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Intake & Exhaust The ins and outs - carburetors, manifolds, mufflers, expansion chambers and more to keep your engine running the way you like

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Old 07-06-2011, 02:06 AM
geoldr geoldr is offline
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Default Drilling into muffler cup

On my youtube one member of this forum commented saying that if I drill holes in the muffler cup it will increase power in in the straights. Is this true? And how do I do that? Just drill straight into the muffler from the opening?
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Old 07-06-2011, 09:55 PM
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Default Re: Drilling into muffler cup

Your power increase will be minimul but the noise will increase a lot. Some believe that if it's louder then it must be faster. That's a myth. The slight increase you might experience is not worth the aggravation you'll cause your neighbors or the negative effect it will have on the hobby.
There are aftermarket exhaust systems, expansion chambers, that will positively effect your power output but drilling holes in your muffler is not the way to go.
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Old 07-08-2011, 12:38 AM
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Default Re: Drilling into muffler cup

Tom knows. Heed Tom. Expansion chambers are a way to adjust your back pressure in a more precise way. And a two-stroke needs a certain amount of back pressure to hold an air-fuel charge and to function properly.
Drilling holes in a muffler is not a very precise way to adjust back pressure. Hole too big, too many holes = problems. You'll have inefficient combustion, you may even end up with a LOSS of power if you overdo it, and you might find yourself shortening the lifespan of the engine over the long run.
And, as Tom mentioned, making a Gawdawful racket will bring unwelcome negative attention to our hobby.
I know money's tight (four daughters, believe me - I KNOW) but saving back and getting the right equipment is truly the way to go.
Ride safe.

"There is nothing wrong with wanting a motorbike that is an extension of your personal taste and fashion sense; if you must ride somewhere, I say do it with style!"
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Old 07-08-2011, 01:31 AM
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Default Re: Drilling into muffler cup

Please don't drill holes on your muffler.
As was stated before, 2-stroke engines need a properly tuned expansion pipe exhaust system for excellent power increase. If done properly with a good muffler it can nearly double the power output and be just as quiet or even quieter that the factory muffler.

I have been in the Harley-Davidson industry for nearly 20 years now.
The old adage "Loud Pipes Save Lives" and the notion of "louder means more power and faster" has been a thorn in the side of the industry for longer than I have been alive.
What has that really done for the industry?
Mandatory factory exhaust as installed and equipped when the bike was first sold for all motorcycles manufactured after 1982.
Random decibel testing at "safety" inspections sprinkled around popular ride routs.
In some states and cities/ counties, if a peace officer cannot find the correct factory stamping on the muffler's canister your bike can be impounded on the spot. Even if you are from another state and passing through to say Sturgis or Laconia bike rallies.

A few bad apples have ruined things for all who enjoy modding their bikes responsibly.
That said, the AMA and MMA and Abate have been successful in postponing some of these draconian laws into coming to effect so far.... but the noose has been tied.

We in the Motorized Bicycle world have no AMA, MMA or Abate to lobby the lawmakers and judges. If the law decides that all MB's everywhere are too loud to be legal, we all are screwed. Never mind that many are just as quiet as a weed eater, lawn mower or even quieter.
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Old 07-08-2011, 01:43 AM
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Default Re: Drilling into muffler cup

Police set sights on loud pipes | The Morning Sentinel, Waterville, ME
"This applies to all vehicles, so if someone is issued a ticket for operating a motor vehicle with excessive exhaust noise, it's a $137 fine," said Lt. Brian Scott, commander of the Maine state police traffic safety unit...
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Old 07-08-2011, 10:22 AM
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Default Re: Drilling into muffler cup

Yes, I think it is even a federal offense to modify a factory stock exhaust system.

But I get Harleys with straight pipes loud enough to rattle the windows go by my house every day.

I hate them. I am going to start writing letters demanding the existing laws be enforced.

I would like their bikes to be impounded, they be made to reinstall a factory exhaust system and pay a nice fat fine or do a little jail time or some community service.

No regards for anyone but themselves have they.
The only thing in my garage with 4 wheels is the lawnmower
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Old 07-08-2011, 11:24 AM
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Default Re: Drilling into muffler cup

It all depends on which exhaust pipe you're dealing with. In any case drilling the end cap probably isn't the hot set up.

I would suggest taking the muffler apart and inspecting the baffles. The most recent kit I bought had a very restricted muffler that needed to be modified just to run well. After opening up the restriction a little it runs very well and is close the quitest I've heard.

Here's a before and after

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Old 07-08-2011, 09:06 PM
dmb dmb is offline
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Default Re: Drilling into muffler cup

i love the sound of the old 2,3 and 4 cylinder two strokes at the races.speedway yes xr750's yep, iv'e stood with the starter with 2 top fuel funny cars at ocir [your brain shakes] but those kids on the 50cc 2 strokes raceing around the camp site at 6am would drive me nut's
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Old 07-30-2011, 03:34 PM
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peeduh peeduh is offline
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Default Re: Drilling into muffler cup

Do what YOU want. It's your bike.
out of the people that I've met by running into on the streets on gas bikes, only one had his cap still on, both older and younger than me so it's def not an age thing.
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Old 08-19-2011, 03:13 PM
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IreBo IreBo is offline
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Thumbs up Re: Drilling into muffler cup

well i have to say that i have 6 gas bikes and every one of them i have messed with the exhaust but one and it is the slowest bike in the fleet and is the same model and engine as 2 of my others. i first drilled 1/4 hole in the cup. it made a slight diff. then i started to make bigger holes and even cut the pipe in side the muffler. ive used grinders to slot the bottom instead of holes, and even just took off the cap and drilled into the tube to get more flow while trying to keep noise down. all mods did help power at topend and took a bit away from bottom end, ie takeoffs. the motor runs way better being unrestricted. idle and overall vibration was improved. i modded a rudimentary expansion chamber (banana style) and that got my top end more rpm's fore sure!!

but i think that no matter what you do you will never be as loud as a Harley with a set of screaming eagle pipes on it.they are a factory upgrade from the dealer. those are seriously loud and rattle everything when they go down the rode... almost painful to be next to one. i think some folks chiming in live in towns in jurisdictions that are much stricter than others. shoot i live in California. one of the most restrictive, overly progressive, anal places in the U.S. and have been followed by a cop that thought i was on a scooter (go ped) when he saw it was a bike he said sorry and to continue on my way....said if it was a scooter he would have confiscated it. and he also said "nice bike, ive been thinking of building one myself..." so even cops are into them!

i say give it a shot! ride up a hill, pay attention to the power , then take off the cap with the one screw and try the hill again.... you will notice more power and the motor doesn't make that pre detonation tick. if you don'tlike the power just screw the cap on.... i keep a leatherman in my pocket and remove the cap as needed.. i go on some long back country rides and notice a fuel savings and more power. i cork it back up when i get into town...EZ!

i can also understand the folks who want to keep motorbiking on the low down as we are really in a gray area and in these times all governments are looking for more ways to generate revenue , but that's ware the system comes in. a petition and a strong seance of unity will make these super fuel efficient rigs legal some day if we really wanted!! power to the people!!

Last edited by IreBo; 08-19-2011 at 03:20 PM.
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