Gear ratio for LS swap?? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

FDEddie · 05-05-2008, 05:42 PM

Ok....Here we go! I'm sending my PCM to Speartech for the reprogram. I'll be
running a 6.0l LQ4/4L80E in my '72 short bed with 275/60-15 tires, 28" diameter.
This will be a driver, so economy is at the top of the list, but I don't want it to
be a dog either. The new truck/vans with this combo (3/4 and 1 ton) run a 3.73
standard. I was thinking 3.08. What do y'all think??

Thanks in advance for your input

killer71 · 05-05-2008, 06:39 PM

i had 3.08 gears in killer and i'd definit. recommend it especially for the hiway.....
i chose those gears just for the reasons you are gonna use your truck for!

Wrenchbender Ret · 05-05-2008, 07:14 PM

Ive got 3.08 in my 70 stepside with 700-4R & 350 engine. It works real good but is sluggish at times. You can pull it down to direct drive & it pulls strong & still doesn't over rev.

silverado84355 · 05-05-2008, 07:32 PM

Since your gonna have the overdrive I would go 3.73.

LONGHAIR · 05-05-2008, 08:15 PM

3.08 is to high for an overdrive transmission especially with 28" tires. I would go with 3.73s but you might get away with 3.42 if you do most of your driving at highway speeds.

68GMCCustom · 05-05-2008, 08:17 PM

I would say 3.42 would be a nice compromise. To me, anything under 3.23 would be too tall for performance at lower speeds.

I have a TrailBlazer SS with 4.10's and a 4L70 and the r's are certainly too high on the hiway for economy, but 3.73's wouldn't be tall enough either. I had 3.73's on my '01 Sierra C3 with a 6.0/4L60HD and it was "close" to the hiway sweet spot of 2k at 75-80mph, but still ran about 2300-2400 rpm IIRC.

67_C-30 · 05-05-2008, 08:53 PM

I agree with other guys. 3.08's with OD will be pretty gutless at certain speeds. The 6.0" will do better than the smaller engine, but I'd still go 3.42 or 3.73.

68GMCCustom · 05-05-2008, 11:45 PM

or....put 4.10's in it and add a gear vendors overdrive to the tail of the 4L80...for a double overdrive 8 speed!

killer71 · 05-06-2008, 12:37 AM

Quote:

Originally Posted by 67_C-30

I agree with other guys. 3.08's with OD will be pretty gutless at certain speeds. The 6.0" will do better than the smaller engine, but I'd still go 3.42 or 3.73.

don't agree guys, sorry...the 5.3L 4l60e with 3.08's was gr

*truckmanloco* · 05-06-2008, 04:05 AM

It all depends on the transmission 4l60e or 4l80e,you cant go wrong with 3.73s its not to deep of a gear to kill your gas mileage, but still a good gear.

ksbeatty · 05-06-2008, 05:14 AM

I have put a 700r4 with 4.10s in with 285's. I have not checked the RPM's yet but I can tell they are higher than I like. I don't want to steel the thread but do they make the 3.42 for the GM corp rear and a Dana 44 front?

05-05-2008, 05:42 PM	#1
FDEddie Registered User Join Date: Mar 2007 Location: Orlando, FL Posts: 21	Gear ratio for LS swap?? Ok....Here we go! I'm sending my PCM to Speartech for the reprogram. I'll be running a 6.0l LQ4/4L80E in my '72 short bed with 275/60-15 tires, 28" diameter. This will be a driver, so economy is at the top of the list, but I don't want it to be a dog either. The new truck/vans with this combo (3/4 and 1 ton) run a 3.73 standard. I was thinking 3.08. What do y'all think?? Thanks in advance for your input

05-05-2008, 06:39 PM	#2
killer71 Registered User Join Date: May 2006 Location: at work Posts: 2,552	Re: Gear ratio for LS swap?? i had 3.08 gears in killer and i'd definit. recommend it especially for the hiway..... i chose those gears just for the reasons you are gonna use your truck for! __________________ R.I.P. Killer 71 10/26/07

05-05-2008, 07:14 PM	#3
Wrenchbender Ret Registered User Join Date: Oct 2005 Location: Overland Park, Ks. Posts: 5,206	Re: Gear ratio for LS swap?? Ive got 3.08 in my 70 stepside with 700-4R & 350 engine. It works real good but is sluggish at times. You can pull it down to direct drive & it pulls strong & still doesn't over rev.

05-05-2008, 07:32 PM	#4
silverado84355 Registered User Join Date: May 2007 Location: Carlsbad,NM Posts: 99	Re: Gear ratio for LS swap?? Since your gonna have the overdrive I would go 3.73.

