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Old 08-24-2009, 06:53 PM   #1
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performance exaust, mpg increase?

http://www.mpgenhance.com/exhaust.htm

this says yes anyone have any evidence of this ?
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Old 08-24-2009, 07:01 PM   #2
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Quote:
Originally Posted by that site
We do not have personal documented evidence of improving mpg’s by changing exhaust here at MPGEnhance.com as high performance exhausts were added on our vehicles years ago before we ever started logging fuel mileage benefit. However, improvements in engine power and efficiency were certainly noticeable.
I have a link in my sig to a good discussion about exhaust.

IMO, if you're driving for economy then you'll never measure a difference between a stock exhaust and a performance exhaust. Stock exhaust has to flow the maximum power that the engine can make WOT @ redline; driving for economy, you'll never move a fraction of that amount of exhaust...I doubt a stock exhaust on a common vehicle will restrict flow at all during economy driving.
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Old 08-24-2009, 07:16 PM   #3
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Honda does have somewhat restrictive exhaust manifolds, but they've moved on recently to longer runners. Smaller, longer primaries and a well designed collector help exhaust air move with better velocity, improving engine breathing and power production. The size of the primaries (smaller= lower) is probably the most important factor in determining what rpms power is available. More torque at lower engine rpms will allow you to drive in a lower range thus improving mileage. It's all about driving in the most efficient rpm range that maximizes economy!

http://www.gassavers.org/showthread....rmance+exhaust

a larger pipe would mean less emissions picked up by an o2 sensor=more gas used to compensate=more power

but when would that loop end, could you tune your car to undo this, maybe put a resistor on the o2 sensor line to trick it into what it would normally be(somehow), and i believe at that point you would know whether or not a free flowing exhaust is better for economy, possibly..

ive heard of people wrapping o2 sensors in aluminum foil(to keep warm) to lean out the mixture, (i think), i hope theres real mechanics here

motorcycles use free flow exhaust to keep their engines more clean, and last longer?, my thoughts on why a performance exhaust might be worth buying, although i highly doubt they are

however i stand to be proven wrong
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Old 08-25-2009, 05:04 AM   #4
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First of all, I'd like to clarify that less restrictive exhausts don't necessarily have to be louder. So don't mistake the nest-of-angry-bees mufflers for someone who is trying to save gas, they are typically just trying to make spectacles of themselves.

However, since it takes work to push exhaust gas out the tailpipe, if you can reduce the amount of work to push out the exhaust it will improve overall efficiency.

Contrary to THC, I believe that a free-flowing exhaust can improve gas mileage noticeably. I consider the exhaust on my Buick to be a key part of my gas mileage. Of course it is only one component in an entire system, and most people do not re-engineer the entire drivetrain to the extent that I have...

-Bob C.

p.s. if your Subaru's muffler has fallen off, it does not sound like a big block. It sounds like your muffler fell off.
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Old 08-25-2009, 05:56 AM   #5
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Look at it this way.

Why would a manufacturer who spends billions to develop and manufacture their product, be dumb enough to design an exhaust system, so it threw away all the rest of their efforts.

.25 MPG is worth millions of dollars to the manufacturer. They simply have a different set of parameters, on of which is longevity.

The Honda VX intake and exhaust systems were significantly smaller than stock, because it improved fuel economy.

Size is just a part of the equation, velocity and harmonics are other factors.

regards
gary
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Old 08-25-2009, 07:30 AM   #6
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Marvin was on the cheap generic mufflers and getting 20-21mpg, a muffler is a muffler right? Uh, nope, when they started rotting out on me in less than a year, I paid a whole extra 5 or $10 and got a walker "Sound FX" unit, gas mileage jumped to 23mpg right there.
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Old 08-25-2009, 10:00 AM   #7
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Quote:
Originally Posted by spotaneagle View Post
motorcycles use free flow exhaust to keep their engines more clean, and last longer?, my thoughts on why a performance exhaust might be worth buying, although i highly doubt they are
I thought that common motorcycle exhaust configurations were made specifically for the purpose of being loud.

Quote:
Originally Posted by R.I.D.E. View Post
Why would a manufacturer who spends billions to develop and manufacture their product, be dumb enough to design an exhaust system, so it threw away all the rest of their efforts.

.25 MPG is worth millions of dollars to the manufacturer. They simply have a different set of parameters, on of which is longevity.
That's a concept that I often suggest on intake and exhaust questions. Major auto manufacturers have some of the best engineers in the world and huge motivation to make fuel economy a priority (but not the only priority). Exhaust is very mature technology with huge amounts of data. Their engineers can easily make it cost-effectively do everything for everyone -- quiet, efficiency, power, etc...

I can't believe that they would be negligent enough to not spend a relatively minor effort on an efficient exhaust (or intake).
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Old 08-26-2009, 06:36 AM   #8
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Quote:
Originally Posted by theholycow View Post
I thought that common motorcycle exhaust configurations were made specifically for the purpose of being loud.
Thats like saying all SUV drivers are dual-straight-piped, muddin', rednecks.
the serious attention *****s get performance exhausts then cut out all the baffles to make it loud. as with cars, a well-made system isn't that loud unless you're winding it out at WOT. some motorcyclist choose to have ridiculously loud pipes but factory, performance, and common setups aren't loud. you just don't notice them because they don't do anything to stand out. I'm just saying don't generalize. My motorcycles pretty quiet.

back to topic, While your average aftermarket exhaust is just going to be bigger with a practically non-existent muffler, a well-thought out and properly sized exhaust can most certainly improve on the factory system on most cars. Some cars it isn't cost-effective to do so for economy. By far the mfrs first 2 concerns are cost and quiet, in that order (because people will scream and cry bloody murder if the exhausts 1 dB more than their old car BUT they won't notice 1 mpg difference for an exhaust that never made it out of the factory.

When replacing mufflers, different ones DO make a difference. quiet and restrictive aren't synonomous but part of a triangle with cost... have to have 2 of the 3: cheap=quiet+restrictive OR loud+free flowing. expensive=free flowing+quiet [typically, there are exceptions to every rule if you search enough]
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Old 09-04-2009, 06:28 PM   #9
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Hmm, I wonder what kind of change would come from a piped cat....
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Old 09-05-2009, 03:58 AM   #10
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I think the federal law about that stuff does cover piping through your cat.
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