[allan5oh]

Originally Posted by mudpuddle

Yes exactly. The low compression high boost set up used on the engines built by pittsburgh power increase the efficiency of the combustion process. More horse power same or only slightly higher fuel use.

If the horsepower used is the same and your using the same or slightly higher amount of fuel, then either the efficiency has stayed the same or dropped slightly.

[allan5oh]

Originally Posted by mudpuddle

Solo, if you turn your engine up it would change the power curve slightly and if you optimized your set up for the new power curve you could see a slight difference in mileage. The changes would be very small though because you make such a small change.

I don't think so, besides if he never used the engine in the 475-550 HP range, the HP would be *EXACTLY* the same as his old 475 hp. There wouldn't be a lick of difference. If he used more then 475 hp, odds are he would be wasting HP by going up the hill faster, and fuel mileage would drop slightly.

Everything else below 475 hp behaves exactly the same. Same pressures, same injector width, same boost pressure, same restriction.

My point to allan though is that a small displacement low horsepower engine operating at near max power output will not be a great deal more fuel efficient than a larger engine working at a much lower percentage of its power potential.

That's assuming that the small engines efficiency drops so bad, you're now less efficient then the larger engine.

To get the 8+ mpg he claims Allan must be driving in a similar way and probably using a fairly low average speed (what is your average speed Allan).

60

Allan makes the case that a m11 will always get much better fuel mileage. I don't dispute that the m11 will kill the cat on flat land with 65,000 gross. My point is put the same two trucks in the rockies loaded to 79,000 and the mileage difference will be much closer.

Even fully loaded going through hills(ontario) I rarely get less then 7 mpg. Considering most 15 litre engines have a tough time getting 7 mpg even on flats, I doubt their fuel mileage will go up in the big hills.

To get the maximum efficiency from your m11 Allan rebuild the engine lower the compression increase the turbo size reset the fuel pump and injectors then regear the truck to match the new power curve and you would see a nice increase in average speeds (better climbing power) while keeping your mileage the same or even climbing a little. Efficiency with this new setup would be better because you will use lower fuel pressures to maintain a given road speed. Lower fuel pressures combined with your smaller displacement would the give you the fuel mileage advantage back over the larger displacement engine.

lower fuel pressure, you're talking about mechanical engines, not our current engines that have been out for the past 15 years. The m11 is already more efficient then most engines out there.

Split shifter. Bruce's customers at pittsburgh power get 900+ horsepower out of big cam cummins engines with egt readings in the 1100 to 1200 degree range. The large turbo and lower compression ratio keep the combustion temperatures well in control. Iron eagle ran one of these engines in the past and he could probably tell us from experience the temps he saw and the mpg he got.

And the MPG gain was from a more efficient breathing engine, not from simply having more horsepower. The low injection pressures, etc, is just an artifact. He probably tinkers around with bigger injectors too. So instead of injecting the fuel at higher pressure shorter, he injects it at a lower pressure longer.

I am in no way saying that a 15 litre engine will get better mileage than one of a much smaller displacement in all conditions as an average. What I am saying is the larger more powerful engine will dramatically close the gap when large amounts of power are required to maintain a given speed.

So you're saying that the large engine's efficiency at higher horsepower(say 400 HP) will improve, and a smaller engine will drop like a rock?

Like I said, 7+ mpg through hills. Show me any 15 litre engine that can touch that. You cannot.

[mudpuddle]

You might be seeing the words in the articles but your clearly not grasping what Bruce is saying. You seem to only equate efficiency with the absolute fuel mileage number. As I said I don't argue that that tiny engine you drive behind will get better fuel mileage. What you don't seem to grasp is that if you build the same engine to make much more torque and power you can get the same fuel mileage you currently enjoy while going a lot faster on the hills by changing the setup on your truck. Eight mpg is great at an average speed of 50 mph but its is simply fantastic at average 60mph. Bruce didn't say in the articles the drivers were going the same speed and getting the same mpg. He clearly said they are able to get the same mpg while able to go much faster in hills and when heavily loaded. As I said in a previous post flat ground with light loads you are absolutely correct But you have to spec the truck for the intended job. As Maniac said earlier no M11 is getting 8mpg in the areas we are running with the weights he and I run, but plenty of 550 cats are getting over six.

I no longer do the dedicated load I did last year I now am working in the I68, I77 area hauling over dimension with flats and I still manage 6.1 mpg I do not, however idle my truck. I went to all heavy and all hills and I only lost .2mpg. If you only ran hills and heavy would you only loose .2mpg, I doubt it.

