Ls swapped rear end question - The 1947 - Present Chevrolet & GMC Truck Message Board Network

gmcountryboy · 03-09-2017, 02:29 AM

Hey fellas, new to the site have a 1967 C10 I've been building for quite some time, stock chassis, carb'd 6.0 ls lq9, stock crank and rods, hyperutetic pistons @ 10.5:1 comp, ARP bottom end, 229/236 cam on a 108 lsa with the ls3 heads, runnin a single plain intake. Engine dynoed at 556 hp at 6500 rpm.. M21 trans, currently has 3:08 but I want somethin a bit peppier. Truck mostly will be driven around town and taken to the track every now and then. Wondering what you guys would recommend for a rear end gear, 3:73 or a 4:10. Truck has 29x18.5 Mickey Thompsons, any input is appreciated!!
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68Stepbed · 03-09-2017, 09:31 AM

That engine will love the 4:10's, but not sure how much the transmission will help on the freeways. 3.73's would certainly make it peppier, and still do good at highway speeds.

I run 4:10 in my carbed LS1 with a similar cam, but I'm using a 700R4 with overdrive.

Andy4639 · 03-09-2017, 09:43 AM

My 6.0 with 4l80e over drive the 4:10 are good.

**steelhorse** · 03-09-2017, 12:28 PM

I like 3.73 for the street unless it is a 4x4 with big tires.

davepl · 03-09-2017, 01:10 PM

4.10s here with a 4L80E (overdrive), it's about right. Lots of gear in town. I wouldn't go much more than 3.55 or at most 3.73 without overdrive though. Just me.

**LockDoc** · 03-09-2017, 02:00 PM

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Unfortunately the M21 is a standard car 4 speed with no OD so 4.10's would be a bit low. The 3.73 would work great for that application and that is what I would recommend.....

Just my 2¢ worth.

LockDoc

chevy72blu · 03-09-2017, 06:49 PM

I have 3.73's with a 29" tire and a 4l60e. I think its perfect. Stock LS1, though, and I already cant get any rear traction

.

Depends on how much time you plan on spending at the track. I'd go 3.73's with or without O/D but my truck is much more about just enjoying the cruise these days.

jessemthompson · 03-09-2017, 08:56 PM

With 556hp on tap I think a 3:55 would be a good setup. Your gonna have a hard time not blowing the tires off regardless of your gearing, but the deeper you go the less traction you're gonna have.

B. W. · 03-09-2017, 09:31 PM

X5 on 3.73, if the trans had OD I might go 4.10

Heavymetl · 03-09-2017, 09:41 PM

Having raced a manual trans for several years now...for the track you'll want a 4.30 or 4.56. But since that's obviously pretty terrible for the street, just go with a 3.73 and have fun. Getting outta the hole with a clutch and sticky tires isn't easy!

67 chevelle · 03-10-2017, 10:08 AM

Quote:

Originally Posted by LockDoc

-
Unfortunately the M21 is a standard car 4 speed with no OD so 4.10's would be a bit low. The 3.73 would work great for that application and that is what I would recommend.....

Just my 2¢ worth.

LockDoc

Agree , plus most of these trucks came with that gear , you'll want a posi

03-09-2017, 02:29 AM	#1
gmcountryboy Registered User Join Date: Jan 2014 Location: Sturgeon county alberta Posts: 4	Ls swapped rear end question Hey fellas, new to the site have a 1967 C10 I've been building for quite some time, stock chassis, carb'd 6.0 ls lq9, stock crank and rods, hyperutetic pistons @ 10.5:1 comp, ARP bottom end, 229/236 cam on a 108 lsa with the ls3 heads, runnin a single plain intake. Engine dynoed at 556 hp at 6500 rpm.. M21 trans, currently has 3:08 but I want somethin a bit peppier. Truck mostly will be driven around town and taken to the track every now and then. Wondering what you guys would recommend for a rear end gear, 3:73 or a 4:10. Truck has 29x18.5 Mickey Thompsons, any input is appreciated!! Posted via Mobile Device Attached Images

03-09-2017, 09:31 AM	#2
68Stepbed Registered User Join Date: Mar 2005 Location: 10-Uh-See Posts: 5,609	Re: Ls swapped rear end question That engine will love the 4:10's, but not sure how much the transmission will help on the freeways. 3.73's would certainly make it peppier, and still do good at highway speeds. I run 4:10 in my carbed LS1 with a similar cam, but I'm using a 700R4 with overdrive. __________________ Matt 68 C10 stepside, LS1/700R4, TCI Engineering suspension system

