Echo CS-590 Timberwolf Muffler Mod - Flow bench Measurements

[Chris-PA]

If the ports aren't open, the carb wouldn't be flowing either, as the carb only flows when a vacuum is created in the crankcase. Therefore matching the flow of carb to the displacement as closely as possible is desireable.

The swept displacement corresponds to the piston falling each cycle and is the most the engine could pull in each cycle with 100% volumetric efficiency. At a given rpm it won't be anywhere near that high as a flow rate but I don't have any figures handy so I just used the port open time as a back-of-the-envelope guess. It's probably not that high either.

I also don't know how much averaging of the flow is happening, but the intakes are very short so probably not much. So the carb has to be sized to accommodate the peaks.

Anyway it looks to me like the carb is adequately sized. Anyone know how big the venturi is?

 

[bmwpowere36m3]

If the ports aren't open, the carb wouldn't be flowing either, as the carb only flows when a vacuum is created in the crankcase. Therefore matching the flow of carb to the displacement as closely as possible is desireable. We must remember that the flow measurements are done at and arbitrary pressure, which may be different to the pressures/vacuums that the engine draws through the carb.

+1

The CFM numbers are relative... don't put too much stock into their absolute values. They are influenced by setup of flow bench.

 

[Chris-PA]

The CFM numbers are relative... don't put too much stock into their absolute values. They are influenced by setup of flow bench.

Sure - just ballparking anyway. I looked up some Delivery Ratio numbers and it looks like they can get up to 75% of the swept volume, which is better than I remembered. So 600,000 * 0.75 = 450,000 - so the carb & filter are pretty well matched if the flow bench data is representative.

 

[Team FAST]

So... Can we assume you'll be further modifying the muffler looking for a few more CFL of flow? And did you by chance do any test cuts befor the mods or are we sticking with follow bench numbers?

And thanks for a great thread by the way. Love to see more flow numbers on different mufflers. Those as how are obviously pretty stuffed up from the factory. How's about say Husky 346xp, 545, 555, 550, 562 mufflers? Love to see those quantified.

You're welcome.

I am not sure how much further I will take it based on the intake (carb) flow numbers. I haven't even run the saw, other than a 30sec start to make sure it worked. I won't be doing any serious tree work until the fall. It will definitely get tested then.

I only test what I have personally or what has been provided to me. I do not have access to all those other mufflers. That would also require additional work to machine adaptor plates plus my personal time.

What I am planning is to build a dyno. I've had that in the works for a few years for my trimmer project. That's the best way to quantify changes.

 

[Team FAST]

I would love to flow the ports on the cylinder by itself. If anyone has a dead cylinder, let me know

 

[Team FAST]

Here's one other little interesting thing I discovered during testing. If you leave the screw out that holds on the cover, you gain an additional .5CFM flow (over stock)
Stock =10.5 CFM and stock with that screw removed = 11 CFM

Easy quick little fix

 

[James Miller]

Here's one other little interesting thing I discovered during testing. If you leave the screw out that holds on the cover, you gain an additional .5CFM flow (over stock)
Stock =10.5 CFM and stock with that screw removed = 11 CFM

Easy quick little fix

View attachment 520362

Is that bolt hole open to the inside of the muff I never looked when I had mine off. The saw does pick up noticeably with the deflector opened and a retune.

 

[Team FAST]

Is that bolt hole open to the inside of the muff I never looked when I had mine off. The saw does pick up noticeably with the deflector opened and a retune.

It does go into the internal cavity of the muffler. When removed on the bench, airflow escapes through the hole.
I'm probably going to leave mine installed.

 

[blsnelling]

Very interesting results.

My concern is this. Without dyno testing, you won't know what affects incremental changes have on actual power made. At some point, more flow won't make more power.

Over the years, I have found that a modest muffler mod gives most of the gain, without the excessive noise that comes with more radical muffler mods.

I'm sure your well aware of all this, but just wanted to point it out for everyone.

 

[Team FAST]

Very interesting results.

My concern is this. Without dyno testing, you won't know what affects incremental changes have on actual power made. At some point, more flow won't make more power.

Over the years, I have found that a modest muffler mod gives most of the gain, without the excessive noise that comes with more radical muffler mods.

I'm sure your well aware of all this, but just wanted to point it out for everyone.

I completely agree. Which is why, based on the carb intake flow numbers, I am not inclined to make any additional changes to the muffler, based on the flow gain I measured just from modifying the deflector.

I need to install it on the saw and tune it up.

Dyno testing a two stroke...if I ever get there...is a HUGE can of worms. Many Many variables.

 

[Team FAST]

Here are the corrected airflow results. This data has been corrected for test flow calibration (using a standard flow orifice calibration plate from Superflow), and temperature differences caused by the adiabatic heating of the air through the bench.

What this means, is that if someone took these same parts and repeated the measurements on their own calibrated flow bench (applying their own corrections based on test conditions) then you should get very similar results. Think of this like SAE Corrected Horsepower numbers on a dyno.

The values changed a little but the basic relationships of the test configurations and conclusions remain unchanged.

 

[RedFir Down]

Thanks for taking the time to test this muffler, interesting findings!
I think there is a small error. In post 7 you have Screen and deflector remove @ 20.5 and in post 31 it's @ 10.6.
Again, kudos!

 

[Team FAST]

Good catch! I fat-fingered it onto the powerpoint slide. I've made the correction. Should be 19.6

 

[svk]

Great work. Do you have any intention to do this with different models?

 

[Chris-PA]

Does anyone know what venturi size that carb is?

 

[c5rulz]

 

[Team FAST]

Does anyone know what venturi size that carb is?

Chris,

Best I can measure without disassembling the carb, it is 15.5mm

Walbro HDA 268a 547

 

[Chris-PA]

Chris,

Best I can measure without disassembling the carb, it is 15.5mm

Walbro HDA 268a 547

Hey thanks! I've got an HDA that size on my 62cc Chinese clone, and I have often considered putting a larger carb on it. Given this data though I don't think it's something I will bother with unless one falls in my lap.

 

[Team FAST]

Just for giggles, I installed a velocity stack on the carb and tested it. Despite looking Bad-ass, and despite my hopes and dreams....alas...it provided no benefit. The carb flows exactly the same with or without the velocity stack.

*BUT* with a Velocity stack installed, and a blanking choke plate (the kind that swings completely out of the carb throat) I could remove the stock choke butterfly and install a K&N style air filter (which has very low restriction) and make some pretty hefty gain on intake airflow. So the velocity stack can improve flow....





I also managed to install the Echo air filter cover, to better simulate the exact flow that the carb experiences when everything is installed on the saw.

The plastic cover reduces flow to the carb by 0.3CFM as compared to flowing the carb with the air filter and no orange cover. So that's probably a negligible amount. Plus, there may be some dynamic pressure effects from the engine fan and the swirl filtration scheme they use.

 

[Chris-PA]

*BUT* with a Velocity stack installed, and a blanking choke plate (the kind that swings completely out of the carb throat) I could remove the stock choke butterfly and install a K&N style air filter (which has very low restriction) and make some pretty hefty gain on intake airflow. So the velocity stack can improve flow....

Did you try no choke plate and no velocity stack? My bet is that simply removing the choke plate is where the gains are.