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#1 |
Old member
Join Date: Jan 2002
Location: Liberty, & Garden City S.C. , U.S.
Posts: 19,936
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Thinking about swapping out the 4:10 gears for a Pos trac 3:38 are 3:08 to gain some gas mileage. I don't hot rod my truck so I'm not real concerned with loosing some torque since I have the 4L80E in it also. It has a good 1 and 2 gear.
I want better than 15 MPG! What do all of you think, lets hear what you got. ![]()
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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. |
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#2 |
Registered User
Join Date: Oct 2013
Location: Dresden, Ontario
Posts: 647
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Re: Opinion's wanted
I wouldn't assume that lowering you gear ratio that much will give you better mileage. I know people will tell you that lower numerically gears will give better mileage but this is dependant on many factors especially with an overdrive transmission. You need to keep your engine in its peak operating range to deliver the best mileage. A lugging engine will give poor mileage as much as an over revving engine.
I'm not saying that the 4:10 will give the best mileage but you may find a 3:73 or 3:55 will be a better solution with the overdrive trans. Tire size also plays a roll in overall gear ratio. I see you have a LS engine so a higher ratio may be fine in a relatively light truck compared to today's behemoths? Most modern trucks no longer offer a 3:08 ratio for good reason as they are not necessarily good in a truck. I can tell you I changed from 3:31 to 3:73 in my 2007 F150 and my mileage went up.
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1970 Short Wide 5.3 4L60E BlackBear tune 3:73 gears, Boyd's Tank 2.5 / 4 drop 5 lug disc brakes Vintage Air 18x8 Ridlers 255/55 frt. 18x9.5 275/60 rear |
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#3 | |
Hittin E-Z Street on Mud Tires
![]() Join Date: Nov 2004
Location: Greenville, SC
Posts: 23,090
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Re: Opinion's wanted
Quote:
3.73 will help a bit, but you're not going to jump to 18-20 mpg, but you might see a 1+mpg improvement. For power/economy, the 3.73 is the sweet spot for these trucks. 3.08 and OD are a NO NO in these trucks. Just search on here how many times guys tried that combo and the trucks lugged so bad in OD they went to a lower ratio. A 3.42 might be an OK option, but if you're used to a 4.11, your truck will probably feel like a dog to you with that swap. If I remember right, the trucks with the 5.3L came with a 3.42 standard and the 3.73 and lower gears were optional (my Z71 had the 3.73 G80).
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Jesse James 1967 C10 SWB Stepside: 350/700R4/3.73 1965 Ford Mustang: 289/T5-5spd/3.25 Trac-Loc 1968 Pontiac Firebird: Project Fire Chicken! 2015 Silverado Double Cab 5.3L Z71 2001 Jeep Wrangler Sport 4.0L 5spd 2020 Chevrolet Equinox Premium 2.0L Turbo 2011 Mustang V6 ~ Wife's ride ![]() American Born, Country by the Grace of God ![]() 1967 CST Shop Truck Rebuild! My 1967 C-10 Build Thread My Vintage Air A/C Install Project "On a Dime" Trying my hand at Home Renovation! 1965 Mustang Modifications! |
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#4 |
Registered User
Join Date: Aug 2006
Location: Redmond, WA
Posts: 6,332
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Re: Opinion's wanted
I run 4.88s with overdrive! The overdrive makes it about the same as 3.08s with a 1:1 transmission like the TH400, and that's about as low numerically as you'd ever want to go on these trucks I think...
Best thing to do is do the math as to what your engine RPM would be in overdrive at 60mph; decide what the lowest number (1250?) your engine makes good solid torque at and go from there. There's no super-magic difference in mileage with gears, it's the same amount of work being done. Steep gears waste friction, tall gears pull your engine down out of its efficiency band. Hence my comment about where your engine (more accurately, your cam selection) makes good torque. It might even be the case that you are best cruising at your peak torque RPM since that's where your volumetric efficiency is highest, but that puts you at a higher RPM than needed and you lose efficiency to ring drag and other items that don't matter at WOT. So I figure as long as your engine is making efficient torque, that's a good cruise RPM. But too tall of gearing can pull you down out of that. Another point to consider is that if you have very tall gearing and want to speed up a little or climb a hill without downshifting you might use so much throttle that your vacuum dips and the power enrichment circuit kicks in; that'll ruin your mileage.
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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 |
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#5 |
Special Order
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Location: Mt Airy, MD
Posts: 85,859
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Re: Opinion's wanted
You want 3.42s. Noticeably taller than the 4.10 while keeping the grunt to pull that 3.08s lack. I think that is the sweet combo for light trucks. 3.73s are a small step away from 4.10s in straight drive, but more noticeable when you're talking O/D, if you go with those. That's the easy one for these years, plenty out there to swap-in.
