SuzukiSavage.com - cutting exhaust for drag pipe

savagebob Full Member Offline SuzukiSavage.com Rocks! Posts: 235	cutting exhaust for drag pipe 09/02/13 at 15:04:08 Ok so I've got this BCB drag pipe here, looking at how it fits, the drag pipe goes right up over the header sealing on the widest part. Therefore, I'm tempted to cut all the tapered part off of the header off ensuring maximum diameter flow through that part. do you guys do that?
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bobert_FSO

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Re: cutting exhaust for drag pipe
Reply #1 - 09/02/13 at 15:31:23

I wouldn't cut it. The header pipe is a double or triple wall pipe. If you cut it above the end where they all converge, the inside pipe might rattle around inside the outside pipe.

You won't gain much by cutting it off. Remember, these big singles need some backpressure to be able to make mid-range torque.

Also, once you cut that header pipe, you can't go back to a stock (yuk!) or other 1-3/4 inch mufflers.

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Serowbot YaBB Moderator ModSquad Offline OK.... so what's the speed of dark? Posts: 28651 Tucson Az Gender:	Re: cutting exhaust for drag pipe Reply #2 - 09/02/13 at 15:32:58 +1... Don't... Not only will you not gain much,.. you will lose power...
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savagebob Full Member Offline SuzukiSavage.com Rocks! Posts: 235	Re: cutting exhaust for drag pipe Reply #3 - 09/02/13 at 18:04:57 ok I wont cut it, it just seems to me like back pressure by the baffles just past the connection is going to cause gases to get caught up between the header and drag pipe creating some weird flow dynamics.. was tempted to cut it right back and weld the drag pipe on so it's a relatively equal diameter all the way through.
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WD Serious Thumper 2005 No Login Offline Professional "scooter trash". Posts: 5207 Rosemark TN Gender:	Re: cutting exhaust for drag pipe Reply #4 - 09/02/13 at 18:08:57 You need the torque cone effect or you'll kill what little throttle response it is going to have prior to sorting out the jetting.
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Dave YaBB Moderator ModSquad Offline SuzukiSavage.com Rocks! Posts: 18098 Camp Springs, Kentucky Gender:	Re: cutting exhaust for drag pipe Reply #5 - 09/03/13 at 04:52:44 Even if you did cut it (don't).....you still have that same small diameter pipe all the way up to the cylinder.
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Charon

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Re: cutting exhaust for drag pipe
Reply #6 - 09/03/13 at 07:09:18

It's unfortunate we have no way to distinguish between "back pressure" and "reflected pulses" in these discussions.

"Back Pressure" is caused by restriction to flow. It increases with flow volume or speed. It causes pumping loss in the engine, which reduces power and efficiency. Back pressure is not a good thing, and is not necessary for any engine I know of. The best way to eliminate back pressure is to remove the exhaust system entirely, which leaves atmospheric pressure as the only back pressure. However, there are other side effects such as noise, uncontrolled flames, and so on.

"Reflected Pulses" are caused by any discontinuity in the exhaust system. These discontinuities are usually a change in cross section of the pipe, where it becomes either larger or smaller, including where the pipe ends into the essentially infinite cross section of the open air. These reflected pulses can be either positive or negative, depending on the change in cross sectional area. They can arrive back at the exhaust valve in such a way as to help or hinder engine "breathing." This is where the length of the pipe and the engine speed interfere with each other, either constructively or destructively. Because engine speed is usually widely variable and exhaust system is essentially fixed, peaks and valleys appear in torque curves. Ain't nuttin' simple about it.

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Eschew obfuscation.

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babyhog

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Re: cutting exhaust for drag pipe
Reply #7 - 09/03/13 at 12:25:42

Charon wrote on 09/03/13 at 07:09:18:

It's unfortunate we have no way to distinguish between "back pressure" and "reflected pulses" in these discussions.

"Back Pressure" is caused by restriction to flow. It increases with flow volume or speed. It causes pumping loss in the engine, which reduces power and efficiency. Back pressure is not a good thing, and is not necessary for any engine I know of. The best way to eliminate back pressure is to remove the exhaust system entirely, which leaves atmospheric pressure as the only back pressure. However, there are other side effects such as noise, uncontrolled flames, and so on.

"Reflected Pulses" are caused by any discontinuity in the exhaust system. These discontinuities are usually a change in cross section of the pipe, where it becomes either larger or smaller, including where the pipe ends into the essentially infinite cross section of the open air. These reflected pulses can be either positive or negative, depending on the change in cross sectional area. They can arrive back at the exhaust valve in such a way as to help or hinder engine "breathing." This is where the length of the pipe and the engine speed interfere with each other, either constructively or destructively. Because engine speed is usually widely variable and exhaust system is essentially fixed, peaks and valleys appear in torque curves. Ain't nuttin' simple about it.

You took the words right out of my mouth... Cool

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savagebob Full Member Offline SuzukiSavage.com Rocks! Posts: 235	Re: cutting exhaust for drag pipe Reply #8 - 09/03/13 at 14:27:05 anyone ever fitted a larger dia. header pipe?
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Dave YaBB Moderator ModSquad Offline SuzukiSavage.com Rocks! Posts: 18098 Camp Springs, Kentucky Gender:	Re: cutting exhaust for drag pipe Reply #9 - 09/04/13 at 04:35:18 savagebob wrote on 09/03/13 at 14:27:05: anyone ever fitted a larger dia. header pipe? Yes.....Lancer and a few others have. A 1.5" diameter pipe is about as big as you want to go....any bigger and it doesn't run well.
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