No Silencer?

[Warrioreater400ex]

Hey this might be a dumb question, is it ok to run for a minute or two without the silencer, my eseries broke, and i have one coming in friday, but i also have replaced a buncha other stuff, steering stem, tie rods, chains, sprockets, plastics etc while it was tore down. what i was wondering is i have everything done but the silencer, would it bend the valves or hurt anything if i cranked it up and just kinda rode around the yard, not hammer on it or anything. Its just that im going riding somewhere on sat and i dont want to have any surprises on friday night!:eek2: :confused:

[Cody_300ex]

No, you will not bend a valve by just running the headpipe. Yes, it will be outragosuly loud. You can ride it as hard as you want to. The only ways you could mess you engine up is if you were running in an extremly lean condition which I very seriously doubt. Or if you drop some fine like sand, salt, or sugar in the head pipe and start it up. :)

[mike02ex]

its going to be so loud your not going to want to hammer it, trust me, friend had a 250x with no silencer and i hated riding near him.

[RideRed250ex]

There is no backpressure at at, maybe a couple minutes won't hurt it but won't riding like that all the time burn up the valve seals?

[nosliw]

here's how i see it, i may be wrong but this is the first thing that came to mind.

when you replace your stock muffler for an aftermarket one, you get more flow, so you have to rejet. by taking the muffler completely off, the flow is going to be tremendous, which would require a rejet. so in the short time you ride you will be running pretty lean.

[UglyMotha™]

Originally posted by RideRed250ex
There is no backpressure at at, maybe a couple minutes won't hurt it but won't riding like that all the time burn up the valve seals?



no it won't and quit running around saying that :o :rolleyes:

[300ex73]

It works on almost the same principle as a automobile. Not running a muffler doesn't decrease backpressure, it increases it, which can cause excess heat in the cylinder, around the valves. This causes them to warp, not bend. Running with no silencer on an atv could cause the same thing. The silencer gives the exhaust an expansion point, that at the same time does not allow atmospheric pressure to try to force exhaust flow back into the cylinder which would in turn would cause more backpressure.

Anyways. imo, I wouldn't recommend running without the silencer, just to play it safe.

[muddy400EX]

so does it screw it up or not? ive always wondered this. the way i see it, if you richen it up, it should run fine, but iono

[300ex73]

Actually, running with just the headpipe, as short as it is, will cause the mixture to richen itself. The excess exhaust pressure won't allow as much fresh air to enter the cylinder, so the unburnt fuel still in the exhaust gas will cause it to be too rich. And if you would like to test it for yourself, grab a new spark plug, and remove the silencer. Take off, but be very light on the gas. Get out and run your quad up to full throttle in SECOND gear, then shut the quad off, and let it coast. Check the diodes on the plug, they should be really black, and possibly fouled.

[6858-400ex]

just to be safe if i were u i would not runit at all

[bulkdriverlp]

obviously your getting a lot of facts here, i dont know myself, but if i were you i wouldnt even start it without silencer, cmon think about it, is it worth screwing something up.

[enduro400rider]

mine was ok when i did it a couple of days ago but i only rode it for about 5 min to test some new stuff out that i put on it i woulda had the silencer on but its gettin polished oh and its load as hell too sounds kinda cool but i know alot of people that would get mad if i ran like that all the time

[wilkin250r]

Originally posted by 300ex73
It works on almost the same principle as a automobile. Not running a muffler doesn't decrease backpressure, it increases it, which can cause excess heat in the cylinder, around the valves. This causes them to warp, not bend. Running with no silencer on an atv could cause the same thing. The silencer gives the exhaust an expansion point, that at the same time does not allow atmospheric pressure to try to force exhaust flow back into the cylinder which would in turn would cause more backpressure.


Where are you getting your information?

[Warrioreater400ex]

well, im so confused, but just for the info, i started it up and just to make sure it didnt run to lean i kept the choke on just a little, rode it about 200 ft and noticed a miss in it, so then i turned the choke off, it ran perfect, so i rode prlly another 1800 feet to test everything else out and put it up, ran fine, not too hot, i didnt ride it too much at all but it idled for a few and i didnt get it WFO but i got it up to 3/4. i know it might not have been genious, but i wasnt just doing it for the heck of it, i jsut didnt want to have any surprises on friday night after i get my silencer on for saturday.

[RideRed250ex]

Originally posted by UglyMotha™
no it won't and quit running around saying that :o :rolleyes:


Where have i said that before? I don't recall saying that but you could show me if you would like... No i am not some motorcycle technition but from what i have heard in the past, that was the idea that i have. It is also in a question format.... I am not stating any facts.... :rolleyes:

[red2004 TRX450R]

Originally posted by 300ex73
It works on almost the same principle as a automobile. Not running a muffler doesn't decrease backpressure, it increases it, which can cause excess heat in the cylinder, around the valves. This causes them to warp, not bend. Running with no silencer on an atv could cause the same thing. The silencer gives the exhaust an expansion point, that at the same time does not allow atmospheric pressure to try to force exhaust flow back into the cylinder which would in turn would cause more backpressure.

Anyways. imo, I wouldn't recommend running without the silencer, just to play it safe.

WHAT ARE U TALKING ABOUT!!!!
U GOT THAT WRONG.

Most people run open headers on racecars.
Flowmaster states there race only mufflers make less backpressure if u have to run full exhaust! That is 4in duel exhaust flows better with a delta "triangle" in it but I think not. 1/4 mile times slowed with race mufflers. But have u ever heard or look through a flowmaster race only muffler. NO!!!