[allan5oh]

Originally Posted by mudpuddle

You might be seeing the words in the articles but your clearly not grasping what Bruce is saying. You seem to only equate efficiency with the absolute fuel mileage number. As I said I don't argue that that tiny engine you drive behind will get better fuel mileage. What you don't seem to grasp is that if you build the same engine to make much more torque and power you can get the same fuel mileage you currently enjoy while going a lot faster on the hills by changing the setup on your truck.

Sure, if you defy physics. His articles talk about:

- reducing backpressure
- reducing restriction on the inlet side
- porting the head
- better flowing turbo
- equalizing fuel pressure in the head
- better injectors
- insulating the manifold

as well as what you're talking about. ALL of the above points increase efficiency while slightly increasing HP and torque. You can't equate "opening up an engine" with better efficiency. It just doesn't happen it's part of a PACKAGE.

Eight mpg is great at an average speed of 50 mph but its is simply fantastic at average 60mph. Bruce didn't say in the articles the drivers were going the same speed and getting the same mpg. He clearly said they are able to get the same mpg while able to go much faster in hills and when heavily loaded. As I said in a previous post flat ground with light loads you are absolutely correct But you have to spec the truck for the intended job. As Maniac said earlier no M11 is getting 8mpg in the areas we are running with the weights he and I run, but plenty of 550 cats are getting over six.

And they can do that with above efficiency helpers, NOT WITH THE INCREASED HORSEPOWER. If you simply took one of those engines he modifies, put in bigger injectors, and cranked out 50-70 hp, you would see a loss because the driver would USE(ie WASTE) that extra horsepower. The modifications go hand in hand. He even says that in his articles. Many times.

I no longer do the dedicated load I did last year I now am working in the I68, I77 area hauling over dimension with flats and I still manage 6.1 mpg I do not, however idle my truck. I went to all heavy and all hills and I only lost .2mpg. If you only ran hills and heavy would you only loose .2mpg, I doubt it.

That's fine, look at it this way, me fully loaded in the hills I'm doing better then you cruising along in the prairies. I don't care if I loose a little more in the hills, I'm still doing better all the time

Besides, the original conversation was about newer trucks, you're talking modifying a mechanical. That really has no bearing whatsoever on the conversation. Besides, even a stock electronic will get better mileage then a modified mechanical. I bet a lot of the modifications he does is to the injection timing, to make it as much as an electronic as he can(the timing maps).

I'll say this:

The average load on a truck is 200-250 HP. If you can reduce this load as much as possible (aero drag, better tires, going slower) then you obviously reduce the horsepower requirement.

HOWEVER:

Certain engines are simply more efficient at this 200-250 hp range then others. Yes a smaller engine will drop more MPG in the hills, but that's more due to the fact that it's getting better mileage, still get better fuel mileage. It will Look at the prius, it's mileage swings 5-8 mpg per tank. But you have to look at percentage. Plus, it's getting 50+ mpg.

Or look at it this way. I buy a truck that gets 4.0 mpg, and only drops to 3.9 mpg in the hills. Who cares, it only gets 4 mpg!

And finally, to sum it all up:

Efficiency gains are though better flow, better thermal efficiency, and friction losses. NOT from extra horsepower.

If you took one of his lovely engines and did all of the flow gains, the ceramic pistons, porting the head, insulated the turbo, but cut it back to 500 hp, it would get the same fuel mileage(or even better) then one modified for 700 hp. All the same mods, but different potential horsepower. Hell, even just put a throttle stop on it.

[Maniac]

Even fully loaded going through hills

Tel us what is "fully loaded" what type of trailer, weights and commodities, and what type of terrain you get 8 MPG in.

Also what speed do you drive at mostly, and what type of traffic, and also is any idling involved?

[mudpuddle]

His location in his avatar is Winnipeg I went to college in grand forks about 80 to 100 miles south in ND and I can tell you that area is flat, flat, flat for miles is all directions.

I takes about 270 hp to maintain 60 on flat ground with no wind. But I can tell you as you begin to go onto 5,6,7 % grades the required horsepower to maintain speed increases exponentially. Whether the engine is electronic or mechanical doesn't matter. The principals of operation do not change: Fuel pressure and injector timing still control the horsepower output of the engine. A properly set up mechanical engine will in fact get equal fuel economy for a given set up. The electronic engine simply gives the engine the ability to change fuel mapping to optimize the engine for more potential operating conditions.

As you stated earlier two engines producing exactly the same horse power at a given time are not getting equal mpg. As I said the smaller engine will get better mileage in most any operating conditions. However the larger engine will by comparison deal better with higher weights and steeper grades because of its much higher torque and better torque rise.
You're beginning to slow down below your target speed as soon as you come to a relatively small hill while my truck is maintaining its speed and my fuel mileage is only slightly worse. At a requirement of 400hp to maintainspeed you are slowing and cannot maintain While my engine is happily chugging along at 73% rated power.

