Stihl MS 461 has me confused on dyno test.

[chadihman]

Tonight I ran the 460 again to see what cooler weather and lower humidity do for hp. The weather here in Pa is wonderful. The weather was very hot and humid the last 460 test and now its 20 deg cooler and the humidity is much lower. The 460 gained .3 hp.
I then ran my stock 461 and found that it had .3 hp more than the dual port 460. I couldn't wait to see the difference in hp with a dual port on the 461 so I quickly installed the dual port muffler on my 461 and retuned the carb. I was a little let down when the #'s really didn't change. How can the 460 gain 20% more power and the 461 nothing? I did notice the oem muffler on the 461 has a bigger outlet hole than the 460. I like the sound of the dual port but I'm going to put the oem muffler back on and retune to save fuel.

 

[Nate66n1]

Are the internals between the two mufflers the same, just throwing out ideas.

 

[moody]

There a there gremlins living inside the 461 muffler from what I've seen.

 

[TonyRumore]

I'm not sure what to think about that, but you do need some back pressure to make a 2 stroke run right. Back in 1985 I bought a new Yamaha YZ490 and it made more power with a spark arrester muffler in place than it did with the standard silencer. The standard silencer was a straight blow threw unit, whereas the arrester added back pressure.

Tony

 

[blsnelling]

My thinking is that it doesn't take as much exhaust opening as many think to make good power.

 

[Justsaws]

Tonight I ran the 460 again to see what cooler weather and lower humidity do for hp. The weather here in Pa is wonderful. The weather was very hot and humid the last 460 test and now its 20 deg cooler and the humidity is much lower. The 460 gained .3 hp.
I then ran my stock 461 and found that it had .3 hp more than the dual port 460. I couldn't wait to see the difference in hp with a dual port on the 461 so I quickly installed the dual port muffler on my 461 and retuned the carb. I was a little let down when the #'s really didn't change. How can the 460 gain 20% more power and the 461 nothing? I did notice the oem muffler on the 461 has a bigger outlet hole than the 460. I like the sound of the dual port but I'm going to put the oem muffler back on and retune to save fuel.

461 is "dialed" in better from the factory as a unit compared to the 460, which has lots of basic wiggle room.

Keep on testing, shoot some holes in the "power is louder" theory.

 

[Nitroman]

Any differences in the intake section? One flows better than the other?

Did you let the dyno cool to the same temp as it was when you ran the first powerhead?

 

[chadihman]

Are the internals between the two mufflers the same, just throwing out ideas.

Oem mufflers are the same except the 461 had a bit of a larger outlet hole. I used the same dual port on both saws for testing.

 

[chadihman]

Any differences in the intake section? One flows better than the other?

Did you let the dyno cool to the same temp as it was when you ran the first powerhead?

Does the dyno temp really matter? I do see the load decrease a little as the oil warms and flows easier through the flow valve but that doesn't matter because I just adjust the flow closed a little more to hold the saw at a steady loaded rpm.
I let the saws idle for a minute then pull them down to 8000 rpms for 30 seconds before testing. I really think I'm going to get the performance trends system as you suggested. An rpm sweep could be done in 10 seconds.

 

[chadihman]

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461 is "dialed" in better from the factory as a unit compared to the 460, which has lots of basic wiggle room.

Keep on testing, shoot some holes in the "power is louder" theory.

Yep I think Stihl did there homework on the 461. I'm going to make a muffler with an adjustable outlet for testing.

 

[BloodOnTheIce]

The dual port on the 460 makes a massive improvement because that's the muffler that was
originally designed for that saw. And all muffler since have been just choking the saw down
to meet EPA standards. That's why the dual port on the 461 makes no improvement, the muffler
on the 461 is designed for optimal power from the factory, and has never been choked down.

 

[chadihman]

The dual port on the 460 makes a massive improvement because that's the muffler that was
originally designed for that saw. And all muffler since have been just choking the saw down
to meet EPA standards. That's why the dual port on the 461 makes no improvement, the muffler
on the 461 is designed for optimal power from the factory, and has never been choked down.

