Powertuned Question

[Harley]

Hello,

I was wondering how you guys determine the port timing and area for your modified saws.

Does anybody use a computer?

And what is the difference between a "woods" saw and a competition version? I.E. what makes the woods saw more dependable?

Thanks for your help.

Harley

 

[kdhotsaw]

port timing

hello harley,
You have to do a lot of studing and a lot of porting and modifing to arrive at the proper set of port figures for either a good woods saw or a full blown race saw. chain saw motors are basically detuned 2-stroke engines. just by changing or increasing the port timing and modifing the exhaust you can get 30- 45 percent more power without losing any reliability. I've have some modified 371's used every day for 4 years that are still running fine. They have had the rings replaced. On a competition saw it a different story, you take the port timing to the limit, cut off the cylinder head and build a head with a combustion chamber with about 1/2 the cc's in the chamber. this gives more compression and lowers the squish clearance. then you install a bigger modified carb or carbs. convert the saw motor to a reed valve induction, install a header and expansion chamber, and play with the ignition. now you can go play with the big boys

ken [email protected]
530-589-2744

 

[kdhotsaw]

computer software for porting

Hello again Harley
In regards to the question on computer software for 2 stroke engines there are currently 5 companies designing computer programs for two cycle engines i've played with their sample programs and they look pretty good to me. if you would like to look at a evaulation of them go to (www.macdizzy.com) This site also has a 8 chapter section on engine porting plus a dyno test on before and after dyno tests on a 80 cc atv engine. went from 6.5 hp to 13.5 hp. this is a big site with page after page of engine data and tests. dynomite engine site. Some of the articles give you actual porting figures which is very hard to find.

ken [email protected] 530-589-2744

 

[Harley]

Thanks Ken.

That site is what made me ask the question. I downloaded a freeware program and was messing with it.

So, you port purely by experience?

Heres a general question. What RPM do you tune for? Do "modified saws" run at a higher RPM in the cut versus a stock saw. I noticed in another current post that someone mentioned 1400 RPM. What RPM is too much?


Again, thanks for the info.

Harley

 

[Harley]

Also, I just looked back at Gypo loggers post of the dyno test from his walkerized 026. After tuning it picked up about 2500 RPM free speed.

However it seems as though the peak torque remained arround the same area of RPM's. It looks as though it got wider, after tuning. The horsepower peak increased by 2500 RPM.

Thanks

Harley

 

[kdhotsaw]

Porting software

Hello Harley,
No, we dont port purely by experience but after you modify enough motors you begin to realize what porting figures work the best for what you want the saw to do. early on i did a lot of computations using formulas from the most successful 2 stroke engine builders. you have to figure out where to put the ports using time area figures. also what rpm and where you need the torque curve its the same computations the computer software do in a seconds. it just takes you a lot longer to do the math. the available computer software programs are all compiled from data in the two top engine developers books, Gorden Blair and E GordenJennings
Most of my racing saws cut in the 12000-12500 rpm range. We push hard and adjust the raker height so the saw wont pull down out of that rpm. Thats where the saw cuts the fastest. on a modified woods saw they actually cut at a higher rpm because the fallers dont want to push that hard all day to make there cuts Each faller has his own method of cutting and rpm he likes to cut at . Some of them bump the knots at 13000-13500 rpm. This is very hard on the crankshaft big end rod bearing .It doesn't get adequate lubrication at that rpm.
ken kdhotsaw

 

[tundraotto]

kd so you make the cutter/raker height difference pretty small to keep the saw on the powerband you have made the best power at? ie. i dont know what small filing down is for your saw but...as a general idea?

 

[kdhotsaw]

Raker height

Hello Otto,
What are you doing? staying up all night to see if dennis finishes that 372? Ha. Ha.
The raker height is dependent on the saw motor size, width of the log, sawing technique, Type of chain(full comp. or skip)And a number of other vairaibles. But mainly you dont want to pull the motor down to come out of the power band
On a woods saw It seems like .025 to .030 works the best. just depends on saw size and the cutter

ken kdhotsaw

Ps. I like the looks of your porting on your muffler just smooth out the drill holes.

 

[tundraotto]

howdy ken - please excuse my redneck canuck friend for showing my patented powertuning techniques - i just dont have the time in my hands to do all the stuff anymore so i will dedicate my free time to racing chain - lol - beer 30 all the time while here

anyway, run full comp on oak mostly at 24" .050 i wanted to try .030 to get some chunks but got talked out of it - the way i figured it out in my head was that the bigger chips have no way to clear without being cut again by the other cutters - ie wasting good power. im close but im not that far-lol or maybe i am:alien:

thank you especially for both (dennis & kd and i guess you too you friggin lambert) for giving me a chance to try some proven tricks and some good ole advice - its greatly appreciated

____________
the arkie woodchopper

 

[tundraotto]

i wish i would have made a vaw file of a stock 372 and a new one after dennis was done - 2 stroke sounds like it is - when its really badass it probably is....???? - oh well, i will post the after .vaw file for your listening pleasure - i just cant wait....you reading my mind kd, this is really exciting for me

 

[HUSKYMAN]

Dennis you better hurry up on that saw and ship it expedited. I think Otto is going to explode with anticipation

 

[Dennis]

Huskyman, no worries...breaking in as we speak...just thought I would post this little pic for you, its a bit blurry...had to take a pic of a pic...as my scanner screwed up...but it could soon be your new favorite hometown...

Jonsered, Sweden. This is the R&D factory when I went over there in 1997..I will see what other pics I can come up with.

 

[Harley]

Thanks for the information Ken.


Harley