03-09-2017, 09:43 AM	#3
Andy4639 Old member Join Date: Jan 2002 Location: Liberty, & Garden City S.C. , U.S. Posts: 19,936	Re: Ls swapped rear end question My 6.0 with 4l80e over drive the 4:10 are good. __________________ 1971 LWB Custom, 6.0LS & 4L80E, Speedhut.com GPS speedometer & gauges with A/C. 20" Boss 338's Grey wheels 4 wheel disc brakes. My Driver Seeing the USA in a 71 Upstate SC GM Truck Club 2013,14 and 2016 Hot Rod Pour Tour http://upstategmtrucks.com/ Get out and drive the truck this summer and have some fun! It sucks not being able to hear! LWB trucks rule, if you don't think so measure your SWB! After talking to tech support at Air Lift I have found out that the kit I need is 60811. Per the measurements I gave them. Ride height of truck inside spring and inside diameter of springs.

03-09-2017, 12:28 PM	#4
steelhorse Senior Member Join Date: Apr 2008 Location: Franklinton NC Posts: 1,309	Re: Ls swapped rear end question I like 3.73 for the street unless it is a 4x4 with big tires.

03-09-2017, 01:10 PM	#5
davepl Registered User Join Date: Aug 2006 Location: Redmond, WA Posts: 6,332	Re: Ls swapped rear end question 4.10s here with a 4L80E (overdrive), it's about right. Lots of gear in town. I wouldn't go much more than 3.55 or at most 3.73 without overdrive though. Just me. __________________ 1970 GMC Sierra Grande Custom Camper - Built, not Bought 1969 Pontiac 2+2 427/390 4-speed Coupe 1969 Pontiac 2+2 427/390 4-speed Convertible

03-09-2017, 02:00 PM	#6
LockDoc The Older Generation Join Date: Aug 2006 Location: Montezuma, Iowa Posts: 25,346	Re: Ls swapped rear end question - Unfortunately the M21 is a standard car 4 speed with no OD so 4.10's would be a bit low. The 3.73 would work great for that application and that is what I would recommend..... Just my 2¢ worth. LockDoc __________________ Leon Locksmith, Specializing In Antique Trucks, Automobiles, & Motorcycles (My Dually Pickup Project Thread) http://67-72chevytrucks.com/vboard/s...d.php?t=829820 -

03-09-2017, 06:49 PM	#7
chevy72blu Registered User Join Date: Apr 2004 Location: Las Vegas, NV Posts: 2,188	Re: Ls swapped rear end question I have 3.73's with a 29" tire and a 4l60e. I think its perfect. Stock LS1, though, and I already cant get any rear traction. Depends on how much time you plan on spending at the track. I'd go 3.73's with or without O/D but my truck is much more about just enjoying the cruise these days. __________________ RIP EastSideLowLife '72 C20 SWB convert. 5 lug, LS1/4l60e

03-09-2017, 08:56 PM	#8
jessemthompson Registered User Join Date: Nov 2011 Location: Williamsburg, VA Posts: 956	Re: Ls swapped rear end question With 556hp on tap I think a 3:55 would be a good setup. Your gonna have a hard time not blowing the tires off regardless of your gearing, but the deeper you go the less traction you're gonna have.

03-09-2017, 09:31 PM	#9
B. W. Registered User Join Date: Nov 2014 Location: Bigfork, Montana Posts: 1,137	Re: Ls swapped rear end question X5 on 3.73, if the trans had OD I might go 4.10

03-09-2017, 09:41 PM	#10
Heavymetl Registered User Join Date: Feb 2012 Location: Southern Ohio Posts: 292	Re: Ls swapped rear end question Having raced a manual trans for several years now...for the track you'll want a 4.30 or 4.56. But since that's obviously pretty terrible for the street, just go with a 3.73 and have fun. Getting outta the hole with a clutch and sticky tires isn't easy! __________________ 1970 C10 Turbo LM7 5.3/LS6 cam PT7675/4L80E/Holley Dominator EFI/E85 Moser 9" 3.25/4 wheel discs 11.16@121.07



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