![]() |
|
![]() |
#1 |
Registered User
![]() Join Date: Dec 2012
Location: Vancouver, Washington
Posts: 1,644
|
Gear ratio advice
My truck is currently getting its rear differential rebuilt (a lot of problems found internally). It currently has open carrier with 3.08 gearing, but here is my chance to change the ratio for a bit more umph! We are switching to Posi as well. I’m running 27in diameter tires, and I’ve studied the RPM charts. Now thinking about 3.42 or 3.55 for it. Any opinions on one vs the other? Running a 327 with TH350 trans as well. Thanks in advance
__________________
1968 Chevrolet C/10 LWB - 327, TH350 - 4/5 Drop |
![]() |
![]() |
![]() |
#2 |
Senior Member
![]() Join Date: Mar 2015
Location: washington
Posts: 2,243
|
Re: Gear ratio advice
I think you will be running right in the sweet spot with 3.42 or 3.55 gears.
Stock camshaft? If so you might consider the 3:42 ratio. With a mild camshaft do the 3:55 and don't look back. Rick |
![]() |
![]() |
![]() |
#3 |
Registered User
![]() Join Date: Dec 2012
Location: Vancouver, Washington
Posts: 1,644
|
Re: Gear ratio advice
Thanks for the reply. My cam is not stock and I have been leaning towards 3.55
__________________
1968 Chevrolet C/10 LWB - 327, TH350 - 4/5 Drop |
![]() |
![]() |
![]() |
#4 |
Senior Member
![]() ![]() Join Date: Jan 2005
Location: CA
Posts: 5,480
|
Re: Gear ratio advice
I have 3.73 gearing. With a TH400 trans, my truck was a bit intense on the freeway at speeds over 60 MPH. I had. '67 years ago that had 3.07 gearing. It was great on the freeway, but it was a dog around town. Going somewhere in the middle makes a lot of sense. Personally, I would be inclined to lean more toward a ratio that is better for freeway driving, but it really depends on how you plan on using your truck. If you have a relatively quiet exhaust system, then that will make higher numeric gearing more tolerable at higher speeds.
|
![]() |
![]() |
![]() |
#5 |
Registered User
Join Date: Apr 2009
Location: PNW
Posts: 553
|
Re: Gear ratio advice
Cam specs?
What is your ratio of freeway/highway to city driving? |
![]() |
![]() |
![]() |
#6 |
Registered User
![]() Join Date: Dec 2012
Location: Vancouver, Washington
Posts: 1,644
|
Re: Gear ratio advice
It’s a mild cam. Have no idea of what went in when the PO rebuilt the engine. Gonna guess city/freeway is going to be about 50/50
__________________
1968 Chevrolet C/10 LWB - 327, TH350 - 4/5 Drop |
![]() |
![]() |
![]() |
#7 |
Registered User
Join Date: Oct 2015
Location: IN
Posts: 209
|
Re: Gear ratio advice
If you have a truck 12 bolt rearend, then go with 3.42 gears since they don't make 3.55 gears for the truck 12 bolt rearend.
They do make 3.55 for car 12 bolt rearends. |
![]() |
![]() |
![]() |
#8 |
Registered User
![]() Join Date: Dec 2012
Location: Vancouver, Washington
Posts: 1,644
|
Re: Gear ratio advice
Thank you good to know that. Appreciate the help
__________________
1968 Chevrolet C/10 LWB - 327, TH350 - 4/5 Drop |
![]() |
![]() |
![]() |
#9 |
Registered User
Join Date: Jan 2019
Location: St Peters, MO
Posts: 439
|
Re: Gear ratio advice
I'm also planning to have a spare 12 bolt rebuilt as a posi this year. I really like my 3.08s but also have a 700R4 with lower 1st and 2nd gears than the TH350. I love running 75+ at 2000 RPM, but most of my driving is local. I go back and forth on 3.08 or 3.42, but currently leaning toward 3.42 as I don't think I'd give up too much with 4th + lockup. If I still had the TH350 I'd almost certainly go with 3.42 gears.
__________________
1967 C20, 350 SBC w/Comp roller cam, 700R4 w/3.42 posi, PS, 4-wheel PDB, Old Air AC & GM Tilt column. |
![]() |
![]() |
![]() |
#10 |
Registered User
Join Date: Apr 2009
Location: PNW
Posts: 553
|
Re: Gear ratio advice
|
![]() |
![]() |
![]() |
#11 |
Registered User
Join Date: Oct 2013
Location: Lincoln, NE
Posts: 115
|
Re: Gear ratio advice
The difference between 3:42 and 3:55 is not likely to be noticeable, darn near identical. Throw a dart at a paper with the two ratios written on it and choose the one that the dart is closest to.
|
![]() |
![]() |
![]() |
#12 |
Registered User
Join Date: Oct 2005
Location: Overland Park, Ks.
Posts: 5,216
|
Re: Gear ratio advice
If you have been running a 3.08 & go anything lower you are going to be disapointed the first time you get out on the highway. You will be waiting for the thing to shift again.
George |
![]() |
![]() |
![]() |
Bookmarks |
Thread Tools | |
Display Modes | |
|
|