs/mi. That is also your engine rpm at 60 mph. Other speeds are proportional, so if you want the engine speed at 70 mph:

2667 x 70/60 = 3111 rpm at 70 mph.

Ray

[Farm Built-72]

I have a 72 Chevy C10 that still has the 4 speed and 3.07 gears in the rear end. It also has 30-9.5x15 tires on the back. Running down the highway at 65 it usually runs around 2300 to 2400 rpms.

[JJorgensen52]

I had a 3.73 behind my SM465/307 and got between 10 and 13 mpg, best cruising in town around 35mph.

If you shoot me your email address I can send you an excel spreadsheet that will give you all the information you're looking for - I have it on my laptop from when I was considering the NV4500 swap.

**EDIT** I figured out how to attach it directly. The spreadsheet is set up with two sheets, for NV4500 and SM465, as I was comparing the two. You can change tire height and rear end ratios (highlighted in yellow) to see what the speeds look like for different ratios and tire heights. Gives you MPH in each gear in 100RPM increments.

[treveiger]

Raycow thank you very much, im going to print this out tonight so i can keep it for further reference.

JJorgensen52 That is awsome thank you, im deffenitally saving that lol.

Farm Built-72 With the 3.07 rear end does it take a lot to take off? I would think not if you used 1st gear.

Thanks

[Farm Built-72]

With the 4 speed it doesn't take a lot for it to take off. I originally had a 250 inline six with a bad clutch so you had to baby it in 3rd and 4th or the clutch would start slipping. Recenty just put in a 350 with a new clutch and it seems to have plenty of power with this set up. Haven't driven it much with the new motor as I am still working out a few bugs, but will let you know more when its all finished.

[special-K]

What does the SM465 have to do with the cruising RPM?All transmissions are 1:1 final drive ratio,then add overdrive if that's what the trans is.It looks to me like you are calling the rear you swapped out an SM465?What ratio is the 5-lug rear you swapped in?What diameter tire?Give us that info for a baseline.

[treveiger]

Originally Posted by special-K

What does the SM465 have to do with the cruising RPM?All transmissions are 1:1 final drive ratio,then add overdrive if that's what the trans is.It looks to me like you are calling the rear you swapped out an SM465?What ratio is the 5-lug rear you swapped in?What diameter tire?Give us that info for a baseline.

The tranny i have now is the sm465 and i was trying to figure out the rpms i will be running at different speeds with different rearend gears and different size tires to try and figure out what exactly i should do and what im getting into. The 5 lug rear end i got i have no idea the gears that are in it so next time im at the farm ill have to look.

[LostMy65]

Originally Posted by JJorgensen52

I had a 3.73 behind my SM465/307 and got between 10 and 13 mpg, best cruising in town around 35mph.

If you shoot me your email address I can send you an excel spreadsheet that will give you all the information you're looking for - I have it on my laptop from when I was considering the NV4500 swap.

**EDIT** I figured out how to attach it directly. The spreadsheet is set up with two sheets, for NV4500 and SM465, as I was comparing the two. You can change tire height and rear end ratios (highlighted in yellow) to see what the speeds look like for different ratios and tire heights. Gives you MPH in each gear in 100RPM increments.

Thanks for the xls.
Had it do towing with that combo?

[gmc 2500 4x4]

20168, where did this number come from? old post lol

[hounddogs!]

Originally Posted by gmc 2500 4x4

20168, where did this number come from? old post lol

Tire diameter * pi = Circumference, which is going to translate to distance traveled.

You're looking for tire rotations per mile.

5280 * 12 = 63,360 inches in a mile
63,360 / pi = 63.360 / 3.14159 = 20,168

[gmc 2500 4x4]

i have a post up looking for the answer on going from 456 to 354 gears, what ratio adapter i would need with out changing speedo drive gears

[gmc 2500 4x4]

i found my answer at PATC Tranmission