['02SilverBullet]

Ok most of you guys know the simplistics of any engine... more air in + more air out = more HP and a more EFFICIENT engine considering proper tuneing and so forth. It only makes sense to get better mileage out of a modified engine. The part I DONT get is... Considering the best driving habits one can have to conserve fuel....When does a modified car start to really lose fuel mileage? It SEEMS a 400 hp fi GT COULD get just as good (if not better) mileage as a stock one IF the driver could stay out of the boost. At what point really does the power of the engine REALLY start affecting fuel economy? Yeah I have seen big FI cars that get like 8 miles to the gallon but why is that? Is it the tune they are running? Is it cams? combination of everything?

Discuss......

[97Cobra]

more hp more fuel is burned... you can grab a TB, Headers, Cai, and mid pipes which will flow more air letting your car breath better and thats like breathing through a star and taking the straw out and breathing with your mouth open... it makes a difference... but as soon as you get quite a bit more hp you need to upgrade your fuel system that will supply you engine with more gas faster. more gas faster/burned faster = drop in mpg...

its just like a stock engine when you romp on it. the computer tells it it needs more fuel so it dosnt burn up the pistons which causes poor fuel mileage.... this kinda what you where looking for?

[StangAddiction]

if you drive normal...you'll get normal mileage either way....

[Kobra Killer]

It depends on what you modify. The air/fuel ratio stays the same.
If you just help it to breathe better (intake & exhaust) all is the same.
If you change the cam, gearing etc, you move the RPM performance range (usually up).
More RPMs means more a/f flowing through the engine.

[StangAddiction]

Originally Posted by Kobra Killer It depends on what you modify. The air/fuel ratio stays the same. If you just help it to breathe better (intake & exhaust) all is the same. If you change the cam, gearing etc, you move the RPM performance range (usually up). More RPMs means more a/f flowing through the engine.

i agree...but a good tune still equals good gas mileage...I've gained 100 rwhp and didn't lost much if any gas mileage...

[ReverendDexter]

It also depends on the mods.

In my head, there are three types of modifications:
a) Mods that increase the amount of fuel you can burn.
b) Mods that decrease the amount of energy required to get power to the wheels.
c) Mods that increase the efficiency of the burn.

I got almost 20% more power to the wheels in my Corolla from doing things in group b.

Increasing the efficiency of your intake and exhaust means you're not expending energy to pull air in or force air out.

Reducing parasitic loss was HUGE for me. That's where I got almost all of my gains. I removed the A/C, converted to manual steering, and went from a clutch fan to an electric fan.

If you're gonna go forced induction, a turbo is TREMENDOUSLY more efficient. A turbo is powered by the heat energy elsewise lost in your exhaust. It's basically a free lunch. With a supercharger, something like 50% of the power made by the blower is reconsumed just to run the supercharger. This means that under perfect efficiency, a 300hp motor that becomes a 450hp motor with a supercharger would've become a 600hp motor with a turbo. Of course, perfect efficiency doesn't exist, and I'm sure my example has been oversimplified.

['02SilverBullet]

It seems also that with a higher HP/TQ engine under "normal" driving conditions one would exert LESS force to get the SAME affect and there you would also use less fuel.

I have known about this paticular scenario for a while and a friend of mine at work had to learn the hard way LOL. Anyway he has had a 6 cylinder mazda pick up for a while thats hes been driving back and forth to work. Well with gas the way it is and all and his good luck with his truck he decided to go get him another one. He goes and gets an '04 4 banger mazda... same body style, cab configuration, bed length and all. He statrs driving THAT truck back and forth to work and found out that the 4 banger gets WORSE milage than what his V6 gets. I found this out a few years ago. SOme 4 bangers have to work too hard to maintain highway speeds. There is no doubt that a 4 cylinder does better at stop and go city driving. But SOME of em just do ROTTON on the highway.

Anyway sorry for getting a bit off topic.

[HBK_2007]

ya ive wondered about this too. i was considering getting me a 4banger ranger for a winter beater but with that side note, i think a 6 might be better. how would one make a ford AODE (from a 96 gt to be specific) more effiecent?

[ReverendDexter]

Originally Posted by HBK_2007 ya ive wondered about this too. i was considering getting me a 4banger ranger for a winter beater but with that side note, i think a 6 might be better. how would one make a ford AODE (from a 96 gt to be specific) more effiecent?

Shift kit, and different gears. (Lower gears will help your city mileage).

My Corolla is a perfect example of the 4-cylinder highway speed poor gas mileage issue. If I could stay at 60 or under, it didn't matter how hard I drove that car, I'd get better than 30 mpg and that was with 3.90s in it (yes, RWD corolla). But if I drove 65-70, my mileage would drop to about 23mpg.

[HBK_2007]

would a different stall rpm tq convertor help or hurt? also, would larger brakes, say from stock to 14" rotors, hurt mpg?

[onederful100]

before SC: 17-22 mpg's
after SC: 11-14 mpg's
looking at my fuel pressure at WOT it goes up to 65-70 psi, at idle it's about 30. idk what it was NA bc i didnt have the gauge then. having more hp to me, means a heavier foot also, its no fun having more hp and not using it. after CAI and exhaust only i did pick up a couple mpgs. so in conclusion, the more hp you have the more you're going to use it, hence less mpg's.

[StangAddiction]

I don't beat on my car often... Nor do i have a heavy foot.. I hit it from time to time...I'll even admit to street racing sometimes, but 90% of the time, i drive normally...


As for turbos, a friend of mine has a 1992 corolla in which he swapped in a 4age... He turbocharged it and made slightly better mileage then he did N/A with the 4age... Megasquirt tuned.. Turbos do improve the efficiency..