346 WXP Stock vs mod. Dyno Runs

[dbabcock]

Here are the Walkerized dyno runs that I replotted the correct way, with RPM as the independent variable, so direct comparisons can be made between their stock and modified 346 XP.

 

[tundraotto]

well done Doug - nice work!

That saw really comes alive doesn't it. Thats beating a lot of bigger stock saws at those mods - whatever the particular mods may be...

 

[WOLF_RIVER_MIKE]

Thanks Doug. Another piece of the puzzle for Stock -n- Chopped is falling into place?

 

[dbabcock]

I'll have to go over these dyno runs in more detail. I know the Land and Sea dyno is accurate, but I still need to take a closer look at the plots on Walker's site. I think I'll also call John W. and talk to him about redoing his plots so I don't have to spend an hour in Excel making each one readable. In the end, however, it's how the saw does in the wood that counts. Dynos only help get them there a little easier.

 

[treeclimber165]

You mean that the dyno charts on Walker's site don't make sense to you guys either? I thought I was just ignorant or something, but I could not make sense of them. The graph marks on the sides and bottom didn't jive in my mind.

 

[Dagger]

Db..this is some a your best work yet pard!...keep it up.
So many times I get so frustrated with all the comparisons made by people using company lit for their info. And you are giving them good info on just how much deciet is going on!.

Another good comparison would be a chart on the real Vs, advertised weight!

You remember back last spring, when I told of "dishonerable" practices by a particular company, and that a certain supervisor there said to me. "Just Who says we have to use James Watts formula" when the practice of using a different calculation for horse power was being used for the Lit????
I got so much hate mail from that post I figgered I would be banned from here....or something worse...
I left a good job cause a policies like that, of course, it turned out to be a blessing
nevertheless...anyone with a dyno who has run any saws on it seldom can duplicate those specs. and your work here is wonderful!

Now...let me stir up some ****.......to those who claim, or believe no life is lost by those increased rpms.

caculate the piston speed difference in 2 saws, same model, one souped up...and one stock.

figure out, with hours as a baseline...how much farther the fast saw's piston travels in the bore than in the stock one.
use feet for the distance calculation....then as the hour/time baseline is continued, very soon the distance can be calculated in miles....and imagine just how much more wear is going on in the same amount of hours.

 

[eyolf]

At first glance it sounds like you're asking for some difficult calculations, Dag. But wouldn't a simple ratio work as well...say comparing 12,500 to 14,500, for example, gets a figure of .86 or its reciprocal, 1.16.

What we're not talking about is the increased stress on rotating and reciprocating parts, which may be near the load limits at the higher rpm.

A pulp, sawbolt, and firewood operator that does business at the same Husky-Jonsered shop I used to frequent used Husky 55's for years, but decided to experiment with a 242xp a while back. He loved the light weight, and of course, was able to produce a bit better with the high speed saw...but he also noticed less life out of the saws. I bought 10 cords of 8' firewood from him this fall, and he's sold on the lightweights (now 346xp) because they are easier on the operator, and the slightly higher production helps make up for the higher cost of replacing more saws sooner.

The rest of us that don't literally wear a saw out in months probably won't notice a 16% reduction in service life.

 

[bwalker]

Dagger, I agree with you on your point about wear being a function of rpm, but what about mean piston speed's influeance on the whole mess. I would bet the rod aspect ratios for these saws is such that the piston speed is fairly slow, even at high rpm.

 

[dbabcock]

Daggerization

Hey Dagger,
I was in a really boring financial meeting today and found myself initially fidgeting, then later dozing off, so in order to keep myself awake I decided to scribble down some stuff in relation to your "extra piston mileage" question above. It's really pretty amazing how far a piston really goes over the lifetime of a saw. I have no idea what the life of a typical saw is, or what the dominant wear mechanism is, but I found out a few interesting facts nonetheless.

I figured on a stroke of 50mm just for the helluvit, as well as a saw RPM of 12,000 just to make rounding off a little easier. What I came up with is a peak piston speed of about 70 MPH (mean value of abot 50 MPH for a sinusoid). At this speed, the piston will have traveled about 5,000 miles in 100 hours of run time. That's not all. Maximum piston acceleration puts a pretty heavy load on the connecting rod as well with a peak of about 4,000 G's. If the piston weighed 1 pound, this would result in a force of 4,000 lbs at TDC and BDC where the piston reverses direction (not figuring the con rod, of course). I can't even begin to imagine what it would be like driving a car at 70 MPH and coming to a stop in an inch. Attached is the "****", mang ( I really need something better to do with my spare time).

 

[dbabcock]

Oh yeah, BWalker,
You'll notice that the force on the con rod also goes up as the square of the RPM. A 20% or so increase in RPM would cause con rod stress to increase by almost 50%!

