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Old 05-30-2010, 01:39 PM   #1
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svt back pressure question

PPl with straight piped svtfs, is the low end horrible? I've been wanting some sound so I was thinking about ditching the magnaflow muffler but How is the low end? Usually I know it would kill it but I'm not sure with the VCT


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Old 05-30-2010, 02:20 PM   #2
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This has been covered numerous times. Back pressure is a ~~~~MYTH~~~~~

If the primaries on your header are really large, that would hurt low end. Once you get past your header, big exhaust only gives you power, it doesn't take it away.
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Old 05-30-2010, 02:25 PM   #3
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^ yup, pretty much...especially if you have a cat.
Although without a cat, I'm sure you can probably get some additional scavenging effect further down the exhaust than the header...?

Back pressure...that's funny!
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Old 05-30-2010, 02:28 PM   #4
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Sure is. I've lost count of how many times I've seen people asking about it or saying that it "kills" the low end.
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Old 05-30-2010, 03:57 PM   #5
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i do like the gurgling noise it makes though when you downshift. or is that not back pressure that does that? either way i love that noise. haha
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Old 05-30-2010, 04:46 PM   #6
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Ugggh...no, it is not back pressure. It is exhaust scavenging.
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Old 05-30-2010, 05:32 PM   #7
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I'm planning on same size exhaust just taking out the muffler.

The gurgling is from shots of fuel when you're not on the gas
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Old 05-30-2010, 05:56 PM   #8
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Shots of fuel? What's that? When you let off the gas, the ECU enters what's called Cruising Fuel Shut Off. Not sure what "shots of fuel" are but I do know what exhaust scavenging is...
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Old 05-30-2010, 08:37 PM   #9
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"exhaust scavenging" Whats the exhaust scavenging for? food?






sorry couldnt help my self :P

but really what does this mean?
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Old 05-30-2010, 09:00 PM   #10
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Dictionary.com lists definition #3 as:

"to expel burnt gases from (the cylinder of an internal-combustion engine)."

Anyway, an exhaust pulse has a "head," a "body," and a "tail." The head and body are at a much higher pressure than atmospheric and are also at a high velocity. The tail is at a much lower pressure, and while it's on its way out of the exhaust port, it causes a lower pressure difference between the header and the combustion chamber, helping to suck the remaining exhaust gas out and pull the intake charge in.

The faster you can get the head and body of an exhaust pulse to move, the more of a pressure differential you will have between the header and combustion chamber, pulling out the exhaust more efficiently and also pulling in the intake charge more efficiently. This is what long tube headers accomplish.

As I said before, having huge ass header primary tubes will *slow down* the exhaust gases, which decreases the scavenging effect, which will make less power (in N/A form).

You don't need exhaust scavenging with a turbo (as much) because scavenging relies on intake/exhaust overlap. Too much overlap blows boost right out of the cylinder before it has time to pressurize, wasting power.
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