Well the last piece of the puzzle for my upcoming project was an exhaust header. I've already ordered a BB 351 kit including the pumper carb, the FMF Q4 slip on (paid $288 free shipping, no taxes), a Ricochet skid plate and a D606 130/90 rear tire, so I have been reading up various posts on the header and found the FMF Megabomb for under $192 including shipping with no taxes (shipped to upstate NY).

If anyone is interested PM me and I'll let you where I found it for that price.

 

Its the best header you can get in my opinion

 

What part of the powerband is enhanced by the 'megabomb'?

I have bought the powerbomb header b/c it was bigger in diameter than stock. But I see them both on race bikes in the mags (both mega & powerbomb). The topend power seems to be better w/ the powerbomb but that could be b/c of the fcr carb too.

 

I am no expert but from what I have read they both enhance power, the Powerbomb in higher RPM's and the Megabomb at lower RPM's which is what I am looking for. Plus they are both claimed to lower the exhaust decibels to some degree, another goal of mine.

 

When I was reading an write up on adventure sight about the 351 kit, the initial test guy found he actually lost horse power when he installed the over-sized header. iirc he seamed to be testing it with a variety of combos and ultimately settled on the stock header. I'm really curious as to what's what now because I'm hoping to eventually do the 351 kit (can't justify at the moment because my motor has less than 1000 miles on it). My plan was in the meantime to do whatever muffler/header combo I'd carry straight over to the 351 kit (waste not, want not!). This means if I'm not going to gain hp by putting on the header in the long run, I'll skip it for now. If anyone has a linky that shows someone made a good comparison from stock header with slip on to mod header with slip on on the 351 I'd love to see it.

 

There are a couple of different trains of thought when it comes to header sizing. First it is generally considered that a smaller diameter will help the low end by increasing the velocity at which the gases vent through the header and hurt (to some extent) the higher end of the RPM scale.

Then there is the fact the bigger the engine the higher the volume of exhaust gases to be vented and the need for a larger diamter of the header.

The 351 kit will effectively increase the volume of the cylinder by 41%, quite an increase in volume. FMF is already proclaiming a gain in power on an otherwise stock size engine, of course it is their job to sell their products but there must be some truth to their claims otherwise they would loose respect and be out of business.

I am counting on the Megabomb offering an increase in power across the RPM range but will be more concentrated on the low range.

We'll see once I have it all installed and get the fine tuning done.

 

They tell us their part gives more power than the sock, obviously they do since that's the only reason why anyone would ever buy these king of aftermarket "performance products".

They don't loose credibility even when there IS no truth to their claim because:

1) People who bought the products will tell others that they notice more power.
Of course they do! Who would outright admit having just wasted x hundred dollars on some useless gizmo. We want to believe the gains are there.

2) VERY few people take their bike to dyno to actually test if there REALLY are any gains or not.

I like to listen to the people who have done some objective testing to get data. The data (that I've read about) show no gain what so ever from FMF header. Even with 351 kit. With stock 250cc engine the bigger header probably hurts even more.

--
Mikko

 

I just put a power bomb on my 07 250.
It's stock other than 128 jetting, lid removed, and the backfire screen removed.
I had a stock header, with home made 1.5" secondary pipe, and muzzy can.

It was pretty fast with that setup. In fact, removing the screen was the icing on the cake. It had strong low end, and excellent midrange power. It was the fastest it's ever been.

After installing the PB, and Q4, it was pretty obvious I had to jet. I'm not one of those guys that thinks you need to rejet every time you touch the bike, but this was obvious. It was down on power, and cutting out starting around 8000 RPM.
I put in a 132, and I don't think it's quite there yet.
It feels fast, but doesn't have the same 'hit' down low. On the other hand, it revs VERY freely in the lower midrange. More so than before. Once I put a 135 jet in, I'll post the results.
At this point, I'm up in the air whether I think it's too big for the 250. I thought the stocker (1.25") was too small, but I think this (1.5") might be too big.
I need to jet, and live with it for a while.

 

Reading this thread, everything makes a a lot of sense. After I installed the powerbomb, the bike definitely felt more powerful on the highway and through out the rev range. I only noticed the increase in power and did not notice any loss at any rpms. The only strange and disappointing thing was that it became much harder to loft the front in first gear without using the clutch and just abruptly flicking the throttle. I also thought it became slightly quieter as well. My findings concur with what you guys are saying about the powerbomb...that it increases HP but kills the low end torque and the dB. Ironic as I originally installed it to try to make it easier to loft the front without the clutch and I ended up making it harder. The Megabomb was not available at the time. I do however enjoy the improved power with the Powerbomb.

 

I don't know how you're doing it on a 125 main jet. Elevation?
I think I was fat at 128, with the stock header, but once the backfire screen was out, that bike was spot on.