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"BUILDING A BETTER WAY TO SERVE THE USA"......67/72......"The New Breed" GMC '67 C1500 Wideside Super Custom SWB: 327/M22/3.42 posi.........."The '67" (project) GMC '72 K2500 Wideside Sierra Custom Camper: 350/TH350/4.10 Power-Lok..."The '72" (rolling) Tim "Don't call me a redneck. I'm a rough cut country gentleman" R.I.P. ~ East Side Low Life ~ El Jay ~ 72BLUZ ~ Fasteddie69 ~ Ron586 ~ 67ChevyRedneck ~ Grumpy Old Man ~ Last edited by special-K; 12-21-2015 at 07:34 PM. |
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#6 |
laying low
![]() Join Date: Mar 2001
Location: Searcy, Ark. USA
Posts: 13,269
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Re: Opinion's wanted
Andy you have the 6.0 engine and it makes good power but I don't see it getting you to the high teens mpg. If you are already in the mid teens, 14 or 15 mpg you may not see much more than that with a gear change. Like others I think a good gear choice is in the 3.42 to 3.55 range. JMO
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Boog 69 Chevy stepside, 358/T350, 4.11 posi, 4.5/4 drop, rallys, poboy driver primer is finer 91 Chevy sportside, Tahoe, Yukon & GMC Crewcab All GM..'nuff said. I stand for the flag and kneel at the cross |
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#7 |
I am a Referee of life.
Join Date: Jun 2000
Location: Greensboro N.C.
Posts: 13,993
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Re: Opinion's wanted
I haven't looked to see what the Ratio is on a new truck but up to the end of the 700R4 era 3.42:1 was standard and 3.73:1 was optional w the 700. I figure GM hired and paid people a lot better versed than me in this to determine what was best all around gear. So I would look into matching what the factory did. I'm assuming it was a 3.42:1 or so. The 3.73:1 isn't a lot of difference but you would notice it some.
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The 47-present Chevrolet and GMC Truck Message Board Network,it's owners,moderators,members,and associates of any type should not be held responsible for my opinion. You can't fix stupid,not even with duct tape. "My appearance is due to the fact that "GOD" does punish you for having too much fun!" Barrett-Jackson has perfected alchemy,they make rust into gold! "You can lead a horse to water but you can't saddle a duck" "Cleverly disguised as a 'Responsible Adult' "Sometimes your Knight in shining armor is just a retard in tinfoil" |
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#8 | |
Registered User
Join Date: Oct 2006
Location: Dundee, Oregon
Posts: 311
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Re: Opinion's wanted
Quote:
My truck is currently running a LS1(5.7)/4L60e combo with 3.42 gears and 275/60/15 rear tires. I feel like it is "lugging" when cruising at 55 to 60 mph. I too, am pulling right at 15mpg consistently. For this issue, I have a large order from Randy's ring and pinion sitting on the shelf waiting for me to install. Eaton posi, 3.73 gears, and bearings to do the job. Also being installed at the same time will be rear disc brakes. Good luck on your gas mileage quest, I would like a little better too. I'm sure mine will do better if I wasn't driving a crooked mountain road to work. |
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#9 |
Registered User
Join Date: Jan 2012
Location: Petal,Ms.
Posts: 428
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Re: Opinion's wanted
I agree with 68, higher is not going to help much, I have 6.0/ 4l60e/ 373 in my camaro with a 228/584 cam and get 21 miles to gallon highway, 17 city. I think maybe get a good tune will and you will get the best results.
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#10 |
Old member
Join Date: Jan 2002
Location: Liberty, & Garden City S.C. , U.S.
Posts: 19,936
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Well not dead set on the numbers of gears yet, just want to find out what everyone likes. If the 3.73 is not much help MPG wise and only 1 MPG differance like Jesse states I'll stay where I'm at!
Right now running 60MPH I'm turning 2300RPM's on flat ground. But once I get to 70MPH I'm up around 2800RPM's and I drive a lot on the interstate anywhere from 65-80 MPH. I'd like to get the truck down below 2500RPM's at those speeds. I checked my MPG last night when I filled up. 36 gallons @ 510 miles =14.16 MPG. I have a 42 gallon tank. That is a mixture of miles also City,interstate and country driving! Yes it's not wrong. The tune was done professionally! The motor combo is all stock. ![]()
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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. |
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#11 |
Hittin E-Z Street on Mud Tires
![]() Join Date: Nov 2004
Location: Greenville, SC
Posts: 23,090
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Re: Opinion's wanted
That's about right. My LS 00 Z71 got the same mileage. 13.5-14mpg around town, maybe 14-15mpg average. It only got 18mpg if it was 100% highway and the cruise was set on 70mph.
