No muffler = poor MPG???

D15, D16, D17 and Mini-Me swaps
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No muffler = poor MPG???

By Coplies
- Thu Oct 07, 2010 12:21 am #217212 I took my muffler off to see what it would sound like and now I'm getting really poor mpg. Could the lack of back pressure be causing this or is it a coincidence
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By teal_dx
- Thu Oct 07, 2010 1:05 am #217220 are you gunning it more often to sound like a ricer w/ no muffler? the way you drive can make a huge difference. But also no back pressure means less low end power than a stock D series already has so they would hurt mileage too when you accelerate.
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By suspendedHatch
- Fri Oct 08, 2010 11:39 pm #217607 Shortening the length of the exhaust tube will cause a loss in low end power and shift the power band forward in the RPM band. However, there's no reason to connect that with a loss in fuel economy.

Did you reset the ECU?

Backpressure is not a factor unless the muffler was clogged.
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By teal_dx
- Sat Oct 09, 2010 4:28 am #217637
will cause a loss in low end power and shift the power band forward in the RPM band.


lets get into specifics for a second... Wouldn't this possibly hurt fuel economy?
Reason... Every time your car moves, you require low end power- 100% 0f the time. Unless you're accelerating moderately fast or faster, you may not use the mid-range power or never use high end power if you just roll around town.

So by losing back pressure, you're taking the power you would use 100% of the time and putting it in the range you would use say 50% of the time.

So your car would then be less efficent = slight loss of MPG.
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By Coplies
- Mon Oct 11, 2010 9:19 pm #217930 I didn't do anything to the ecu. I know that i have been getting on it more than usual but not that much. I am on track to get like 25 mpg and 28 is the lowest I have ever gotten, even when I was hauling ass for the whole tank.

So I know what back pressure is, but why does it cause a lack in low end power? What does it do for the motor
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By ghskid06
- Mon Oct 11, 2010 9:27 pm #217931 :woot: teal for logical thinking!
Yea losing back pressure therefore having to drive at higher rpms would hurt fuel economy. Even if you were to drive it like normal you would still be losing a small percentage of your mpgs because you would not be covering as much ground on acceleration, even though your motor would not be acting any differently.

Why did you want to cut your muffler off? Put it back on. Back pressure keeps combustion happening properly. At lower rpms timing differences etc have a bigger impact. For example a car may shake at idle, but then beast higher rpms. I dont think it would harm your economy that much, but put it back on anyway.
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By Coplies
- Mon Oct 11, 2010 11:55 pm #217948 I'm putting it back on this weekend, i am done being a typical rice burner. But I am still curious as to how the back pressure affects the combustion.
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By That One Dude
- Tue Oct 12, 2010 1:23 am #217961 Without proper backpressure, exhaust scavenging is effected. Scavenging is where the exhaust pulses from one cylinder essentially pull the exhaust pulses of another cylinder. It's why when you look at a 4-2-1 header you see 1-4 and 2-3 paired. Exhaust manifolds/headers are designed with scavenging in mind so that they can efficiently expend the exhaust gases out of the cylinder. The intake charge also helps with that. When the intake valves open, the exhaust valves are still open and the piston is still moving up on the exhaust stroke. The intake charge is significantly cooler than the exhaust gases and when they contact each other, a thermal shockwave occurs causing the exhaust gases to be pushed out.
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By eg84dr
- Wed Oct 13, 2010 1:32 pm #218180 ^mr scientific aircraft mechanic right here lol
x2 woot for teal on logical thinking
im always happy to see someone challenge the all mighty suspended hatch hehe :thumb:
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By That One Dude
- Wed Oct 13, 2010 11:28 pm #218258 Hell, I learned that from an old muscle car guru... The airplanes I work on are powered by turboprops and turbofan engines.

By dawg316
- Thu Oct 14, 2010 7:23 pm #218360 would even sticking a cheapo cherry bomb glass pack help ? it is longer piping, but also its straight thru at the same time ? how would that affect it ?
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