I cannot agree more with Maniac, this is the real world and you must weigh mileage against time to deliver and the ability to increase revenue with more available trips. If it was only fuel mileage we would all be puttering around in trucks powered by Briggs and Stratton making five deliveries per year.

Now if you want to really get serious about efficiency lets drop the engines, transmissions, and drivelines and install a diesel generator in the engine compartment and use electric wheel motors and we can get to some true fuel efficiency.

[allan5oh]

Originally Posted by Maniac

Tel us what is "fully loaded" what type of trailer, weights and commodities, and what type of terrain you get 8 MPG in.

Also what speed do you drive at mostly, and what type of traffic, and also is any idling involved?

I usually get 7.5-8 going from Toronto to Winnipeg.

I'll get 8-8.5 on the flat prairies, even right at 80,000 lbs.

I did 2 weeks of Winnipeg to Minneapolis, 5 trips, and never used 120 gallons on the return trip. One was as low as 105 gallons. This includes either a stop in steinbach, or roseau per round trip. Light loads doing that.

[sodbuster]

1 imperial (british) gallon = 1.20095 us gallon. maybe that is way your getting great mileage. :lol:

[mudpuddle]

Originally Posted by sodbuster

1 imperial (british) gallon = 1.20095 us gallon. maybe that is way your getting great mileage. :lol:

That could explain a lot of the difference :lol: :lol: :shock:

[allan5oh]

Originally Posted by mudpuddle

His location in his avatar is Winnipeg I went to college in grand forks about 80 to 100 miles south in ND and I can tell you that area is flat, flat, flat for miles is all directions.

Yup, flat

I takes about 270 hp to maintain 60 on flat ground with no wind.

270 hp? at what weight? The reason fully loaded trailers cause you to have less fuel mileage is that they require MORE HORSEPOWER. Even a non-aero truck will take a good 30-50 extra hp to push through the air.

But I can tell you as you begin to go onto 5,6,7 % grades the required horsepower to maintain speed increases exponentially. Whether the engine is electronic or mechanical doesn't matter. The principals of operation do not change: Fuel pressure and injector timing still control the horsepower output of the engine.

Yup, I agree with you there to a point. You can increase horsepower with the same amount of fuel by lowering BSFC.

A properly set up mechanical engine will in fact get equal fuel economy for a given set up. The electronic engine simply gives the engine the ability to change fuel mapping to optimize the engine for more potential operating conditions.

And that's why electronic engines get better fuel mileage. They have more precise control. The injectors are also more complex, including pilot injection.

As you stated earlier two engines producing exactly the same horse power at a given time are not getting equal mpg.

yes

As I said the smaller engine will get better mileage in most any operating conditions. However the larger engine will by comparison deal better with higher weights and steeper grades because of its much higher torque and better torque rise.

And what does torque require? Fuel. Torque is linear to fuel injected per injection cycle. Larger engines have more torque because they inject more fuel. Horsepower is linear to amount of fuel injected over time(rpms).

You're beginning to slow down below your target speed as soon as you come to a relatively small hill while my truck is maintaining its speed and my fuel mileage is only slightly worse. At a requirement of 400hp to maintainspeed you are slowing and cannot maintain While my engine is happily chugging along at 73% rated power.

Again, PERCENTAGE OF HORSEPOWER MEANS DICK SHIT REGARDING EFFICIENCY. I don't think you're grabbing on here. The only people that I know of that say this are truck drivers. Go ask any cummins/caterpillar engineer that. I think you'll get a funny look.

If we're both making 400 hp, the only thing that matters is who is injecting less fuel to make that 400 hp. The fact that you have potentially more horsepower is irrelevant. Especially since you're not using it at that time.

I cannot agree more with Maniac, this is the real world and you must weigh mileage against time to deliver and the ability to increase revenue with more available trips.

I agree. It all plays into being a businessman, not a truck driver. If it makes financial sense to have "big cat power" go for it. If it makes sense to go 70, or even 75, then go for it. I'm never going to disagree with someone that has done the math(real BUSINESS math not "truck driver math") and figures their operation is better with these things.

Now if you want to really get serious about efficiency lets drop the engines, transmissions, and drivelines and install a diesel generator in the engine compartment and use electric wheel motors and we can get to some true fuel efficiency.

Or we could drop in cat's or cummin's prototype engine that recaptures exhaust heat, uses it to heat refrigerant that spins a generator. 50% efficient. Ours aren't 40%.