Author Topic: Saw compression  (Read 419 times)

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Offline aclarke

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Saw compression
« on: July 30, 2014, 04:36:33 pm »
Lots of people building "work saw" motors with 220+ psi compression by machining down the chamber and base. While this seems to be a common practice, at what point does the compression kill the power from the associated pumping losses?   

On the flip side, many of the top 5 cube stock appearing race saws run 130-140 psi and make tremendous power on gasoline and alcohol.   

 Curious what everyone else's thoughts are to really high compressions and where it starts to become counter-productive?

Adam

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Offline 660magnum

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Re: Saw compression
« Reply #1 on: July 30, 2014, 05:42:54 pm »
You cannot run that kind of compression for a full tank without over heating. So it is only good for cookie cutters
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Offline Cut4fun .

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Re: Saw compression
« Reply #2 on: July 30, 2014, 07:22:07 pm »
I like around 170-180psi on my work saws and gtg saws in past. Ran just fine and held their own.   

I have a stock porting echo 8000 right now with 195psi and no decomp.

Had a woods ported 166 with 190psi.  Nothing to write home about IMO

I'll take good porting with 170-180psi,  over super high 220psi plus and ? . But that is just me.
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Offline Cut4fun .

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Re: Saw compression
« Reply #3 on: July 30, 2014, 07:24:33 pm »
Wayne told me he can pull his 5ci SA race saw over with 1 finger.
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Offline mdavlee .

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Re: Saw compression
« Reply #4 on: July 30, 2014, 07:56:10 pm »
I've used saws with 230 lbs of compression milling. Tuned richer than normal for sure. The last 046 cylinder had 205 and the husky 390 had 200. I could run all of them a whole tank with no overheating tuned to normalish rpms. I don't run work saws over about 13.7k.

Offline man of stihl

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Re: Saw compression
« Reply #5 on: July 30, 2014, 09:22:21 pm »
My Stihl 880 has 230 lbs and I have ran tanks of fuel through it without problems. Running it rich of course.
Ron

Offline aclarke

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Re: Saw compression
« Reply #6 on: July 30, 2014, 10:41:39 pm »
I've machined a bunch of cylinders for folks (worksaw/Racesaw) over the years and generally  believed that motors with can type mufflers did pretty well with higher compression.  Recently, I've been fooling around with a husky 181 racesaw I built 3-4 years ago that ran well but didn't turn up as high as the port timing numbers might suggest.  Re-cut the chamber to get about 150 psi static psi and it gained 1500 rpm.  Makes me wonder....  lol. Adam

Offline mdavlee .

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Re: Saw compression
« Reply #7 on: July 31, 2014, 09:16:08 am »
It's hard to say without doing one cylinder on one saw and keep cutting the chamber and base and resetting the timing each time. If I had a lathe at home I would consider trying it.

Offline aclarke

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Re: Saw compression
« Reply #8 on: July 31, 2014, 09:42:53 am »
Yep, be a pain to test this! 

Offline Cut4fun .

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Re: Saw compression
« Reply #9 on: July 31, 2014, 09:47:54 am »
I thought Randy  said something about testing early on when he got started that higher psi was his formula for work saws. Cant remember what all he said though or findings he had.
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