FMF Powerbomb to stock 08 Muffler

[COV225]

Does anyone know if the FMF powerbomb will fit the stock 2008 YZF shorty muffler?

I am interested because.....

....I had decided that I was going to purchase at least a slip on exhaust for my bike to get back all the power that it lost to the cone baffles in the shorty exhaust. Before making a purchase I decided to experiment.....Armed with my Makita drill and Blue Point 3/8" pencil die grinder I completely disassembled the muffler. Using the die grinder I cut out the cone that mounts at the exit "mouth" of the exhaust since it was the most restrictive. I left in the middle baffle since it is completely perforated from the factory and not "too" restrictive. The muffler was assembled with fresh packing and new rivets. After adjusting the carb slightly according the EGA machine I tested the scoot that night. Much to my surprise (I had great doubt about any positive gains) the powerband now was stronger from the bottom to the top. The bike now revs quicker and faster and feels very much like...dare I say 2-stroke? Also the sound is very similar to stock pipe I had on my 2007 YZ450.

Again I want more power but want to keep my muffler so I am looking into the FMF powerbomb. Thanks.

So inconclusion: gutting the restrictive short muffler works and provides favorable powergains if you like that style of power.

[FinchFan194]

is it much louder? The one thing I like about my stock 08 pipe is its pretty quiet. I like the raspy sound to it too.

[COV225]

No its not. The Dr. D full system I had on my 2007 YZ450 was much louder.

[FinchFan194]

Thanks man I will give it a try how much did you richen you jetting by?

[COV225]

Not sure off the top of my head but I beleive I adjusted the fuel screw and changed needle clip position.

[Demo_Slug]

the 08 header is nice. its a big fat Ti header. I run one on my 08 WR. why down grade? if you want a lower volume header get a stock 07.

[grayracer513]

the 08 header is nice. its a big fat Ti header. I run one on my 08 WR. why down grade? if you want a lower volume header get a stock 07.

In the first place, I rather doubt the PowerBomb could be counted as having a lower volume than an '08 header.

In the second, the '08 header is too large a diameter for a 27 cubic inch cylinder except as a compensation for the overly restrictive '08 muffler. You will find no effective free flowing aftermarket race systems with a header that large in diameter because it is too large to be optimal.

To assume that a bigger header is better because it has more volume is too not understand how a performance exhaust system works.

Besides which, pulse reflex resonators like the PowerBomb provide other functionality that a straight header does not.

[Jim813]

In the first place, I rather doubt the PowerBomb could be counted as having a lower volume than an '08 header.

In the second, the '08 header is too large a diameter for a 27 cubic inch cylinder except as a compensation for the overly restrictive '08 muffler. You will find no effective free flowing aftermarket race systems with a header that large in diameter because it is too large to be optimal.

To assume that a bigger header is better because it has more volume is too not understand how a performance exhaust system works.

Besides which, pulse reflex resonators like the PowerBomb provide other functionality that a straight header does not.

Would this effectively mean that restrictive muffler such as an FMF Q-series or Pro-circuit 496 slip-on would work well with the stock 08 header, while more open slip-ons such as an FMF 4.1(without insert) would most likely work better with a smaller diameter header?

[grayracer513]

Would this effectively mean that restrictive muffler such as an FMF Q-series or Pro-circuit 496 slip-on would work well with the stock 08 header, while more open slip-ons such as an FMF 4.1(without insert) would most likely work better with a smaller diameter header?

If the quieter mufflers are in fact restrictive, or more so then the more straight through types, they could very well benefit from a larger header, yes.

[COV225]

So does anyone know if they matchup....

[grayracer513]

So does anyone know if they matchup....

They don't. The header is, I'm fairly certain, the same size as the '06 header outlet, which is smaller than the '07 and '08-9. FMF makes a spacer to use with their slip-on pipes that might be useful.

https://www.thumpertalk.com/forum/showthread.php?p=6160447#post6160447

[COV225]

Yeah I was aware of the diameter differences since 06. I ask because FMF list a separate part number for the 08-09 models.

[grayracer513]

If they list a part specific to the '08, that generally means it will fit the '08 muffler.

In matters like this, calling or writing to the manufacturer themselves is usually a faster and more accurate source of info. Not always, of course.

[COV225]

Most definately and I did call them and they recommended a full system while not answering my question. So here was my next best choice for an answer.

[grayracer513]

...I did call them and they recommended a full system while not answering my question...

Now that's what I call customer service.

[Demo_Slug]

you are putting words in my mouth. and making a huge under estimation at that. chillax.

In the first place, I rather doubt the PowerBomb could be counted as having a lower volume than an '08 header.

In the second, the '08 header is too large a diameter for a 27 cubic inch cylinder except as a compensation for the overly restrictive '08 muffler. You will find no effective free flowing aftermarket race systems with a header that large in diameter because it is too large to be optimal.

To assume that a bigger header is better because it has more volume is too not understand how a performance exhaust system works.

Besides which, pulse reflex resonators like the PowerBomb provide other functionality that a straight header does not.

[grayracer513]

you are putting words in my mouth. and making a huge under estimation at that. chillax.

Just working with the evidence you presented.

[Demo_Slug]

If the quieter mufflers are in fact restrictive, or more so then the more straight through types, they could very well benefit from a larger header, yes.

do you think the shorty muffler is restrictive? ?

[grayracer513]

do you think the shorty muffler is restrictive? ?

Why, yes I do, but before you jump up and point out that the OP has one, perhaps you need to reread the first post regarding the point that he has modified the muffler so that it is less restrictive than it originally was.

Just a thought.

[Demo_Slug]

Why, yes I do, but before you jump up and point out that the OP has one, perhaps you need to reread the first post regarding the point that he has modified the muffler so that it is less restrictive than it originally was.

Just a thought.

FIrst assuming that people are dumb is bad mojo and pointless.

and I'm perfectly aware of his modification, he clearly stated it. and I would not "jump up and point out". Or at least I hope I wouldn’t. I try not to post “angry”.

Personally, I believe the stock headers are of high quality and are a good value. and they are made of Ti. Which is a nice perk. You can pick them up on eBay for $100 to $150. or maybe cheaper if you get lucky. Power bomb is steel, and can be had for $150 to $170. and is a hassle given that FMF wont answer questions about the header.

the question is if his modification has altered the exhaust to the point that it is free flowing? Where ever you happen to draw that line. But it is still short.

Now this is just me, but In his situation, I’d save the cash and stick with the 08 header..I have experience with the 08 yz exhaust on WRs with the promoto end cap. Which I was told removes the cone.. I missed the install, so maybe that is true, maybe not. But I got to ride two bikes with this exhaust. They work pretty good. But, A quality aftermarket system will still eat its lunch. But that’s another topic.

Can you honestly say that the FMF power Bomb will 100% be the best solution here? What would you do with your money?