Horsepower vs Fuel Efficiency

Riley P

Riley P

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I know it is usually one or the other, but I want to know what products/mods are out there that give your car more horsepower without sacrificing fuel economy. I absolutely love that my car gets 36mpg at 120km/h on the highway, as I am on the highway a lot, but I also love horsepower.
Is it limited to just exhaust/intake/tune? Or are there other ways to juice up the power while retaining driveability and excellent fuel consumption?
 
I think NOS as you flick the switch and you have instant power but turn it off again and
your back to your 36mpg. If you do not give too big a shot I think it can be very reliable.

Most all other power adders will give you a hit in the mpg maybe other then the Magnuson
that has a internal bypass and only kicks in under high throttle levels.

Not sure about the Paxton or other superchargers and if they are always under some
sort of boost.
 
I had a Paxton supercharger on an 87 Mustang GT and my highway MPG was unchanged from stock. Obviously when driving it hard it used a lot more fuel though.
 
Porting heads would also increase the fuel consumption. Yes it will give you more power, but it will use more fuel... remember the 14:1 ratio? You can always run leaner to save gas... but at what cost?

Speaking of fuel economy, does anyone has first hand experience with GM's Active Fuel Management system? The one that shuts off 4 cylinders on 8 cylinder cars when not needed?
 
Lean is fast! But not on my car.:D I would love a Maggie, but that is an investment.To make myself feel better for now, I will just have to make my own WEEEEEEEEEEEEEEEEEeeeeeeeeeeeeeee whine noise when I punch it. Nitrous is probably the cheapest way to make good hp when needed, but it still scares the crap out of me.
 
i loved nitrous when i had my stang ! if its done right you can run a small shot every light and it will last forever.

with FI, as long as you stay out of boost your fuel mileage should not change, but you need to be retarded to have FI and stay out of boost.

- Kons
 
desi said:
Speaking of fuel economy, does anyone has first hand experience with GM's Active Fuel Management system? The one that shuts off 4 cylinders on 8 cylinder cars when not needed?
Click to expand...

I have it on my G8 GT. It's supposed to provide 34 MPG on the highway but the weather hasn't been warm enough to put that claim to the test. It switches quickly and easily between the two modes so no issues there. There is a slight vibration when it's on.
 
Maybe a question for off topic, but when the engine is in 4 cyl mode and it is not firing on a cylinder it would usually fire on, does it still compress the air in that cylinders compression cycle, or is it smart enough to somehow pop the exhaust valve and let the air go right through to the exhaust?
 
Riley P said:
Maybe a question for off topic, but when the engine is in 4 cyl mode and it is not firing on a cylinder it would usually fire on, does it still compress the air in that cylinders compression cycle, or is it smart enough to somehow pop the exhaust valve and let the air go right through to the exhaust?
Click to expand...

According to the GM docs I have, it closes intake and exhaust valves and cuts fuel delivery to the deactivated cylinders. It uses hydraulics to remove contact with the pushrod and keeps the valves closed.
 
Very interesting. It seems like there would still be losses as the piston would be creating a vacuum in the "sealed" cylinders and the activated cylinders would have to compensate for this. I guess until GM goes to valves activated by solenoids, it would be difficult to allow the engine to just freely pump air on the cylinders that are deactivated...unless I am missing something. If anyone can fill me in, that would be great!
 
Here is a write-up:

"All corporate politics aside, the engineers at GM Powertrain have designed yet another mechanical marvel, and it's
all due to some remarkably modest changes to the very robust Gen III architecture on which the Gen IV is based.
The new DOD-specific hardware includes two-stage switching lifters, a lifter oil manifold assembly (located in the
valley of the engine), a redesigned lube circuit and oil pump, electronic throttle-by-wire operation, a
pressure-activated muffler valve, and an improved E40 engine controller running DOD-specific software.

"In order to eliminate the pumping losses," says Meagher, "you need to disable both the intake and exhaust
valve." This results in a completely sealed, deactivated cylinder, which is essentially an air spring being acted
upon by a piston. Virtually all the work put into it during compression is returned to the crank during
decompression, finally giving credence to the old joke about piston-return springs. (That's nothing. Wait 'til
you hear about the muffler valve...)

"Currently, we could disable just the fuel delivery," says Meagher, "but the valves would still be opening and
closing and each cylinder would still be doing work pumping air in and out. So there would be no net gain in
efficiency--you wouldn't have eliminated the pumping losses at all.

In support of cylinder deactivation is some very interesting choreography from things ranging from throttle
valve modulation to active exhaust tuning, but it all starts with the additional job tasked to the lifters.
"We disable the valves through a device called a switching lifter," explains Meagher. "This differs from a normal
lifter in that there is an inner body and an outer body connected by a spring-loaded pin. For V-8 operation,
the pin is fully expanded by the spring so the two pieces act as one and the lifter acts like a regular lifter.
When we want to disable the valve operation, we deliver high-pressure oil to a groove in the lifter that leads
to the outside end of the pin, forcing the pin to collapse the spring. Now the two parts of the lifter are free
to move relative to one another and as the cam lobe pushes on the follower the inner portion of the lifter
pushes against another spring at the top of the lifter and does not transfer force to the pushrod."

A look at the lifter cross-section reveals an elegant, yet simple design that has the potential to change the way
we think about traditional pushrod engines. (Ironically, when DOD is working, it hinges on lifters that do not lift!
Something we never thought we'd ever want.) In order for the switching lifter to work effectively, the engine
needed a redesigned oiling system. Both iron and aluminum versions of the engine block have redesigned oil galleries
o support DOD oiling requirements. Those oil galleries are supplied by a lifter oil manifold assembly (LOMA) located
in the lifter valley of the engine. Under cylinder deactivation, the LOMA routes oil to the applicable lifters by means
of four lifter oil solenoids, which are controlled by a new E40 engine management controller. To supply the additional
needs of the cylinder deactivation circuit, a higher capacity oil pump is fitted to the LH6 engine."
Click to expand...
 
Last edited:
Riley P said:
I know it is usually one or the other, but I want to know what products/mods are out there that give your car more horsepower without sacrificing fuel economy. I absolutely love that my car gets 36mpg at 120km/h on the highway, as I am on the highway a lot, but I also love horsepower.
Is it limited to just exhaust/intake/tune? Or are there other ways to juice up the power while retaining driveability and excellent fuel consumption?
Click to expand...

all things being equal, freeing up airflow in and out will increase the torque your motor will make at a given rpm. it will allow you to use less fuel to produce the same tq; thus increasing your mpg.
the fundamentals are found by looking at the Otto cycle P/V curves. increased pressure ratio increases work output. increased pressure ratio comes from more air, more fuel or (as someone else mentioned) the combination of both in order to maintain AFR's. choice in camshaft will probably have the most dramatic effect on economy due to changes in overlap and DCR.
it's always a balance; big ponies = thirsty ponies, but you can increase tq/hp without destroying mileage.
so, to answer your question; aside from induction, exhaust and tune, you could go with a not-too-agressive cam and some free-er flowing heads, lighten up the rotating components etc etc. or opt for FI, although the price will chew away at any fuel economy $$ you save.

...or just buy a car that's good on fuel for the DD needs, and keep a monster in the garage.
 
Heads, cold air intakes, headers, superchargers will all net you the same fuel economy street or highway when driven normaly-however at WOT-you'll use more fuel -any increase in horsepower will require more fuel to be consumed at WOT-fuel equals horsepower.

So in todays's day and age you can have your cake and eat it too!
 
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