Yes, these trucks are lighter than the LS trucks their motors come from, but you can negate the lighter bodies with the "aerodynamics of a brick" and they about cancel each other out. Seriously, next time your up to 75mph lift your foot off the gas and watch how fast the truck slows down... now do the same thing in a modern truck... they slow down MUCH slower when you let off. They're heavier buy way more aerodynamic. My 67 with a 350/700R/3.73 gets 11-12 mpg, but I drive around town and leave it in 3rd most of the time (mostly under 45mph driving). If I take her out on the interstate and keep it around 65-70 I can get about 15mpg with OD.
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Jesse James 1967 C10 SWB Stepside: 350/700R4/3.73 1965 Ford Mustang: 289/T5-5spd/3.25 Trac-Loc 1968 Pontiac Firebird: Project Fire Chicken! 2015 Silverado Double Cab 5.3L Z71 2001 Jeep Wrangler Sport 4.0L 5spd 2020 Chevrolet Equinox Premium 2.0L Turbo 2011 Mustang V6 ~ Wife's ride ![]() American Born, Country by the Grace of God ![]() 1967 CST Shop Truck Rebuild! My 1967 C-10 Build Thread My Vintage Air A/C Install Project "On a Dime" Trying my hand at Home Renovation! 1965 Mustang Modifications! |
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#12 | |
Registered User
Join Date: Mar 2008
Location: Kimberly, Id
Posts: 390
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Re: Opinion's wanted
Quote:
Hey Andy, What is the size of the tire you are running on it? Metric numbers please. I'll do some calculating for you with this info. Thanks
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Mike 1972 C10 Cheyenne SWB Black Supercharged Project 1972 K10 Cheyenne SWB Copper and White http://67-72chevytrucks.com/vboard/s...d.php?t=654175 1969 Camaro Protouring LS7 T-56 Project |
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#13 | |
Registered User
Join Date: Jan 2011
Location: Townsend MT
Posts: 1,725
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Re: Opinion's wanted
Quote:
It seems to me that engines get the best mileage at their peak torque. |
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#14 | |
Registered User
Join Date: Aug 2006
Location: Redmond, WA
Posts: 6,332
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Re: Opinion's wanted
Quote:
They can't get their best mileage at peak torque because peak torque is at an RPM that has -great- volumetric efficiency (good) but a lot of friction (bad). If you have 30 hp of frictional losses it may not matter relaive to 450ftlbs but it sure does relative to the 40hp it probably takes to push a truck through the air at highway speeds. That's why lower RPMs are usually better. If you had a graph that included frictional losses, torque, and the amount of power it takes to move our truck through the air you could plot the ideal RPM, but I don't have that kind of data. My stock 402 peaks torque at 420@3350, but you sure wouldn't want to cruise at 3350. So, we generally wind up at "the lowest RPM at which the motor makes good, efficient torque". Sadly we didn't dyno my own motor that low, but if the curve is at all symmetrical, 1500 would probably be ideal. That's about the lowest RPM where I think it makes 350ft lbs.
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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 |
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#15 | |
Old member
Join Date: Jan 2002
Location: Liberty, & Garden City S.C. , U.S.
Posts: 19,936
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![]() Quote:
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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. |
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#16 |
Registered User
Join Date: Sep 2009
Location: ottawa,canada
Posts: 4,550
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Re: Opinion's wanted
6.0/4l80e with 3:42 posi, 28" tires, I can roast the tires at will and cruise along 65-70 mph 1900-2200 rpm.
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my build threads '86 C10 http://67-72chevytrucks.com/vboard/s...d.php?t=415628 '67 C10 http://67-72chevytrucks.com/vboard/s...d.php?t=635078 '63 GMC http://67-72chevytrucks.com/vboard/s...d.php?t=674682 |
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#17 | |
Old member
Join Date: Jan 2002
Location: Liberty, & Garden City S.C. , U.S.
Posts: 19,936
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![]() Quote:
This is where I want to be! ![]()
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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. |
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#18 |
Registered User
Join Date: Sep 2005
Location: sc
Posts: 1,203
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Re: Opinion's wanted
I feel ya!
I got 13ish with my set up. Swapped to the T56 and did not pick up what I hoped, now at 15. I just don't think I will see HIGH Teens or LOW 20s. 5.3/60 does though....
