For all you kids out there. LEAVE IT IN. 250cc will not benefit any with open exhaust. Youll just get more riding areas closed down do to excessive niose.
That’s where ur wrong bc on my 22’ kx 250 x I put a fmf q4 and a spark arrester limits power big time like 5-10 hp big time so yes state parks might be illegal just put it back and most of the time they won’t check
@@chanceguilherme2589 You can, it's just not a good idea. you'll get 2hp max, and the forest fires these things prevent is worth keeping the small metal screen.
Geniune question how would a dirtbike even start a fire?, I ride I got a cr85 but I don’t understand cus my bike has never backfired before or anything that could cause a fire so I’m kinda lost??
@@robertbutler5615 sparks or other hot flammable shit can travel down the pipe. Usually theres just a metal screen on the exhaust tip. removing it just makes you liable for burning down a forest
@@ocker58 I run a spark arrester, it more of a legal thing. If the dnr sees me shooting flames Imma get a ticket which means less money to dump into my truck and bike
It's not FmF just knows what they are doing, of course they do, like the commentor above said they have so many regulations/laws to navigate through so they do everything to make sure they comply, just like car manufacturers with catalytic converters. On the other hand if they knew it wouldn't change performance for the better they would not make it so simple to remove.
When I hear people say “engine like a little back pressure” it makes me cringe... scavenging and back pressure are two different things and no engine wants back pressure
Most people aren’t tuning experts tho. And it’s not easy to get a 2 stroke running consistent. Start fucking w this stuff and ur going to have to do a little tune up to account for the loss of pressure. I think you’re right in some cases, but the newer motors are build to operate under that pressure. Remove it and you’ll prematurely wear it out. I remember an exhaust guy begging me not to straight pipe my f250 (I wanted to do a hood stack straight out of the turbo.) he said cat back only. The motor will spin too freely and blow it up. It’s cool until you need a new motor. This guy was experienced and adamant I not do that. That’s a big truck motor tho, not sure if the same applies here, but I’m assuming so 🤷♂️
People who think backpressure is a good thing don’t actually know anything about how exhausts work. Backpressure is always bad. The whole point of an exhaust is to get the gasses out as quickly as possible for the next cycle. Exhaust velocity and scavenging is what matters.
👏 Well explained. People do not seem to understand that exhaust scavenging is NOT the same thing as backpressure. I made a short about how needing backpressure for performance is a myth, a while back. Got comments from people telling me that without backpressure, you'll burn up your valves... It doest take that much effort to think about it for 5 seconds and realize that what they are complaining about is literally the need for exhaust scavenging... 😂
What YOU don’t understand is that without a proper tune a bikes A2F will be ruined by the lack of backpressure. That’s what we mean when we refer to that. That’s what people like you forget! Not everyone gets a tune. Backpressure is necessary without a tune.
@@blizzthebike Thats clearly the part you do not understand. Think of it this way. An engine is basically an air pump. With that being said an air pump with back pressure is clearly less efficient than a pump without back pressure. Hang on ill post a link to a video and let a professional give you an explaination. Hold up a sec
@@jonathanmoulton9251 actually that is unburnt fuel loading up in the pipe then spontaneously explodes, so yes back pressure does play a roll in it, but hey man I’m not no expert, I just been working on power sport my whole life lol
That’s a spark arrestor - required for public trail riding in most states… and the police regularly do checks, by sliding a stick down the pipe. If they don’t bump into one (the basket looking thing) you’re getting a big fine
Can everybody agree a motor is an air pump (you all better say yes). More in, more out is the simplest way to prove back pressure is bad. It is much more complicated, I know. When goin out if you speed up the air faster then goin in then you can got more in (scavenging). If you straiten the flow you can get more out buy (scavenging + resistance too). Bigger out then in (but not too big) will help. Too big can cause low pressure spots actually sucking in air from the tail pipe leading to opposing forces. You can do simple test at home with a small fan, cardboard, ducting and tape. Do it your self. See if you can increase air velocity from a fan using those materials. Its fun and you just may learn something.
