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Old 06-10-2011, 10:16 AM   #1 (permalink)
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What engine only mods for better efficiency?

What can be done to a good running engine to make it more efficient? By that I mean it already would have good plugs, coils, new oil, new air filter, etc. basically in great running order.

My thoughts go to polishing the intake and exhaust ports on the head so that the engine strains less. Possibly a slightly bigger exhaust system. Or more powerful coils for better combustion. A custom grind cam, but it would be very much blind guessing. Higher compression for more power with less throttle. Lighter rotating assembly like a lightweight flywheel, crankshaft, valves, cam gears, rockers, spring retainers.

I also wonder what makes for a more fuel efficient engine as means to more horsepower or more torque. By that I mean, some cars have long intake runners to make more torque. Other cars have short intake runners to make more horsepower. No doubt this would need to get matched with things like cylinder volume, bore, and stroke. But one or the other might fetch better efficiency.

Most of my ideas come from making an engine more powerful to race but it stands to reason that if an engine doesnt have to strain as hard to make power then it should get better MPGs. So long as those mods dont cause it to use more fuel.

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Old 06-10-2011, 10:34 AM   #2 (permalink)
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Quote:
Originally Posted by Floordford View Post
My thoughts go to polishing the intake and exhaust ports on the head so that the engine strains less.
Nope.


Quote:
Possibly a slightly bigger exhaust system.
Nope, unless its turbocharged.


Quote:
Or more powerful coils for better combustion.
Nope (ok, maybe marginally, we're talking a fraction of an mpg)


Quote:
A custom grind cam, but it would be very much blind guessing.
Yes, but only if the custom grind increases low end power.


Quote:
Higher compression for more power with less throttle.
Yes, but only to the point at which it starts effecting timing and you have to retard it which eliminates any benefit. So, this is a very hard thing to balance.


Quote:
Lighter rotating assembly like a lightweight flywheel, crankshaft, valves, cam gears, rockers, spring retainers.
Yes. Included in this are piston rings that aren't as tight, OEMs have used these on recent engines to improve efficiency. They've also used offset crankshafts to reduce friction losses.


Quote:
I also wonder what makes for a more fuel efficient engine as means to more horsepower or more torque. By that I mean, some cars have long intake runners to make more torque. Other cars have short intake runners to make more horsepower. No doubt this would need to get matched with things like cylinder volume, bore, and stroke. But one or the other might fetch better efficiency.

Most of my ideas come from making an engine more powerful to race but it stands to reason that if an engine doesnt have to strain as hard to make power then it should get better MPGs. So long as those mods dont cause it to use more fuel.
The easiest and IMO best thing to do to increase engine efficiency is to use a smaller engine. Increasing the load DRASTICALLY increases the efficiency of the engine. If the power output isnt enough, add a turbocharger.
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Old 06-10-2011, 12:14 PM   #3 (permalink)
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Let's take a look at the differences between the 4.6 Modular ( 2V ) and the 5.0 Ford.

Reduced bore for lower emissions

Low fiction valvetrain

Low friction piston rings

Undersquare bore to stroke ratio

Fast burn combustion chambers, small valves and ports for high velocity

Long runner intake manifold

For economy, the closer you can keep it to stock, the better it will run because it was optimized from the factory to run in the lower ranges most of the time. Anything that enlarges the ports lowers the velocity of air into the port at lower rpms, unless there's a displacement increase or some form of supercharging. Headers are not bad if they are built for no compromise in tube size and length, along with collector dimensions.

Cam timing, overall tune and gearing are the arbiters.
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Old 06-10-2011, 01:41 PM   #4 (permalink)
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As has already been said, the biggest thing you can to do an engine to reduce its fuel consumption is to replace it with a smaller one.

Another really major thing you can do is to not use it. Turn it off when you're sitting at a light, turn it off when you're coasting, and so forth.

Another thing is to operate it in its most efficient regime, typically right around 2000 RPM with a decent amount of load on the engine. Which means pulse and glide (or pulse and coast).

If you're talking about modifying an existing engine to get economy out of it, you can easily spend thousands or tens of thousands of dollars making changes that can get you a couple of percentage points of FE. Not worth it in any way, unless you're looking to set records. (In which case, the "smaller engine" idea is probably a better way to go.)

Since efficient driving is all at low RPMs, any changes you make that help the engine to work well at low RPMs have a chance of improving economy. Long tubular headers are one thing that comes to mind. A cam ground for torque at very low revs is another. A long-tube type intake might be as well. Increasing bearing clearances for low-friction operation. Friction reducing coatings on moving parts and on oil-shedding parts. Compression increases will help, possibly at the expense of requiring higher-octane fuel. Smaller valves to give good flow velocity at low RPMs. Lighter everything (including valve springs) so you spend less energy moving things around. And so on.

