Dumb question about the modded saws?

[alderman]

In the real world if a saw is modded somewhat to produce a faster more powerful saw, would you expect to get the same hours out of it as one that hasn't been modded? I'm not talking about changing to different parts, but working over the original piston, cylinder, and muffler to improve performance.

:chainsawguy:

 

[Slamm]

You should get the same to better life out of it. That is if the work was done properly and not on the extreme side of things.

Sam

 

[Crofter]

Alderman, what do you want to hear?

Dont listen to addicts and dont listen to suppliers!:greenchainsaw: I wouldnt trust reformed sinners too far either.

I would say that modified saws are much easier to abuse and less tolerant to mistuning. I wouldnt put one in the hands of someone who tends to lug a saw. My saws are modified and I like the feel but if I had to pick one to last the longest possible time I certainly would only do modest compression increase and very little in the way of widening the ports. There are bragging rights that go with performance increase, so there is a tendency to ignore incidentals but I would bet that after about 15% increase in output (beyond what comes from muffler modding) that wear starts to increase very quickly if you really track it.

 

[wi50]

I'd have to say it won't last as long. Sure it runs cooler and makes more power but when these saws get tons of hours, cranks and berrings fail. Modded ones only have more strain on the parts.

Now how much wood could one cut with a stock one running X fast and a modded one running at XX? How much wood could a saw cut in the lifetime of the parts? One would likely run longer but cut slower, than the other running fast, but cutting more wood.

The operator will likely have a large effect on the life of a saw, likely more so than the mods done.

Lets look at an engine weather it's in an over the road truck, or a farm tractor. I do more work on engines that are the same engine or series of engine, but pumped to a higher horsepower than I do on the lower horsepower applications. Head gasket failures are more common, sleve pitting, etc. all more common per hour given a higher power output.

 

[alderman]

I was just curious

I'm not the mechanical type so I'm impressed reading about the gains made by those that have the aptitude for making changes that produce more power and faster speed. I was just wondering if there was a downside at all to get this much gain.

 

[oneoldbanjo]

This may be considered blasphemy on this site.....but why should I believe that a modded saw runs cooler? If you open up a muffler and let the exhaust flow out a little easier.....isn't any potential cooling effect offset by the higher rpm's that you are running? How does letting the exhaust out of the muffler faster have any affect on cooling the engine.....unless you are using additional fuel/oil to act as a coolant? I don't have any trouble believing or understanding that better breathing makes more power - but I can't see how you get more power and less heat. I am an engineer and all my training says that with more power you get more heat....not less. Has anyone actually done any testing that proves a modified saw runs cooler than a stock one....a test that includes actual tests and not just rumors. Seems like somebody needs to take some heat readings from a saw both before and after it is modified to verify these rumors. I can see some potential for a slightly cooler muffler if you let the exhaust flow through it with less restriction - but I am not convinced that the cylinder or piston would be any cooler.

My schooling also shows that stresses in moving parts go up considerably with increased rpm.....double the speed and the stresses don't just double....they increase by a factor of 4. The formulas for stresses have the Velocity-Squared as part of the equation involved in the calculations...so anytime you increase speed you are greatly increasing the stresses and reducing and factor of safety built into the parts.

I have done muffler mods to my saw and am fine with the potential for some reduction in life......I will never wear any of my saws out just cutting firewood to feed my OWB as I only burn about 6 chords a year.

 

[CentaurG2]

A candle that burns twice as bright, only lasts half as long. Meditate with me young grasshopper on this truism… ahhhh, ohmmmmm.

 

[wi50]

it'll run a little cooler because of the airflow going through the cylinder. Air flow will cool more than it heats.

I have a naturally asperated gas tractor that we run for pulling competitions. There's no water in the block, full of hardblock and I pump a little water through the head to cool it. Idle it for a little time and it's just cooking hot. At the end of a run you can put your hand anywhere on the engine but the header, it really runs cool when opened up. Of course it's fighting ignition timeing, cam timeing and profile, those are not set up to run well at idle.

