Muffler dyno testing. Advice needed.

[chadihman]

I want to test muffler mods on my dyno. I plan on welding a port for a back pressure gauge. I have 1" close black pipe nipples that I'm going to weld to the muffler. I have three different caps each one has a different size hole drilled in the end of the cap. My plan is to test different size openings and see how they effect HP and torque from 7000-12000 rpms. I was wondering were a good place would be for the outlet for a good test? Should my drilled cap be inside the muffler or outside? Any ideas on how to plug the stock opening without welding the hole shut or should this trst be done with the stock hole as is? I'm testing this on a stock MS 460 and a stock 461

 

[chadihman]

Maybe I should forget using a muffler and just make a flange welded to a pipe to bolt right onto the jug.

 

[TBrown]

Maybe I should forget using a muffler and just make a flange welded to a pipe to bolt right onto the jug.

Maybe weld a 1 1/2" npt nippple to a stock flat cover then drill desired holes in pipe caps. Could cap factory hole with fender washers and 8-32 machine screws or similar.

 

[TBrown]

I should of read closer, the nipple idea was in your first post.. id go bigger than 1" to test the too large of exhaust opening discussion.

 

[Chris-PA]

I suspect there will be a difference between having a (partially) enclosed can/volume on the outlet vs a short pipe with various restrictions. If any air is pulled back into the cylinder at any point in the cycle, if there is a semi-enclosed volume outside the port, then some of what gets pulled back will be old exhaust & unburned fuel. If it is just a small volume stack, even with a restriction, then what gets pulled back will contain more oxygen.

That leads to the next question - will you retune for each? I think you should.

 

[MustangMike]

My opinion, since muffler modding always involves adding to / making ports, leave the factory hole alone and add another port were you can vary the size.

The last test would be to remove the muffler cover to see what happens when it is completely open.

If you want to test a M-Tonic saw, let me know and I will try to get my 362 out to you. Not sure where in PA you are, but I'm about an hour from the border on 84.

I'm looking forward to seeing this, it should be very informative.

Also, do you recommend any specific filters? I saw previously that the filter made a large difference.

Thanks.

 

[redfin]

I think you are on the right track forgoing the stock front piece of the exhaust. I would find another rear section and weld the opening shut.

You can fab a front cover to include the "variable opening" and your gauge. It may not be a bad idea to incorporate the gauge into the rear portion of the muffler.

I like what your doing Mister. Good work.

Edit: I was just thinking about the gauge, and wondering if would be a good idea to incorporate a schrader valve to record highest backpressure. Or if if would be better to see what it does throughout the rpm range. Then again you may have issues with the temp of the exhaust damaging the schrader.

 

[chadihman]

I suspect there will be a difference between having a (partially) enclosed can/volume on the outlet vs a short pipe with various restrictions. If any air is pulled back into the cylinder at any point in the cycle, if there is a semi-enclosed volume outside the port, then some of what gets pulled back will be old exhaust & unburned fuel. If it is just a small volume stack, even with a restriction, then what gets pulled back will contain more oxygen.

That leads to the next question - will you retune for each? I think you should.

Very good point I was thinking along the same lines. Maybe a 1 1/4 or 1 1/2" pipe by 3 or 4" then the cap with a smaller hole would be close to a muffler can. Yes I know I have to retune.

 

[mdavlee]

You could make a slot to slide washers or small sheets of metal with various sized openings in them. Do it on the front of the muffler.

 

[chadihman]

Also, do you recommend any specific filters? I saw previously that the filter made a large difference.

Thanks.

I tested a 460 and the Stihl HD filter did the same as a max flow filter. The Stihl HD will probably plug faster with saw dust. I would recommend a Stihl HD with a wrap to easily remove and clean. I had an older standard filter on my a 460 that gained a good bit when I pulled the filter off while running a 9000 rpm loaded test. I kept pushing the filter on then removing and I was amazed at the power change.

 

[MustangMike]

Thanks for the info, unfortunately, we can't run em without filters!

 

[procarbine2k1]

If you are going to plug the stock exit, maybe you could use a piece of thin gauge sheet metal in lieu of the screen? No welding, and simple removal.

 

[MustangMike]

If you are going to plug the stock exit, maybe you could use a piece of thin gauge sheet metal in lieu of the screen? No welding, and simple removal.

Smart Idea

 

[chadihman]

Well I guess since mostly everybody mods there mufflers I'll keep the stock hole and add to the front cover. I'll add my back pressure port in the rear can portion of the muffler. Are you guys against adding a short pipe to the front of the muffler with different size holes in a cap on the end of the pipe? Or should I make a hole in the center of the cover with a slide that I can slide open or shut?

 

[MustangMike]

I go for option #2. While I have seen pipes, I think the second option more accurately reflects what most of us would do.

 

[Chris-PA]

My W.A.G. is that if you have the can a little pipe section off the front won't matter. I doubt you would come anywhere near any tuned resonance.

 

[chadihman]

I'll do the variable hole in the front cover then a pipe and see what happens. Kill to birds with one stone. I ported and machined my brothers 460. It blows over 200 psi and runs well. I'll have to see what difference that makes.

 

[XSKIER]

Use a sliding guillotine type. Infinitely variable, adds no volume, keeps the opening rectangular, closer to a finished "muffler mod" and will calm the peanut gallery.

Like this, but make yours out of 18ga sheet.

http://www.thunderproducts.com/tpi_valve.htm

 

[Joesell]

I tested a 460 and the Stihl HD filter did the same as a max flow filter. The Stihl HD will probably plug faster with saw dust. I would recommend a Stihl HD with a wrap to easily remove and clean. I had an older standard filter on my a 460 that gained a good bit when I pulled the filter off while running a 9000 rpm loaded test. I kept pushing the filter on then removing and I was amazed at the power change.

Is it possible that you had such gains without the filter because the saw was instantly leaning out?

I wonder what the difference would be between the different filters and no filter all properly tuned.

 

[chadihman]

Is it possible that you had such gains without the filter because the saw was instantly leaning out?

I wonder what the difference would be between the different filters and no filter all properly tuned.

Yep leaner made more power but I know that the saw was held back from that filter. The max flow and Stihl HD filters flowed more than the saw consumed.