ignition timing on modded saws

[trappermike]

Sorry,after looking in my new spark plug catalogs I've found that some spark plug numbers I just gave are obsolete now,the plugs have been dropped from their offerings.
Bosch has dropped some of their colder plugs,I don't see the WS5E and WS5F anymore,and the only "6" plug is the WSR6F.
NGK does not make the Gold Palladium "V" plug in 1/2" reach anymore such as the B7HV or B8HV.
NGK's best plugs in the "shorty" type 3/8" reach are the "Y" types which features a "V cut" electrode,such as the BM6Y,BM7Y,and BPMR8Y(Coldest),they are also available with resistor(R),or extended tip(P). These are nice spark plugs and maybe the best stock replacements. :msp_thumbup:
I'm trying to find info about Champion possibly now making some 3/8" shorty fine-wire plugs,don't know for sure yet,Champion doesn't seem to like to publish any new catalogs online,I have to search a dealer catalog...
I did find a few Champion numbers for 3/8" racing plugs in their racing plugs data- they listed a J6C and a J4C. There were no details on these plugs so I don't know anything about the design type or availability. I will try to order a few and see, or call a Tech line number I found,so I'll let y'all know what I find out.

 

[one.man.band]

Revisiting timing adjustments. Thoughts?

Revisiting timing adjustments.

Guessing that the the saw manufacturers pick a static timing figure as a compromise between ease of starting, and a
margin of error to combat pre-ignition/detonation/heat for long motor life. Also assuming that today's stock saws are timed
from about 23* to 26* BTDC. (I did not verify either of my guesses by measurement).

Using my homeowner saw for an example:

Idle RPM = 2700
Max Power = 2.0 kW @ 9000 RPM
Max Rev Limit = 12500 RPM

Advancing = mid range boost and top end roll-off.

Mid-range RPM (saw above) = (12500 - 2700)/2 = 4900 RPM.

Finally found an old greasy tattered chilton manual that I was looking for:
From the day of gas guzzling Ford Torino's.

Anyway, champion spark plugs had a graph within the book.

Plug Temperature vs Timing Over Advance vs. Power Output

To summarize:

For 2* additional advance; 1.5% power gained; 3.5% Plug Temp increase
For 4* additional advance; 1.9% power gained; 5.5% Plug Temp increase
For 6* additional advance; 2.1% power gained; 7.0% Plug Temp Increase
For 8* additional advance; 2.2% power gained; 9.25% Plug Temp Increase
For 10* additional advance; 2.0% power gained; 11% Plug Temp Increase
For 12* additional advance: 1.7% power gained; 13% Plug Temp Increase

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At the NGK spark plug web site:

Advancing timing by 10* causes spark plug tip temperature to increase 70 to 100 degrees Celsius.
One (NGK) spark plug heat range to the next = 70 to 100 degrees Celsius.
------------------------------------------------------------------------------------------------
Back to example saw:
Largest gain approx. 8* additional advance, 2.2% therefore power gain is at mid-range 4900 RPM.
(Exactly what kind of power the saw makes at 4900 RPM is unknown).

Even if we saw the increase at the example saw's 9000 RPM power peak.... which we would not.
It would only be 2.2% x 2.0kW = 0.044 kW

Is this worth advancing the timing to the edge of pre-ignition/detonation/heat?

Is a power gain necessary at mid-range?

Or is it better to retain the stock timing or retard the stock timing in the saw to keep CHT down and EGT up
for better exhaust scavenging/supercharging/velocity effect and performance at a higher RPM?

Just thoughts. Realize that example was stock saw, but I don't have #'s for a mod saw to use.

-OMB