 

[deer slayer]

I was always under the impression that a fine tuned engine w/quality fuel, high flow a/f, modded muffler would move more air in, thru, out (such bang blow) their for keeping things cooler than normal getting the most out of fuel economy. If a saw is missed tuned and cheapo gas. Its not burning in "the sweet spot" to rich to lean that the burning process took longer and their for created more unused energy in the cylinder and producing more heat, poor run ability, carbon buildup. I relate it to drag racing, when racing in different elevation they have to tune to get the most performance w/o going to far (lean or rich) or else they blow up or don't go as fast. Just a thought no proof but kinda makes sense to me.

 

[SteveH]

I have no numbers to throw out, maybe someone who has extensively run both stock and modded models can lend some knowledge I don't have. My personal saws are kept stock. My dealer told me recently that he gets a lot of rebuild business from folks who mod or have them modded then run them crazy. He said, well, the engineers [we were talking Stihl, just because that's what he and I use] design these things to be best the way they come from the factory. You can get some gains, etc., modding, but for 98% of users they are not a great improvement. Or, he says. I am happy with the performance I get out of mine stock so don't care. Though it is quite interesting to read about here [I keep my cars stock, too, but have friends who are always souping up theirs and it's fun to drive them....]

 

[Tree Sling'r]

Pizz on the science, modded saws are cool and chicks dig em'.

 

[mooseman]

Correct me if I'm wrong, but the goal is more power, not more RPM. You don't need to go faster to produce more power. Think of an aircraft with a constant speed propeller. The engine always turns the same RPM, but propeller pitch increases the amount of power produced. Thermodynamics says that heat is work, and work is heat, but the greater volume of expanding exhaust gasses will provide more cooling than the extra heat produced by the greater power.
Flowing more fuel/air won't help an optimally designed engine, but noise and pollution restrictions saddle us with engines that are limited buy restricting how much exhaust can flow, which restricts cooling. All that the basic mods do is optimize the engine. Increased power will put more strain on the bottom end, but the engine will be designed to handle it, as what is really happening is the Mfrs. are building say a 7.5 hp engine, and constricting it to 6 hp. in the case of an MS460. Gains from increased compression or RPM will cause more wear.

 

[oneoldbanjo]

I hate to sound like I won't listen to reason....but I want solid proof and not just opinion and speculation.

Changes that make more power will likely make more rpm in actual use.....Brad's 260 no longer runs 14,000 rpm out of the cut and it is running 17,400 rpm.....and it will probably run higher rpm's in the cut as well. That extra power comes from getting more air and more fuel into the cylinder....and burning that mixture makes more heat and makes more power. The reason ports are widened and polished, mufflers are made to flow more freely, and compression ratios are increased is to move more air and fuel and get more energy out of the fuel. I have never head of anyone building up a race motor and then putting in a smaller radiator......race motors that are usually run with larger radiators and oil coolers being added. (Drag and alchohol cars excluded).

Every one of us that uses a saw knows that it gets hot when in use....I don't think anyone can identify a change of a few degrees up or down after a saw is modified. This is especially true when you consider that there may be a week or two between running the saw stock and modified....and even a small twist of the mixture screw will change the fuel/air ratio and it can have a big affect on the running temperature of a saw. The more you tweak that screw toward lean the better the saw runs.....for a short while!

 

[BlackCatBone]

This is a pretty good question i think.

As far as the heat issue, I don't know for sure. The motors in question are air cooled, so more air moving through the system and fanned by the flywheel would mean more cooling. But there is also greater horsepower produced, which would indicate more heat generated....but this is not so simple. Increased compression means greater thermal efficiency, a more efficient usage of the fuel and air. So.....there may be only a small increase in heat generation for the greater amount of power produced. Couple this fact with a muffler modified for much less restriction, and I could buy a net decrease in heat stored.

