2:73 ratio in my new Blazer??
 

Well fellas I bought another K5 Blazer. It is from the Coal Mines in Gillete Wy. Bought new and sold by the Coal Mines. Its a 1986 4 speed with the 208 t-case. I looked at the RPO codes in the glove box and it says it was special ordered with 2:73 gears. I also found the original papaerwork and it says it was a special order package, quad front shocks, 2:73 and some other stuff. It is a plain jane truck. It even has A/C. I thought that was odd for a 4 speed truck. Do you guys have the Ratio/Tire size/ RPM chart?? I need to fiqure out what RPM it will be turning with the factory 31" tires. The motor is froze up because the Mine ran it out of oil:metal:. I have a nice motor on an engine stand that is going in it. Anyway thanks guys again for letting me pluck your brains a little.

Patriot:flagw:

Re: 2:73 ratio in my new Blazer??
 

The powertrain chart in the GM Heritage Center archive shows the 2.73 axle as base (special order not required).

http://www.gmheritagecenter.com/gm-h...let-Blazer.pdf

see page 2 and page 6.

Engine RPM at a particular vehicle speed is calculated as follows:

N/V = [Tire Rev (rev/mi) x Axle Ratio x Trans Ratio] / 60 x V (mph)

N = engine rpm
V = vehicle speed
Tire revs is in rev/mi
Trans ratio would be "1" for high gear


K

Re: 2:73 ratio in my new Blazer??
 

so - doing the math as above, for a 31-10.5x15 tire I show a rev/mile of 672.

plugging that in, I get:

1682 engine rpm at 55 mph
1835 engine rpm at 60 mph
1987 engine rpm at 65 mph
and
2140 engine rpm at 70 mph

You've probably got no business going faster than 70 in a K blazer anyway...

(lol)

K

Re: 2:73 ratio in my new Blazer??
 

Said differently, your N/V ratio = 30.58

so you can take whatever speed you are interested it and multiply it by 30.58 to get the corresponding engine rpm.

K

Re: 2:73 ratio in my new Blazer??
 

Thanks for the info and running the formulas Keith. :metal:

Re: 2:73 ratio in my new Blazer??
 

You are welcome (...my Dad used to do all those calculations in his head...).

K

Re: 2:73 ratio in my new Blazer??
 

Wow 2.73s :eek:

Re: 2:73 ratio in my new Blazer??
 

At least its a 4 speed.:lol: That will help some.

Re: 2:73 ratio in my new Blazer??
 

Yea it shouldn't be too bad, probably better for a driver with a 4 speed as long as you stay sane on the tire sizes. Have any pics?

PS: Thanks Keith, now I'll be up all night looking on the heritage center website. :lol:

Re: 2:73 ratio in my new Blazer??
 

Here are some pictures. 1986 Coal Mine truck for 500.00. Only rust is what you see starting inside the rear gate at the bottom.

http://www.majhost.com/gallery/JeepL...ks/truck_1.jpg

http://www.majhost.com/gallery/JeepL...ks/truck_2.jpg

http://www.majhost.com/gallery/JeepL...ks/truck_3.jpg

http://www.majhost.com/gallery/JeepL...ks/truck_4.jpg

http://www.majhost.com/gallery/JeepL...ks/truck_5.jpg

Re: 2:73 ratio in my new Blazer??
 

That looks like a great deal right there. Motors can be fixed but the cancerous rust is a PITA.