All Big Six MPG thread

[InlineDave87]

Hey guys,
So ive noticed some members care just as much about MPG as Performance. I thought i would start a thread where we can share ideas outside of the norm of what will increase fuel economy like weight reduction and aerodynamics.
Like one that i have is to maximizes VE with stock cam ie, better flowing head, making it easier for the truck to get up to speed and maintain speed. I know my truck really grunts when i try to increase my speed but my ecoboost doesnt careif i want to change from 55 to 65 mph and there is hardly a change in RPM. I consider this idea out of the norm cause of the equation, more air+ more fuel = more power. Meaning if im increasing the power of my truck then im using more fuel. Ill get to test this eventually but for now im on daddy day care duty with my daughter home from school for the summer and my wife working.

 

[aussie7mains]

I'm in. Once you get past vehicle rated factors like aerodynamics axle ratios etc etc, one of the biggest determinates of fuel economy is the thermal efficiency of the combustion process. It has been demonstrated that high efficiency is the pent roof chamber with central spark plug. So having said that straight away we are dealing with what is, by any measure, a rubbish chamber of nearly all pushrod engines. The wedge or bathtub chamber usually will not work with really lean mixtures, like lambda 1.5 or down near there. So all you can do is optimise what we have. An alloy head does help, you can run more CR without problems compared to iron. My take on fuel economy is, as much compression as it will stand, which is usually whatever the factory used, as free an exhaust and intake as you can, this reduces pumping losses, as much advance as you can. as hot as you can safely get it. Other parasitic losses need to be minimised, lowest oil viscoscity as you dare, electric water pump and fan etc.
As to axle ratios etc, extra low rpm is NOT neccesarily the best, operating at peak torque is usually the best place in the scale. No overdrive, thats is less efficient than a direct drive, no auto trans, they are very wasteful, even with a lock up convertor, and heavy. Tyres inflated to maximum pressure etc. The driving style is crucial to maximising fuel economy. Anyway, my tow bobs worth!

 

[63 Sprint]

Probably the simplest and cheapest way to save fuel while driving on highway at speeds above 55 mph is to slow down. The 1989 F150 body style is streamlined like a brick and the front end is pushing lots of air.

This was just proven this past weekend.
Drove 210 miles to pick up another engine and I pushed the truck at 70 to 75 mph pretty much the whole way. The truck was almost empty getting there.

One the way back with a complete engine in the back of the truck. We filled up at a gas station about 1/2 mile away, and drove back home the same route. I kept the speed near 60 mph. When I got home. There was close to a 1/4 of a tank of fuel left over. That was a huge improvement.

 

[THE FRENCHTOWN FLYER]

... one of the biggest determinates of fuel economy is the thermal efficiency of the combustion process.

alloy head does help, you can run more CR without problems compared to iron...

An iron head is better for thermal efficiency, since there is less heat-rejection-to-coolant. To compensate for the poorer thermal efficiency it is necessary to increase the compression ratio when using an aluminum head in place of an iron head. Increasing the burn rate with the use of a fast burn chamber on an iron head is a viable option over switching to aluminum. It also helps reduce detonation tendencies.
Of course, the weight savings of an aluminum head is worth something, keeping in mind that for every pound of weight saved on an engine component you can save an additional half pound on the chassis design.

 

[Blairsville Ed]

This should be a great thread and I’m looking forward to all the input!
The oem had to design our vehicles to survive a large variety of driving conditions. We can customize and modify to more precisely fit our particular driving conditions which can maximize mpgs. Light loads and flat terrain vehicles could probably get by with a smaller carb and less rpm.
Now that I have a truck with a 300 and a 240, it seems that the 300 has no problem pulling my pontoon up a launch while the 240 needs more carb opening. So which is more efficient pulling a load.
Ive read that you need a 195 thermostat for better mpg but a 195 motor will detonate more easily than a 160 degree. Are the combustion temps the the important issue or the overall block temp?
Is a smaller carb which needs a larger throttle opening at cruise more efficient?
Is there an advantage to less lifter preload?
What‘s the best timing curve for max mpg?
Spark gap?
Air intake temperature?

 

[InlineDave87]

Ive read that you need a 195 thermostat for better mpg but a 195 motor will detonate more easily than a 160 degree. Are the combustion temps the the important issue or the overall block temp?
Is a smaller carb which needs a larger throttle opening at cruise more efficient?
Is there an advantage to less lifter preload?
What‘s the best timing curve for max mpg?
Spark gap?
Air intake temperature?

