The 1947 - Present Chevrolet & GMC Truck Message Board Network

The 1947 - Present Chevrolet & GMC Truck Message Board Network (https://67-72chevytrucks.com/vboard/index.php)

- Engine & Drivetrain (https://67-72chevytrucks.com/vboard/forumdisplay.php?f=24)

- - gearing and ratios (https://67-72chevytrucks.com/vboard/showthread.php?t=641208)

SnowNeck

08-27-2014 08:27 PM

gearing and ratios

1985 chevy, 350 crate motor, carbed, 700r4 trans, 35 inch tires, axle gears 3.08s, transfer case is np 208, good or bad idea?

Dunenutt

08-27-2014 08:29 PM

Re: gearing and ratios

Probably want to go 3.73 with the OD.

kwmech

08-27-2014 10:53 PM

Re: gearing and ratios

35'' tires and a 700................4.56 gears

crazy longhorn

08-27-2014 11:46 PM

Re: gearing and ratios

35" tire, I would also go 4.56 on the gear ;) longhorn

Captainfab

08-28-2014 12:03 AM

Re: gearing and ratios

I agree with a 4.56 gear with those 35" tires. The 3.08 gears with 35" tires would just be absurd.

SnowNeck

08-28-2014 01:01 AM

Re: gearing and ratios

Quote:

Originally Posted by Captainfab (Post 6819973)

I agree with a 4.56 gear with those 35" tires. The 3.08 gears with 35" tires would just be absurd.

Alright sounds pretty conclusive, 4.56s it is. Haha and just curious if i switch the gears, how would it run with 33s? Mpg? performance? over all? Cause most likely it'd be a lil while b4 35s.

tjsblazer

08-28-2014 01:14 AM

Re: gearing and ratios

Check out this website. Great driveline / gear / tire calculator. Use the drop downs to input your tranny and transfer, then input your tires and change up the gearing till you get the rpms where you want them at specific speeds. Can also do a side by side comparison.
http://www.grimmjeeper.com/gears.html

crazy longhorn

08-28-2014 03:12 AM

Re: gearing and ratios

Quote:

Originally Posted by SnowNeck (Post 6820026)

Alright sounds pretty conclusive, 4.56s it is. Haha and just curious if i switch the gears, how would it run with 33s? Mpg? performance? over all? Cause most likely it'd be a lil while b4 35s.

If you are running 33" tire now,IMHO, they will need a 4.10-4.33 gear to work out properly. I will step back, & let Capt chime in....I respect his opinion also ;) Longhorn

SnowNeck

08-28-2014 08:05 AM

Re: gearing and ratios

Quote:

Originally Posted by crazy longhorn (Post 6820080)

If you are running 33" tire now,IMHO, they will need a 4.10-4.33 gear to work out properly. I will step back, & let Capt chime in....I respect his opinion also ;) Longhorn

Which sounds good, but if I'm going over to the 35s sometime this winter there's no use putting gears that match up with 33s, see what I'm saying? Might as wel gear for 35s, an run 33s for a while

kwmech

08-28-2014 01:02 PM

Re: gearing and ratios

Even 33s with a 4.56 will be fine. I had a 1990 suburban years ago that I had put in 4.56 gearing with 31'' tires, and the 700 ... best change I ever made. You got to remember when the trans shifts into 4th and locks up the convertor you are reducing the effective ratio by almost a third. So your 4.56 becomes just around a 3.2 ratio final drive. Stick with the 4.56

95 S_Trucker

08-28-2014 02:32 PM

Re: gearing and ratios

I had 3.08 and 35 on my 85, I don't think it ever shifted into overdrive until 60+

Another option would be a 3/4 ton rear or swap to 1 tone axles, if you still have 2 10 bolts.

crazy longhorn

08-28-2014 10:55 PM

Re: gearing and ratios

Quote:

Originally Posted by SnowNeck (Post 6820167)

Which sounds good, but if I'm going over to the 35s sometime this winter there's no use putting gears that match up with 33s, see what I'm saying? Might as wel gear for 35s, an run 33s for a while

It sound to me that you have it figured....no point in doing it 2 times;) longhorn

All times are GMT -4. The time now is 03:23 PM.