Kevin Crawford

I realize there is plenty of exhaust post about rotary engines to keep them quiet or increase power. I quickly realised there isn't any information about people running j-pipes on rotary engines to cancel sound waves "reduce drone." Does anybody have any useful information pertaining to an n/a 13b exhaust setup.

t_g_farrell

iTrader: (1)

Had to look it up. Thats new territory I think. Never heard of it before.

j9fd3s

iTrader: (3)

+1 never seen anyone try it before. there is no real reason it would be any different than any other engine though

t_g_farrell

iTrader: (1)

I wonder if it would negatively affect the dual pipe scavenging due to the rotor pulse being out of phase, or would it just affect sound.

midnight mechanic

is there enough room for a j-pipe exhaust? seems like it would lessen the drone.

WANKfactor

iTrader: (1)

Yeah, ive been looking into this to fix a slight drone on a "quiet" exhaust i put on my daily. From what i can gather, step 1 involves taking accurate sound recordings to ascertain the frequency you are working with, step 2 involves thinking caps on and careful calculations.
Not sure if im game to stuff around with it at this stage,, seems finnicky.

Maxwedge

iTrader: (1)

Much easier to add bottle-style resonators. J-pipe might be effective but you need room for all that snaking around, and every bend adds restriction.

WANKfactor

iTrader: (1)

agreed, thats easier, if you dont already have one, but the j-pipe should not add any restriction: its just a dead end pipe tee-ed off the existing system. No gas flow at all, just sound waves, of the specific frequency you have tuned it for, bouncing back to hopefully cancel themselves out.

Maxwedge

iTrader: (1)

Thank you, I misunderstood the jpipe. So it's like all the little "pockets" and "bottles" on a modern car's plastic intake? The ones to quiet the under-hood sounds. Except, on the exhaust.

DaveW

As inferred above, the add'l dead-end pipe volume will only tune out a specific relatively narrow frequency range. Other frequencies may not be helped, and in fact may be made louder. So it's a case-by-case basis that needs experimentation.

yeti

iTrader: (1)

I think this would be fun to play around with if you set up a trombone system.

WANKfactor

iTrader: (1)

Ha, maybe you could plumb a trombone in and just stickey tape the keys down one at a time until you get the right one. Might be easier lol

Maxwedge

iTrader: (1)

Found a YouTube video showing how to identify the specific sound waves you want to cancel (using a phone app) and build the J-pipe to do it. It explains the concept pretty good.

using SCIENCE to ELIMINATE exhaust drone: I FINALLY did it!

https://www.youtube.com/watch?v=l9CrmkIxDQU&t=246s

I would start experimenting at the "test pipe" or "pre-silencer" location (CAT replacement pipe). It's easy to fab a test pipe and lots of companies already make them for the 1st gens. It would be easy to unbolt that pipe and test different length j-pipes there, without ruining your $1000 exhaust in the process.

j9fd3s

iTrader: (3)

i was just thinking you could weld in (or the welder could or whatever) a 90 degree fitting, and then you could clamp on the J pipe section, until you get the length right

Maxwedge

iTrader: (1)

That's a great idea and could use the "trombone" idea mentioned above. If your had about a foot of tube after the 90, and another foot long capped tube one size up, that fit over it, you could slide that outer tube to adjust the length and fine tune it. Hit the sweet spot and make a final version.

WANKfactor

iTrader: (1)

Thats a bloody good idea.