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Old 03-08-2020, 04:58 PM   #1
hammerweight
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Default Kerker 2:2

Hey guys,
Anyone out there have any experience with baffles for the Kerker style meg/cocktail mufflers?
Just picked up a set of 2 into 2ís for my FXR, but mufflers are empty.
Thanks.
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Old 03-08-2020, 07:26 PM   #2
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Default Re: Kerker 2:2

What year is your bike? Those are likely going to be expensive, that's Kerker. Not running baffles is probably costing you throttle response and power, though it does wonders for your eventual need for hearing aids.

I checked online for some replacements, and they're not inexpensive as I said. If you had some model # info off the pipes, it would be easier to find something. Assuming they're a full-exhaust, or are they slip-ons fitting the OEM header pipes? A couple of pics and some end of pipe measurements would help.
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Old 03-08-2020, 07:39 PM   #3
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Default Re: Kerker 2:2

Hereís a couple of pics...
Itís a complete original system.
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Old 03-08-2020, 07:43 PM   #4
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Default Re: Kerker 2:2

My Bike is a 1984 FXR Disc Glide, currently with Vance and Hines long shots...been dying to ditch them since I purchased the bike...lol
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Old 03-09-2020, 03:36 PM   #5
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Default Re: Kerker 2:2

What's the I.D. of the end of the exhaust pipe w/o the cap? If you removed the cap, how-long before the pipe necks-down to 2" and then 2-1/2"? (that would be two different measurements).

I looked online a bit to see if I could find something which would be a Kerker slip-in, but to give you a fit, I'd need to know the above.

What I'm thinking, is that you might have to build a pair of baffles. How-about using a long, narrow-diameter perforated tube, w/a disc on one end at say, a 2-1/2" diameter, then the length of the tubing going to another larger-dia. disc, which fits inside the Kerker at the end of the megaphone cap?

Here's a crude drawing. The two round caps on either end of the perforated baffle tube just need to fit snugly in the megaphone so they don't rattle, and the larger of the two should somehow be fitted to the end cap securely.

Something like this for the inner perforated tubing:
https://www.revzilla.com/motorcycle/...andard-baffles

and then fabricate an (inside the megaphone) disc at either end to tightly-fit the I.D. of the megaphone, for those discs.
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Old 03-12-2020, 07:28 PM   #6
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Default Re: Kerker 2:2

That’s precisely what I was thinking^^^^
Can’t see why it wouldn’t work...
Thanks man!
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Old 03-12-2020, 11:05 PM   #7
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Default Re: Kerker 2:2

I don't know much about harmonics in exhaust chambers and piping. I recall reading about I believe it was Jerry Branch who worked on the Harley KR flathead racer, and who found that downsizing the valves and intake ports increased flow because it caused the gas flow to speed-up. That made the head flow better on the intake side.

Speaking of your Evo V-twin, perhaps there is something similar to be found on the exhaust side. A smaller perforated tube in the megaphone may cause the gases to flow more-quickly, because they don't have room to expand as-much to fill the volume of the megaphone. The exhaust gases in a larger perforated tube may move more-slowly, because they expand to fill the larger volume, thereby slowing the exhaust charge flow.

The dimensions of the megaphone are supposed to send a reverse-wave back towards the cylinder head. This is used to help the cylinder head charge of fresh, unburnt gases entering the cylinder head, stay in the cylinder head, until ignited for the 'power' stroke.

However, this 'packing-effect' is available within a fairly-narrow band on the tachometer, and is not uniform across the rev band. To be available for the most-useful part of the area below redline on a street bike, the dimensions should be designed to provide this 'packing-effect' for midrange, and not on top-end, just-below an engine's redline. The Kerker exhaust isn't designed as a top-end towards-redline exhaust, as it's a 2-into-2, which cannot make-use of one cylinder's exhaust pulses to help to pull the other cylinder's exhaust from the cylinder head. Essentially, the Harley-Davidson V-twin engine is operating as two single-cylinder exhausts, due to the separate pipes.

In the heyday of the single-cylinder 500 cc grand prix 1940's-1950's British engines, their engines would display problems running through parts of the rev-range because the exhaust megaphone was tuned to operate best at the top of the rev-band, where a racing motorcycle used in grand prix competition runs most of the time. The mid-range was not important, because the engine rarely was operating there. This example of poor mid-range exhaust flow was referred-to as megaphonitis. Kevin Cameron of Cycle World could do a much-better job of describing all of this, complete with personal stories of battling these issues, on racecourses everywhere.

Again, I have no formal education about exhaust harmonics/gas flow, I don't own or operate a flow bench, and I don't have a resume of successful racing achievements in tuning. Take these comments with a grain of salt, and anyone who cares-to correct this post, please feel free to throw my screed into the street. Just don't refer to Wikipedia as your basis for objection.

Last edited by Elektron; 03-12-2020 at 11:16 PM.
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Old 03-13-2020, 12:10 PM   #8
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Default Re: Kerker 2:2

The English writer John Robinson was a mighty engine and frame designer. His books are still around, thankfully. Here's a bit w/an excerpt on pipes -- not directly useful to you, Ham, but a taste of his work.

https://books.google.com/books?id=lD...page&q&f=false
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Old 03-16-2020, 10:00 PM   #9
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Default Re: Kerker 2:2

I guess if you wanted to “butcher” the system, you could do a crossover and scavenge opposing cylinders....
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Old 03-17-2020, 02:53 PM   #10
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Default Re: Kerker 2:2

Yeah, but I don't think you're looking to do that, I bet your goal is to mellow-out the 'bark' and to restore a more-sociable tone to the exhaust.

Just try the homemade inserts and see how things come-out. Wrapping them with acoustic insulation may also help for a time. That stuff deteriorates over time.

If you were looking to build something from scratch, then all the theory is in-play, assuming that you want to make use of it.

I have a V-4 muscle-bike for which a 4-into-4 exhaust is available but on the dyno this system has been shown to cost ~15 RWHP compared to the stock system, which uses a resonator box and integral megaphones. Sure, the look is cool, with 4 megaphones, but the cost in RWHP is for me, a deal-killer. I've ridden the same model bike both with a stock exhaust, with other systems and with the 4-into-4 mentioned, and the negative difference in power and throttle response is very-noticeable, and disappointing for the 4-into-4.

I suspect that your fabrication of a pair of inserts will tone things down sound-wise in your v-twin, and make riding more-pleasant, and quieter.
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