Beneficial back pressure is a myth. Maximize exhaust velocity while minimizing exhaust pressure. Any amount of pressure seen at the back side of the exhaust valve is lost hp and retained heat. People mistake exhaust velocity for backpressure, velocity is what creates the scavenging effect every combustion event. The only time "back pressure" (Drive pressure) is ok is with turbo vehicles, and the ideal drive pressure is 1:1 with MAP.
@@okerhrh4139 The majority of your exhaust velocity is created at the header... I'd estimate around the first 12in of exhaust. In almost all cases for modern bikes, the removal/addition of the spark arrestor alone isn't gonna have a noticeable impact on performance either way. The only thing it changes is the tone of the bike, and often people get a placebo effect from that tone change and think the bike makes more power.
the exhausts are designed to be run without the baffle, i worked at sc project for a little bit designing full race systems, we always shipped them with the baffles, but they were never intended to be left in there, if anything the increased resistance in pushing out the exhaust, takes away from the air and fuel you can push into the cylinder, meaning you get a weaker explosion, which means less power, the optimal back pressure is without the baffles, with them you're just choking down the engine
@@repoman28d you try and get a full race spec system and run it with and then without a baffle, you will feel a difference, yes, the other parts of the exhaust have a effect too, but choking down the entire exhaust, making it move slower and there for letting in less air into the cylinder will make it run worse and produce less power
@@astontoftero3404 the screen isn’t slowing flow nearly at all. It’s simply preventing a potential live spark free and starting fires. Off road guys understand and the mx guys don’t use them because they aren’t required on a closed course. The amount of power a modern 4 stroke mx bike off the showroom floor is more than most can handle and the difference felt between a spark arrestor or none is negligible.
@@repoman28d clearly you haven't seen a baffle, let me explain, in the muffler part of the exhaust, you have a little piece of metal that makes the diameter of the exhaust go down, meaning it chokes down the entire exhaust. It is not a spark arrestor, it is a baffle that chokes down the exhaust as a consequence of making it quieter
What does do something though is a spark arrestor and if you are riding trails DONT RIDE WITH OUT ONE. Shit like that is why there are so few places to ride now. (my state has 7 that is it and you can only ride May to Nov.
@@Jmacfann I put studs in the winter and ride. Never has been a day I couldn't ride the 650 don't like to take off in the snow but keep it moving like a car. Drunken old lady with broken hip on the back on a sheet of ice fun times.
It acts as an "artificial valve" in 2 strokes where air/fuel mixture may normally be lost to the exhaust. The extra pressure in the exhaust mitigates this allowing for more fuel to be in the cylinder for ignition. For anything 4 stroke mitigate back pressure. You actually want as low of pressure on 4 strokes when that exhaust valve opens
It's a dirt bike so km pretty sure that for when you do trailing or off roading In muddy conditions that filter is supposed too keep rocks an little pebbles, stuff that's not supposed too go into your exhaust but some people dont really see that useful but yeah it sounds cool gives it a little more hp. But your right keep it on for trailing.
With a 4-stroke engine, the valves are all shut during the compression stroke, so you don't need any external pressure to get good compression - the cylinder is effectively sealed.
Back pressure is a myth. To my knowledge it was a myth started in the 1970's so people wouldn't modify car exhaust and take out restrictive emissions equipment. There is a reason race cars/ bikes don't have restrictions in the exhaust system
"Back pressure" is a misnomer. It's not usually the pressure that is helping anything when it comes to exhaust efficiency, it's velocity. Higher velocity gasses in the exhaust help to draw exhaust gasses out of the combustion chamber through a process called "scavenging." If the exhaust is too wide open, the speed of the gasses in the exhaust drops and the engine has to work harder to push the exhaust gasses out of the combustion chamber. Any energy that is spent moving the exhaust gasses is energy that doesn't make it to the rear wheel. Now the one part that does have to do with pressure is about a pressure wave, not a constant pressure. This is usually discussed on the intake side of things, but it applies to some degree to the exhaust as well. Look up "hemholtz resonance" to learn more about how pressure waves can be used to increase horsepower.
Idk where your from but where i live tracks are more polices than trails. If your caught removing a spark arrestor your banned from the track for life and can revieve a huge fine
Yes we know bikes like back pressure..I thought I would have a genius idea of taking the baffle out of my 2 stroke...sounds lovely..so loud..went like a wet Fart.. no back pressure = slow as fuc£ performance 😂😂
