General range of increase in HP from porting/muff mod

[StihlyinEly]

Hey folks:

I know this is going to vary a lot depending on the various chainsaw models in question, but I'm curious in a general sense about the range of horsepower (or however you want to represent "power") percentage increase one can hope for from a woods port and muff mod.

My 038M is ported, but it came to me that way. I'll likely be getting my stock (well, it does have a muff mod now) 460 ported as well. Since I got that saw stock, I'll have a feel for the power increase.

Meanwhile . . . and thanks!

 

[mtngun]

Timberwolf posted this computer simulation on his 460/660 build thread.

OEM 460 power = red solid line
OEM 460 torque = red dotted line

Woods Port power = blue solid line
Woods Port torque = blue dotted line

TW claimed 42% increase in power -- at 12,000 rpm. Of course, TW IS A PRO and does top notch work. Plus, this particular woods port included a pop-up piston.

Note that the modded 460 makes less power than OEM below 7000 rpm. Of course, we don't cut at 7000 rpm, so that's irrelevant, but my point is that porting can hurt low end power, especially if it is not done right. TW has taken care to increase the power at useful RPMs.

I'm not sure how the various types of cutting speed tests correlate to power, but I suspect that cutting small cookies tends to test power at high rpm, while my milling speed test tends to test power closer to 9000 rpm, where the power increase is modest.

 

[FATGUY]

Timberwolf posted this computer simulation on his 460/660 build thread.

OEM 460 power = red solid line
OEM 460 torque = red dotted line

Woods Port power = blue solid line
Woods Port torque = blue dotted line

TW claimed 42% increase in power -- at 12,000 rpm. Of course, TW IS A PRO and does top notch work. Plus, this particular woods port included a pop-up piston.

Note that the modded 460 makes less power than OEM below 7000 rpm. Of course, we don't cut at 7000 rpm, so that's irrelevant, but my point is that porting can hurt low end power, especially if it is not done right. TW has taken care to increase the power at useful RPMs.
I'm not sure how the various types of cutting speed tests correlate to power, but I suspect that cutting small cookies tends to test power at high rpm, while my milling speed test tends to test power closer to 9000 rpm, where the power increase is modest.

Interesting, this saw was obviousley modded to run in a certain operating range. It's increadible how the power drops off at a certain point,

 

[West Texas]

As my signature shows, I have two 361's that have been ported by a couple of pro's, along with the muffler mods too. Then I have the 026 with my own muffler mod.

In the case of my 026 muffler mod, it eliminated the 'jake brake' effect of a constricted muffler and I estimate about a 20% increase in power, as I still operate it at normal range rpms. With my square chisel chain, and I routinely out cut my friends with their 026/260 saws.

In the case of the two 361's, my before and after performance shows that I am operating with great power; but, at a much higher rpm (faster chain speed) with both of these saws, which means I fly through the wood at a much faster pace than before I got them worked on by the pro's.

 

[mtngun]

If I were retired, I'd build a dyno so I could experiment with modding saws and actually know what the heck I was doing.

 

[edisto]

Interesting, this saw was obviousley modded to run in a certain operating range. It's increadible how the power drops off at a certain point,

Porting will make the power curve more "peaky". Gains at high rpm usually come at the expense of low-end power.

What is incredible about that curve is that the peak is a plateau.

It is a simulation, but it still is amazing that you can get a peak that much higher without it falling off abruptly as you increase rpm.

If I were retired, I'd build a dyno so I could experiment with modding saws and actually know what the heck I was doing.

How much fun would that be! Everyone that takes a Dremel to their saw says it runs like a 'raped ape' afterwards, but it would be fantastic to see what the actual results are.

If I had a dyno, my saws might never make it into wood again.

 

[timberwolf]

It is a simulation, but it still is amazing that you can get a peak that much higher without it falling off abruptly as you increase rpm.

To get a little more power you do not need to trade off low end just to gain top end. At first with mild mods it is possible to keep the low end and just extend the upper end a little. Mild gains of 10%-20% mostly through improved cylinder filling and emptying, cleaner scavenging and inproved combustion from higher compression.

But as more peek power is chased it will without doubt call for sacraficing breadth of powerband and lower end. The narower the powerband the more difficult it is to match chain and gearing and keep the saw cutting at the ideal RPM and not bogging it.

The simulation does not measure output at the bar so makes no acounting for friction loses, flame speed limits and a few other dynamic variables. This is where a dyno is the tool. But seting up dyno runs and dealing with the data take a lot of time. I just have not spent as much time on it yet as I would have liked.

 

[mtngun]

But seting up dyno runs and dealing with the data take a lot of time. I just have not spent as much time on it yet as I would have liked.

Is your dyno home made or store bought ? What does it use as a brake ? Does it agree reasonably well with your computer models ?

Yes, I imagine it takes time, that's why it will have to wait until I retire. Work and family responsibilities constantly interfere with the more important things in life.

 

[blsnelling]

Porting will make the power curve more "peaky". Gains at high rpm usually come at the expense of low-end power.

I don't have a dyno, but I would expect a woods port to actually broaden the power curve, with gains at both low and high RPMs. Only when you start chasing even higher RPMs would I expect to start narrowing the powerband. I always say that I port for torque, but doing so also buys you RPMs. My typical ports jobs see a ballpark gain of about 1500 WOT tuning RPMs. That's not always the case, but a pretty fair average. And you'll feel those gains across the powerband.

