let's get to the bottom of this "holes in the muffler&q

[JIBTEXHNKA]

i know, i know, search the boards. i searched them, i searched them again, and i searched them a third time. then i searched again, and i've narrowed the possibilities down to 2:

1: many informative threads are too old and have been deleted
or
2: we have very different views of what constitutes "beating a topic to death."

i was hoping we could have a comprehensive discussion about this; maybe consolidate all the information into one thread and then sticky it so you won't get people asking the same thing every other day.

so here is my question, or rather, here are my questions:

what exactly is the material you're drilling into? how deep is deep enough, how deep is too deep, or are you just piercing the external shell and it's hollow inside?

what patterns/hole sizes/etc have you tried? what sounds good, what sounds bad?

what are the chances that a muffler that sounds good to one person might sound horrible to the next (e.g. "it sounds like a muffler with a hole in it")?

does this modification negatively and significantly affect performance (because of lack of backpressure, etc)?

if so, are there ways to avoid this without needing to make other adjustments?

[Easy Rider]

so here is my question, or rather, here are my questions:


I'm sorry but the answers to most of your questions ARE in the existing threads..........except for telling YOU what YOU will think of the holes once they are done.

And I think my "summary" is in a post somewhere too.
The GZ is a 250cc thumper. Some have likened it to a lawn mower. It will never sound like a Harley.

I don't think anybody who has drilled out their muffler says "Wow, that's just great. It's amazing how much better it sounds."
(Well, except maybe one long departed rider who posted other "suspect" information too.)

Most everybody's reaction is: Ho hum. Not worth the trouble.
So, there you have it.
Put away the stick. The horse is dead. :roll:

[jonathan180iq]

http://www.postimage.org/aV2wp4u9.jpg (http://www.postimage.org/image.php?v=aV2wp4u9)

This photo if the property of Dfutch and shows a muffler with the end cap drillout.

The size of the drill bit is of personal preference. The bigger the hole the more sound. There is absolutely no performance gain that comes from this. You will also most definately be lowering your already low resale value.

Bigger holes and more sounds mean that more air is coming out. If this is what you want, then go ahead and drill away.

Be aware, though, any significant change to the flow of exhaust gasses will unbalance your carb mixture and you may need to adjust your jetting. There are people whol have drilled the exhaust and have had no reason to change the jetting. This does happen. But, it must be detemined on a case-by-case basis. There is no one-stop-shop- for correct jetting. It depends on climate conditions and altitude and the minor difference between each bike. For example, it is possible that two bike of the same year in the same town will react differently to holes being drilled in the exhaust.

All of that being said, generally, something as simple as a few holes or even a change to a slip-on muffler may not require rejetting. There is just no way to say for sure how your bike will react. Like I said, it's case by case.

As far as sound acceptance goes, yes, it's all up to personal preference. Personally, I think it sounds rhaspy and cheap. If you want a nice loud thumpy exhaust or simply something different, there are many universal muffler options on the market that can be had for anywhere between $45-$200. But, like anything else, any significant change to the flow of air and gasses may require a rejetting of the carbs.

The baffle design of this muffler has two rear end caps. Both of the metals are hard so make sure you have proper drill bits, if this what you decide to do. Drilling through one end cap will alter sound a bit, drilling through both end caps will alter sound even more. Drilling through both end caps will also increase the chances of needing a rejet as the exhaust gasses that normally would be trapped in the packing material will not be escaping freely.

On a final note:
Anyone on here is welcome to post here and dispute everything that I just posted. Differing opinions are always welcome. But, if you decide to drill out your exhaust and then find that you need a rejet and don't know what to do or how to do it or end of screwing something up, it will be no one's fault but your own. You are also altering a perflectly good working system for a little "change in sound". There is no performance gained by doing this.

Some people question what constitues a topic being beaten to death. Well, I think that idea comes from the fact that this "muffler mod" - "drilling holes" - "removing baffles" - "drilling exhaust" - "better sound" question comes up every week.
I'm not going to go back and post a link to ever single discussion here. You can do that and see for yourself.

My biggest problem comes from the fact that this simple topic gets so much attention. So, maybe it's a good thing that you opened up a thread to put it all in one place.

The bottom line - If you want to try it out, go ahead. If you hate it, you're stuck with it or you can cap the holes with rivets. Rivets only get so big so don't go overboard or you have no other options.

The exhaust note will change. I hope you like it.

You may alter the carb mixture and your bike won't run properly. If that happens, see above.

Best of luck with your decision,
Jonathan

[davidc83]

When I bought my little gz (used with 400 miles), it had 4 holes drilled in the muffler. It does sound a little different than the stock GZs, but it is not worth the trouble to drill the holes. Instead of sounding like an angry sewing machine (stock), it sounds like a weak lawn mower. The rebel 250s with their dual exhausts sound better.

[Easy Rider]

The bottom line - If you want to try it out, go ahead. If you hate it, you're stuck with it or you can cap the holes with rivets. Rivets only get so big so don't go overboard or you have no other options.


Actually, stainless steel bolts work nicely, with an appropriate tap. :)
Had to go 1/16 larger than the drill bit though.

