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aftermarket headers VS stock?

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What is the difference between aftermarket headers and stock headers?

If there is no difference then a slip-on exhaust would be just as good as full exhaust upgrade?

Is my logic correct here?

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Depends.

Slip ons almost without fail, are louder than stock and generate no more power. So slip ons are pointless.

Headers can be better than stock or worse than stock. What matters is what are you trying to change powerwise? Headers can have a pronouced effect on moving the power on the curve. A fat short header will increase max power at the expense of mid range A thin long header will boost low end but take the top off of max power. And then there is everything in between. There are some headers and pipes that actually reduce power everywhere. You have to watch who is selling what.

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Depends.

Slip ons almost without fail, are louder than stock and generate no more power. So slip ons are poinless.

Headers can be better than stock or worse than stock. What matters is what are you trying to change powerwise? Headers can have a pronouced effect on moving the power on the curve. A fat short header will increase max power at the expense of mid range A thin long header will boost low end but take the top off of max power. And then there is everything in between. There are some headers and pipes that actually reduce power everywhere. You have to watch who is selling what.

Thanks, what I really want is low end power. In your opinion where do you think the YZ exhaust installed on a WR moves the power? low-mid-high?

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When I first got my WR250F (nearly three weeks ago), I removed the pea shooter, drilled the original can (second baffle) and did the free mods and it improved the power noticeably over stock.

I recently added a YZ250F pipe and can to my WR250F, rejetted it to match.

The power is now MUCH better all across the entire range.

I decided to go with a YZF take off pipe because first, it was cheaper, and available, and secondly because I don't think I'm a good enough rider to realize the difference in changing to a $800+ exhaust system.

AIS removal didn't change the power at all, opening the air box, disconnecting the gray wire and changing the throttle stop delivered more positive change.

I've looked at many posts online, here at TT and elsewhere regarding the stock WRF pipe. The internal structure between the YZF pipe and the WRF pipe is very different.

I don't have a flow bench, so I don't really know what the actual difference in flow between the two is, but the YZF pipe and can seemed to bring the bike alive all across the power band.

Nowhere near the HP claims made in advertising with some aftermarket exhaust components, but enough additional flow to take (full) advantage of the change to the JD kit.

My thought on pipes is, the YZF pipe is a great improvement over the stock WR pipe, and the money some spend for aftermarket exhaust slip ons and/or full systems is (for me) going to riding gear, a stabilizer, bark busters, rad braces and a skid plate.

If I want more power down the road, my next consideration is to maybe look at cams.

I'd do a big bore, but, this is a fun bike and big bore kits will shorten your crank life.

If it turns out to be not enough power, I'll probably just move up to a 450 instead of franken the powerplant out.

But, at present, power is simply excellent from bottom to top with no flat spots I can detect. I think the current setup will deliver more power than I am likely to need riding heavy single track.

If I were riding open desert, or anywhere I could often get past third gear, more power might be useable.

For now, I think smashing into a tree at 40MPH is more than enough :smirk:

You might find getting the suspension setup properly for your weight, riding ability and course will make a much bigger useable difference in how much you enjoy the bike than all the exhaust changes in the world

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I've got a 2009 WR-250F.

After I did all the free mods and rejetted the carb, the bike still felt a bit plugged-up.

It ran well and I could have left it as-is, but I had the feeling it was still choked-up via the stock automobile-like muffler.

I tried the backyard trick of drilling holes in the rearward baffle wall, which made it better, but it still felt plugged-up.

I then said, "Screw this" and bought an FMF Powerbomb head pipe and an FMF Q muffler.

Big difference, and I'm so glad I did it.

Power was increased at the low end, middle, and top end.

Yes, everywhere, which tells me that the stock exhaust system is simply restrictive.

Noise has increased, but is still acceptable.

I wouldn't use it if it were too loud.

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When I first got my WR250F (nearly three weeks ago), I removed the pea shooter, drilled the original can (second baffle) and did the free mods and it improved the power noticeably over stock.

I recently added a YZ250F pipe and can to my WR250F, rejetted it to match.

The power is now MUCH better all across the entire range.

I decided to go with a YZF take off pipe because first, it was cheaper, and available, and secondly because I don't think I'm a good enough rider to realize the difference in changing to a $800+ exhaust system.

AIS removal didn't change the power at all, opening the air box, disconnecting the gray wire and changing the throttle stop delivered more positive change.

