I must be getting older - starting to want the stuff I saw but couldn't have as a kid/young man

[ZooMad75]

I agree and I went from a gmt400 1500 with a 5.7 getting 10 mpg to a gmt400 2500 with the 7.4 getting 12 mpg.
I am hoping my other square with the 2003 8.1 I am putting in with an nv4500, gets more like 18-20 mpg based on what the guys here are getting with a little tweaking of the ecm.

Not to derail the detail but…I like your style but you might be a tad optimistic on 20 mpg with an 8.1. Best I’ve achieved is 16mpg on a couple of trips. Granted that’s with a heavy pig at 7400ish pounds and the aerodynamic equivalent of a drive in movie screen. I think there’s some room for improvement but not on my truck in its current form.

Get the weight down is critical. Not running a camper would greatly improve the aero for sure. Gearing and tire size will net some results too. With the nv4500, 4.10 gears and 315/75r16 tires at roughly 34.6 diameter nets just under 2100rpm at 70mph. The 4.10’s give up a little grunt down low but the 8.1 makes it so you wouldn’t notice it. Not sure of your end plans for the truck but depending on on what they are target for 2000-2100 rpm at your ideal highway cruising speed. That keeps the engine in the meat of the torque curve and limits most needs to downshift to pick up speed to pass or climb grades in fifth.

I think 18ish mpg is attainable with an 8.1 it’s going to be a challenge that’s not all in the tune. Back in my workhorse days we had a dealer in California selling “tuned” pcms for 8.1 equipped rv’s. Made some bold promises like they all do , more power and better fuel economy. It’s been a while but I want to say they claimed up to 10% better fuel economy on th tune alone. On a 22k pound gvw class a rv getting 6-8 mpg that’s a bold clam.

Those of us at the company had our suspicions what they did to achieve this by leaning out the overall fuel table. Our suspicion was validated when a rv with a bright red pcm with the shops name on it came into another dealer with a blown 8.1. Teardown found multiple pistons with holes in it. A pretty clear case of going too lean and elevating combustion temps to the point of melting pistons. Warranty claim denied obviously and the tuner shop who also happened to be a servicing workhorse dealer reached out to bitch on behalf of the customer that we denied th repair. It was a pretty short conversation with a reminder that his tune was not factory nor validated to the level GM normally did to avoid this. Moral of the story being don’t lean that tune out for fuel economy so far that it will burn up under a moderate load.

Tech derail complete, you can go back to the regularly scheduled wedding planning content.

 

[imiceman44]

Not to derail the detail but…I like your style but you might be a tad optimistic on 20 mpg with an 8.1. Best I’ve achieved is 16mpg on a couple of trips. Granted that’s with a heavy pig at 7400ish pounds and the aerodynamic equivalent of a drive in movie screen. I think there’s some room for improvement but not on my truck in its current form.

Get the weight down is critical. Not running a camper would greatly improve the aero for sure. Gearing and tire size will net some results too. With the nv4500, 4.10 gears and 315/75r16 tires at roughly 34.6 diameter nets just under 2100rpm at 70mph. The 4.10’s give up a little grunt down low but the 8.1 makes it so you wouldn’t notice it. Not sure of your end plans for the truck but depending on on what they are target for 2000-2100 rpm at your ideal highway cruising speed. That keeps the engine in the meat of the torque curve and limits most needs to downshift to pick up speed to pass or climb grades in fifth.

I think 18ish mpg is attainable with an 8.1 it’s going to be a challenge that’s not all in the tune. Back in my workhorse days we had a dealer in California selling “tuned” pcms for 8.1 equipped rv’s. Made some bold promises like they all do , more power and better fuel economy. It’s been a while but I want to say they claimed up to 10% better fuel economy on th tune alone. On a 22k pound gvw class a rv getting 6-8 mpg that’s a bold clam.

Those of us at the company had our suspicions what they did to achieve this by leaning out the overall fuel table. Our suspicion was validated when a rv with a bright red pcm with the shops name on it came into another dealer with a blown 8.1. Teardown found multiple pistons with holes in it. A pretty clear case of going too lean and elevating combustion temps to the point of melting pistons. Warranty claim denied obviously and the tuner shop who also happened to be a servicing workhorse dealer reached out to bitch on behalf of the customer that we denied th repair. It was a pretty short conversation with a reminder that his tune was not factory nor validated to the level GM normally did to avoid this. Moral of the story being don’t lean that tune out for fuel economy so far that it will burn up under a moderate load.

Tech derail complete, you can go back to the regularly scheduled wedding planning content.

