Old Dirty Feta and the MS500i--the Hi-Tech Wood Lobotomizer

[Gary Courtney]

25-4250 They are designed to fit the K&N for the 044/440, etc. HD setup.

eBay link where I got mine: https://www.ebay.com/itm/K-N-25-4250-Airforce-Air-Filter-Foam-Wrap-1-5in-Tall-Red/132907922442?ssPageName=STRK:MEBIDX:IT&_trksid=p2057872.m2749.l2649

TY

 

[jacob j.]

Cylinder pics... squish is at .026 with the base gasket.

Is that where the Junior Mints go?

 

[drf256]

Nicest factory exhaust port I’ve ever laid eyes on.

I wouldn’t personally open that rear cover. Looks like it’s got enough venting, especially if you take a look at how much there is on older Stihl AF covers (and still enough to run well).

With the numbers shown, I’m not sure much could be improved with porting. Maybe a welder popup or a machined slug from another saw? Maybe squaring up the uppers?

Saw has 14/17* Blowdown on a quad. I find the entire evolution fascinating. And 84* intake makes the theory of “being square” even more questionable to me. None of the saws I build are “square”.

I see Stephen is showing 119 primary and 122 secondaries, but it looks opposite to me when I view the cylinder. Could be an illusion.

 

[AlfA01]

Nicest factory exhaust port I’ve ever laid eyes on.

I wouldn’t personally open that rear cover. Looks like it’s got enough venting, especially if you take a look at how much there is on older Stihl AF covers (and still enough to run well).

With the numbers shown, I’m not sure much could be improved with porting. Maybe a welder popup or a machined slug from another saw? Maybe squaring up the uppers?

Saw has 14/17* Blowdown on a quad. I find the entire evolution fascinating. And 84* intake makes the theory of “being square” even more questionable to me. None of the saws I build are “square”.

I see Stephen is showing 119 primary and 122 secondaries, but it looks opposite to me when I view the cylinder. Could be an illusion.

The exhaust port is clean, Al. It's really small...

The upper transfers are difficult to see. Ring method is the best method to get accurate numbers.

Some pics for better reference...

Exhaust port


Intake port...

 

[drf256]

So both open on the exhaust side first, but the secondary sure looks like it opens first to me.

 

[drf256]

35* of crankcase compression.

A small exhaust port at 105* with a lot of arc to it.

Only 14* of Blowdown.

Factory intake floor at 84*, and a BIG port.

Pretty much defies any common knowledge I’ve learned about porting theory. Hope others chime in. The injection may be overcoming any lag from standard Venturi siphoning.

My head spinning a bit here, I’m gonna need a brakeband for it.

 

[AlfA01]

So both open on the exhaust side first, but the secondary sure looks like it opens first to me.

It's a bit of an optical illusion. The cylinder design is more upright, and the case is more sloped. Exhaust side of the uppers do open quite a bit earlier.

 

[drf256]

Regardless, the piston crown is perpendicular to bore.

 

[AlfA01]

Regardless, the piston crown is perpendicular to bore.

Yes, but the those uppers are about 5* difference from leading edge to trailing edge. I'll get some better pics in the PM.

I made some minor mods, which I want to test later today and then back on the bench.

 

[drf256]

Every bit of those angles are engineered in.

 

[blsnelling]

35* of crankcase compression.

A small exhaust port at 105* with a lot of arc to it.

Only 14* of Blowdown.

Factory intake floor at 84*, and a BIG port.

Pretty much defies any common knowledge I’ve learned about porting theory. Hope others chime in. The injection may be overcoming any lag from standard Venturi siphoning.

My head spinning a bit here, I’m gonna need a brakeband for it.

I have always used more intake than was popular. Also, I've been opening the exhaust side transfers first for several years.

That low of an exhaust and short blowdown do surprise me.

 

[huskyboy]

I’d guess there trying to keep the torque good with that short stroke? Isn’t the stroke 34-35mm and the bore 54mm or so on this saw?

 

[StephK87]

I’d guess there trying to keep the torque good with that short stroke? Isn’t the stroke 34-35mm and the bore 54mm or so on this saw?

yes, 54mm bore and 34.6mm stroke

 

[drf256]

I’d guess there trying to keep the torque good with that short stroke? Isn’t the stroke 34-35mm and the bore 54mm or so on this saw?

Stroke on a chainsaw is relatively short by design for compactness.

The longer the stroke, the more torque, it's like a longer bike pedal.

A longer stroke also vastly increases time x area of a port. If you do the math, the amount is astonishing.

I believe that is why husky went with longer strokes and layed the cylinders back at angles to make it fit.

 

[huskyboy]

I agree with you al, thanks for explaining for me. Do you think they were trying to keep the torque less peaky with the lower exhaust on the short stroke with the stihl maybe? Seems like a very short stroke for a 70-80cc saw compared to norm. Even more over square than the 462.

 

[00wyk]

Bump that lil 572's bore up to 53 or 54mm and you got a completely different saw.

 

[TreeLife]

Bump that lil 572's bore up to 53 or 54mm and you got a completely different saw.

As overbuilt as the bottom end is, I believe they will put a bigger jug n slug on it at some point.

 

[BonScott46]

As overbuilt as the bottom end is, I believe they will put a bigger jug n slug on it at some point.

Yeahhhh Buddy!

 

[Deets066]

As overbuilt as the bottom end is, I believe they will put a bigger jug n slug on it at some point.

You could send yours to US Chrome and get her bored out.... you know... for science and stuff

 

[TreeLife]

You could send yours to US Chrome and get her bored out.... you know... for science and stuff

I just dont have that level of disposable income for fun. I spent a fat hunk on the damn thing and then some monkey business lol