LS swap. Whats a good street gear ratio.Pics inside with detail.

Disclaimer: Links on this page pointing to Amazon, eBay and other sites may include affiliate code. If you click them and make a purchase, we may earn a small commission.

Nasty-LSX

TogetherforeverCovid19
Joined
Nov 22, 2014
Posts
1,069
Reaction score
1,120
Location
HOUSON TX
First Name
Mi Hung Lo
Truck Year
85/86/87
Truck Model
c10/k10/k20
Engine Size
LSX
I am still waiting for a large amount of parts to come in before I start pulling the truck apart.
(old lesson learned) never take anything apart till you have everything you need to replace it lol.

I will be starting a build thread in the forums as soon as everything is in. For now I would like to
get a posi put in. I will be using a
Detroit TrueTrac . The engine is a 2015 6.0 with a
4l70e from GM PERFORMANCE. these are the gearing specs from first to fourth.. 3.06, 2nd: 1.62, 3rd: 1.00, 4th: 0.70 I want to be able to do 70 MPH at 2000 rpm.
Any ideas? thanks

You must be registered for see images attach
You must be registered for see images attach
 

bucket

Super Moderator
Staff member
Super Moderator
Joined
Aug 3, 2010
Posts
28,956
Reaction score
23,466
Location
Usually not in Ohio
First Name
Andy
Truck Year
'77, '78, '79, '84, '88
Truck Model
K5 thru K30
Engine Size
350-454
What's your rear tire size?
 

Derrick

Full Access Member
Joined
Dec 12, 2017
Posts
544
Reaction score
271
Location
near Milwaukee, Wisconsin
First Name
Derrick
Truck Year
2003
Truck Model
1500
Engine Size
5.3
I found a calculator for this all you need to do is play with ring and pinion ratio (rear gear)
http://spicerparts.com/calculators/transmission-ratio-rpm-calculator
You must be registered for see images attach

I just assumed you are running 32s if incorrect put in your tire size in. I think 3.73 will work for you. even with 31s you just hit 70 mph with 2k rpm
 

bucket

Super Moderator
Staff member
Super Moderator
Joined
Aug 3, 2010
Posts
28,956
Reaction score
23,466
Location
Usually not in Ohio
First Name
Andy
Truck Year
'77, '78, '79, '84, '88
Truck Model
K5 thru K30
Engine Size
350-454
Tires in pic look to be 275/60/15. Without looking it up, I think those are in the 27-28" range.
 

Derrick

Full Access Member
Joined
Dec 12, 2017
Posts
544
Reaction score
271
Location
near Milwaukee, Wisconsin
First Name
Derrick
Truck Year
2003
Truck Model
1500
Engine Size
5.3
those are small tires. lol 3.73 gears will not work then.


You must be registered for see images attach


You must be registered for see images attach
 

DoubleDingo

Full Access Member
Joined
Jul 3, 2012
Posts
10,014
Reaction score
14,159
Location
Right where I am
First Name
Bagoomba
Truck Year
1981, 1965
Truck Model
81-C20 Silverado Camper Special-TH400-4.10s; 65-C20 with 4:57 gears and Borg Warner Overdrive
Engine Size
Carb'ed Vortec 350; 1972 L48 350
I was going to say 3.54 if you can find them. 70 with a 32 inch tire is about 2600 in 3rd, add-in OD and you'd be about right. Smaller tire, may still be okay if not better.
 

Nasty-LSX

TogetherforeverCovid19
Joined
Nov 22, 2014
Posts
1,069
Reaction score
1,120
Location
HOUSON TX
First Name
Mi Hung Lo
Truck Year
85/86/87
Truck Model
c10/k10/k20
Engine Size
LSX
I think 3.42 would be a good gear for rear. it also has a 2800 FTI stall. TURBO coming soon.
 

Rusty Nail

Full Access Member
Joined
Jan 29, 2015
Posts
9,734
Reaction score
9,530
Location
the other side of the internet
First Name
Rusty
Truck Year
1977
Truck Model
C20
Engine Size
350sbc
3.23 for teh win.

I had an '81 Trans Am with a Pontiac 406 in it and the 3.23 disc brake posi ...that mother f would FLY!
 
Last edited:

Rusty Nail

Full Access Member
Joined
Jan 29, 2015
Posts
9,734
Reaction score
9,530
Location
the other side of the internet
First Name
Rusty
Truck Year
1977
Truck Model
C20
Engine Size
350sbc
I am still waiting for a large amount of parts to come in before I start pulling the truck apart.
(old lesson learned) never take anything apart till you have everything you need to replace it lol.

I will be starting a build thread in the forums as soon as everything is in. For now I would like to
get a posi put in. I will be using a
Detroit TrueTrac . The engine is a 2015 6.0 with a
4l70e from GM PERFORMANCE. these are the gearing specs from first to fourth.. 3.06, 2nd: 1.62, 3rd: 1.00, 4th: 0.70 I want to be able to do 70 MPH at 2000 rpm.
Any ideas? thanks

You must be registered for see images attach
You must be registered for see images attach


Those wheels KICK.ASS!
 

Derrick

Full Access Member
Joined
Dec 12, 2017
Posts
544
Reaction score
271
Location
near Milwaukee, Wisconsin
First Name
Derrick
Truck Year
2003
Truck Model
1500
Engine Size
5.3
I would still recommend 3.08 rear still you will hit 70 mph at 2k rpm with 25s.
 

4WDKC

Full Access Member
Joined
Jan 27, 2016
Posts
2,366
Reaction score
1,090
Location
Southern Florida
First Name
Kacy
Truck Year
1987
Truck Model
V10
Engine Size
350
323, is only 95 more rpm than 308, personally i think the tires will look to short on the truck.

You must be registered for see images attach
 

Nasty-LSX

TogetherforeverCovid19
Joined
Nov 22, 2014
Posts
1,069
Reaction score
1,120
Location
HOUSON TX
First Name
Mi Hung Lo
Truck Year
85/86/87
Truck Model
c10/k10/k20
Engine Size
LSX
323, is only 95 more rpm than 308, personally i think the tires will look to short on the truck.

You must be registered for see images attach

Im thinking your right. I may go next size up. I have not bought them yet. Wheels will be 18/12.5 rear and 18/10 up front from CCW. CLASSSIC wheels with 4/6 drop
 

Forum statistics

Threads
41,851
Posts
903,487
Members
33,365
Latest member
rossivey
Top