I am looking for some info on CMI's new mufflers. I would like to know if anyone has data that indicates if these increase the back pressure above acceptable levels and raise EGT's.
Also, what effect do they have on the water flow in the tailpipe at idle? Does the water build up in the tail pipe and increase chances for reversion.
Why would they do what?
Design for backpressure - some is good at low rpms, increases torque. Too much restricts flow/power/increases EGT/burns valves. My question was has anyone measured this to be sure it is ok. I was not able to get any specific information/data from CMI on this.
Design for retaining water at idle - I don't think they would do that on purpose but without seeing it up close I don't know if the design will trap water. By the picture you posted it appears that there is a ledge where it slides on the tailpipe that could hold water. I can not tell from the picture if this ledge is 1/16", 1/8", 1/4", ...
I have been intrigued by them since seing a picture in the latest Powerboat magazine April issue page 28.
Although they look a bit different. From looking at the pictures, the ones in the mag look like a more finished product than the ones in the above post.
I wonder if one could shim them to stay a bit more open during idle for a bit more sound?
I have them on my Outerlimits with 565ci whipple motors, they work great. It does take some RPMs to overcome the spring pressure and IMO I wouldn't run them on a N/A motor. I think Nortech did some testing for CMI, maybe Terry can confirm that.
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CMI Sound Elimination Systems mufflers are the next generation of sound reduction technology form CMI. These mufflers enable boaters to operate their performance boats in stealth mode by reducing sound emissions to levels as low as 85 decibels (dB) -- a level well below the most strict sound emission regulations. CMI's Sound Elimination Systems mufflers are designed to curtail exhaust noise emissions on any marine exhaust system with tailpipes ranging from four to six-inches in diameter, which covers the full range of inboard or stern drive-powered recreational and performance boat applications up to 1500 horsepower. [size=4]The mufflers are strategically engineered to muffle sound without restricting the exhaust or creating unwanted backpressure, which can inhibit the engine from reaching peak performance power.[/size] A superior design results in fewer parts than competitive models, which will ensure long-lasting durability and reliability for marine applications.
When you say spring pressure, I assume you speak of closed to open in that you have to get rollin some get them to open. I am going to be running the Ilmor 625's w/ dry exhaust. Any opinion for that application. Are you running dry or wet exhaust? Wonder if the springs could be changed out top opon quicker or will relax some over time? Was your performance affected?
When you say spring pressure, I assume you speak of closed to open in that you have to get rollin some get them to open. I am going to be running the Ilmor 625's w/ dry exhaust. Any opinion for that application. Are you running dry or wet exhaust? Wonder if the springs could be changed out top opon quicker or will relax some over time? Was your performance affected?
The muffler starts to open around 1400 rpms. You can't run these with completely dry exhaust. They need some water.
Here is a response I received from CMI on a question about adjusting them.
"The mufflers were not intended to be adjustable. However, there is a way to do it, but we don’t recommend it because you could create too much back pressure. We tested 1200 hp engines at Lake of the Ozarks, including the 50’ drive by at ¾ throttle, and they passed the 86 db requirement. Even with the mufflers open, they are not as loud as not having any mufflers at all."
Do they have parts in them that look like a high maintenance item or need to be replaced once in a while.
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I ran a set of these mufflers on 900 SC. 28 inches H2O back pressure @ 5350 rpm; Db's @ 850 rpm 85.4. I also checked my other boat w/ 502 EFI; 25 Inches H2O @ 5200 rpm. 84 db's @ idle. The 900 sc the egt's didn't change one bit, with the addition of these mufflers. I have over 100 hours on the 900sc mufflers, and about 50 hours on the 502 EFI, No problems with either sets. I had both sets of my mufflers apart, I could adjust the spring tent ion with the shaft they have in them. There is a threaded spring shaft that has a jam nut. All I did was screw it out a little and tighten the jam nut. The other (502 EFI) I took the jam nut out, and made less pressure. These things are really neat, you can do allot with them. But I wouldn't tell them I did this, they probably wouldn't warranty them. I have had mine lond enough, they are probably not under warranty anymore anyhow.
Bawana
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