I would be happy with 18mpg.
I seem to have heard claims from Larry that 20 was attainable by driving low rpm ,counting on the torque down low.
And yes my suburban will be pretty smooth, no wind resistance and running narrow tires slightly over inflated to reduce rolling resistance. I might be running with the 4.10 axle in it now with 255/85/17 which measures 34.5"×10" or put my 4.56 axle with a 37x12.5

 

[ZooMad75]

I would be happy with 18mpg.
I seem to have heard claims from Larry that 20 was attainable by driving low rpm ,counting on the torque down low.
And yes my suburban will be pretty smooth, no wind resistance and running narrow tires slightly over inflated to reduce rolling resistance. I might be running with the 4.10 axle in it now with 255/85/17 which measures 34.5"×10" or put my 4.56 axle with a 37x12.5

I know Larry and I have bench raced the idea of fuel mileage with an 8.1 may times. 20 mpg is a perfect world scenario, optimum everything with it going downhill with a tailwind. Keep in mind Larry’s stone stock 2001 2500hd 8.1/6-speed could pull 13’s empty on the highway.

The two times I’ve pulled 16 in mine were on the same stretch of I-70 between Denver and Grand junction. I know it sounds counterintuitive driving at elevation in the mountains and all. But I think the reason behind both times comes down to me not hauling ass through there. I typically run between 65-70mph through there given the twisty nature of the road and driving 7k pound house on wheels.

I know the sweet spot is 65mph. Going north of 75 will drop the mileage by multiple points. Which is more due to aero drag than a hungry 8.1.

 

[76zimmer]

But I hear of rigs pulling 10k and getting 20+.
And then there are those who tell the truth.

A friend, myself and two others hauled 8500lbs of bikes and trailer from Mi. To Fl. with an 8.1 and 4L85 and got 9.5 avg. in tow/haul mode.

 

[ZooMad75]

But I hear of rigs pulling 10k and getting 20+.
And then there are those who tell the truth.

A friend, myself and two others hauled 8500lbs of bikes and trailer from Mi. To Fl. with an 8.1 and 4L85 and got 9.5 avg. in tow/haul mode.

I loved RV people trying to tell me they got anything north of 10mpg in a 22,000 pound gvw motorhome. I knew one of two things were at play. One, they sucked at math. Or two, they were liars. What was more common on those was 6-8mpg. A p-chassis 16k gvw unit might tickle 10mpg with a stiff tailwind but single digit values were the norm.

What really cracked me up was the boomers that bought the Banks long tube headers and exhaust system for the rv’s. They were gorgeous stainless headers with a racy muffler that was like 4” inlet/outlet. Banks promised a crazy increase in mileage that nobody ever got. Mainly because the owners thought they were driving a LS6 big block chevelle as the sounded awesome on every freeway on ramp. One guy admitted it that the exhaust sounded too cool not to put your foot in it.

 

[imiceman44]

I know Larry and I have bench raced the idea of fuel mileage with an 8.1 may times. 20 mpg is a perfect world scenario, optimum everything with it going downhill with a tailwind. Keep in mind Larry’s stone stock 2001 2500hd 8.1/6-speed could pull 13’s empty on the highway.

The two times I’ve pulled 16 in mine were on the same stretch of I-70 between Denver and Grand junction. I know it sounds counterintuitive driving at elevation in the mountains and all. But I think the reason behind both times comes down to me not hauling ass through there. I typically run between 65-70mph through there given the twisty nature of the road and driving 7k pound house on wheels.

I know the sweet spot is 65mph. Going north of 75 will drop the mileage by multiple points. Which is more due to aero drag than a hungry 8.1.

I already know that from my years of playing with different cars, different driving styles.
I will not always drive like a grandpa, although I am old enough to be one, but I know I can get better than the smaller engines that rev too high to get the power, and when I need more power I can push the go pedal.
I had a k5 with a Perkins t6.354 and sm465 with 35" tires and 3.08 gears.
I was getting average 20mpg around town, 30 on highway.
My 32 gallons tank would last me a whole weekend on the trails then come out with half a tank.
When I want to conserve fuel I will do everything to get the best I can get.
I am not saying I will get a certain number but I will squeeze whatever can be squeezed.
Unfortunately lately with my L29 20% of the time I am frustrated and need to vent, so I take it out on my gas tank and my wallet, but it puts a smile on my face

 

[tarussell]

I already know that from my years of playing with different cars, different driving styles.
I will not always drive like a grandpa, although I am old enough to be one, but I know I can get better than the smaller engines that rev too high to get the power, and when I need more power I can push the go pedal.
I had a k5 with a Perkins t6.354 and sm465 with 35" tires and 3.08 gears.
I was getting average 20mpg around town, 30 on highway.
My 32 gallons tank would last me a whole weekend on the trails then come out with half a tank.
When I want to conserve fuel I will do everything to get the best I can get.
I am not saying I will get a certain number but I will squeeze whatever can be squeezed.
Unfortunately lately with my L29 20% of the time I am frustrated and need to vent, so I take it out on my gas tank and my wallet, but it puts a smile on my face

Time for another derailment of the thread - what adapter and bellhousing did ya use for the Perkins to 465 marriage ? Got any pics ? Sounds like a cool combo.