Yea, i watch richard holdner and the guys from engine masters alot, or use to when i had the subscription. Hotter temp at 195 is better for fuel economy as a hotter chamber will make better torque from cylinder pressure.
Dave and the steves proved air intake temp is less important as fuel temp.
As far as timing and detonation goes. From what i watched when an engine does this its either cause it needs more fuel or the more likely, less timing. Cylinder pressure is too high causing a hot spot on the head, less timing will take that heat out. This is also why aluminum heads are better for high performance cause they take higher compression and not detonate as easy.
Another idea ive had is trying to add fuel vapors to the intake to help the engine make a more complete burn. Ive seen guys make like a percolator tank to make their car run on “fumes” (on youtube) but run into issues once at high way speeds. And one guy with a dodge 1500 318 claimed he got 32 mpg from using both fumes and efi on his truck claiming he needed less throttle to run down the high way.

 

[63 Sprint]

Edited (removed unnecessary content)

Sometimes it’s not only about fuel consumption. It’s about using fuel that is much cheaper to buy.

I’m feeling the pinch having to buy 93 octane fuel for my truck. This is why I’m working on another project. At time’s getting 18.4+ mpg is not all cracked up to be because of the fuel cost. It seams that it would be better to have a slightly less efficient engine that is able to use 89 octane fuel. The cost of cheaper fuel could save the owner much more dollars in the long run even if the vehicle gets 2 less mpg.

 

[Frank]

Something to always keep in mind concerning speed and fuel consumption: Inertia is calculated @ I = ((1/2 mass)X Velocity) squared. Everyone knows driving slower saves gas, the reason has mostly to do with this law of inertia. The smaller old cars aren't too bad aerodynamically, but these pick ups are. When I was trucking it was calculated that 78% of the fuel consumed at highway speed was to move the air in a semi.
At low speeds the squaring of the speed (velocity) is not too pronounced, but as speeds increase, the work required to A) get the vehicle going faster, and B) push the air out of the way- increases exponentially. Doubling speed quadruples these work loads.
Thus, the air pushing against the vehicle is 4x as much from 25mph to 50 mph, 30mph to 60mph, etc. The fuel required to make the mass speed up is also 4x as much. (And stopping distance is 4x as much.) Driving at 71 mph, the air resistance is twice that of 50 mph.
In 63Sprint's road trip example above, driving 75 vs 60 = 56% more wind resistance against his brick-nose pickup.

 

[sixtseventwo4d]

Outside of driving habits; one of the more taken for granted is the ignition system. Even with premium parts little errors cost; more and more the new is faulty, either in design or function.

 

[pmuller9]

If you want to build a 300 six dedicated for MPG then you need to look at piston rings
The piston rings are responsible for the majority of your engine friction.
In one test where the engine was run at 2800 rpm, there was as much as 20 lb-ft of torque and 15 hp difference between standard 1/16" 3/16" ring set and the 0.7mm and a 2.0mm gas-ported metric ring set.
There was also a 15 degree difference in water temp and 20 degrees difference in oil temp.

Piston Rings and Engine Heat: Do You Really Need a Bigger Radiator?

How much can the profile of your piston rings affect the amount of heat your engine generates? What we found might surprise you.

www.motortrend.com

The 300 six uses a 5/64 3/16" ring pack so the improvement would be even greater.
There is also the benefit of greater life in cylinder and ring wear with the gas-ported metric ring set.

If you consider that it may take only 50 hp or less to move your vehicle down the highway at a certain speed, then the difference in power gained between piston ring types would be a significant improvement in fuel mileage.

 

[pmuller9]

The other consideration is the radiator fan.
There are plenty of online test showing the power needed to turn the various types of water pump mounted mechanical fans at different rpms.
Having control of an electric fan so that it only operates when needed is far more efficient than turning a mechanical fan constantly.

 

[pmuller9]

As we all know, the EFI head is more efficient than the 240/300 carburetor heads.
Polishing the combustion chamber surfaces and radiusing all sharp edges around the chamber will increase the margin for detonation.
A zero deck height piston will maximize quench which will increase the detonation margin again.
If you want to go the extra mile you can have the piston tops coated with a heat barrier.

 

[InlineDave87]

If you want to build a 300 six dedicated for MPG then you need to look at piston rings
The piston rings are responsible for the majority of your engine friction.
In one test where the engine was run at 2800 rpm, there was as much as 20 lb-ft of torque and 15 hp difference between standard 1/16" 3/16" ring pack and the 0.7mm rings and a 2.0mm ring set.
There was also a 15 degree difference in water temp and 20 degrees difference in oil temp.

Piston Rings and Engine Heat: Do You Really Need a Bigger Radiator?

How much can the profile of your piston rings affect the amount of heat your engine generates? What we found might surprise you.

www.motortrend.com

The 300 six uses a 5/64 3/16" ring pack so the improvement would be even greater.
There is also the benefit of greater life in cylinder and ring wear with the gas-ported metric ring set.

If you consider that it may take only 50 hp or less to move your vehicle down the highway at a certain speed, then the difference in power gained between piston ring types would be a significant improvement in fuel mileage.

