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Old 10-31-2010, 01:44 PM   #1
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Im a newb to pipes and I am going to attempt to build a drag sled out of a 94 zr580 - I have a set of slp pipes + silencers - I assume they are trail pipes but they are very skinny as well as the silencers - is there enough back pressure to run them straight and tube them out the side/bottom? aside from saving a few lbs will it add any hp and will jetting be a pita?
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Old 10-31-2010, 06:04 PM   #2
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Old 11-01-2010, 08:21 AM   #3
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Never run straight pipe on a 2-stroke sled. You will loose significant horse and make it more likely to blow up. 2-strokes need a certian amount of back pressure and a certian shape for the exhaust waves to bounce off of. Straight pipe gets ride of both.
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Old 11-01-2010, 10:54 AM   #4
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I am by no means an expert on expansion chamber/2-stroke pipe design, but it is my understanding that the silencer is considered part of the "tuned length" of the pipe. The dimensions of the chamber are what really effect the performance, but the size and length of the smaller diameter outlet from the "bulge" plays a role too. As far as I know, there are no real gains to be had from running the pipes without silencers, especially if the pipes were designed to be used with them.
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Old 11-01-2010, 11:03 AM   #5
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yes and No on weather you can run with out. pipes might be made to run with a the silencers or they may not. Theres math formuala to building pipes. Running with out the silencers isnt going to blow your sled up might make you less horse might give you more. You may have to re jet cause the increase in air flow through the motor. I am around the vintage guys a lot alot of them build there own pipes theres old tech to build them by hand and theres computer designed. I dont know if this is true but I was talking to a old guy about pipes on sleds he said that they use to build stingers. How you know the length of the stinger is take paint and paint it on the end of the stinger non high temp and let it burn off where it stops burning off and peeling thats where you cut the pipe. That might be snake oil I dont know if that is true or not. You could try running your pipes with out the packing on the end just make sure you measure the length of what you silencer is and the diamater of the pipe. Make sure they are the same. Keep a eye on your jetting I would go up 2 sizes just to be on the safe side.
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Old 11-01-2010, 12:12 PM   #6
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<div class='quotetop'>QUOTE (crashmaster @ Oct 31 2010, 01:44 PM) <{POST_SNAPBACK}></div>
 Quote:
is there enough back pressure to run them straight and tube them out the side/bottom?[/b]
Just looking at this again. If you ditch the silencers and extend the pipe leading out of the reducer, make sure the pipe you use matches the inner diameter of the pipe. Do not reduce the pipe cross section to less than this inner diameter.

(EDIT: teamgreen already said that, sorry.)

Also, I'm not familiar with the silencers you've got, but if they're like the typical dirtbike/atv silcencers with the perforated pipe and fiberglass packing, there is no advantage to running without the fiberglass packing. It is my understanding you can actually lose power that way.
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Old 11-01-2010, 01:44 PM   #7
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Thanks for the input guys! If the silencers do not restrict much of the air flow then I will likely just keep them on. I'm just looking to pinch all the HP I can without getting too far into motor mods - its bascially going to be a toy for the girlfriend to tear the yard up with!
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Old 11-01-2010, 02:58 PM   #8
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Silencers... silence.. but on in frame pipes ( dirtbikes, quads, sleds) the silencer acts as part of the stinger section, the stinger section acts as a bleed-off for back pressure. All the action has allready happend in the diffuser and baffle sections but without the correct length stinger to bleed off the pressure you will overheat, seize your engine, make very little power ect.
If you want to run without silencers you need drag pipes that are designed with the correct length stinger.

The book "two stroke performance tuning" by adam graham bell explains 2stroke expansion chambers very well... I highly recommend the book if you want to learn more about 2stokes, a bit out dated by todays standers but still tons of really useful info.
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Old 11-01-2010, 03:54 PM   #9
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<div class='quotetop'>QUOTE (Frozencat @ Nov 1 2010, 02:58 PM) <{POST_SNAPBACK}></div>
 Quote:
Silencers... silence.. but on in frame pipes ( dirtbikes, quads, sleds) the silencer acts as part of the stinger section, the stinger section acts as a bleed-off for back pressure. All the action has allready happend in the diffuser and baffle sections but without the correct length stinger to bleed off the pressure you will overheat, seize your engine, make very little power ect.
If you want to run without silencers you need drag pipes that are designed with the correct length stinger.

The book "two stroke performance tuning" by adam graham bell explains 2stroke expansion chambers very well... I highly recommend the book if you want to learn more about 2stokes, a bit out dated by todays standers but still tons of really useful info.[/b]
thanks, I'll check it out! and basically making "stinger" tubes is what I was thinking about doing, just wasnt sure if it would make any HP gains
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