Dumb question about the modded saws?

[Crofter]

Andyshine, I agree; my 372 was probably very similar to yours as it had the same father. It got a further treatment by TW and while it was apart it was quite apparent that it had the black carbon spot on the underside of the piston crown on exhaust side about the size of a thumbprint. That is a sign that you have been running on the edge for max piston temperature. Probably did that when I had it on pipe and made multiple cuts.

You sure do pull a lot more fuel through a heavily modded engine and a lot of it goes out the exhaust at the end of scavenging so there is no doubt evaporative cooling on the exhaust and maybe even head temperature could be lower at some points of operation but if you let her at it steady it will overheat.
Granted I am talking about something way past what I would recommend as a woods port.

Yes, increasing compression and charge turbulence will create more efficient compression; add to that higher rpm and you could have less actuall heat loss into the head for a given amount of fuel burned or a given amount of output, but, and that is a big BUT, thermal efficiencies will be more than cancelled when you burn more fuel and create twice the output. Lower operating temperatures for a modded saw wont be an easy sell!

I am just stirring things; I admit to liking a modded saw myself. I think Brad is right that you can get more work out of the same saw modded even if it needs a set of rings a bit sooner. I am sure that the piece work cutters that Sling'r has for a lot of his customers think it is a good bargain.

The bottom line is you have to know what you really honestly want the saw for and build accordingly. If you want to beat every other saw at the back yard races you have probably given up a bit of longevity as a work saw.
Not all saws have the same potential for percentage gain over stock. Two examples are a Husky 359 and a Dolmar 7900. It is not impossible to cut in half the cut times of the Husky which amounts to roughly a 100% increase in power but you wont come near to doing that increase with the Dolmar without major parts swapping and cylinder work. There is no "One size fits all" sort of treatment.

 

[sawinredneck]

Sorry Frank, I've no beef with you, you "get it". But I think a few of the newer members are mixing in a set of valves where there are none!

 

[mooseman]

If you are running a tuned pipe, all bets are off. There is a reflection wave that increases the presure inside the muffler, when the pulse hits the far side restriction and bounces off, pushing some of the new fuel/air mix that was used to scavange the cylinder bak into the exhaust port, densifying the charge. This loses most of the extra cooling that you would have gotten from this gas repidly expanding, and drawing off heat.. The faster that gas expands, the higher the rate of cooling. Of course, if there is too much flow, you will lose too much of the incomming charge, and run lean...it's a fine line.

 

[Crofter]

Sorry Frank, I've no beef with you, you "get it". But I think a few of the newer members are mixing in a set of valves where there are none!

Hadnt read your previous post when I sent mine off. Yep, lots of 4 stroke thinking you have to leave behind in understanding a two stroke.

As you say you, have to keep in mind what percentage increase you are getting to predict whether you will run hotter or colder. Saw modification is such a broad term it confuses more than informs. A stock appearing race saw can easily put out three times the horsepower while a very functional woods port or work saw mod should not be much more than a third faster. That is a ten to one difference in power increase over stock.

 

[Guarddog1]

I think people believe it runs cooler but I think by using more fuel and allowing the unused fuel to carry the absorbed heat out of the cyliender this is how the (runs cooler) comes along. Combustion should happen at similar temps unless the compression ratio is increased or the timing is changed if it should result in similar exhaust temps no matter how fast it moves. Now for the kicker cat mufflers they do increase heat buy trying to burn hydrocarbons that are left in the exhaust.

 

[HEAVY FUEL]

You can't put a price tag on FUN!!:greenchainsaw:

 

[Erick]

Kind of a trick question.

Do you measure a saws life by time (months/years of service) or by the amout of work done (bft/cord cut)????

I think if you measure it by production a modded saw will last longer than a stock saw.

 

[Evan]

my opion. a bone stock muffler modded saw will live longer if treated the same as modded saw.

if you mod it itl break, that holds trrue for saws-trucks. while stocker keeps chugn along.

i mod everything i own and work on it often have been that way for years thats just me.

 

[micah79]

i have modded saws that have literally hundreds of hrs .of commercial firewood tree felling bucking production on them .from my builder however i use all of his advice and tuning notes supplied to me by him the builder included in my modification price . . redline kart extreme pressure oil at 35.1 or klotz techniplate. are the two i use . he has supplied me with redmax 621,redmax/ ryobi,4000 husky 262xp dolmar 6400 7900 and some efcos / olympyk and i have not had a problem , i tune for the day with a tach. he also tought me this and i have alot of fun . these are ported for tourqe . all saws are premium pump gas , port improved not race ported. i feel if all builders advice is used you can far outwey the benifit of a stock saws board foot per hr cut. it sure is a blast running them.

 

[B_Turner]

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.

One downside is volume level.

 

[Sawdustmaker]

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

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

READ THAT!!!!!!!!!!!

thanks a bunch moose

I almost posted to bump it up but i know that pi$$es p.pl

 

[GASoline71]

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

Most don't need 'em... but want 'em.