Timberwolfs 460 above shows about a 50% gain in power. I suspect that's a fairly aggressive port job, probably more than a woods port. No? That would explain the less broad than stock powerband. Like Brian said, the farther that envelope's pushed, the important the setup and operator.

 

[StihlyinEly]

To get a little more power you do not need to trade off low end just to gain top end. At first with mild mods it is possible to keep the low end and just extend the upper end a little. Mild gains of 10%-20% mostly through improved cylinder filling and emptying, cleaner scavenging and inproved combustion from higher compression.

But as more peek power is chased it will without doubt call for sacraficing breadth of powerband and lower end. The narower the powerband the more difficult it is to match chain and gearing and keep the saw cutting at the ideal RPM and not bogging it.

The simulation does not measure output at the bar so makes no acounting for friction loses, flame speed limits and a few other dynamic variables. This is where a dyno is the tool. But seting up dyno runs and dealing with the data take a lot of time. I just have not spent as much time on it yet as I would have liked.

That's a whopper of a power gain! I got almost all of timberwolf's explanation. Thanks so much for everyone who is contributing. I'm learning as we go. One day I might become smart. Uh, well, maybe or maybe not.

Anyway, I bolded a couple terms I didn't understand. Anyone want to explain them? My head's not quite full enough yet today.

 

[edisto]

Anyway, I bolded a couple terms I didn't understand. Anyone want to explain them? My head's not quite full enough yet today.

Ideally, scavenging is the replacement of the exhaust gasses with a fresh charge, realistically it is the mixing of the two in the desperate hope that what stays in the cylinder is mostly charge.

Google Schnurle (or Schneurle is you haven't got an umlaut to spare) loop.

Flame speed is just like it sounds, i.e., the speed with which the flame front travels.

 

[edisto]

I don't have a dyno, but I would expect a woods port to actually broaden the power curve, with gains at both low and high RPMs.

You can wish in one hand and crap in the other...bet I know which one fills up first!

I'm a little surprised (but happy) that you can keep the low end with mild work. That's having your cake and eating it too!

 

[spacemule]

How much fun would that be! Everyone that takes a Dremel to their saw says it runs like a 'raped ape' afterwards, but it would be fantastic to see what the actual results are.

Yeah, but you got to consider, most folks don't know what a raped ape runs like. And if they do, you should be leery of them.

 

[StihlyinEly]

Ideally, scavenging is the replacement of the exhaust gasses with a fresh charge, realistically it is the mixing of the two in the desperate hope that what stays in the cylinder is mostly charge.

Google Schnurle (or Schneurle is you haven't got an umlaut to spare) loop.

Flame speed is just like it sounds, i.e., the speed with which the flame front travels.

Thanks for the assist, and for the help with further browsing. I don't really know what a flame front is, either, but from context I'd guess it's the leading edge of expanding ignited fuel/oil mix within the cylinder.

 

[edisto]

Yeah, but you got to consider, most folks don't know what a raped ape runs like. And if they do, you should be leery of them.

Should they PM you?

 

[spacemule]

Thanks for the assist, and for the help with further browsing. I don't really know what a flame front is, either, but from context I'd guess it's the leading edge of expanding ignited fuel/oil mix within the cylinder.

A flame front is what happens shortly after someone blames a crap saw on UPS.

 

[edisto]

Thanks for the assist, and for the help with further browsing. I don't really know what a flame front is, either, but from context I'd guess it's the leading edge of expanding ignited fuel/oil mix within the cylinder.

If you've flames elsewhere in your saw, you might need to call your dealer.

 

[edisto]

A flame front is what happens shortly after someone blames a crap saw on UPS.

I never thought I'd ever have to put it to the test, but I guess I am man enough to acknowledge when Space says something clever.

 

[timberwolf]

Is your dyno home made or store bought ? What does it use as a brake ? Does it agree reasonably well with your computer models ?

Yes, I imagine it takes time, that's why it will have to wait until I retire. Work and family responsibilities constantly interfere with the more important things in life.

Here is a bit on the dyno I put together over the winter, still want to go to some more advanced software to make it more user friendly. As far as agreeing, yes and no. The software and dyno agree in the mid/operating range, down low the dyno does not show much as there is the clutch kicking in, then up past the working RPM up in the 11K -13K plus range the dyno drops off much faster than the computer model. I think this makes sense with the limitations of the computer model and the fact that the dyno measures wheel HP so to speak and shows friction and other losses that the computer does not count. Also I need to add a bit to the calculations to acount for bearing loss and windage on the dyno it's self that drop the HP readings a bit. Thats where some better software would be nice.

http://arboristsite.com/showthread.php?t=43602&page=2

Trick to getting it all done is don't sleep.

 

[West Texas]

Timberwolf knows Ed and Big Dave who did the mod's on my two 361's, and they are raped apes in the wood. I've had both for several years; cut a lot of wood. And entered them in friendly GTG's and a couple of contest events.

I use square chisel semi skip chain on both, cutting these hard dead emory oaks on local ranches for firewood. I've got my money's worth out of both saws.