Ported Milling Saw

[JHctRednek]

I am working on another MS660 and I want to build this one mainly for milling. So I am looking for a broad torque range and I am wondering how transfer timing plays into a broad torque range. I have looked at most of the porting posts and I guess I am a little confused.
The last MS660 I built was with a pre decomp cylinder and the timing was set by mildly cutting the squish band to get 99 degrees exhaust, 121 degree transfer timing and 80 degrees intake. I broke the saw down again to change the intake timing to 84 degrees. I really like how the saw runs felling and bucking rounds and it works good for milling but I would like this one to be even better for milling.
This MS660 is a STIHL decomp cylinder, I have cut the squish band to get as close to 100 degrees exhaust as I can but I can only get to 98 degrees due to plating limitations. For the intake I am planning to set around 85 degrees based on my experience with the last build but I am a little confused with AUSSIE1's post from the understanding port timing numbers thread:
Raising the transfers can bring torque down a little and flatter from a high ex duration as long as blowdown allows it.
Increasing the inlet helps balance the need of the transfers and exhaust as long as the duration doesn't exceed the crankcase.

So I was thinking of going to 120 degrees on the transfers which I think is a safe number but would 118 degrees be better? Or is 122 degrees better?
Thoughts?

 

[Trx250r180]

Mastermind set my 660 up for milling ,he did some stuff different than a normal saw build ,may be worth a pm to him

 

[mdavlee]

What rpm do you think you'll be pulling in the wood? The longer blowdown will help save some torque to lug better but it's not a big change from 18-24 degrees of blowdown.

 

[JHctRednek]

mdavlee, I haven't got a tach but I would imagine I am looking for 7500 to 10000 rpm. Reading previous posts about milling with 660BB kits that's the range of rpm MtnGun usually discusses. I know that my basically stock 298xp is pretty forgiving when milling, but runs quite a bit slower rpm wise, than my MS660 was in stock form.

Trx250r180, that's good to know that mastermind built you a milling 660. I would also be interested to know why he changed transfer timing in his different 660 builds (mastermind meets the ms660 vs woods porting the ms660 tips and tricks threads) from 120 to 122 degrees.

 

[Trx250r180]

mdavlee, I haven't got a tach but I would imagine I am looking for 7500 to 10000 rpm. Reading previous posts about milling with 660BB kits that's the range of rpm MtnGun usually discusses. I know that my basically stock 298xp is pretty forgiving when milling, but runs quite a bit slower rpm wise, than my MS660 was in stock form.

Trx250r180, that's good to know that mastermind built you a milling 660. I would also be interested to know why he changed transfer timing in his different 660 builds (mastermind meets the ms660 vs woods porting the ms660 tips and tricks threads) from 120 to 122 degrees.

the saw was in the aftermarket crank thread he did if this helps at all ,there may be some #s in there ,rasmin platt crank i think

 

[JHctRednek]

Yeah I found that thread, no way I was ever finding it otherwise. thanks!
So in that thread Mastermind used the following
The exhaust is 98°
Transfers are 118°
Intake is 83°
That seems like a pretty low blow down of only 20 degrees, I would have thought that a little more blow down would be better.
Trx250r180, How does that saw work milling? I read in the post it would mostly run 32" bar and your using it to mill fur and cedar?

 

[mdavlee]

The stihl cylinders seem to run better at 18-22 degrees. Some other saws run better with a longer blow down but they have tighter crank cases and need the extra time to fill.

 

[JHctRednek]

The stihl cylinders seem to run better at 18-22 degrees. Some other saws run better with a longer blow down but they have tighter crank cases and need the extra time to fill.

Is there a certain crankcase volume to blowdown ratio? Most of what I have read doesn't talk to this. I know that from reading the older porting posts, guys like timberwolf took great pains to measure crankcases, etc. but why was never discussed in detail.

 

[Trx250r180]

Yeah I found that thread, no way I was ever finding it otherwise. thanks!
So in that thread Mastermind used the following
The exhaust is 98°
Transfers are 118°
Intake is 83°
That seems like a pretty low blow down of only 20 degrees, I would have thought that a little more blow down would be better.
Trx250r180, How does that saw work milling? I read in the post it would mostly run 32" bar and your using it to mill fur and cedar?

I have a norwood portomill it is on ,when the 660 was stock it did ok still but i had to use all the throttle milling a wider plank like 20 inches ,now it has more bottom end grunt and pulls fine at around 2/3 throttle ,at wide open in the stuff i cut it sounds like it is reving too high in the cut to me and the extra chainspeed does not seem to be any faster ,it is nice to know i have the extra grunt if run a longer bar on an alaska type mill now ,my mill has an adjustable crank to raise and lower the powerhead for the thickness of the boards and has a table of sorts with little wheels so it rolls on a ladder for tracks ,the table has handlebars and a hand throttle so you do not have to be so close while milling ,i am currently running a 28 inch bar with ripping chain ground at 10 degrees

 

[JHctRednek]

Hey thanks for the help guys, and Mastermind as well, with the exhaust at 98° atdc I am gonna raise the transfers to 118° atdc as you guys have suggested. I'll let you know how I like it compared to the other saws when I get it broken in.

Thanks again