engine efficiency

[allan5oh]

This is a continuation between me and Mr. mudpuddle from a different thread:

I'm stating that % of HP used does not affect fuel economy, he's saying it does.

Anyways, onto my argument:

Take to of the same engine(say a c15) one 475 hp and one 600 hp, and have them both cruising along a nice hill at 50 mph both using 475 hp.

They'll both get the exact same fuel mileage. The fact that the second has 600 potential hp is irrelevant.

They're injecting the same amount of fuel, the same amount of time, and BSFC is exactly the same for both.

[mudpuddle]

Again i will ask you to read the articles. The 600 hp engine can be geared differently due to increased hp. The fuel pressure required to maintain 1300rpm in a six hundred hp engine (to produce 475hp) will be considerably lower than the fuel pressure required to turn the 2100 rpm required to produce 475hp from the 475hp engine. BSFC is DIRECTLY related to volumetric efficiency. Lower compression ratios and higher boost pressures (the setup for high HP engines) produce better BSFC than high compression and lower boost (the setup for lower hp).

I don't want to get into the same pissing contest as the last thread on this subject, I do think you could open your mind a little and do some more investigating on this. Gearing, setup, tires, driving style all go into fuel mileage. Just stating as fact that any driver in any conditions will get two mpg better with a m11 than with a 15 litre cat is wrong.

Load a m11 powered truck with a 79,000 lb load and load a 550 cat with the same load and head west on I 80 from coast to coast and compare the mileage figures you will be surprised at the similarity in the average mileage.

[allan5oh]

Again i will ask you to read the articles. The 600 hp engine can be geared differently due to increased hp.

Sure, but is that a good thing? I've driven a few different trucks on the same exact run, and it was always the 11 litre engines spinning higher that got the best fuel mileage. All driven exactly the same.

The fuel pressure required to maintain 1300rpm in a six hundred hp engine (to produce 475hp) will be considerably lower than the fuel pressure required to turn the 2100 rpm required to produce 475hp from the 475hp engine. BSFC is DIRECTLY related to volumetric efficiency.

only if BSFC has gone up at 2100 rpms. It probably has, but I'll tell you right now an m11 is more efficient at 2000 rpms then a cat is at 1300 rpms. If they're both making the same HP at their respective rpms, which engine is the winner?

Yes it's true, increasing volumetric efficiency lowers BSFC, but that doesn't take into account many factors. You can have two of the same engines, exactly the same volumetric efficiency, but one is more thermally efficient.

I also know a guy who states that acert c15's tend to do the worst on his dyno when you consider BSFC. As far as I'm concerned, dyno testing BSFC is the only way to go.

Lower compression ratios and higher boost pressures (the setup for high HP engines) produce better BSFC than high compression and lower boost (the setup for lower hp).

OK, I'm definitely willing to listen to that. I read a few of his articles, but I don't see where he said that. I'd love to have cold hard #'s as well. The problem is he might have changed the exhaust, the turbo, etc.. So it's not a fair comparison.

Also, I'd like to compare stock engines. Modified engines flow better at lower HP then stock engines, so of course they're going to be more efficient. It is *NOT* due to the extra available HP.

I don't want to get into the same pissing contest as the last thread on this subject, I do think you could open your mind a little and do some more investigating on this.

My mind is more then open, trust me. I don't consider this a pissing contest at all! Maybe I'm coming across the wrong way...

Gearing, setup, tires, driving style all go into fuel mileage.

Yes, but they can all be equated to "required horsepower" and "required fuel to make said horsepower". Of course I'm talking about cruising down the highway at a steady state. Since most of us cruise along the interstate 90%+ of the time it's a good way to look at things.

It's a very simple equation:

Required HP(steady state, or average) * BSFC = amount of fuel you burn in an hour

If you're using 250 hp, and your engine uses .35 gallons of fuel per horsepower-hour, you're burning 87 lbs of fuel an hour. 87 / 7 = 12.5 gallons in an hour. 70 mph / 12.5 gallons = 5.6 mpg.

everything relates to BSFC!

Just stating as fact that any driver in any conditions will get two mpg better with a m11 than with a 15 litre cat is wrong.

I was *NOT* stating that as fact, but rather using it as an example of how important it is to get engine choices RIGHT. It could cost you $10,000+ a year!

Load a m11 powered truck with a 79,000 lb load and load a 550 cat with the same load and head west on I 80 from coast to coast and compare the mileage figures you will be surprised at the similarity in the average mileage.

I really doubt it, to be honest.

BTW, so far this month I've averaged a little above 8.5 MPG. Calculated at the tank, of course.