[jonathan180iq]

Here are some other options outside of drilling holes...


http://www.postimage.org/aV2wqCLJ.jpg (http://www.postimage.org/image.php?v=aV2wqCLJ)


http://www.postimage.org/aV2wqRJA.jpg (http://www.postimage.org/image.php?v=aV2wqRJA)


http://www.postimage.org/Pq2ffZY0.jpg (http://www.postimage.org/image.php?v=Pq2ffZY0)

Or you could get really creative...

http://www.postimage.org/aV2wrW4r.jpg (http://www.postimage.org/image.php?v=aV2wrW4r)


http://www.postimage.org/aV2wsrvi.jpg (http://www.postimage.org/image.php?v=aV2wsrvi)


http://www.postimage.org/Pq2fgsTJ.jpg (http://www.postimage.org/image.php?v=Pq2fgsTJ)

[jonathan180iq]

The bottom line - If you want to try it out, go ahead. If you hate it, you're stuck with it or you can cap the holes with rivets. Rivets only get so big so don't go overboard or you have no other options.


Actually, stainless steel sheet metal screws work nicely, with an appropriate tap. :)
Had to go 1/16 larger than the drill bit though.

This is certainly another option. :cool:

[Easy Rider]

Actually, stainless steel **bolts** work nicely, with an appropriate tap. :)
Had to go 1/16 larger than the drill bit though.

This is certainly another option. :cool:

Oops, brain cramp. NOT sheet metal screws! :roll:

[jonathan180iq]

I know that no one has brought this up in a while but I decided to put an end to the debate by showing everyone in the world what the difference is between the factory exhaust and the drilled exhaust.

If I can't live with it, I'll just cap the holes.

http://www.youtube.com/watch?v=0FapvADgGn4

[JIBTEXHNKA]

eh, you just convinced me not to do it. thank you very much, haha

[jonathan180iq]

After riding to work this morning I can say that it's not really all that bad.

You can only hear it when the RPMs are below 3k.
Also, the video sounds a little hollow. It's a bit deeper than that.

It's not really a plus or a minus. It's just slightly deeper and you can hear that there is a muffler on the bike. That's all.

I'm going to leave it like this and see how I feel about it in a few weeks.

Also, I get my UNI replacement filter this afternoon. Once I rejet, we'll see how the sound changes.

I think the previous version that I heard of a drilled exhaust has something else done to it because it was hideous.
Different from what I have done here.

[cconleyjr]

I drilled 6 small holes in my baffle wasn't really a significant change but I like it because I can hear the bike run over the wind at high speeds now

[patrick_777]

I just tapped the holes in mine and capped them with bolts. Then I sprayed over them with high-temp grill paint. The sound is much more subdued and I'm hoping to maybe up the mpg a little bit.

We'll see.

[rayzuki]

I have decided not to do this. I really wanted to. I would like some more noise. Not stupid like a harley but just a little more to get me noticed but I think I will just leave things alone on this.

[Sarris]

I have decided not to do this mod. First, I have a couple HD's that make a shit load of noise, so the quiet GZ is a nice change. Second, I'd have to rejet and mod the carb to get it to run right. This mod also usually causes the pipes to blue, and mine has over 12k with no blueing. Third, I don't want to screw up my gas mileage as I'm getting 72 mpg consistantly.

I figure I'm patient enough to live with it the way it is. The dealer adjusted my GZ carb (popped the carb caps) at the 600 mile service, so mine doesn't run lean. No flat spots, no popping, and it accelerates strong and smooth.

Anyway, you gotta know that even if you get a 10% increase in horsepower, you'll maybe have 20 hp max all said and done. It just isn't worth the negatives and the hassle to gain 2 hp maybe. I think if you bought a GZ to fast, you've really have bought the wrong bike. It is what it is.

:2tup:

[cconleyjr]

I travel alot at 55 plus and had a hard time hearing the engine over the wind. I wasn't looking for a hp increase or anything like that. My gas mileage hasn't changed i still get 67 to 70 mpg.

[jonathan180iq]

I travel alot at 55 plus and had a hard time hearing the engine over the wind. I wasn't looking for a hp increase or anything like that. My gas mileage hasn't changed i still get 67 to 70 mpg.

The change in gas mileage comes if you also shim your needle. This shim allows more fuel to flow and, consequently, to burn, which lowers fuel economy.

[jonathan180iq]

I could only stand the holes for all of 2-3 weeks. They have been capped. Don't do it. It's only cool for about 45 minutes.

[D Futch]

To each his own as the pic on page one shows I have 4 holes in mine and I like it just fine. When I got the bike the guy I baught it from had cut off the muffler at the small heat shield by the foot peg, So I welded it back on and ran it with the stock muffler for a day or two and then I put the holes in and I like it just fine. have had it that way for the last 1000 miles or so. :roll: But as I said to each his own!!!!

[rexolio]

I'm a total newbie - I know NOTHING - but wanted to share my experience. Take it for what it's worth and give much more weight to the more experienced guys in this thread...

I bought mine with no mods to the muffler. A couple of weeks ago my uncle, an old motorcycle rider from way back who still rides told me I ought to drill some holes (he had just done this to a new bike he bought.) So, I let him (what do I know, anyway.)

He drilled 4 holes, about the same size as D Futch. He drilled through 2 baffles on all 4 holes, then he drilled through at least one in the original hole.

I have to say, I really like the sound (doesn't sound like a lawn mower to me.) It has a nice deep sound, and I like the "thumps" when it's idling.

I will also say that I was surprised when a few hills I drive on my way to work were less of a challenge. Before, my bike would quickly start to strain on them and bog down toward the top. After the holes, although I'm sure it doesn't take the hills like a bigger bike, it rides over them with much more power than before.

I also was pleased to find that my gas mileage seems to have increased from 62 mpg (in the 4 weeks prior) to 67 mpg (during the last 2 weeks.)