Basic RPM question...

[Metal Twister]

I have a 77 Blazer with a 350 / 350 203TC. I dont have a Tac and have no idea what the rpm is at highway speed? Im running 356 gears at the present time and Im trying to figure out what gearing I need to go to turn my new 38's? What is the typical rpm range for say 60 mph w/ auto and 350ci. in the stock configuration?

 

[blazinzuk]

http://www.grimmjeeper.com/gears.html

Mess around with numbers till your hearts content

 

[nvrenuf]

Recheck that current ratio, 3.56 is not valid.

 

[blazinzuk]

Recheck that current ratio, 3.56 is not valid.

True dat, probably a 3.73 with the year

I was happy with 4.10s and 38s for quite a while. Certainly wasn't snappy off the line and could have used more gear but it wasn't bad.

I could also cruise at 75 mph and get 10 mpg so thats why I left it.

 

[Metal Twister]

True dat, probably a 3.73 with the year

I was happy with 4.10s and 38s for quite a while. Certainly wasn't snappy off the line and could have used more gear but it wasn't bad.

I could also cruise at 75 mph and get 10 mpg so thats why I left it.

I'm more interested in building this to pull an expo style trailer more than hwy travel. In looking at this chart http://www.ramblerman.com/blazer/geartabl.htm Im thinking somewhere towards the 5.29 range is where I need to be. This is based on a 1.1 final drive ratio and I honestly don't know what the automatic rpm runs at? I'm guessing 42 - 4500 rpm?

 

[Metal Twister]

Recheck that current ratio, 3.56 is not valid.

My bad... Brain Fart with too many numbers in my head! 3.73 is correct.

 

[nvrenuf]

IMO, I would shoot for either 4.56 or 5.13 depending wether you want more economy or grunt. SHooting for somewhere in the low to mid 2000's rpm's will probably work good.

 

[nvrenuf]

Also, for the sake of the math measure the actual tire height as very few tires are 100% true to their marked size.

 

[Metal Twister]

Also, for the sake of the math measure the actual tire height as very few tires are 100% true to their marked size.

38 Swampers, they claim 38.2"

 

[Metal Twister]

IMO, I would shoot for either 4.56 or 5.13 depending wether you want more economy or grunt. SHooting for somewhere in the low to mid 2000's rpm's will probably work good.

From what Ive seen 4.56 is about the lowest I can go with a D70 if I wish to go that way? Something to keep in mind...

 

[dremu]

38 Swampers, they claim 38.2"

Yabbut they'll measure different loaded on the vehicle. Break out the tape measure.

-- A

 

[Metal Twister]

Yabbut they'll measure different loaded on the vehicle. Break out the tape measure.

-- A

Well swallow my gum, Yep...37"

 

[nvrenuf]

From what Ive seen 4.56 is about the lowest I can go with a D70 if I wish to go that way? Something to keep in mind...

For a D60 & D70 the carrier break is up to 4.10 / 4.56 +, so your 3.73 carrier will not work for a standard 4.56 or bigger ratio unless it's an aftermarket thick gear set (if there is such a thing for a D70).