Quadmxer....I could be wrong about the dyno sheets that I have looked at. I have modifed a few 4 strokes and have had bad luck with them. Not because they weren't together right, but because I was never happy with the power they put and modified them too much. I've recently purchased a 400ex and I'm not happy at all with the lack of power. You are right, I guess i'm a die hard 2 stroke fan. I have spent many hours on a wr400f and it and the Raptor don't really compare if you ask me(motor wise). I wish Yamaha would have put the wr/yzf motor out instead of the Raptor, Then maybe it would be different. I have a nice 400ex that I would be willing to trade for a 250R if anybodies interested. I'm not trying to put down anyones machine...Different strokes, for different folks I guess. Again, this is all just my opinion. I roadraced an F3 Honda(only 97 hp) so there's no need to explain the power of one to me.

 

I agree, I've been around the ATV scene for a while and have found that most highly modded 4 stroke atv engines are time bombs. In addition to that they don't take well to mods, you really have to sink some cash into them to get some power out of them. The main problem with highly modified 4 strokes is the heat build-up. I have been present to witness 2 440exs seize. Between the 440 kit the cam and high-rev boxes they just creat too much heat especially since they are air-cooled.

 

trx250rob i am not tryin to disrespect anyone but how hard were the 440's ran one u punch one out u cannot not run it the same as u did before it will run hotter the material removed is less heat u can dissipate and that is a down fall of the 400ex it is aircooled but for instance if u bore any thing out far even a v-8 it u will have to run it different it is really common sense if u do not understand the working of an engine or its limits do not try to mod it up just leave it alone

 

That is exactly what I am saying, most people that mod an engine do it because it's not fast enough. Most people are not going to bore and bike out to ride it more leisurly they bore it to run with the banshees. I know the proper way to run these thing is to take a run (drag) let it rest or run it in gear a little then take another run and let it cool of and baby it. I've seen 440ex, more than one, take run after run. The subject was are they reliable and by most peoples riding style I would say no.

 

<< The subject was are they reliable and by most peoples riding style I would say no. >>




Actually the subject is what it would take to make a 400EX run with the Raptor on the road and we all got sidetracked. The added heat comes from more friction created by a larger cylinder bore which isn't much. You can do the math yourself but if you bore a 400EX from stock (85mm) to .200&quot; overbore (90mm-which is about 440cc) the circumference of the cylinder is increased about 15mm. This will add friction but very little. Come on, we're talking 1/2 an inch. If you raise the compression of the piston you will also get added heat but an adequate exhaust will help expel that excess heat. A more aggresive cam only acts to add more air to the cylinder allowing you to add more fuel which will create more power. The cam by itself doesn't add any extra heat to the engine. Higher revs will add heat to the cylinders as well by creating more friction. I do understand that you will not be able to get rid of all this extra heat and that it can do damage to your engine but running a stock engine all day without letting it cool down is not good either, especially if you trail ride in mud or sand where the cooling fins on an air cooled engine can get covered and lose their cooling ability. The 400EX especially is vulnerable to overheating because it is air cooled, but all of the new sport and high performance quads I see coming out are liquid cooled and the cylinders are being coated to help with the heat as well. By the way has anyone actually measured the cylinder or exhaust tempuratures before and after to see how much heat is gained? Hmmm. That would be an interesting experiment. It is not just a 4 stroke problem either. Banshees are known overheaters as well, especially when trail riding because the radiater just doesn't get the cool air needed to cool the liquid. While I do understand the issues with heat I still do not agree that modified 4 strokes are timebombs just waiting to go off. By the way how often does a fully modded 2 stroke need a teardown?

 

thank you and i do agree that the temp experament would be a learning experience and a 2-stroke can be modded up to the max but i had 250r and it was pretty hot reeds,jets,boost bottle,nd more but had to be redone every 50 to 100 hrs and that expensive i will stay w/ the 4-strokes for now ride on