 

[Dagger]

Daggerization huh....hehe you kill me pard!!!

good work...but....tell the story this way....it is the distance covered by that piston that is impressive.

lets call that 50mm(1.96805 in) stroke saw a 2 inch stroke...tad bigger for ease of illustration.

in 1 rpm the piston travels 4 inches in distance....2 up, an 2 down.

in 1 minute,at 12000 rpms, the piston has traveled 48,000 inchs, or 4000 ft.
at 10000 rpms, the piston has traveled 40,000 inchs, or 3333 ft.

now...that is 633 ft less for the lower rpm level.
less say that saw will run 20 minutes on a tank a gas.

in 20 minutes the stock saw's piston has traveled 12660 ft less than the faster saw. Thats 2.4 miles.
Now, I reckon I wont get any arguements on which skirt will show more wear in....say just 20 tanks a gas...(48 miles difference of length that those 2 piston traveled.)

I cant read your **** sheet cause this dang small monitor,(I'm moteling it tonite, so Im on a laptop) so I cant say what I think about your caculations. The results seem off to me a little...but I think your mind is quicker than mine, so if you are, you probably would have caught it. you are correct in the acceleration force goes up at the square of rpm.
So as we say...can you imagine that force of 4000 g's...whew!

 

[tundraotto]

How about this for a twist for you thinking of life expectancy:

It's pretty obvious that we get the same amount of work done a heck of a lot quicker with a good modded saw, than with a stock saw. This actually means that the modded saw runs for a shorter period of time.

I think if you figure out that; a modded saw cuts say 30% faster, right? Well, are the modded rpms 30% higher than stock? No they are not - therefore I would like to conclude that all this piston travel distance is actually less in a modded saw - in real life a well modded saw should last longer than a stock one, at least as far as to piston wear. You guys havent seen the forest for the trees this time.

 

[dbabcock]

Dagger,
The calculations I did were initially to set up equations for instantaneous piston speed or acceleration at any point in the crank rotation so I could see what the maximum speed and acceleration were. This is the only way one can calculate peak con rod load. When I figured piston speed for the total distance, I used the peak to RMS conversion for a sine function which is .707. I'll have to think about this, but that may be where the error is. Average speed is what is required. Linear piston movement, as you suggest, makes it out to be 4473 miles for 12,000 RPM with a 50mm stroke (hence a 100 mm round trip time). Using the .707 mean value, I come up with about 4965 miles. I'm sure this is where the problem lies. I am absolutely sure of the peak velocity and acceleration, however.

Otto,
If the RPM and power of a saw go up, the the time in the cut will go down. That's for sure, and you bring up an absolutely excellent point. What should also be considered is that you can't defy the laws of physics in that an increased power of say 30% is going to allow you to cut any more than 30% faster. At best, the contest in longetivity between modded vs. stock saws would be a draw (heat notwithstanding). In actuality, you'll just be able to cut more wood in a given time, therefore use the saw more.

 

[dbabcock]

Just went over it. Should have used 2/pi as a multiplier of the peak piston speed to get the average(mean) rather than .707 which is used for RMS coversion of the maximum value. This gives the exact same mileage as your linear calculation. Leave it to me to do the differential calculus correctly and screw up the simple linear algebra average....doh.

 

[tundraotto]

This is what I mean though Doug; as the saw is tuned the torque is increased (as you pointed out this is the important figure along with at what rpm it is generated). The torque might be generated at a higher rpm but not ex. 30%. The cutting speed however is increased by 30%. What I mean is that you are increasing the cutting speed by 30%, but only increasing the cutting rpm range by only say 1000-2000rpm (about 10-20%). Therefore, theoretically the piston will travel less distance for a given wood pile. The muffler mods given by all the tuners withstanding the heat is even lower than stock (again allowing for shorter cutting time even thoug at a slightly higher rpm). In the end you should see a modded saw outlast a stock one at least in theory.

 

[tundraotto]

I might have had too many beers again, but what do you think?

 

[dbabcock]

Yup, if you can increase the torque and don't increase the RPM as much to do the cutting (say with a deeper raker), the saw will cut faster, with a higher power output but with less relative chain speed. I think that's right, but I've got Remy on my side tonight.

 

[tundraotto]

yes, this is what I was trying to say in more words, LOL, save some Remy for Clearwater!

 

[dbabcock]

Don't worry, I always have at least 5 or 6 bottles "in stock". You show up in Clearwater next year and I guarantee you'll be in Remy heaven. You and I are the only regulars that really like the stuff. I'll bring plenty. Trust me.

 

[tundraotto]

that's a deal Doug - like I promised before I will bring us so many cubans you'll think you're running rich I look forward to it.