I've looked at many posts online, here at TT and elsewhere regarding the stock WRF pipe. The internal structure between the YZF pipe and the WRF pipe is very different.

I don't have a flow bench, so I don't really know what the actual difference in flow between the two is, but the YZF pipe and can seemed to bring the bike alive all across the power band.

Nowhere near the HP claims made in advertising with some aftermarket exhaust components, but enough additional flow to take (full) advantage of the change to the JD kit.

My thought on pipes is, the YZF pipe is a great improvement over the stock WR pipe, and the money some spend for aftermarket exhaust slip ons and/or full systems is (for me) going to riding gear, a stabilizer, bark busters, rad braces and a skid plate.

If I want more power down the road, my next consideration is to maybe look at cams.

I'd do a big bore, but, this is a fun bike and big bore kits will shorten your crank life.

If it turns out to be not enough power, I'll probably just move up to a 450 instead of franken the powerplant out.

But, at present, power is simply excellent from bottom to top with no flat spots I can detect. I think the current setup will deliver more power than I am likely to need riding heavy single track.

If I were riding open desert, or anywhere I could often get past third gear, more power might be useable.

For now, I think smashing into a tree at 40MPH is more than enough :smirk:

You might find getting the suspension setup properly for your weight, riding ability and course will make a much bigger useable difference in how much you enjoy the bike than all the exhaust changes in the world

Great post, this what I was looking for clear concise information. You sir are a gentleman and a scholar.

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Depends.

Slip ons almost without fail, are louder than stock and generate no more power. So slip ons are pointless.

Headers can be better than stock or worse than stock. What matters is what are you trying to change powerwise? Headers can have a pronouced effect on moving the power on the curve. A fat short header will increase max power at the expense of mid range A thin long header will boost low end but take the top off of max power. And then there is everything in between. There are some headers and pipes that actually reduce power everywhere. You have to watch who is selling what.

I totally disagree with your position on slip ons. They do in fact generate more power and most manufacturers offer a quiet insert. I'm a big fan of slip ons especially in used bike applications since they come with fresh packing and in most cases a sparky.

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I'd do a big bore, but, this is a fun bike and big bore kits will shorten your crank life.

Not always. I've put 262 kits in a few YZ's and WR's and they are all still running last I heard.

You wouldn't think 12 cc's would do much but it does. If you go with higher compression they really bark.

If you want a neato header pipe Yamaha makes the best one one. And I've tried them all.

SillyExhaust.jpg

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Not always. I've put 262 kits in a few YZ's and WR's and they are all still running last I heard.

You wouldn't think 12 cc's would do much but it does. If you go with higher compression they really bark.

If you want a neato header pipe Yamaha makes the best one one. And I've tried them all.

SillyExhaust.jpg

sillyexhaust.jpg

Uploaded with ImageShack.us

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its where they relocated the boost bottle from early 80s MX bikes that needed to be refilled with snake oil to run properly

A YZ silencer will help your WR make more power everywhere.

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I just put a YZ "slip on" to my WR header and it feels like I got some low and mid increases. I re-jetted with what JD recommended and it seems good. Much cheaper than an aftermarket setup.

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Don't get confused. I understand a WR exhaust makes pretty big compromises for quiet/spark arrester/durability.

A YZ has a no compromise exhaust standard.

An aftermarket system is very unlikely to be universally better. Might make a little more power for a lot more noise. Might be lighter and less durable. Might make a bigger hit (usually straight after a "hole" in the power band) This "hit" often feels like the pipe makes "heaps more power". Back to back dyno tests?

Re the original question. Rocket and FMF brand headers were smaller in diameter than stock on my '08 YZ. I use the Mega Bomb as it was expensive and looks trick. Didn't lose any power over stock on the Dyno.

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Does anyone known if the stock yz headers and the stock wr headers are the same?

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The stock headers on both bikes are different sizes the yz header is bigger in diamiter and the wr is not as big in diamater when I put my slip on on my bike it helped the power quite a bit but when I did that I had to use a reducer so that it would fit right

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Re the original question. Rocket and FMF brand headers were smaller in diameter than stock on my '08 YZ. I use the Mega Bomb as it was expensive and looks trick. Didn't lose any power over stock on the Dyno.

Sometimes aftermarket headers are smaller diameter than stock. Bigger isn't always better since it is all about velocity not necessarily volume.

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