Britbike forum Forums Thread Like Summary - Straight pipe exhaust

If I’m thinking about taking the baffles off the exhaust what should I also consider?

Just try it. Take off the silencers and go for a ride. You may not find a significant increase in performance, but if it's a 650 / 750 twin Triumph, or a Commando, my bet is you will. If it doesn't run smoothly throughout the rev / throttle opening range, that can be made good by careful carburation adjustments. You can theorise until the cows come home but there's nothing better than experimenting for real and seeing what works.

Oh, just to add to the 'loud bikes save lives' debate, I believe this to be be very true. As both a driver and bike rider, I have noticed that, despite the laws of physics, I hear loud bikes coming up behind me, or approaching on main roads I'm waiting to turn out on, a long way before they get near me.

the key is to only use them briefly

The loud pipes theory depends on the sound going forward, but your exhaust pipes point back the way. So loud pipes just annoy people who have not hit you, the ones that do hit you never get to hear the pipes.

Your neighbours?

Apart from that, you will have to cross any carburation changes if/as required.

I put a used 12 disc Supertrapp muffler on my modified T140D with the stock 2 into one head pipe..Sharp response at lower speeds and a better pull at high rpm.compared to a straight through aftermarket muffler..It' has a full sound but not overly loud. John Healy said when some tracks required exhaust noise reduction he used a Supertrapp and found more power....

theoretically, with all other things being equal, assuming the correct phase of the moon, less exhaust restriction should give better cylinder filling and more power, just like water can flow through a clear pipe faster than one with baffles.

but clearly that isn't the whole answer. i'm guessing the effects of a muffler would modify high rpm cylinder filling at overlap, by slowing the gases that otherwise would cross over the piston crown and exit the exhaust valve. i'm also guessing that the sonic resonance of various types of mufflers would increase and decrease torque at various rpms in the same way that changing pipe length or adding a megaphone would. i've found with a high-rpm-focused motor that changing the lengths of the pipes just a few inches makes a significant difference in top sped.

mufflers come in so many varieites that i think the best way to find out what works is to talk to people who try things and then try them yourself and see.

I think it’s not the best likeness to compare water passing to air air flow. If you pour water down a megaphone it won’t fill the mega, just pour directly from the centre.

The best likeness I think is to a sine wave. A good system should send the wave back up the pipe I believe. The “loud pipe” “blat blat blat” noise is a good indication that isn’t happening. It leads to not only poor cylinder scavenging but poor filling. Although this is probably in one sense the same thing. You need some back pressure as I understand it to allow the cylinder to fill properly, during the overlap the inlet charge starts entering before TDC on the exhaust stroke this pushes out the remaining spent gasses in the cylinder. If you haven’t got that back pressure I “think” you’ll have one of two situations or both.
Fresh induction gasses finding them self in a hot exhaust system (which will show up as backfire)
Poor performance from poor cylinder filling with fresh mixture.



If you have a megaphone, a good example/test is to put the mega along different parts of the down pipe, so start off at the end of the pipe and then try it further along. I’ve found it works best if the pipe is several inches behind where it enters compared to just being in enough to be secure.


Really??? Will you be riding the bike or posing down the local pub? I don’t mean to be rude but if your not really going anywhere on it then it probably won’t bother you, but if your going for a decent ride on some decent roads, or even in and out of urban traffic then it will get tiresome quickly being constantly up and down the box on a bike that won’t pull the skin off a rice pudding.



Yeah, I don’t think it works just like that. Read my note above.


Well you’ll definitely have that.

Contrary to what most others who have replied seem to think, in my experience removing silencers makes a very significant improvement in performance throughout the throttle opening and rev range, as long as the carbs are adjusted to suit. Try it for yourself. You'll get dozens of different and entirely opposing opinions on here or any other forum. I won't say any more, it's no skin off my nose what anyone else does or thinks, if it's only motorcycle stuff.

I think we are judging the Harley Crowd unfairly, Somebody explained to me what they're actually doing is LARPING. A form of entertainment called Live Action Role PlayING.

The fact that they are on motorcycles is purely incidental to the need to get dressed up and act as a certain character.

From wiki: “A live action role-playing game (LARP) is a form of role-playing game where the participants physically portray their characters.[1] The players pursue goals within a fictional setting represented by the real world while interacting with each other in character. The outcome of player actions may be mediated by game rules or determined by consensus among players. Event arrangers called gamemasters decide the setting and rules to be used and facilitate play.”

i knew i'd seen that somewhere. gordon jennings:

These several difficulties should convince anyone that a different approach to the
problem of effectively silencing the expansion chamber is required. Lacking a more
effective solution to the problem, we may eventually be forced to revert to a
straightforward muffler in place of the expansion chamber and live with the loss of power
and performance that entails. I do not believe that will be necessary, as I stumbled upon
a phenomenon a few years ago that meant very little at the time but now assumes major
importance: The then-existing general racing regulations required that a motorcycle's
exhaust system terminate at some point forward of the rearmost edge of the back tire, and
I was planning to race a bike with its cylinders reversed to provide rear-facing exhaust
ports (for reasons that were important, but not pertinent here). The only major flaw in
this scheme was that even with the motorcycle built on a longish wheelbase and with its
engine located well forward, there was not quite enough room for the exhaust pipes
within the length allowed by the rules. The expansion chambers themselves would fit,
but there was some 12-inches of outlet pipe left hanging back behind the rear tire, and not
enough room to curl these outlet pipes back within the limit. While groping for a
solution, I hit upon the idea of simply sliding them forward, inside the baffle cones.
There, they would still function as pressure-bleed resisters, and further contemplation led
me to the conclusion that the expansion chambers might even work better with their
outlet pipes positioned inside. With the forward end of the outlet pipe located at the
chamber's maximum diameter, ahead of the baffle-cone, there should be a somewhat
Two Stroke TUNER’S HANDBOOK
70
stronger reflection from the baffle, and that might very well give the engine a somewhat
better boost. Or so I thought.
Anyway, I gave the scheme a try, and while certain other modifications prevented
drawing any absolute conclusions from the experiment, the bike did prove to be very fast,
and it seemed certain that while my “inside stingers” might not offer any real power
advantage, they probably were at least as effective as those attached in the more
conventional manner. But that is not to say that I did not notice a difference - and the
difference was in sound. With those inside outlet pipes, the typical expansion chamber
crackle was very noticeably subdued. That made sense, as the chambers' outlet to
atmosphere was taken from a point where the pulse was at its lowest amplitude - rather
than from the high-pressure area at the tip of the baffle-cone.


^^^this is out of goron jennings two stoke tuner's handbook, a very exceelent read that covers a lot more than just two strokes. his chapter on exhaust systems is one of th ebetter parts of the book. available online in free pdf

well, remember that with a hot gas, it will expand to fill a megaphone as soon as it enters it. with an open pipe, the decrease in pressure will be immediate and sharp, while a megaphone will average out the same decrease over the length of the megaphone and return a weaker, but longer pulse.

im interested in your experience with slipping the megaphone up the pipe. it sounds like the anti-reversion cones people sometimes put up in the front of the pipe to cut back on gas return at the exhaust valve.

did you put the megaphone on stock pipes? i tried out a 17-inch open reverse cone megaphone on stock triumph 650 pipes in place of a muffler, clamping them n the end, with a 2-size bump in the main jets i went from 114 to 117 mph in the mile with no other changes

pipes are so complex i don't believe in anything except cut-and-try and listening topeople who test things

I've had scads of bikes over my younger years and the fastest one, faster than my Norton 750, was a performance modified '69 Bonnie with "TT pipes" which as I recall were just tuned headers. Isn't this what racers use? Isn't this the ideal performance config? I remember the 2-stroke guys talking on and on about "expansion chambers" but never 4-stroke guys.
Anyway, I'm watching this thread because the "mufflers" on this current machine ('72 Tiger) don't and I seem to be missing some power.

As to whether a nasty loud bike is safer, I used to think this way. As teenagers we used to stuff a roll of chicken wire up the muffler to get past inspection after getting an "excessive noise" violation. After a pass, we'd drive around the corner and pull it out and blast away, probably within earshot of the inspector.

Now I don't know. I think there is some safety value in a loud bike and ANY safety might be worth the bad karma incurred.

My Triumph land speed racer.,friend is the rider..Setting a new class speed record at the now closed Ohio one mile track. The bike has no tach but It's always geared never to exceed 7000 rpm at the target speed..Oh, hear the clean moderate fast shifts and no clutch slip? Tiawan 6 plate having no problem with the thundering 55 rwhp.

I have a 1963 Parilla 250 Wildcat scrambler. They were aimed at competition and came stock with a unbaffled reverse cone megaphone as a "muffler." They also have a pretty radical cam. If I start it up without the "muffler," it is loud, but not overly obnoxious. If I start it up with the "muffler" on it, it is ridiculously, blood from the ears, and really piss off the neighbors LOUD. It sounds like an F-1 racer starting up and is quite enjoyable, albeit in small doses.

Ed from NJ

I have a couple of reasons not to run open pipes
1) It gives little piggy an excuse to pull you over
2) A loud exhaust gets tiring after a few miles

BTW I have a silencer on my race bike 68548883_2851412968205558_1660346017746255872_n by Sigma Projects, on Flickr

The nice thing about these old turds being around so long is that any modifications that can be conceived by man or beast have already been tried. Some work, some don't. Some people believe some things work and if you believe that's good. Before you start hack sawing up some expensive parts to see what happens it's best to inform yourself about how bikes work. The best person I've found to explain this is Kevin Cameron. His "Sportbike Performance Handbook" is well written and easy to read. There are lots of drawings so you don't have to visualize anything and some math formulas even I understand. All in all a good read on a cold winter's night.
I don't think anyone hates (strong word)Harley riders, again you can't see the smile on the guys face when he's writing. Mostly it's good natured poking fun.