How many port jobs do you do for pro fallers and cutters? I'm just curious...

Gary

 

[Taxmantoo]

he has supplied me with redmax 621,redmax/ ryobi,4000

You've got the silver/gray/yellow Ryobi 10532 with a woods port?

 

[Erick]

Most don't need 'em... but want 'em.

How many port jobs do you do for pro fallers and cutters? I'm just curious...

Gary

98% of the port work around here is sold to production cutters.

 

[PES+]

Just personal observations

Cooler is not always better......and I can absolutely agree that the type of user and their habits make all the difference in the world.

When muffler modded you can run extra oil which is often not a great idea to go too far with in a stock restricted muffler without plugging the exhaust passages from the screen back to the port which loses power and increases heat and once back to the port eventually breaks loose and wedges between the piston and the cylinder.

Hopefully the user would notice this before it gets to this extreme but I have seen it often enough.

When you then move to increasing compression with less restricted muffler and richen the mixture to keep things cooler you have also increased the amount of oil....which needs heat to get out and if the cylinder is run cool enough the excess oil builds up in the combustion chamber which increases compression which generates more heat etc which coupled with dirty cooling system leads to an increasing octane requirement until you get craters and eventual seizure.

Once you move into changing the intake shape you start to get into losing the all around running abilities of the saw. Start opening up and reshaping transfers and it can get more finicky.

I won't even touch on the effects of lubrication during porting as there is still so much guess work and rules of thumb that there is little documentation to support any theories with any certainty that I have found.

I have seen some effects of port work starving bearings depending on what was done......and also seen that adding more oil did nothing to help in these cases and just made things worse elsewhere.

If you have a saw modified I would hope that the modder would either ask what you run for fuel and oil and in what ratio or tell you what they recommend.

If a builder knows a user and watches the way he cuts with the saw and his general demeanor the builder can usually build something which will last a long time....yes indeed sometimes longer than stock but not much.

Now this saw built to this user can be destroyed in short order if lent to another cutter who cuts and does maintenance very differently.

Manufacturers do not build saws to purposely run in a way that will wear out faster but need to build a machine that will be sold all around the world and will live a long life under pretty severe conditions including fuels of very poor quality.

Emissions requirements are part of the equation as well as sound levels.

Then again I could be totally wrong.....

 

[damifino]

So what are we talking, you mod a saw and get nine good years out of it instead of ten. You loose a year but have a blast while its running. I know there is no way of knowing just how much xtra wear there will be on a modded saw and it depends alot on the saw, type of mod., type of work the saw is used for and the person useing the saw but If it feels good do it. Modding a saw is no less crazy then owning ten saws like 90% of everyone that belongs to this great site.

 

[Sawdustmaker]

So what are we talking, you mod a saw and get nine good years out of it instead of ten. You loose a year but have a blast while its running. I know there is no way of knowing just how much xtra wear there will be on a modded saw and it depends alot on the saw, type of mod., type of work the saw is used for and the person useing the saw but If it feels good do it. Modding a saw is no less crazy then owning ten saws like 90% of everyone that belongs to this great site.

Very well put.

 

[tek9tim]

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.

Depends entirely on the level of mod you're talking about, but it seems the people who mod their saws are the ones that spend more time squeezing the trigger anyhow.

As to numbers on temps, I know Dean at WHS played with that back in the day too, he got along the same lines as timberwolf's findings.

I know this thread is already a long ass read, and most things have been said, but to pick up a few and add my opinion... It was said that muffler mods will decrease heat on the exhaust side of the piston/cylinder, which is certainly correct, and anybody have an answer for where an overheated piston melts first? (That's rhetorical, you all know)

I think that some people get hung up on the no-load RPM gain that happens when you tune in a ported saw to run at its sweet spot. Of course, there is a gain in the in-the-cut RPM, which means that the piston is making more trips and shock loads on the crank and rod bearings than a stock saw is If you factor in higher compression and stronger combustion, each shock load is stronger. By default, your bottom end is not going to last as long. Then this is where we enter the gray area of work accomplished in a given time period.

Bottom line, I can get behind muffler mods making saws last longer, but not port work/compression increases. But WTF does my opinion matter?

I think this thread should have been titled differently, not really a dumb question. Lots of different educated opinions about it, which aren't entirely common knowledge. It is a can of worms, since lots of guys try to justify port work with the durability card.

 

[parrisw]

More power= more heat, more strain. You do the math!!! However modded things, saws, cars, bikes, are just plain cool. I like em!!!!

 

[Sawdustmaker]

More power= more heat, more strain. You do the math!!! However modded things, saws, cars, bikes, are just plain cool. I like em!!!!

not true, more power = more work done= less energy left to go into heat. (i do know it is not this simple but think it is applicable)

but, as gas expands, it cools. (gas law)