2:73 ratio in my new Blazer?? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Patriot · 02-02-2012, 01:51 PM

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

. 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

Keith Seymore · 02-02-2012, 03:11 PM

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

Keith Seymore · 02-02-2012, 03:19 PM

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

Keith Seymore · 02-02-2012, 03:23 PM

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

Patriot · 02-02-2012, 03:42 PM

Thanks for the info and running the formulas Keith.

Keith Seymore · 02-02-2012, 05:40 PM

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

K

1BadAction · 02-05-2012, 10:19 PM

Wow 2.73s

Patriot · 02-05-2012, 10:21 PM

Quote:

Originally Posted by 1BadAction

Wow 2.73s

At least its a 4 speed.

That will help some.

1BadAction · 02-05-2012, 10:47 PM

Quote:

Originally Posted by Patriot

At least its a 4 speed.

That will help some.

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.

Patriot · 02-06-2012, 12:34 AM

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.

1BadAction · 02-07-2012, 08:05 AM

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

02-02-2012, 01:51 PM	#1
Patriot Registered User Join Date: Oct 2009 Location: Summerset SD Posts: 312	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. 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

02-02-2012, 03:11 PM	#2
Keith Seymore Registered User Join Date: May 2009 Location: Motor City Posts: 9,229	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 __________________ Chevrolet Flint Assembly 1979-1986 GM Full Size Truck Engineering 1986 - 2019 Intro from an Old Assembly Guy: http://67-72chevytrucks.com/vboard/s...d.php?t=342926 My Pontiac story: http://forums.maxperformanceinc.com/...d.php?t=560524 Chevelle intro: http://www.superchevy.com/features/s...hevy-chevelle/ Last edited by Keith Seymore; 02-02-2012 at 03:27 PM.

02-02-2012, 03:19 PM	#3
Keith Seymore Registered User Join Date: May 2009 Location: Motor City Posts: 9,229	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 __________________ Chevrolet Flint Assembly 1979-1986 GM Full Size Truck Engineering 1986 - 2019 Intro from an Old Assembly Guy: http://67-72chevytrucks.com/vboard/s...d.php?t=342926 My Pontiac story: http://forums.maxperformanceinc.com/...d.php?t=560524 Chevelle intro: http://www.superchevy.com/features/s...hevy-chevelle/

02-02-2012, 03:23 PM	#4
Keith Seymore Registered User Join Date: May 2009 Location: Motor City Posts: 9,229	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 __________________ Chevrolet Flint Assembly 1979-1986 GM Full Size Truck Engineering 1986 - 2019 Intro from an Old Assembly Guy: http://67-72chevytrucks.com/vboard/s...d.php?t=342926 My Pontiac story: http://forums.maxperformanceinc.com/...d.php?t=560524 Chevelle intro: http://www.superchevy.com/features/s...hevy-chevelle/

02-02-2012, 03:42 PM	#5
Patriot Registered User Join Date: Oct 2009 Location: Summerset SD Posts: 312	Re: 2:73 ratio in my new Blazer?? Thanks for the info and running the formulas Keith.

02-02-2012, 05:40 PM	#6
Keith Seymore Registered User Join Date: May 2009 Location: Motor City Posts: 9,229	Re: 2:73 ratio in my new Blazer?? You are welcome (...my Dad used to do all those calculations in his head...). K __________________ Chevrolet Flint Assembly 1979-1986 GM Full Size Truck Engineering 1986 - 2019 Intro from an Old Assembly Guy: http://67-72chevytrucks.com/vboard/s...d.php?t=342926 My Pontiac story: http://forums.maxperformanceinc.com/...d.php?t=560524 Chevelle intro: http://www.superchevy.com/features/s...hevy-chevelle/

02-05-2012, 10:19 PM	#7
1BadAction Registered User Join Date: Dec 2010 Location: Dallas, TX Posts: 160	Re: 2:73 ratio in my new Blazer?? Wow 2.73s __________________ 2010 Basalt Black Porsche Cayenne GTS - Daily driver 1991 2500 Suburban, Black - 454/80E tow monster, soon to go under the knife... Again. 1979 16' Action Marine/"Johnny Cash" Merc Bridgeport Champ Motor - Metalflake Maniac

02-06-2012, 12:34 AM	#10
Patriot Registered User Join Date: Oct 2009 Location: Summerset SD Posts: 312	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.

02-07-2012, 08:05 AM	#11
1BadAction Registered User Join Date: Dec 2010 Location: Dallas, TX Posts: 160	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. __________________ 2010 Basalt Black Porsche Cayenne GTS - Daily driver 1991 2500 Suburban, Black - 454/80E tow monster, soon to go under the knife... Again. 1979 16' Action Marine/"Johnny Cash" Merc Bridgeport Champ Motor - Metalflake Maniac



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