exhaust header question

borjawil · Posted: March 25, 2009, 10:42 am Post subject: exhaust header question

So i was once told that without the mufflers on the header pipes that when you cut off the power cold air will rush through the pipes to the valves and possibly warp them. Well i ve seen lots of bikes with home made pipes with out mufflers and pipes with look to be exhaust tips or short mufflers on them. How do they run these short pipes without the effect of the cold air? I like the sound of the headers without the mufflers, and i know people drill out the baffles on their exhaust, wouldnt that just make it a longer header pipe basically?

woodman · Full Member Joined: Oct 12, 2008 Posts: 256

On an 81 the pipes are double walled, a pipe within a pipe with an air gap. The bad part is the outer pipe has cooling & drain holes in it. Look furthur down on the posts and youll see how an adaptor can be used to get around this problem that was shown to me last week

borjawil · Posted: March 25, 2009, 12:53 pm Post subject: Re: exhaust header question

well i have an adapter that connects on the inside pipe allowing mufflers to connect properly. my question is more how home made pipes dont have the problem of cold air reaching the engine when shut off

BigGeorge · Full Member Joined: Apr 13, 2008 Posts: 267

Well first of all where are you getting this rush of cold air from? Unless you park your bike with the open end of the pipes facing a wind storm on a winters day where is this cold rush of air you are refering to? Ok, even if cold air were introduced into a hot pipe it would most likely end up being warm air by the time it reached the valves.... I think whom ever told you that is jerking your chain... I ran straight pipes on every bike I had in my younger days until I learned its next to impossible to get a bike to run properly with them, but it had nothing to do with warped valves, but rather the lack of back pressure, but thats something entirely different than what you are talking about......BG

borjawil · Posted: March 25, 2009, 1:58 pm Post subject: Re: exhaust header question

i see. yea the person said the vaccum or something causes air to rush up the pipes or some thing. i dont know. Anywho thank you for answering my questions. Smile

yamaman · Posted: March 25, 2009, 2:34 pm Post subject: Re: exhaust header question

borjawil wrote:

So i was once told that........

Never heard that one before mate!

Exhausts have their uses, look at 2 strokes, fairly useless without chambers. Not quite to the same degree, however still important, are the dimensions of a 4 stroke pipe - muffler and how it relates to a particular engine & its state of tune!

The site I've attached here is very good at explaining how exhaust gasses work if your a scientist! But the pics tell a story. Though they are talking jets, it's the same principle for exhaust gasses! The gasses need room to expand & contract. In most cases, lobbing off half the exhaust will just result in a poor state of tune as well as being painfuly loud.

Things like drag cars run short direct pipes (and keep their valves), but to build a expansion chamber to suit their flow would end in a huge system, so they cut their losses & run as they do. As everything, it's a compromise!

www.allstar.fiu.edu/ae...ocket3.htm

Some good info here on back pressure BG:

www.uucmotorwerks.com/...uemyth.htm

woodman · Full Member Joined: Oct 12, 2008 Posts: 256

Putting a small screw with a wingnut & some washers in the end of the pipe will help give it some back pressure and help a little on the tuning and youll still be able to get the obnoxious noise you want Rolling Eyes

xsjohn · Posted: March 26, 2009, 11:54 am Post subject: Re: exhaust header question

Haven't seen these Snuff or Nut's in a while but I used them years ago......coud set them intermediate for some semblance of sanity.......xsjohn

borjawil · Posted: March 26, 2009, 5:02 pm Post subject: Re: exhaust header question

interesting. thanks for the help and ideas!

oldskoolcool · Full Member Joined: Sep 08, 2007 Posts: 372

thats why i bought pipes with removable baffles...$11.00 from JP cycles. so for those days when i want no baffles out they come. But the bike does run alot better with them. Very Happy

BigGeorge · Full Member Joined: Apr 13, 2008 Posts: 267

oldskoolcool wrote:

thats why i bought pipes with removable baffles...$11.00 from JP cycles. so for those days when i want no baffles out they come. But the bike does run alot better with them. Very Happy

The reason your bike does not run as good when you remove the baffles is the mixture becomes leaner and also your bike will run hotter with a leaner mixture .. When ever you make changes to the air intake or exhaust you should make changes to the carb mixture to compensate..........BG

oldskoolcool · Full Member Joined: Sep 08, 2007 Posts: 372

Quote::

The reason your bike does not run as good when you remove the baffles is the mixture becomes leaner and also your bike will run hotter with a leaner mixture .. When ever you make changes to the air intake or exhaust you should make changes to the carb mixture to compensate..........BG

yeah i didn't know that already...

JLukasik · Full Member Joined: Jun 27, 2008 Posts: 11

No pipe at all could lead to valve damage, but if there is some sort of exhaust they should survive.

woodman · Full Member Joined: Oct 12, 2008 Posts: 256

used to run the wingnut & washers on a 72 Sportster with drag pipes, you wouldnt believe the difference they make. That was 37 years ago though and they give me headaches now but whatever turns you on. It works !

wesleyonoel · Full Member Joined: Oct 02, 2007 Posts: 60

Ah, Snuff-or-Nots (at least that's what I remember)...... Used to be very popular on the 250 and 305 Honda scramblers with the upswept pipes on the left hand side of the scooter. As I recall, original equipment was a pretty big 2-into-1 muffler arrangement that was thought to be rather unsightly. Don't recall any difference in performance with the exhaust wide open or "snuffed"............those scooters weren't much more than noise anyway. Not disparaging them.......I still own a 250 model! Interesting pieces of Japanese motorcycle history............Wes

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