Author Topic: Saw compression  (Read 1561 times)

0 Members and 22 Guests are viewing this topic.

Offline aclarke

  • Nitro Hotsaw
  • *******
  • Posts: 1676
  • Karma: 172

  • Total Badges: 25
    Badges: (View All)
    Fourth year Anniversary Third year Anniversary 1000 Posts Second year Anniversary Level 5 500 Posts
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

Share on Facebook Share on Twitter


Offline 660magnum

  • Global Moderator
  • Nitro Hotsaw
  • *******
  • Posts: 6437
  • Karma: 249
  • For The Love Of Chainsaws
  • Location: NCO

  • Total Badges: 39
    Badges: (View All)
    Seventh year Anniversary Sixth year Anniversary Fifth year Anniversary Fourth year Anniversary 5000 Posts Third year Anniversary
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
We should share what we know... someone may learn...
That knowledge can live after us... and that "Pays It Forward".
Be all that you can be . . .

Offline Cut4fun .

  • Administrator
  • Nitro Hotsaw
  • *******
  • Posts: 23708
  • Karma: 664
  • OHIO REDNECK Saw Repair Getter Done
    • Redneck Chainsaw Repair

  • Total Badges: 53
    Badges: (View All)
    Tenth year Anniversary Nineth year Anniversary Level 8 Apple User Eighth year Anniversary 20000 Posts
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.

Offline Cut4fun .

  • Administrator
  • Nitro Hotsaw
  • *******
  • Posts: 23708
  • Karma: 664
  • OHIO REDNECK Saw Repair Getter Done
    • Redneck Chainsaw Repair

  • Total Badges: 53
    Badges: (View All)
    Tenth year Anniversary Nineth year Anniversary Level 8 Apple User Eighth year Anniversary 20000 Posts
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.

Offline mdavlee .

  • Global Moderator
  • Nitro Hotsaw
  • *******
  • Posts: 1968
  • Karma: 171

  • Total Badges: 31
    Badges: (View All)
    Level 6 Sixth year Anniversary Fifth year Anniversary 1000 Posts Fourth year Anniversary 500 Posts
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

  • Nitro Hotsaw
  • *******
  • Posts: 1219
  • Karma: 71
  • NW PA
  • Location: nw pennsylvania

  • Total Badges: 31
    Badges: (View All)
    Level 6 Fourth year Anniversary Spammer 25 Posts in one day Karma Good 1000 Posts Third year Anniversary
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

  • Nitro Hotsaw
  • *******
  • Posts: 1676
  • Karma: 172

  • Total Badges: 25
    Badges: (View All)
    Fourth year Anniversary Third year Anniversary 1000 Posts Second year Anniversary Level 5 500 Posts
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 .

  • Global Moderator
  • Nitro Hotsaw
  • *******
  • Posts: 1968
  • Karma: 171

  • Total Badges: 31
    Badges: (View All)
    Level 6 Sixth year Anniversary Fifth year Anniversary 1000 Posts Fourth year Anniversary 500 Posts
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

  • Nitro Hotsaw
  • *******
  • Posts: 1676
  • Karma: 172

  • Total Badges: 25
    Badges: (View All)
    Fourth year Anniversary Third year Anniversary 1000 Posts Second year Anniversary Level 5 500 Posts
Re: Saw compression
« Reply #8 on: July 31, 2014, 09:42:53 am »
Yep, be a pain to test this! 

Offline Cut4fun .

  • Administrator
  • Nitro Hotsaw
  • *******
  • Posts: 23708
  • Karma: 664
  • OHIO REDNECK Saw Repair Getter Done
    • Redneck Chainsaw Repair

  • Total Badges: 53
    Badges: (View All)
    Tenth year Anniversary Nineth year Anniversary Level 8 Apple User Eighth year Anniversary 20000 Posts
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.

 

Related Topics

  Subject / Started by Replies Last post
56 Replies
2927 Views
Last post December 27, 2013, 02:20:57 pm
by 1manband
2 Replies
4337 Views
Last post January 16, 2012, 02:38:52 pm
by swartwood1
Compression

Started by ed McCulloch

8 Replies
3421 Views
Last post February 07, 2012, 03:07:10 pm
by Al Smith
9 Replies
1053 Views
Last post November 16, 2012, 06:49:19 pm
by yikes
2 Replies
675 Views
Last post March 31, 2013, 04:58:50 pm
by Cut4fun .
3 Replies
435 Views
Last post December 14, 2013, 02:00:48 pm
by KilliansRedLeo
29 Replies
1513 Views
Last post March 08, 2014, 08:06:53 pm
by aclarke
2 Replies
563 Views
Last post April 04, 2014, 08:15:01 pm
by dynodave
0 Replies
444 Views
Last post May 31, 2014, 10:09:37 pm
by super44
11 Replies
812 Views
Last post August 18, 2014, 09:40:32 pm
by splitter2784