Best exhaust for MPG

[mattri]

Not looking for a big power gain, this is a daily driver, just want to be as efficiant as possible. Motor is completely stock EA82 in a 92 4WD Loyale, 5spd. I was thinking of going with the stock Y-pipe to a highflow cat then 2" back with a turbo muffler. What would this do to performance and MPG? Matt.

[HattoriHanzo]

You should notice an improvement in upper rpm performance with a less restricted exhaust, might hurt torque a little down low, though. MPG may suffer a little, the faster exhaust can get out the faster fuel can get in, if that's all your doing shouldn't make much difference though.

[idosubaru]

over the past 10 years i've played with a few exhaust set up and put 30 - 45,000 miles per year on my car so i pay attention to mileage. it's not going to make a huge difference. also will depend on your driving style and conditions.

 

you can eek a few more mpg out of an XT6 for sustained long distance (highway driving), just by removing your intake snorkel, installing a K&N and welding on a good straight through muffler. no need to mess with piping size even for that. stock i think an AWD automatic will run about 26 mpg, after those mods you can get 29-30 on all highway miles.

 

but when you make mods and try to *feel* that power and start mashing the gas you'll get worse mileage. for mileage, keep your ignition system in good working order (NEW). for sustained highway driving this matters little, but for typical daily driving be sure not to have excessive dead weight in your car. like tool boxes, enormous jacks....etc.

 

like the last post mentioned, you'll notice a little more power up high and less down low. it's not magic, but you can tell.

[mattri]

Thanks for the replies but I seem to be going in the wrong direction. What should I do for more torque down low, where I would use it the most driving around town? Matt.

[NorthWet]

Nothing occurs in a vacuum... except astronomical things.

 

Any change to the exhaust system does not really do much good unless you make complimentary changes to the intake and the valve timing. It is all a connected system. In general, if you want more low end torque, go with longer (and narrower), primary pipes on the exhaust, longer/narower intake runners, smaller carburetor primary throat (if carbed), and a more conservative cam (or at least adjust its base timing). All of these will shift the torque curve lower, and kill the power on the top end.

 

Doing just some of the above will shift the torque curve lower, but will also likely lower the peak and make it lower at other odd places. And still kill the top end.

 

In general, your best bet is to make sure that the ignition and fuel system is perfoming optimally. You can do pretty much anything after the catalyst/muffler to reduce backpressure (which, despite what others say, no engine needs to work right).

[erik litchy]

You should notice an improvement in upper rpm performance with a less restricted exhaust, might hurt torque a little down low, though. MPG may suffer a little, the faster exhaust can get out the faster fuel can get in, if that's all your doing shouldn't make much difference though.

 

a little bigger exhaust will improve toqrue down low as you call it. i know first hand

[NoahDL88]

Its about Velocity, not backpressure, the exhaust needs 240-260 feet per second velocity through the pipes, your power will be made when this criteria is met. if you have it a little bigger than stock, it will flow that at a lower RPM, if you make it much bigger it will flow that FPS at a high RPM, in that case thats when the power will be made. If its too big the flow slows down too much and you don't get any scavenging.

[NorthWet]

AAAAHHHHGGGG!!!

 

What happens beyond the first major obstruction to pressure waves (e.g. muffler/catcon) DOES NOT effect scavenging. Scavenging effect is caused by positive/negative pressure waves being reflected from transitions in the pipe and appearing at the valve at times that will positively influence air flow at the valve.

 

The first major obstruction is like a dampener to the pulses, and by the time the pulse tries to make two transits of the obstruction it has no real effect... not to mention that its timing will be so wrong as to be harmful.

 

Although there MAY be something to gas velocity, it would exist in the primary/secondary exhaust tubing, and really is just not letting the velocity change significantly from what is seen at the exhaust port... as a change in velocity would be caused by a change in passage crossection/area, which in turn would cause a major pulse reflection node.

[MilesFox]

i have a 2" cherry bomb on the sedan, immediately after the y pipe. i have run the car y pipe only, y and bomb, y, bomb and straight pipe

 

here are the results"

open y pipe will scream in the upper rpm, break a wheel loose if accelerating out of a turn. but the takeoff is slow so you have to slip the clutch a little to get past the bog, i found myself taking gears up or downshifting becuase it doesnt want to pull at low rpm, 200-2500 rpm. but on the highway you have excellent throttle response and your foot is light on the gas. but city driving this will hurt you because you are always in a lower gear and higher rpm

 

y pipe and glasspack, i have the 18" long cherry bomb although i probably should have used the longer one. anyway, this brought some torque for the low rpm take offs, and improved mid gear pull, i didnt have to winf her up, and she would pull the next gear at the same speed and load. it did choke down the higher rpm acceleration, but that was made up for by shifting sooner and pulling from 2000 rpm. this improved on city driving

 

y pipe, glasspack, straight pipe. I later installed a 2 in pipe back to the rear diff. this quieted the car down considerably and took the noise out from under the passenger area. the torque was good for low rpm, the car pulls excellent from 2000 rpm, and actually broadened the torque curve to 3500 rpm, as the straight pipe kept the velocity of the exhaust pulse

 

on the highway the revs arent as quick as i like them to be, but she gets up good by shifting at 3500 rom and pulling from 2500. once you get to speed, around 3-3500 rpm, she holds her speed with little pedal effort, and the pipe still flows like it should

 

but my results are compared to running with no exhaust rather than running with a stock exhaust. overall im happy and the car is very driveable, and would have good off road characteristics

 

on the highway averaging 65-70 mph for 360 miles for a full tank i got 27 mpg

[NoahDL88]

I'm sorry, i could be wrong about the exhaust velocity, but i was going by what all my automotive instructors said, what the engineers said when we went on our field trips and what the guy who builds the mopar dragster said. they certainly could be wrong.