How do "Performance Mods" effect a car's economy???

[Domman56]

Originally Posted by dremd

reduced exaust backpressure will not help
2 reasons
1) the increased flow will be directly ofdfset with decreased throttle position.
2) reduced scavenging will bring the power band up.

Um not sure you can count this accrate statement either When TURBO cars have less restriction they often produce more boost therefore producing more HP and Torque Many turbodiesels pick up gains in this way so it May be more efficient to reduce it in turbo cars

[IsaacCarlson]

and I can get 40 mpg when I want to. I have been getting about 30-35 lately because I have been enjoying the lack of ice/slippery roads..... Also need to do some more modding...

[bgd73]

This is great question...

Learn your commute and type of gas at local stations
ie: maine even uses fermented wood to add ethanol..some days it may not even be 85 octane....

ALL companies ship cars constipated. They want it real quiet, polite, no odors...


this means it is killing itself with EGR, is double honeycombed, pipes too small, ignition not strong...and alot of times the fuel system isn't up to par. the fuel injection years have alot of leeway, it is the only bonus, easy stuff like CA intake is great.

After working drivetrain to more power, you may learn that bigger wheels or a taller gear can be used as well, that is advanced into the hypermiling quest, but happens all the time.

there really is a routine for this question, just hang around.

[mpgfan]

Im happy to see there is a lot of input for this question. I just read through this real quick since I'm at work. I thought that the answer would be a little more exact, but I do understand everyone is going to have their on view point on this. I will definitely continue checking on this. I really enjoy learning new ways and thoughts about increasing fuel efficiency and horsepower. Thanks everybody and keep the answers coming! Im sure Im not the only looking for this

[Chalupa102]

A few years ago when i put on an aftermarket header and larger exhaust muffler, i thought it would help f/e but really wasn't keeping track at the time. Fast forward to 3 weeks ago i was able to get a stock muffler installed for cheap. I also found a guy 2 weekends ago who wanted to trade his stock exhaust manifold for my aftermarket header. It was a pretty long day with the drive and doing the work ourselves, but it was well worth it and i made some nice money from it too.

Right after i did the stock muffler, i noticed a small incline f/e and torque. After i went back to the stock exhaust manifold, i noticed even more of an increase. If my scangauge2 is correct, the switch back to stock will definitely be a nice boost in MPG. I'll know for sure after i fill up tomorrow.

[comptiger5000]

Chalupa - That can definitely be true. The key as to whether stock or modded is better for MPG is whether modded adds low end torque, or moves the powerband up. If the powerband gets moved up too much, you lose MPG. If it gets moved down, or kept mostly the same, with gains both high and low, MPG can go up.

[johndavidson5]

Originally Posted by Domman56

Um not sure you can count this accrate statement either When TURBO cars have less restriction they often produce more boost therefore producing more HP and Torque Many turbodiesels pick up gains in this way so it May be more efficient to reduce it in turbo cars

Usually there is large piping after a turbo to increase the pressure differential across the exhaust turbine. This lets it spool up faster and helps it work more efficiently. This is also why turbo mufflers usually provide much less restriction. The fact that the turbo is in the stream somewhat makes up for these mufflers' lesser sound absorption.

Back pressure doesn't make torque, it is flow restriction. This can help control flow in cars with cams with larger overlap by restricting exhaust speed out of the cylinder at low rpm, which improves vacuum on the intake stroke. Most headers are tuned for high rpm scavenging because most people who buy them are looking for more HP, but if you tune for low rpm scavenging (which would mean very, very long header primaries) and have a cam that supports low rpm power (less overlap) you will have good vacuum and little back pressure. In fact, if your headers are tuned correctly you will have negative pressure at that rpm you chose, and that's why headers make power in the first place. It will just be at your cruising rpm, and instead of the goal of making power it will be to lessen the work your engine has to do (exhaust helps the piston pull itself out and pull fresh air in).

[99kleansi]

Anyone care to argue that an aluminum performance cylinder head is less efficient then an old iron head?

[mcrews]

Originally Posted by mpgfan

I accidentally stumbled upon this site and have become very intrigued with different ideas to improve my efficiency. I would like a car that can get good gas mileage but can still be pretty quick when needed. I would like to know if anybody has any insight as to how adding things like intake, headers, and/or exhaust to a car would impact its efficiency? Im looking to have a car make decent power while still maintaining the stock fuel injectors and fuel pump. Thanks in advance!

Maybe it's just me but I dislike philosophical bantering.
What do you drive? or want to drive?

For example (and personal experience)
an Infiniti Q45 2002 & newer: for several yrs at the infiniti forum guys tried everything to get more power. chips, cold intake, exhuast mods, all the possible bolt on stuff. Despite the manufacuter claims, NOTHING, I mean NOTHING imporved performance. 3 reasons: 1. the engine was pretty tweaked from the factory 4.5L 340hp (in 2002). 2. the ecm chip was designed to compensate for any changes from stock. 3.........lost my thought.

a V8 mustang. There is alot of room to make increases from the stock setup. THe engine design (obviuosly I'm not talking about the cobra paks etc)allows for alot of improvement.

It really helps to discuss in the framework of a specific car or a couple of cars.

[DamageX]

Lightweight forged pistons can help power and efficiency. I imagine that the anti-heat and anti-friction coatings would also help but I don`t have any first-hand (or even second-hand) experience with them. Crank scraper or windage tray, maybe? Also, converting from a slushbox to a manual gearbox is an improvement on both fronts.