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January 22nd, 2005, 05:35 PM   #11
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While we are on the subject

I like to side with Berger 100%.

Dale,
Does a more open exaust produce less low end and more top end power?
Is there such a thing as back pressure with 4st's? Does back pressure increase low end power?
Thanks,
John
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January 22nd, 2005, 06:04 PM   #12
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Re: While we are on the subject

Originally Posted by jmumme
I like to side with Berger 100%.

Dale,
Does a more open exaust produce less low end and more top end power?
Is there such a thing as back pressure with 4st's? Does back pressure increase low end power?
Thanks,
John
Such is a loaded question for which I will attempt to answer in a short and sweet reply.

Increased back pressure (ie exhaust restriction post valve) can slightly reduce over scavenging which is the result of an improper state of tune. (ie. incorrect camshaft selection, porting, etc. for the intended rpm range)

An engine properly tuned and operated in the intended rpm range will not benefit from a post valve restriction, however, an engine built for top end may indeed receive a slight boost in power below the torque curve.

More important regarding a closed exhaust (smaller outlet ID than that of the head pipe and / or muffler) is the effect it has regarding finite wave tuning. (Commonly referred to as acoustical tuning ala the two-stroke) Increased camshaft duration gives said waves a larger window for which to work both in favor and against power. Said effect is rpm dependant. When using a restricted exhaust (for noise) with a long duration camshaft (such as the LRX1) one will experience a considerable loss in low rpm power albeit quite a large boost on top. Both results are attributed to the finite wave reflections from the closed end piece.

I also believe that in addition to other reasons Husaberg and KTM to stick with their current short duration camshaft design in order to prevent low rpm power loss while keeping the exhaust somewhat quiet and small.

That is the best I can do without getting too heady and taking up a bunch more space.

Best Regards,
Dale
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January 22nd, 2005, 07:34 PM   #13
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You don't seem heady..
I didn't realize just how loaded it was.
Thanks for taking the time to explain the basics Dale!
You're the man..
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January 23rd, 2005, 04:43 AM   #14
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Originally Posted by LINEAWEAVER
Small = poor power / quiet
Big = good power / loud
And don't I know it

Thanks,
Simon
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January 23rd, 2005, 05:07 AM   #15
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Dale,

Has anyone experimented with an internal megaphone design silencer?

i.e. An oval outside canister with the inner pipe being a megaphone design.

I wonder if a perforated megaphone could provide some sound silencing with the benefits provided by the megaphone shape.
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January 23rd, 2005, 08:30 AM   #16
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Originally Posted by Splat
Dale,

Has anyone experimented with an internal megaphone design silencer?

i.e. An oval outside canister with the inner pipe being a megaphone design.

I wonder if a perforated megaphone could provide some sound silencing with the benefits provided by the megaphone shape.
Splat,

It is more effective to have the megaphone using a reverse meg, then installing a silencer afterwards.

Cheers,
Simon
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January 23rd, 2005, 10:13 AM   #17
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Originally Posted by Simon
Originally Posted by Splat
Dale,

Has anyone experimented with an internal megaphone design silencer?

i.e. An oval outside canister with the inner pipe being a megaphone design.

I wonder if a perforated megaphone could provide some sound silencing with the benefits provided by the megaphone shape.
Splat,

It is more effective to have the megaphone using a reverse meg, then installing a silencer afterwards.

Cheers,
Simon
Gentlemen,
I tested both designs in the early nineties while developing the CG / Suzuki DR 350 for ISDE competition. A reverse cone of proper dimension fit to the the correct taper and length megaphone, attached to the proper length and ID head pipe, topped off with a suitable muffler (ie inlet and outlet proportional to or larger than that of the reverse cone exit) proved best overall.

Note:
Contrary to popular belief and all else remaining equal said reverse cone reduced power everywhere once camshaft duration and overlap exceeded a particular point.

The taper perforated core megaphone / reverse cone design muffler as described by Splat was quite popular in the seventies in particularly with regard to multi cylinder roadrace and dirttrack equipment.

Hope this helps.

Sincerely,
Dale
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January 23rd, 2005, 08:29 PM   #18
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Hi Simon:

Without having to come up with entirely new technology for noise reduction one way to increase horsepower and reduce noise levels could be to utilize two muffler/silencers. This has already been done. At some point I will probably get a Looney Tuned Exhaust dual exhaust for my wifes YFZ450 quad. The magazine test results were favorable and it was quiet.
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