Yes cams with not a lot of over lap will like some back pressure but high lift high duration cams love very very little back pressure.

My buddy ran his DR250 all summer with out a silencer on it. The only problem we had is that I still can’t hear and that was like 5 years ago!!!

[300ex73]

I know that on dragsters, indy cars, nascars, all of those run open headers or straight pipes, difference being that they're specially built motors that require open headers to breath right. And another thing is that they're tuned length. These engines put out so much exhaust, that with the correct length header or exhaust, they run just fine. However, on a motor that's not as agressive as these, a specially tuned, full length exhaust works the best.

[nosliw]

this really goes against everything ive used to build my engines. like asked above, where are you getting your information? the suspense is killing me!!!!:scary:

[trynflyn450r]

i think run just a head pipe is ok because once when i was out ridding with my friend the bolts that hold my head pipe on fell out and i had to ride home with no head pipe just right out of the head. and i was about 15 miles from home and my quad still runs great. That was two years ago

[UglyMotha™]

Originally posted by nosliw
this really goes against everything ive used to build my engines. like asked above, where are you getting your information? the suspense is killing me!!!!:scary:




unfortunantly hes' pretty much making it up as he goes, or he just likes hearing his brain rattle :o

[nosliw]

Originally posted by UglyMotha™
unfortunantly hes' pretty much making it up as he goes, or he just likes hearing his brain rattle :o


i figured. :rolleyes:

he sounded pretty confident though :ermm:

[wilkin250r]

I want to know how the exhaust produces less backpressure, because of "atmospheric pressure".

[Trevor]

When ever we have the muffler off of anything we always start it up just for fun a few minnutes won't hurt anything but it sure will piss on your neighbours. I wouldn't run it for more than a couple of minutes though!

[300ex73]

You guys keep making the comparison between your quad motors and racecars. If you want a comparion, here's one. A NASCAR motor is usually about 350 cid, and is running about 800 to 900 horsepower, that's approaching 3 hp per cubic inch. An INDY motor is usually around 190 cid, and runs 700 to 800 hp. that's 4 or more hp per cubic inch. Pro stock dragsters run a motor around 360 cid, and run about a thousand hp. And top fuel dragsters run well over 2000 hp. Your quads motor is about 24 cid(400cc) and runs about 30 to 40 hp, that's not even 2 hp per cubic inch. And as for the cams, they're not nearly as agressive as any of those motors I've mentioned. And as for the exhaust on them, yes, they may all run straight pipes or even open headers, but they're still all a tuned length and diameter to keep the air around us from trying to rush back into the cylinder between exhaust pulses.

As for the mention of atmospheric pressure, the air around us causes about 20 to 30 psi of pressure. Idk where some of you got the idea that i was saying it caused less backpressure. I've been trying to say that if you don't have the correct expansion point for the exhaust, the air around us which is pressurized by atmospheric pressure, will cause you exhaust gas to basically be backed up, because of the force working against it.

You notice how when you don't run a muffler on your car, how it pops really loud. That's backfiring. When your exhaust pressure builds up because it can't get out fast enough, it'll continue to build until you let off the gas. This is because without a proper muffler or resonator, your exhaust can't flow enough.

And as for making this all up as I go. Well, I've been working on cars for quite some time now. I learned just about everything I know from my grandfather, who has worked on cars for about 60 years now, and has worked on quite a few race motors. I have even talked to numerous mechanics, and speed shop owners, and they'll all tell you, that on a motor that's not making more than a 2:1 or higher hp to cid ratio running a tuned exhaust with a muffler is going to work better with your motor towards making power.

[wilkin250r]

What the #*%&! does power to displacement ratio have to do with atmospheric pressure entering your exhaust pipe?!?

Expansion chambers are important for tuned length. But with any restriction at ALL in the muffler, you will ALWAYS have atmospheric pressure or MORE inside your exhaust pipe. You've spent years wrenching headbolts, whoopee. I've spent years studying physics. The purpose of the expansion chamber is to cause a decompression wave and set up a resonant frequency inside the pipe. But you don't need a MUFFLER to be the expansion point, your exhaust can expand into free space and still set up the same resonant frequency. Changing the length of the exhaust pipe will change the RPM at which the proper resonant wave occurs.

When your exhaust port opens up, the exhaust gasses will pressurize the pipe above atmospheric pressure. All that pressure can't exit the pipe immediately because of the restriction of the muffler, that's how it reduces the sound, by SLOWING DOWN the velocity of escaping gas so you don't get a "POP".

So, now that your pipe is ABOVE atmospheric pressure, it will flow OUT the muffler. The reason it flows out is because of the pressure DIFFERENCE between the pipe and the surrounding air. Just like anything else, the air will flow from high pressure to low pressure. If there was no pressure difference, it would not flow anywhere. So exhaust flows out, and pressure inside your pipe drops. It will STOP flowing as soon as the pressure equalizes. It will NEVER, NEVER, EVER EVER EVER create a vacuum lower than atmopheric pressure inside your exhaust pipe.

There are special instances in which you CAN have a vacuum inside your exhaust pipe, but it would require that you have almost NO restriction to the flow of exhaust. With any restriction at all, with any muffler, it is physically impossible for you to have less than atmospheric pressure inside your pipe.

[EPDP99]

score 1 to wilkin

[throwinitup]

who gives a F#CK if you run your fourwheeler without a silencer, you ARE a douchebag... thats my scientific theory i pulled out of my *** like everyone else.