On the mechanical side, there are a few things going on too. The pistons are almost always lightened, which will conteract the increased forces from the reciprocating motion and increased rpms to a point. Unfortunately we have to lose here though. With increased torque at the sprocket, we have to be putting more force on the bearings and crank....that's what we want!! There may also be some danger if the piston is modified too much/too much material taken out at critical points.

All in all, if the work is done smartly and towards the practical end of the spectrum, I'd say you trade a small decrease in reliability for a big increase in fun and performance. I look at the chainsaw as a tool, but not with the expectation that it will last forever.

 

[mooseman]

As I said, if you mod the saw to produce more power, you produce more heat.
If you restrict an engines ability to exhaust the product of combustion, you are not getting the full cooling effect of the charge air expanding in the hot cylinder. Expansion = cooling.
I don't think any ones trying to say that a highly modded saw will run cooler, but If you are only increasing its' ability to move air/fuel, without increasing compression or RPM, you are only bringing it to its' proper tune.
There have been posts here that demonstrated a marked temperature decrease on a muffler modded saw, using an infrared thermometer, so it's not just conjecture.

 

[blsnelling]

I'm sure that a modded saw will wear faster, but it also does more work in that same amount of time. So to me, it's not question of if it will last as long, but if it will do as much work.

I agree 100% with Crofter. In the wrong hands, a ported saw will not last near as long. More careful attention must be paid to tuning and maintenance. If you do those things right, and run it properly, it should live a very long productive life.

 

[mooseman]

Check this out. over 26% reduction in cylinder head temp.

http://www.arboristsite.com/showthread.php?t=6199&highlight=infrared

 

[Andyshine77]

I wouldn't necessarily say the overall internal temperature of muffler modded is much different than a stock saw. However I believe the exhaust side of the piston, and cylinder probably do run cooler do to the fact the hot gases are expelled away from the exhaust port and the exhaust side of the piston..

Yes a modded saw can and will run hotter than most stock saws, it really comes down to the level of modifications to the saw. Take my 372. I had it ported hotter than a normal work saw, so I can't just go out and hook it up to a mill and run it flat out for a whole tank of fuel, it would likely melt the piston. I could probably tun the saw dog rich and run it on a mill, but that's my point, I didn't mod the saw to run it on a mill.

 

[edisto]

This may be considered blasphemy on this site.....but why should I believe that a modded saw runs cooler?

A lot of articles I have seen on 2-stroke bike exhausts say the same thing. Increasing constriction of exhaust flow dramatically increases p&c temperatures. That's why they err on the side of caution when figuring out outlet diameter in a tuned pipe, and why you need smooth turns on the inlet side, but can get away with sharp angles in the diffuser.

Open it up, and it should run cooler. I underdstand what you are trying to say about power=heat, but there is efficiency to consider as well. Waste energy is lost as heat, so with the increase in efficiency (converting the energy in fuel into work), you get the same amount of work with less heat.

Porting does more than just move more mix and exhaust through the cylinder.

 

[sawinredneck]

This has been some funny ####!!!

This IS NOT a four stroke guys! Take all your radiator and drag motor talk and throw it out the window! These are two strokes, bird of another feather!
80% of the heat is held in the muffler on a two stroke. Open up the muffler, then richen it. Heat gets moved, period!
Now, figure with a stock saw 20% of the fuel mix is unburnt. THAT is how it COOLS the engine. The air fuel mixture is used to PUSH the burnt fuel out. This is why the EPA is trying to kill these motors.
Now we woods port an engine. Remember, NO VALVES, so we widen things and make it flow better yet. Probably 30-40% unburnt, COOL, fuel mixture blows through the engine and out the exhaust cooling everything.
Regardless of what Brad got out of a 260, that is not a typical woods port. Typical woods prts are 2-3k engine RPM gains.
So minimal RPM gains, considerable more COOL air/fuel flowing throughout the ENTIRE engine, and LUBRICATING EVERYTHING while doing it, and NO restrictions to hold the heat in the muffler.
There are some FACTS to ponder.