The 1947 - Present Chevrolet & GMC Truck Message Board Network







Register or Log In To remove these advertisements.

Go Back   The 1947 - Present Chevrolet & GMC Truck Message Board Network > 47 - Current classic GM Trucks > The 1967 - 1972 Chevrolet & GMC Pickups Message Board > 67-72 Chevrolet & GMC Pickups Projects and Builds

Web 67-72chevytrucks.com


Reply
 
Thread Tools Display Modes
Old 01-30-2016, 05:14 AM   #1
The72
Registered User
 
Join Date: Jan 2016
Location: CA
Posts: 6
Gear ratios?

Hi this is my first time posting, I've lurked through the threads and you are all very knowledgeable I feel like a dummy.

Hoping you guys/gals can help me out.

I'm trying to get my old truck on the road again. It has been sitting for about 10 years. I stopped driving it after high school. One thing I remember was that it was a gas hogg on the freeway, and I'd like to remedy that if I am going to drive it every now and then.

It is a 72 c15 that had a in-line 6 from factory as far as I know. We dropped a 305 into it off an 86 firebird including the transmission. Here is some info I found about the tranny

Transmission
Type: TurboHydramatic 700R4 4 speed automatic overdrive
Fluid Capacity 9.9 pints

Transmission Gear Ratios


1st 3.06:1
2nd 1.63:1
3rd 1.00:1
4th 0.70:1 (overdrive)

Would I have to find me another gear set up on the differential for a more economical cruiser?
Back then it did have shorter tires. It now has a taller tire much closer to a factory tire for 15" wheels. is it possible this taller tire would agree more with my set up and be less thirsty at 60ish mph?

Thanks a lot, if needed I'll post the exact tire size up in the morning. Thanks again.
The72 is offline   Reply With Quote
Old 01-30-2016, 12:33 PM   #2
72longhornTX
Registered User
 
Join Date: Sep 2007
Location: Houston, TX
Posts: 115
Re: Gear ratios?

I have been using this calculator for years now, you select your trans and put in any info needed if it's 4wd or has an after drive unit on there. Then your tire size and gear ratio. Towards the bottom it will give you the RPM at a given speed in each gear.

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

Big thing is, if you want it to be good on the highway. Find a gear ratio with with the tires and trans you have to get you under 2500 RPM at 75 or 70. Which ever you prefer.
__________________
Current:
2012 Ford F-250 4x4 6.7 Powerstroke
1971 C-20 2wd 350/TH400

Former:
1979 C-20 2wd 350/TH400, 300+hp. Rattle can paint job
1982 K-30 454/700R4. 4in lift with 37" Goodyear MT/R's Lots of goodies - Trail clean up truck
72longhornTX is offline   Reply With Quote
Reply

Bookmarks


Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT -4. The time now is 01:05 PM.


Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2024, vBulletin Solutions Inc.
Copyright 1997-2022 67-72chevytrucks.com