silencer length effect performance

[JoePA]

Just curious how, if at all, does the length of the silencer effect how the engine performs ? Does it move the powerband  up or down the rpm range depending on length?

[rsss396]

I will not claim to be a pipe expert but I can give you theory on how it is said to effect power.

First the Length of a straight stinger and/or silencer has only a small effect on back pressure.
Bends can have some back pressure effect also but Diameter of the stinger/silencer has the most effect

Think of the stinger and silencer as a pressure bleed that does not hold the pressure in the pipe at a exact pressure.
At lower rpms the pressure is less and at higher rpm pressure is greater. Greater pressure in the pipe will help low-mid range power while less pressure will aid topend power.
A increase in pressure in the pipe aids in keeping the fresh fuel mixture from going out the exhaust at low rpms because it will dampen the suction wave in the pipe. At low rpms there is more time for spent exhaust gases to be removed.
But to much pressure will hurt High RPM's because the suction wave needs to be stronger to help pull exhaust gases out in a shorter period. These hot spent gases will soon over heat the piston and lead to detonation or piston damage.


Unfortunately there is not a easy answer to describe exactly what a short or long silencer will do, it is just one part of the puzzle and you have to consider the other variables

[JoePA]

That explains alot and I think you. I remember reading where, as you mentioned, the size of the stinger pipe and how it effects the engine. I just wasn't sure if/how the silencer played a part in that. I think I saw it in an artice where they would just swap out the silencer but kept the stock pipe and it was a very nice gain. It may have been on a bike but figured it would be the same for the quad.

[Sky]

I will not claim to be a pipe expert but I can give you theory on how it is said to effect power.

First the Length of a straight stinger and/or silencer has only a small effect on back pressure.
Bends can have some back pressure effect also but Diameter of the stinger/silencer has the most effect

Think of the stinger and silencer as a pressure bleed that does not hold the pressure in the pipe at a exact pressure.
At lower rpms the pressure is less and at higher rpm pressure is greater. Greater pressure in the pipe will help low-mid range power while less pressure will aid topend power.
A increase in pressure in the pipe aids in keeping the fresh fuel mixture from going out the exhaust at low rpms because it will dampen the suction wave in the pipe. At low rpms there is more time for spent exhaust gases to be removed.
But to much pressure will hurt High RPM's because the suction wave needs to be stronger to help pull exhaust gases out in a shorter period. These hot spent gases will soon over heat the piston and lead to detonation or piston damage.
Unfortunately there is not a easy answer to describe exactly what a short or long silencer will do, it is just one part of the puzzle and you have to consider the other variables

Great explanation. I love learning. Thanks
SO that would explain why a drag pipe is so fat compared to a midrange pipe? Less pressure? I thought the back cone of the "bubble" on the fatter pipe would increase back pressure a high rpm's. Am I on the wrong thought process?

[etccb]

Yes agreed, changing silencers and their back pressure can and will effect your engine's performance. Some changes very very slight and others more.

[rsss396]

If the motor was a large bore with a standard size stinger and silencer, the shorter silencer may help with a very slight decrease in back pressure at upper rpms.
But on a stock cylinder the decrease in pressure would probably not be measurable, whenever you are on the edge of anything small changes can be easier to see

[rsss396]

Great explanation. I love learning. Thanks
SO that would explain why a drag pipe is so fat compared to a midrange pipe? Less pressure? I thought the back cone of the "bubble" on the fatter pipe would increase back pressure a high rpm's. Am I on the wrong thought process?

no the stinger diameter controls the bleed no matter the body size of the pipe, drag pipes are larger because they utilize steeper angles to create stronger diffuser and baffle waves in the pipe. The down side is the waves are shorter in length meaning they only work in a very narrow rpm band making the motor very peaky

[pantera1975]

So in theory the ID of the silencer inlet stinger and the ID of the perforated core should all be the same ID as the outlet of the expansion pipe? For extended length does it hurt to a larger silencer stinger?

[rsss396]

So in theory the ID of the silencer inlet stinger and the ID of the perforated core should all be the same ID as the outlet of the expansion pipe? For extended length does it hurt to a larger silencer stinger?

Yes same I.D. or step up to the next size if you have have tight bends or longer length silencers, especially the with spark arrestors.

IMO, if your motor is a big bore 330-350 running a typical 250R pipe stinger size of 1-1/8 O.D. than at least up sizing the bent part of the stinger and silencer to a 1-1/4 O.D. would be a good move otherwise piston heat and detonation will bite at your heals if you try adding timing and compression

[pantera1975]

Good info here. I got a ATC 5 esr pipe and its 1.125 O.D. 1.25 O.D. slips over it should I keep the perforated cores size the same as my silencer stinger too? This weekend  I strapped for time Steam engine tractor show, John Deeres 50th anniversary garden tractor show and a tractor pull. I need to find time to take the sharp bend out of my stinger yet. The one fellow at Starting Line Products has been a lot of help and there prices for exhaust parts are good as well.

[rsss396]

I think the 1.25 will be fine for the perferated core size but if 1-3/8 works better for assembly reasons it would not hurt anything, but I wonder if a 1-3/8 may work better for silencing because of more hole area to absorb sound? maybe something to experiment with.

I seen your prices for parts from SLP and they are great prices for odd pieces