That was a good read. It also goes along with reducing parasitic loss. Roller lifters/rockers, electric fan, a/c, water pump, even swaping to a manual steering column and adding electric power assist. This might be the reason we can use thinner oils these days cause friction is reduced in these engines. But to get these piston rings for a 300 we may have to go to a custom made piston for proper clearances on the rings so they are not slapping up and down in the ring groves if you just swap to a thinner ring.

 

[pmuller9]

But to get these piston rings for a 300 we may have to go to a custom made piston for proper clearances on the rings so they are not slapping up and down in the ring groves if you just swap to a thinner ring.

Yes, a custom piston would be required.
A custom piston would also allow reduced piston weight and a longer connecting rod for reduced side wall pressure.

 

[Jesse73]

The other consideration is the radiator fan.
There are plenty of online test showing the power needed to turn the various types of water pump mounted mechanical fans at different rpms.
Having control of an electric fan so that it only operates when needed is far more efficient than turning a mechanical fan constantly.

Going along with this, a light duty clutch fan on my truck was worth about 1.5 mpg in town. Part of that is due to less energy being used on turning the fan, I’m sure part of it comes from faster warm up times.
Heavy duty fan clutch IE one that spins the fan faster is about a 1 mpg gain over the fixed fan. Highway speed didn’t see too much noticeable gain although cruising a steady speed is not the same as getting that fan moving again at a stop sign.

Granted, it is an expense to buy both a fan and a clutch to match. Payback on fuel economy would be relatively fast with something like this however .

 

[InlineDave87]

Heres another question i got about emissions components. Mainly the air pump. I only see the air pump plumbed into the exhaust which to me is just “watering down” the reading at the O2 sensor. So are these engines running fat to begin with? And then the EGR also is to help with cylinder pressures/detonation right? In theory its kinda like it makes the engine “smaller” since the egr is non combustible. It all to me kinda contradicts itself, but i may not have the right understanding of how it all works. If you ask me, eliminate both components and install a wide band O2 sensor and do a custom tune to get it right.

 

[aussie7mains]

Heres another question i got about emissions components. Mainly the air pump. I only see the air pump plumbed into the exhaust which to me is just “watering down” the reading at the O2 sensor. So are these engines running fat to begin with? And then the EGR also is to help with cylinder pressures/detonation right? In theory its kinda like it makes the engine “smaller” since the egr is non combustible. It all to me kinda contradicts itself, but i may not have the right understanding of how it all works. If you ask me, eliminate both components and install a wide band O2 sensor and do a custom tune to get it right.

Ive done quite a bit of R&D on natural gas engines that were for mainly transit busses. With any fuel there are curves for mixture strength versus emissions of CO CO2 NO, and hydrocarbons, they are nothing like linear. designers try to tune the engines to give the lowest emsissions of all gases, this is a conflicting area, as co is going down no starts increasing. To reduce NO you need to reduce combustion temperatures, this can be down by a couple of methods, but the admission of inert combustion products is the one used EGR. What I found also is that when engines were given high manifold pressures ,turbo, combustion temps went up, and detonation was a risk, so EGR was used to both lower NO and prevent detonation, if the EGR failed for some reason , detonation was instant, and usually resulted in melting the corners of the piston, which then sprayed hot aluminium onto the bore, which resulted in seizure. We ran our research engines (usually 10-12litres) at 12:1 CR with up to 200kPa manifold pressure, up to about 125kPa you were OK without egr, over that, and its risky. As to fuel economy on the road, all the usual things to do with drag are important, but once all that is considered and sorted, your back to thermal efficiency of the engine. If people want to do some reading on this, id suggest Sir Harry Ricardo's texts are very good here, there is plenty written on this, some done way back, but physics has not changed.

 

[bubba22349]

Heres another question i got about emissions components. Mainly the air pump. I only see the air pump plumbed into the exhaust which to me is just “watering down” the reading at the O2 sensor. So are these engines running fat to begin with? And then the EGR also is to help with cylinder pressures/detonation right? In theory its kinda like it makes the engine “smaller” since the egr is non combustible. It all to me kinda contradicts itself, but i may not have the right understanding of how it all works. If you ask me, eliminate both components and install a wide band O2 sensor and do a custom tune to get it right.

I think the Air Pumps are used put extra O2 into exhaust system and help light off the Cat's.

 

[aussie7mains]

I think the Air Pumps are used put extra O2 into exhaust system and help light off the Cat's.

No, they were used way before Cats, its a dilultion thing, Toyota had them way back. Cats need heat for sure, but adding extra air wouldn't help, you would have to add fuel too.

 

[63 Sprint]

The 1989 F150 4.9 federal emissions engine had an air tube also right at the cat. My understanding is air was put in the cat and the engine was set up to run slightly rich to help light the cat off.