And all of that might net you, what, a 5% improvement if you're lucky?

Actually, one other area where engine mods can help fuel economy noticeably: If your engine has really major shortcomings or design flaws, correcting those can help. A friend with a 60s-vintage Mustang saw better economy when he replaced the awful stock exhaust manifold with real headers, for example.

Cars built in the last 30 years or so won't have easy gains like that available, though. When automakers had to start building for economy, they grabbed the low-hanging fruit first.

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Old 06-10-2011, 02:52 PM   #5 (permalink)
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Quote:
Originally Posted by Floordford View Post
By that I mean, some cars have long intake runners to make more torque. Other cars have short intake runners to make more horsepower.
And the really good ones have Variable Resonance Induction Systems.
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Old 06-10-2011, 04:37 PM   #6 (permalink)
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Well my project behind the thought was to pick up a small fuel sipper and pull the engine before I start relying on it. I can make the changes while its down.

It seems as though polishing the intake and exhaust should work. Im not talking about a major port job where alot of material is being removed. Just a smoothing out of the rough surfaces left by low cost factory castings. Another thought was to actually add material. With the head and intake off material could get welded on to create even more of a tapered velocity effect. Or fill in bad imperfections from bolt mountings. I figure just like the front of a car benefits from being smooth so would the air getting inside the engine.

And I know smaller engines make for better MPGs. But if im working with a car that already has the base line engine then my only option is to either go back in years to see if an older motor with smaller displacement might retrofit or work with what the manufacturer installed. Thats why I wanted to know what mods I can do to an engine can benefit it. No matter the engine. So say i did swap it for a smaller engine, my question still applies.

I also wonder how honest oil companies are when they sell eco and gas saving oils. Thinner oils might do well and synthetics are even better. But I wouldnt run synthetic in my transmission unless recommended by the manufacturer. The reason being is that slippery synthetics can cause the synchros not to grip with the needed friction to help the gear change causing hard shifts.
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Last edited by Floordford; 06-10-2011 at 05:11 PM..
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Old 06-10-2011, 06:22 PM   #7 (permalink)
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People who want more power often talk about making the engine breath better, or that they want a better flow in the exhaust or intake, but engines don't operate off a continues flow, they operate off pulses and those pulses have to be tuned, that is why you do tune ups, keep your engine in tune because an engine fallows alot of the same rules as music because they both run on pulses! fallow the math and design for those pulses and you will use less gas, engines are designed to run over a wide range of engine speeds so tuning it for power, or for gas mileage and you will slightly limit the RPM range that it will run in, unless you have variable intake, this is why cars that are tuned for racing are the worse cars to drive in slow traffic, cars that are designed for gas mileage don't race well.
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Old 06-10-2011, 06:39 PM   #8 (permalink)
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Perhaps you are ready for two cars:
  • existing toy car - enjoy but only drive it for fun.
  • assorted fuel efficient, earn a living car - so you can make the bucks for the fun car
In the fuel efficient mode, you could go with a really old, 1970s or earlier, simple car, bought for peanuts. Plan to replace the tires and possibly a drop-in engine. At about $5-7k, you're on the road and only throw in enough to keep the beater rolling. But the engine and drive train technology would be familiar and you'd be on the road, earning, with the toy car as backup.

Another approach would be to look at early 2000 hybrids. The options are limited: Prius, Insight or Civic. If you want more traditional, go with the Hondas. The advantage is there are is a lot of historical tweaking data. On the Hondas, go for a manual transmission ... you'll be a lot happier.

There are other options but they require . . . different skills. No need to tackle 'a bridge too far.'

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Old 06-10-2011, 07:28 PM   #9 (permalink)
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balance the injectors so that they all perform the same. will help your car to adjust A/F mixture more accurately.
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Old 06-10-2011, 08:15 PM   #10 (permalink)
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Are you talking about working the car you currently have or getting something else?

If you want to use the existing platform, how about a turbo 2.3L?

Stock, blueprinted build, stock intake manifold ( runners equalized, but not enlarged and gasket matched )

High torque cam with roller followers with peak torque in the 1800-2000 rpm range

Turbo header sized best for off boost performance

Dual staged efi with 4 primary injectors optimized for mpg and 4 for boost enrichment

Turbo sized for whatever hp level.

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