I know there are a few threads discussing powerbombs and megabombs, but...


Does it make much difference where the megabomb is placed?  If I was to make my own megabomb, and put it a lot closer to the motor, how would it act different?  Or would it?  I keep thinking about making my own, but I don't want to take off the "heat shield" that is right about where it is normally placed.


So, my big question...  How would it act different, going from the extremes? 2" away from the motor...  Or 2" away from the end of the pipe?

What is the trade off?



edit:  Is my assumption correct, that to get the same effect (whatever it is) that the size of the *bomb would need to change, in relation to where it is on the pipe?  Or is that way off base....

Edited by 98cr250r

Understand what the "bomb" is and is not.  It is NOT an expansion chamber.  This is, it is not simply a wide section of the pipe.  The tubing of the header continues through the inside of the bulb section, and is perforated with some small number of fairly large holes (~ 8-10mm or larger) to allow some of the pressure in the header to "bleed off" into the larger volume of the chamber formed by the bulb.  This pressure then vents back into the pipe once the pressure in the main tube drops.  This essentially makes it a "resonator".


The function of the "bomb" is intended to be less about adding power than it is about widening the power curve by reducing the boosting effects of of the acoustics within the pipe so that it has less focus on one particular RPM range.


The "bomb" does not have to be concentric, either, but can be a chamber of any shape that is tapped into the header (see the stock header on a 2010 YZ450F).  The total size of the area of the hole(s) and the size of the chamber are much more important than the location, although near the midpoint of the header length seems to be where most of them are put.

So, in your opinion, it should work exactly the same, if it was placed right at the beginning of the pipe?  And, if not...  What would you expect the difference to be?



edit: Thanks for the reference to the 2010 YZ450F btw...  looks like the fmf version of that is right past  the mounting flange

Edited by 98cr250r

Any change to the pipe design will make it perform differently. Will you notice it? Probably not. The power bomb is, as said before, just a resonator. If it made a huge difference more companies would be following suit. Anyways, it does change the power curve slightly. If it has a. Perforated tube inside it will be different than just an open chamber. If the perforated tube has a couple holes vs tons of holes, it will act different. If the holes are big vs small, it will act different. If the chamber is closer or further from the cylinder it will change things.

Building a setup yourself is fun for experimentation. See what works and what doesn't. It's people who try that can succeed. Just remember more sound does not equal power. I know a couple people when we were kids that tried to make exhausts for their 80s and it was a nightmare. It sounded louder, he thought the bike was more powerful because of it. In fact, the power was less. It just sounded faster. You need to do actual testing to know for sure if it helps or hurts.

Oh and the same goes for dents in the pipe. The location of the dents makes a huge difference too. The best example is with old 2-stroke pipes. It starts small, gets large, then gets small again. Certain dents in the smaller part near the cylinder can add power. Other dents will decrease power considerably. Now, dents in the larger portion of the chamber further down the exhaust stream makes less difference in power.

In the end, any change you do, will have a result. It may be good, it may be bad. You may need to change carb settings or FI settings, you may not. Try it and see what happens.

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