[allan5oh]

Turbo Boots: What are they and why do they work. Why does keeping your exhaust system insulated allow for a cooler running engine? We all should know that restriction in the exhaust system will rob the engine of performance but why do we want to keep the turbine housing and exhaust pipes insulated? After we realized the benefits of insulating the turbine housing we were informed that we should wrap the first three feet of exhaust pipe from the turbo. Well, that seemed simple enough to us and we’ll always try anything that will enhance performance without sacrificing engine life or fuel mileage. So we ordered a box of header wrap and on the end of the box was a paragraph titled, "How does it work"? One thing that is commonly overlooked by most racers is the matter of heat retention in the exhaust pipes. We have to remember that as soon as the combusted gasses leave the combustion chamber they start to cool down. As they cool they lose velocity and the scavenging effect is reduced. If the temperature of the gasses inside the pipes is kept as high as possible the net effect will be greater velocity, greater pressure drop in the system and higher efficiency. Very recently we have experimented with heat retention materials to improve the efficiency of exhaust systems. These shields retain heat in the exhaust pipes so the exhaust velocity remains very high. This will improve the scavenging effect. This is from Smokey Yunick’s Chevy engine guide in Hot Rod magazine’s high performance series. For those of you who were hot rodders from the 60’s and 70’s you must recognize the name Smokey Yunick.

I found that insulating the turbo itself didn't help, but insulating the manifold helped tremendously.

[Kranky]

I found that insulating the turbo itself didn't help, but insulating the manifold helped tremendously.

Did this lead to higher indicated EGT on the pyrometer?

[solo379]

Again i will ask you to read the articles. The 600 hp engine can be geared differently due to increased hp. The fuel pressure required to maintain 1300rpm in a six hundred hp engine (to produce 475hp) will be considerably lower than the fuel pressure required to turn the 2100 rpm required to produce 475hp from the 475hp engine. BSFC is DIRECTLY related to volumetric efficiency. Lower compression ratios and higher boost pressures (the setup for high HP engines) produce better BSFC than high compression and lower boost (the setup for lower hp).

Correct me if I'm wrong!
So, if I'll turn up my 475 C15 to 550, running the same way i do now, considering the torque will stay the same 1850lb, I'll get a better mileage?

[sodbuster]

I have to put my 2 cents in,

1 gallon of diesel = 147,000 btu’s
it takes 2544.044 btu’s to make 1HP for 1 hour.
That is the minimum of btu’s to make that 1hp for 1 hour if it take more btu’s to get that 1hp to the flyweel then the efficiency of the engine is now the difference in fuel vs horsepower.

Example a 8.3 liter engine modified to produce 450Hp vs a 15 liter engine that produces 450 HP They both have to burn the minimum fuel to get to that horsepower. But the combustion process and it efficiency determines how much actual fuel will each engine really need to produce that 450Hp. Now if both engines are producing 200 HP @ the flywheel, here again there is a minimum of btu’s of energy required to produce this 200 HP over a given amount of time. How well each engine and convert that fuel into work is the difference. I understand what both of your are saying. Allan is saying it takes x amount of fuel to make x amount of horsepower which is right. Mud puddle is say that in the process of creating that horsepower other factors come into play, which I agree.

[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.
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.

Allan can answer to his driving style. Solo you have said in other threads you get around 6.7mpg with your cat. I assume to do this you run moderate speeds, don't accelerate up to speed quickly, and coast down hills and to stops etc. 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).

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.

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.

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.

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.

[mudpuddle]

I have to put my 2 cents in,

1 gallon of diesel = 147,000 btu’s
it takes 2544.044 btu’s to make 1HP for 1 hour.
That is the minimum of btu’s to make that 1hp for 1 hour if it take more btu’s to get that 1hp to the flyweel then the efficiency of the engine is now the difference in fuel vs horsepower.

Example a 8.3 liter engine modified to produce 450Hp vs a 15 liter engine that produces 450 HP They both have to burn the minimum fuel to get to that horsepower. But the combustion process and it efficiency determines how much actual fuel will each engine really need to produce that 450Hp. Now if both engines are producing 200 HP @ the flywheel, here again there is a minimum of btu’s of energy required to produce this 200 HP over a given amount of time. How well each engine and convert that fuel into work is the difference. I understand what both of your are saying. Allan is saying it takes x amount of fuel to make x amount of horsepower which is right. Mud puddle is say that in the process of creating that horsepower other factors come into play, which I agree.

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.

[allan5oh]

I found that insulating the turbo itself didn't help, but insulating the manifold helped tremendously.

Did this lead to higher indicated EGT on the pyrometer?

Yes, indicating that what I did worked.

I noticed it spooled up a touch quicker. I didn't notice a huge increase of boost at the top end, possibly indicating my turbo is a bit undersized.

I also noticed that it makes more boost at lower horsepower levels.

For example, cruising at 60 mph at 7 mpg(50% throttle) it used to make 10-11 lbs of boost. Now at 8 mpg I make the same boost.

It's also less affected by humidity and heat.

[allan5oh]

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]

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]

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]

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?

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.

[mudpuddle]

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

That could explain a lot of the difference :shock:

[allan5oh]

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 **** 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%.