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71 Cheyenne C10 LWB cam'd 6.0/T56 Swap |
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#19 |
Registered User
Join Date: Sep 2012
Location: SoCal
Posts: 529
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Re: Opinion's wanted
i just swapped out my 3.07 rear end with an open diff for a 3.42 with an eaton posi.
no complaints here... miles per gallon went down but smiles per gallon went up |
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#20 |
Registered User
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Location: 2nd left past the stump on a dirt road.
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Re: Opinion's wanted
After doing the math myself and listening to a lot of people on here I think this is spot on:
That's why lower RPMs are usually better. If you had a graph that included frictional losses, torque, and the amount of power it takes to move our truck through the air you could plot the ideal RPM, but I don't have that kind of data. From there my thought are to actually DYNO your actual setup you have now. Both HP and TORQUE. The cam has to figure into this somewhere, so does actual vacuum. (Vacuum at actual cruising speed and load.) Then decide on those 3.08, 3.54, or 3.73. Right now with my 150k motor, older turbo 350, I am at roughly 3300 rpms at 65mph. I aint liking it. |
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#21 |
Registered User
Join Date: Mar 2008
Location: Kimberly, Id
Posts: 390
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Re: Opinion's wanted
Ok Andy here goes the various RPM your engine pulls with the 4L80E and 29.5" tires in 4th gear or overdrive.
4:10 @ 80 is 2800 RPM, 70=2450 and 60=2100. 3:73 @ 80 is 2550 RPM, 70=2230 and 60=1900 3:42 @ 80 is 2340 RPM, 70=2045 and 60=1750 3:08 @ 80 is 2100 RPM, 70=1840 and 60=1580 Hope this helps, Mike
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Mike 1972 C10 Cheyenne SWB Black Supercharged Project 1972 K10 Cheyenne SWB Copper and White http://67-72chevytrucks.com/vboard/s...d.php?t=654175 1969 Camaro Protouring LS7 T-56 Project |
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#22 | |
Registered User
![]() Join Date: Jul 2015
Location: 2nd left past the stump on a dirt road.
Posts: 2,629
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Re: Opinion's wanted
Quote:
I have been thinking about going this route, anyone has the stock spec of lockup on 4l80e converter? Also I would be interested when someone posts their gas mileage if they are using e10 or non-ethanol, reg or super? Some states still do not mandate e-10 yet, last I heard. Last edited by toolboxchev; 12-23-2015 at 12:29 AM. |
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#23 |
Registered User
Join Date: Jan 2010
Location: Loveland, CO
Posts: 1,921
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Re: Opinion's wanted
My 71 with a 5.3/4L60E has 3.73's with a 28" tire. It gets 18 mpg, and cruises at about 2500 rpm at 75 mph, in OD with the torque converter in lockup. It is a blast to drive, but I really do feel it would do better with a 3.42 or 3.55 gear. I would like to be around 2000-2200 rpm at 75. And I run 91 octane 10% ethanol (that's all we can get around here).
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Zach 1970 Chevrolet Custom Camper K20 1971 GMC Super K2500, 12V/NV4500 swap in progress 1971 Chevrolet Custom C10 1972 Chevrolet Custom Deluxe C20, 5.3/4L60E 1972 Oldsmobile Cutlass Supreme, 455/TH400, 3.73 posi 2004 GMC Sierra 2500HD, LB7/Allison, CCSB 2005 GMC Sierra 1500, 5.3/4L60E, CCSB |
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#24 |
Registered User
Join Date: Nov 2000
Location: Huntsville Ontario Canada
Posts: 4,052
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Re: Opinion's wanted
I dont have a ls in the suburban but i did switch to a 3:42 gear and gear vendors from a 3:73. Its great on the freeway but the gv is off unless its on the freeway now. I kinda liked the 3:73 better....
What year is your 6.0 ? i am considering using a 2004 truck as a doner for. 4wd chassis i want to put under the 1967 C20
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1968 Suburban numbers matching all original truck now equipped with 6.0/4L80 on Accuair http://67-72chevytrucks.com/vboard/s...d.php?t=625017 1967 C/20 6.0/4L80 Roofing Truck 1990 V2500 Suburban "Plow Truck" 2005 TAHOE DD |
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#25 | |
Registered User
Join Date: Mar 2008
Location: Kimberly, Id
Posts: 390
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Re: Opinion's wanted
Quote:
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Mike 1972 C10 Cheyenne SWB Black Supercharged Project 1972 K10 Cheyenne SWB Copper and White http://67-72chevytrucks.com/vboard/s...d.php?t=654175 1969 Camaro Protouring LS7 T-56 Project |
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