05-05-2008, 08:15 PM	#5
LONGHAIR just can't cover up my redneck Join Date: May 2004 Location: Columbus OH Posts: 11,414	Re: Gear ratio for LS swap?? 3.08 is to high for an overdrive transmission especially with 28" tires. I would go with 3.73s but you might get away with 3.42 if you do most of your driving at highway speeds.

05-05-2008, 08:17 PM	#6
68GMCCustom Truck and auto performance nut Join Date: Feb 2007 Location: McKinney,Texas Posts: 3,848	Re: Gear ratio for LS swap?? I would say 3.42 would be a nice compromise. To me, anything under 3.23 would be too tall for performance at lower speeds. I have a TrailBlazer SS with 4.10's and a 4L70 and the r's are certainly too high on the hiway for economy, but 3.73's wouldn't be tall enough either. I had 3.73's on my '01 Sierra C3 with a 6.0/4L60HD and it was "close" to the hiway sweet spot of 2k at 75-80mph, but still ran about 2300-2400 rpm IIRC. __________________ Kurt - '68 GMC short step - NIB '09 LY6 6.0L crate motor w/mods, NIB '12 crate 4L85e w/billet 3k stall Circle D, 3.73 posi 12 bolt, DynaTech f-swap headers, 3/4 drop, handling mods, etc. - my toy '72 Chevy LWB C-10 Highlander - 350/350 ps/pb/tilt/ac - not original but close '06 Chevy TrailBlazerSS - LS2/4L70e - little black hot rod SUV - my DD '18 Kia Sorento - wife's econo-driver '95 Chevy S10 - reg cab shortbed, LS, 4.3, auto... my '68's powertrain and chassis build -links broken A surprise phase - carb to efi -links broken

05-05-2008, 08:53 PM	#7
67_C-30 I have a radical idea! Join Date: Jan 2005 Location: Sweet Home Alabama! Posts: 6,513	Re: Gear ratio for LS swap?? I agree with other guys. 3.08's with OD will be pretty gutless at certain speeds. The 6.0" will do better than the smaller engine, but I'd still go 3.42 or 3.73. __________________ '67 C-30 Dually Pickup 6.2 Turbo Diesel, NP435 ‘72 C-10 SWB , 350 4bbl, TH350 '69 C-10 SWB , 250 L6, 3 OTT '69 GMC C3500, dump truck, 351 V6, NP435 '84 M1009 CUCV Military Blazer 67 C-30 Turbodiesel build thread http://67-72chevytrucks.com/vboard/s...d.php?t=254096 My trucks http://s226.photobucket.com/albums/d...ediafilter=all Member of the 1-Ton Club!

05-05-2008, 11:45 PM	#8
68GMCCustom Truck and auto performance nut Join Date: Feb 2007 Location: McKinney,Texas Posts: 3,848	Re: Gear ratio for LS swap?? or....put 4.10's in it and add a gear vendors overdrive to the tail of the 4L80...for a double overdrive 8 speed! __________________ Kurt - '68 GMC short step - NIB '09 LY6 6.0L crate motor w/mods, NIB '12 crate 4L85e w/billet 3k stall Circle D, 3.73 posi 12 bolt, DynaTech f-swap headers, 3/4 drop, handling mods, etc. - my toy '72 Chevy LWB C-10 Highlander - 350/350 ps/pb/tilt/ac - not original but close '06 Chevy TrailBlazerSS - LS2/4L70e - little black hot rod SUV - my DD '18 Kia Sorento - wife's econo-driver '95 Chevy S10 - reg cab shortbed, LS, 4.3, auto... my '68's powertrain and chassis build -links broken A surprise phase - carb to efi -links broken

05-06-2008, 04:05 AM	#10
truckmanloco Account Suspended Join Date: Nov 2007 Location: San Diego ca Posts: 717	Re: Gear ratio for LS swap?? It all depends on the transmission 4l60e or 4l80e,you cant go wrong with 3.73s its not to deep of a gear to kill your gas mileage, but still a good gear.

05-06-2008, 05:14 AM	#11
ksbeatty Registered User Join Date: Mar 2006 Location: Kansas Posts: 300	Re: Gear ratio for LS swap?? I have put a 700r4 with 4.10s in with 285's. I have not checked the RPM's yet but I can tell they are higher than I like. I don't want to steel the thread but do they make the 3.42 for the GM corp rear and a Dana 44 front? __________________ 1969 GMC 3/4 Ton 4x4 2" Lift, A/C, PS, PB 383 Stroker, 700R4, 205, 4.10 GM Medium Bronze (Copper Poly) no new nick name yet. She is to pretty to be the Beater. http://67-72chevytrucks.com/vboard/s...d.php?t=241855

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