Baffle, Perforated vs Louvered

[pano]

From what I have been able to find online, perforated baffles are louder and have more top-end. Louvered baffles are slightly quieter have less top-end but have more low-end torque. Is that your experience?

 

[DannyMotor]

The more backpressure the more torque. The louvered type actually direct the exhaust into the matting material where as the perforated simply geta what it gets.

Personally if i had my choice i would use louvered baffles with less matting... on my old CM200T i used dunstall reverse cones with louvered baffles and only wrapped the last half of the baffle towards the tail pipe. It made the 200 sound like a 500. Haha.

 

[gearheadE30]

Louvers actually cause a very significant amount of backpressure in an exhaust system. I haven't done any back-to-back testing on a bike, but when I was testing exhausts on one of my cars, switching from a louvered muffler to a perforated one, with all else equal, netted full boost (turbocharged) in a little under half the time transitioning from 0 throttle to full at 3000 revs. That is a massive, massive difference. That said, that's a bigger engine with a lot more airflow, so a bike may react differently. Louvers tend to be a bit quieter.

 

[Steve]

The more backpressure the more torque. ...

So, . . . for maximum torque, weld a disk over the back of the pipe.


Ok, that's a little drastic, but shows the absurdity of that statement.
Maximum torque happens when the cylinder-filling efficiency is maximized.


In any engine, there are many things that will affect airflow inside the combustion chamber. If it is designed with a certain amount of restriction, typical of what would be involved with a legal muffler, anything you do to lower that restriction would change the mixture. It is possible that you would be letting some of the incoming fuel mixture right out the exhaust valve before it gets a chance to contribute to the power cycle. In that case, you will definitely lower torque (and horspower).

If you were able to carefully change the timing on your cams to take advantage of the different flow characteristics, you could regain that torque that you "lost" when you added the header.

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[Steve]

From what I have been able to find online, perforated baffles are louder and have more top-end. Louvered baffles are slightly quieter have less top-end but have more low-end torque. Is that your experience?

I only have experience with two headers in my stable.

The 650L has what I believe to be a MAC header. Overall, not too bad, not too loud, but can really scream when the revs go UP.

The '81 850G has what I believe to be a Jardine header. Quite a bit quieter than the MAC, even though they both have perforated baffles.

The difference is in the baffle. The MAC has a perforated tube down the middle that is 1 1/2" in diameter (maybe a bit less, I am not near enough to measure it) and goes straight through. The Jardine's baffle is pretty much the same size, but has a flat disk blocking the middle of it. That forces ALL the exhaust through the perforations, into the matting, around the disk, then back through the matting, back through the perforations agiain, finally, out the back.

Since all the exhaust can go straight through the MAC, the chamber between the perforated tube and the outer wall is simply an echo chamber. Adding batting to that simply deadens the echo.

On the Jardine, any batting added tends to restrict airflow, since the exhaust actually has to flow through it to get around that disk in the middle. It sounds just fine with no batting at all.

Overall, I think the noise level differences you are asking about will depend on the size of the hole in the baffle (the perforated tube) that does not restrict airflow (or noise).

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[DannyMotor]

So, . . . for maximum torque, weld a disk over the back of the pipe.


Ok, that's a little drastic, but shows the absurdity of that statement.

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How is what I said absurd! It's true! If you've ever ridden a bike with straight pipes or no baffles... low end sucks. You NEED back pressure for the gasses to flow evenly with the pulse of the motor. If you don't have any, it can cause scavenging at low rpm. It also plays into the same reason why having some form of a cross pipe or collector will gain you more power by equalizing the exhaust pulse.

In no way was I suggesting anything crazy... hahaha.

The last part of your statement is very true though... you definitely want to play with cam timing and even ignition timing... slightly advanced will help out low end, slightly retarded will help out high-end.

 

[Steve]

How is what I said absurd! It's true!

You said "The more backpressure the more torque." You will get the most "backpressure" by welding the outlet of the exhaust closed.

The last part of your statement is very true though... you definitely want to play with cam timing and even ignition timing... slightly advanced will help out low end, slightly retarded will help out high-end.

It all has to do with timing the valves to maximize fililing in the cylinder. I still find the concept of "backpressure" amusing, though. All that is, is the restriction imposed by the exhaust system. If you reduce the restriction by changing the muffler or the design of the total system (like changing to a 4-into1 header), it will affect how the air flows through the combustion chamber. If your reduction in restriction ("backpressure") causes a drop in power (torque), you need to change the valve timing to compensate.

What I am trying to get across is that you can not change one part of a SYSTEM and still expect it work perfectly. You may have to change other parts of the system, too. Typically, by changing just one part, you may enhance one feature, but usually at the expense of another.

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