Is that an expansion chamber, or cat?

An expansion chamber can be found on 2stroke engines. It might be a catalytic converter

They also run expansion chambers on 4-Strokes, they are different than the 2-Stroke one, but the bigger section on the header is an expansion chamber, all the performance 4-Stokes systems have them, and the Templar has one on the stock system.... It smooths out the pulses, allowing the exhaust to flow smoother

so what an h pipe does for a v8

I agree, the exhaust gives me supermoto vibes when riding from the sound of it, from idle to heavy throttle, odd that it does I know, but it really makes me want to invest in a set of 17's for really bad. I did figure at the same time doing this would be a good opportunity of going down on that rear sprocket a little for the top end gear expansion. Looks like I have a little researching and homework to do!

Sound is a subjective thing for sure, to me its secondary to flowing the most air into and out of the engine.
when time permits (lol, ok) I need to run my inspection camera into the exhaust and check it out. it looks ok from the outside but I have to wonder what sort of restrictions it has inside.
I probably won't be going that until I have a nibbi carb and new intake though...and the I don't have 2 kids under 2 years old anymore lol:zzz:

I'm going to test out a 42T and a 38T. The 38T I suspect it going to be to high but some RBX 250 owners say it a good fit.. Amazon says they will have them to me by Friday. Should be fun to test out.

JT Sprockets JTR897.38 38T Steel Rear Sprocket

https://www.amazon.com/dp/B001AVONLU...MCG20BD0H4HFR2

What carb did you end up using? Did you have to remove exhaust pipe? Any funky restrictive exhaust gasket? I like the choke cable on handle bars. Were you able to use it with the new carb?

No. An expansion chamber on a 2-stroke is a reduction in back pressure implemented with an expanding diameter into a chamber to baffle the impact of explosions from the exhaust port. The chamber reduces in inner diameter to a rat tail with or without a muffler. The expansion chamber reduces intake pressure, and increases power output of the engine. It is very effective in a 2-stroke application. It is an obvious feature on 2-stroke bikes. And I can tell you from experience, it works! But I believe the evidence too!

In a 4 stroke bike, the expansion chamber is a megaphone at the tip of the exhaust (the muffler). There is no expansion "chamber" on a 4 stroke bike. There can be a "collector" which is a broadened but extremely short section of pipe ~2x or 4x the diameter of each individual headpipe in a multicylinder engine (2 cylinder or 4 cylinder), which goes into the muffler segment (which can be a megaphone). On a single cylinder bike, the "expansion chamber" is the muffler (or megaphone).

2.92…damn dude! I like your style lol.
Would be cool to see some before and after numbers: 0-60, top speed in each gear, etc.

Nope! I was able to maneuver between the frame and the pipe with not much struggle. It did want to catch but it was the idle adjustment screw only knocking on the frame, so I just unscrewed it, slid it on in ~giggity~, screwed it back on and attached the hoses. Cakewalk from there on. First glance at it before starting, I did see what you meant and figured greatly that the manifold was going to need to come off lol, but I strived for the latter and came out good!

Oh and I used a Nibbi PE30, I also kept the choke lever in tact, very simple to unscrew it and put it on the new one, even though I no longer need it, as it fires up immediately and runs smooth on idle from a dead cold start!

"The PowerBomb is a “pre-muffler” of sorts which helps to lower the bikes sound output by providing more sound absorbing surface area for the sound medium (exhaust gases)."

This is what they say. FMF doesn't call it an expansion chamber. They mention sound reduction and power increase, but without calling it an expansion chamber. But all of the 2-stroke pipes have integrated full expansion chambers. Maybe this is semantics, but a 4 cycle engine can't benefit from the classic expansion chamber, or they would make pipes with them for 4 stroke bikes.

An expansion chamber is different:
"The basic idea behind an expansion chamber is to use the momentum and pressure of the exhaust gases to create a pump that squeezes more air and fuel into the cylinder during the intake stroke. It does the same sort of thing that a turbocharger does, but it does it without moving parts."

A collector in a multi-cylinder 4-sroke exhaust system is related. The collector is at the union of the headpipes, but before the muffler (which can be a megaphone, which IS in fact an expansion chamber of sorts). Pulses are "tuned" at the collector to create a vacuum following each pulse. This creates an extraction effect, sucking more gases out of the cylinder during the exhaust stroke, and allowing more gases in on the intake stroke. It is also NOT an expansion chamber.

OK. Maybe it isn't an expansion chamber per se. But FMF uses the design. Did I create a power bomb when I did my cat delete? Seems more powerful. I also drill the exhaust. I posted this in the photos and videos section.
Attachment 26843
Attachment 26844
Attachment 26845

Seems like a power bomb:)

Sounds more like a resonator than tuned length headers or an x-pipe.
Which effectively has no effect other than changing exhaust note.
That makes sense.

I wonder if that is a catalytic converter rather than an expansion chamber (or resonator)? Is that it behind the heat shield on the headpipe by the cylinder?