What's the OD of FMF header pipe?

Viewing this the power is corked up by the stock header pipe.-I think I read the FMF header is 1.25" OD, can anyone back that up and is the  big HP gain they show to be believed?





Edited by ViperGTS

If you have the 2017 model the header is different. It gets bigger halfway along, not smaller like the pre 2017 bikes.

I wonder if a full system with header is necessary or if a slip on would get you the same results.

Pre 2017




The later header is 35mm until half way along where it steps up to 38mm


Edited by Garth Knight

Man that yoshi RS-4J is so nice looking I've always wondered if anyone in the U.S. got there hands on one. I'm assuming different emissions or other political crap is the reason we don't see them. 

Interesting the header will be the last thing that goes on the bike sometime this month. Everything else is done pretty much. I'll report if I notice any difference.

13 hours ago, Cyclic said:

I'll report if I notice any difference.

You will .... almost all the power gains come from the head pipe ... :thumbsup:  


I have a home made head pipe from a fellow forum member and had it dyno tested up against my FMF mega bomb and the home made pipe made 1.5 more hp down low and lost 0.5 hp off the top. I can really notice the extra torque. 

By just looks alone it is hard to believe it out performed the megabomb. I like it and somehow I think the bike even runs a tad smoother and sounds a bit better. 




So, what are the OD's of the fmf/Yoshi headers?

1 hour ago, Garth Knight said:

So, what are the OD's of the fmf/Yoshi headers?

I'll try to remember to measure the FMF for you when I get home from work later as it just sits in the garage anyway ....   :thumbsup:

So, what are the OD's of the fmf/Yoshi headers?

FMF MegaBomb


Sent from my Nexus 6 using ThumperTalk mobile app

Thanks, so if we say that is 1 3/4" that is 34mm so no advantage over the stock 2017 header.

look again, 1.375 at best

Yes I am dumb, meant to say 1 3/8" which is the same as the oem 2017 honda at 34.9 mm.

(I got the conversation wrong too 1 3/4" would have been 44.5mm)

My boy didn't really hold the tape at the widest point but after about 6 pictures I figured you guys would get the gist of it.

Sent from my Nexus 6 using ThumperTalk mobile app

Edited by gnath9

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