What have you done to your square lately??

legopnuematic said:

Differential size absolutely plays into mileage.

With everything equal or the same, besides ring gear diameter, the larger unit will get worse mileage. Larger parts, more mass, more friction/contact area.

Which is great for strength, but not economy.

My friends k5, dyno’d with 10 bolt (4.56 gears) and then with the 14 bolt semi float we built (3.73 gears) dropped about 20hp at the wheels. Of course the ratio change plays into that too.

If you put a 10/12 bolt and a 14sf next to each other, the 14sf is significantly larger/beefier in all regards.

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What you mentioned about the dyno numbers is worthy of it's own thread. I'm curious how much HP is actually lost in the drivetrain on a 3/4 ton 4x4 with lockers and 33"+ tires. I know they say roughly 15-20% if you have a RWD with normal tires. But I was pretty surprised when I saw a YouTube video that showed (IIRC) a Nissan Frontier that dyno'd at like 220 hp on stock tires, and lost something like 50 hp on the dyno just swapping to bigger tires. I don't think saying a 30% drivetrain loss is very far from reality on a 4wd with a big rear diff, a locker and big tires.

For anyone interested, I actually have numbers from 2 different dyno runs on a Charger I had done that shows a Mustang dyno vs a Dyno Jet. The Mustang dyno read 18% lower than the Dyno Jet. That isn't a dig on a Mustang dyno, it just is what it is, a lot of guys actually like the Mustang dyno more. If anyone asks which is better I always say, "if you're just looking for dyno numbers to impress people, take it to someone with a Dyno Jet. Otherwise they both work great for getting reliable graphs for tuning."

mattsk8 said:

That's still pretty amazing mileage. Mine is a 350, about 400 hp, 700r4, but 4.10 gear with 33" tires and a 14b diff w/ a Detroit locker. just a theory I haven't looked into, but think the 14b diff eats mileage. Every 3/4 ton Chevy I own or owned never got better than 11 mpg avg. Even my 2005 w/ a 6.0 never gets better than 11.

I used to have a TH400 and got about 9 mpg. I was hoping for 11 on the highway when I put the 700r4 in. I get a smidge over 10 if I'm nice to it. But I can have a conversation with whoever is next to me on the highway now and couldn't with the th400 cuz exhaust roar.

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I used to have an '86 C20 Burb with 454/th400/3.73 14bff and it had no trouble getting 13 mpg on the interstate at 75mph. All the others though... yeah, 10.5-11 mpg max.

PeteJr said:

I understand about that. Just a couple hundred miles more for you to go to Dino's in AZ. Some of us are trying to work on that trip for 2025.
1,600 miles one way for us.
If you're thinking about So. Ill. show, it's great around 400 or so trucks. Think about the Southeastern GM truck show in Lebanon, TN. About the same mileage from Houston.
Plus there's usually about 1,700 all GM trucks there. Awesome event.

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Phoenix is 1200 miles from Houston, half of that distance is between Austin and El Paso. You can fit several small states in Texas LoL.

HotWheelsBurban said:

Phoenix is 1200 miles from Houston, half of that distance is between Austin and El Paso. You can fit several small states in Texas LoL.

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What about Alaska?

bucket said:

What about Alaska?

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Even more small states....

PeteJr said:

Drove my truck about 500 miles on Saturday to/from the Southern Illinois Truck Show in Marion, IL.
Got a shade over 18 miles to the gallon.
I am thrilled !!

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I'd love to know your whole combination. Engine, modifications,tire size. Just saw that you gave some of this info this morning. What's the engine build,and tire size. Thanks

bucket said:

I used to have an '86 C20 Burb with 454/th400/3.73 14bff and it had no trouble getting 13 mpg on the interstate at 75mph. All the others though... yeah, 10.5-11 mpg max.

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I personally think the average burb gets better mpg than the average lwb c/k I think it's the shape.

Ricko1966 said:

I personally think the average burb gets better mpg than the average lwb c/k I think it's the shape.

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My small block 4x4's have never bested 11mpg (including one with overdrive) and my '78 C20 454 Burb, also with 3.73's has never done better than 10.5 mpg. I'm not sure why the '86 C20 got so much better highway mpg.

Ricko1966 said:

I'd love to know your whole combination. Engine, modifications,tire size. Just saw that you gave some of this info this morning. What's the engine build,and tire size. Thanks

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Rick,
Here's my deal:
1983 GMC Sierra Classic, short bed, original 700R4 (rebuilt) with original 2.73 rear gear.
Blueprint 350 "cruiser" & according to their dyno sheet, 355 HP with a 600 Holley carb on 87 octane gas.
I have 235/75/15 tires on original rally wheels.
Other than rebalanced driveshaft, nothing crazy with the driveline.
Turns about 1800 RPM at 70 - 75 MPH.

Didn't take any pics but installed a catalytic converter ( 8" Flowmaster ) and sway bar disconnect kit on the K10 today. Wanted to take a back wheel off the Camaro and put up against the C10 to get some rough ideas on sizing but I couldn't find the wheel lock key. I did at least find the registration card from 2016 and was able to order a replacement. Guess we'll have to wait a few days to look into that.

Halibrands showed up today. Test fit is inconclusive, mostly depends on sidewall profile. The tires will be here soon.


Also got the non- cruise control speedo cable in the mail today so hopefully I can get that half-installed module by PO eliminated.

Got the new rear installed. Tomorrow is new u joints for the driveshaft, new master cylinder and getting the brakes bled hopefully

JamesSam said:

So I got the connector switch wired in for drivers power window. Then old regulator is toast. New regulator was ordered on a whim because it was only $40 but it does not line up directly to the power motor mounts. I was looking in to slotting mount holes but now think I will attempt to return the aftermarket regulator to LMC and try a OEM regulator from Classic Industries and hope it ligns up correctly. I don't want to do this again in a month. I am betting on the original specs for the OEM actually lining up. Anyone have knowledge of OEM replacement regulators? I have only worked with my trucks original, that now does not work. Oh and of course the re-pop that is not made quite right.

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I got my window motor from O'Reilly's Auto Parts. I just checked and they stock Dorman regulators which are about as close to OE as I have found. They are around $62 here, close to Baton Rouge, Louisiana.

I don't know if you have O'Reilly's up where you live but they can usually get anything I need for my Truck.

Cleaning up my truck for VGG wipe on clear coat (matte finish). Also, after coating, I will install a new axle half shaft to replace the one thats bent and has been wiggling for the last 19 years. More photos to come after the clean and coat.

Redfish said:

I got my window motor from O'Reilly's Auto Parts. I just checked and they stock Dorman regulators which are about as close to OE as I have found. They are around $62 here, close to Baton Rouge, Louisiana.

I don't know if you have O'Reilly's up where you live but they can usually get anything I need for my Truck.

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There are O'Reilly's here and I have actually found parts for the truck with them. My nephew just got a job at one that is not to far from here so I anticipate sourcing from them in the future. I'm actually looking forward to driving my truck there, it's about a nice 20 minute ride.