 

[imiceman44]

Time for another derailment of the thread - what adapter and bellhousing did ya use for the Perkins to 465 marriage ? Got any pics ? Sounds like a cool combo.

I will get pictures but I didn't put it together, it was done at a shop here in Sacramento.
But my research showed that this engine was available in busses with a sm465 behind it.
It's a little funky, open on the bottom to drop the flywheel and get to the bolts inside to the engine.
Never had to remove that but I did have to change the clutch which also h ad to be dropped from the bottom.
It's a cast iron bell IIRC and has mounts on the bottom ends like the old cast iron chevy bell.
I know we talked a little about it 12 years ago when I was discussing with you the possibility of switching to a bell from a c60.
I should hopefully have time to dig it out tomorrow and get pictures

 

[tarussell]

I will get pictures but I didn't put it together, it was done at a shop here in Sacramento.
But my research showed that this engine was available in busses with a sm465 behind it.
It's a little funky, open on the bottom to drop the flywheel and get to the bolts inside to the engine.
Never had to remove that but I did have to change the clutch which also h ad to be dropped from the bottom.
It's a cast iron bell IIRC and has mounts on the bottom ends like the old cast iron chevy bell.
I know we talked a little about it 12 years ago when I was discussing with you the possibility of switching to a bell from a c60.
I should hopefully have time to dig it out tomorrow and get pictures

Iceman - when you changed the clutch was the input shaft the larger, and longer, 1-1/2” 10-spline version ?

Just curious on the Perkins stuff since I studied several GM H.D. 465 and non-H.D. 465 to 4BT/6BT Cummins stuff and figuring this stuff out has sort of become a hobby.

Pics would be great !

Here’s a pic of both inputs for the 465’s - 1-1/2” & 1-1/8” both 10-splined.

 

[imiceman44]

Iceman - when you changed the clutch was the input shaft the larger, and longer, 1-1/2” 10-spline version ?

Just curious on the Perkins stuff since I studied several GM H.D. 465 and non-H.D. 465 to 4BT/6BT Cummins stuff and figuring this stuff out has sort of become a hobby.

Pics would be great !

Here’s a pic of both inputs for the 465’s - 1-1/2” & 1-1/8” both 10-splined.

View attachment 521928

No it's the regular 1 ⅛" shaft.
I did have the transmission from the c60 with the 1 ½" shaft and I sold it with the condition I get the input shaft back, I have the snout but the guy ghosted me after I sold it.
I am still looking for one though

 

[tarussell]

No it's the regular 1 ⅛" shaft.
I did have the transmission from the c60 with the 1 ½" shaft and I sold it with the condition I get the input shaft back, I have the snout but the guy ghosted me after I sold it.
I am still looking for one though

Don’t fret too much over try’n to find a medium-duty 465 because the aftermarket has the 1-1/2” shaft.

 

[AJMBLAZER]

Anybody remember these American Racing wheels?

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…why am I like this?

 

[shady]

I remember those. For some reason my memory went right to a square Monte Carlo or Malibu I must have seen once. The one that flashed in my memory was dark, like black or brown.
And I can't think of anyone I ever knew that had anything like it or those wheels lol.
Whoever's it was, it must have made an impression

 

[AJMBLAZER]

I thought they were the cooooolest when I was first into cars. Mid 90’s. However by the time I was buying stuff 5 or so years later they were out of production.

Hard to find now. This set popped up in the next town south of where I grew up. Trying to work out a deal as my folks will be in the area soon.

 

[ktmoutfront]

We called them Dado's. Kind of looked like dado blades for a table saw.

 

[imiceman44]

Anybody remember these American Racing wheels?

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View attachment 522455
…why am I like this?

I scrapped a set a couple of years ago, even at that price no one was biting

 

[AJMBLAZER]

They got uncool.

 

[nvrenuf]

In the early 90’s I worked for Western Auto, I sold a shitton of those wheels.

 

[shady]

I scrapped a full set of stock steel gmt400 wheels w/rings last year. And a set of stock 16" steel square body wheels.
And I want either set back now.
You think I can find any though
A new set is about $1600

 

[obijuank5]

I scrapped a full set of stock steel gmt400 wheels w/rings last year. And a set of stock 16" steel square body wheels.
And I want either set back now.
You think I can find any though
A new set is about $1600

Not sure what you’re looking at, but these wheels will take a gm hubcap and 285s like a champ.

Dorman 939-198 Dorman OE Replacement Wheels | Summit Racing

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