I'm thinking there should be more muffler tuning from the porting guys. Mufflers seem to play a big role in making power. Higher flow and louder isn't always better:msp_sad:

 

[Nitroman]

Does the dyno temp really matter? I do see the load decrease a little as the oil warms and flows easier through the flow valve but that doesn't matter because I just adjust the flow closed a little more to hold the saw at a steady loaded rpm.
I let the saws idle for a minute then pull them down to 8000 rpms for 30 seconds before testing. I really think I'm going to get the performance trends system as you suggested. An rpm sweep could be done in 10 seconds.

I was referring to the oil temp. I should have been more specific.

 

[blsnelling]

I'm thinking there should be more muffler tuning from the porting guys. Mufflers seem to play a big role in making power. Higher flow and louder isn't always better:msp_sad:

As long as it's not choked up, it's going to make power. I think your testing here shows how little difference trying to fine tune the muffler opening makes. It's for that reason that you're starting to see a trend of simply opening up the factory port. Adding more does little more than just make it louder. An example would be the 550XP. I opened up under the existing deflector. It made a big difference. I went back in, opened up the baffles, and all it did was make it louder. It's nothing like trying to tune a pipe. Speaking of which, could I use your dyno to tune the pipe on my 390XP

 

[Trx250r180]

my 461 was modded by Randy so results may be different than stock jug for air flow ,,both the stock opening and dual port cover have been opened up ,i tried a 28 inch fir log for testing stock cover and dual port cover ,it was 3 seconds faster with the dual port cover in a 30 second or so pass in my test ,i was hoping to quiet it down some ,felt like it had some more bottom end down low choking it down with stock cover ,but wide open i lost some power ,here is my muffler opening View attachment 306006View attachment 306007

 

[Grande Dog]

Howdy,
Stihl never left as much on the table as other manufacturers when it comes to performance. With restrictions becoming more prevalent, they'll be leaving even less crumbs behind. I didn't see where your dyno has a timer but, I would bet that the dual port muffler gets from point A to point B quicker.
Regards
Gregg

 

[blsnelling]

my 461 was modded by Randy so results may be different than stock jug for air flow ,,both the stock opening and dual port cover have been opened up ,i tried a 28 inch fir log for testing stock cover and dual port cover ,it was 3 seconds faster with the dual port cover in a 30 second or so pass in my test ,i was hoping to quiet it down some ,felt like it had some more bottom end down low choking it down with stock cover ,but wide open i lost some power ,here is my muffler opening

That makes sense. With an engine being an air pump, the more power it makes, the more air it's moving, the greater the exhaust size will need to be.

 

[LegDeLimber]

What is the dyno oil temp right when you finish the last pull?
do you see a lot of variation between pulls?
I'd think 15~20deg F spread would make an appreciable difference in the load dynamics
and of course the validity of the numbers.

approximately what was starting temp of oil
(and dyno too, surprises will find interesting places to hide )
then the temp after, oh say 20 mins of testing.

now just think in terms of building a wood fire to heat that oil the same amount.
now think of maintaining that temperature differential betwixt your ambient air
and the oil in your system.
I expect the initial raising of temp will have one energy requirement
While maintaining that temp will be a bit different number and delivery rate.

now wrap your head around factoring that into your parasitic losses...
hmm, (I'm running on just gut feeling here)
but might be better to ad a block heater to the oil tank
and bring it up to that mid run point temp,
before you start using the numbers to gauge the saw.

If the temp is swinging too much between pulls,
then I think you'll always be getting that error of the swinging loses to changing the oil temp.
may mean insulating the tank and lines (like a little water heater system)
and keeping that block heater running, but with thermostatic control.

bottom line, we're just looking to identify and chase out as many variables as practical
to make the calculations less laden with correction factors.

To an extent....
The complexities are gonna stay with ya, just what form do you wish them manifest in
and prefer to cope with.

as you may imagine, given My choice it would be as I've written above.

Keep at it Dude, as I said..Wish i was close enough to hang out and
maybe be a "real time" sounding board or extra pair of hands for this
cause I truly like the project and it's intent.

 

[maico490]

Just as in other threads about this Dyno people are getting confused about the oil temperature affecting readings. Yes the saw is turning an oil pump but it is the torque reaction from the pump and it's mountings which are being used to measure the torque via a load cell. Oil temp is largely irrelevant as the flow from the pump is being choked down only to hold the saw at a fixed RPM. The power is not being measured by pressure readings.

 

[RedneckChainsawRepair]

I been getting these for the 044 046 without screens. Insides are wide open too.