361 Shootout

[timberwolf]

These are just computer models, have not pulled the dyno out yet. It will show different numbers, just the way they work, you won't see the real high RPM stuff like with software as the real dyno with bar and chain accelerating a weight is affected by friction, flame speed limits ect.

Few more pics

Dual port muffler for either BB or the hotter 361
Side by side of 361 and 361 BB pistons
Stock transfer ports and then them being done, piston ring is pushed in with piston to help keep them even along the top edge.

 

[mtngun]

Yes, MOTA does make it look like the modded saws would cut at 12,000+. I look forward to the results with your dyno.

Stock 361 transfers.

Ported 361 transfers.

 

[parrisw]

Really nice work!! You never cease to amaze me at all.

Question, on a typical work saw how much do you taper the transfers back towards the intake side? Is just a couple MM fine here? I usually don't go too overboard here.

 

[timberwolf]

It very much depends on the saw and the build just how much to take the transfers back. On the stihls like 066 the ring end pins limit how far back. On the 4 port designs it is easier to keep them lower and wider. In general it is better to go wider before going higher as it gives a longer blowdown. On this one I kept the transfers almost stock height by the time the jug gets lowered. And went back about 1mm on the front and 3mm on the rear.

Nothing wild on the porting here, just a solid fast worksaw. Exhaust was raised only about .5mm intake lowered about 1mm and the ports taken out to full width. Fair bit of work on the transfers to improve flow.

 

[parrisw]

It very much depends on the saw and the build just how much to take the transfers back. On the stihls like 066 the ring end pins limit how far back. On the 4 port designs it is easier to keep them lower and wider. In general it is better to go wider before going higher as it gives a longer blowdown. On this one I kept the transfers almost stock height by the time the jug gets lowered. And went back about 1mm on the front and 3mm on the rear.

Nothing wild on the porting here, just a solid fast worksaw. Exhaust was raised only about .5mm intake lowered about 1mm and the ports taken out to full width. Fair bit of work on the transfers to improve flow.

Really nice looking port work!!!

Thanks. Most of the saws I do are Husky's, 372's 395's ect. Those are my fav's. All of my saws get the cylinders machined, sometimes do a popup as well. Usually works out well that I can raise the ex back up to get a little more blowdown. I think I raised the transfers on the last 372 to get them at 120° with a final blowdown of 20°, but that was a while ago so I'm not totally sure. Can't remember how far I tapered the transfers back, I think probably a few mm.

 

[timberwolf]

About 20 deg blowdown is about the least I would go on the 4 port huskies, any less and they start to feel weak on the top end. 2 port stihls with tighter bases can go a little less than 20 deg if built for torque but not much less. Looking at about 23 deg blowdown on this one.

 

[banshee67]

i dont want to hijack, but i also dont want to start a whole new thread about something to dumb;

what are those 2 plastic rectangular shaped things that snap into the underside of the clutch cover by the bar studs?
i lost one while cleaning the other day, do they serve any purpose? it seems like they are there for the chain to glide across, sort of like a chain slide on a 4 wheeler/dirtbike , but how would the chain even get so far out of line to even come in contact with them in the first place? should i even bother replacing it?

 

[parrisw]

About 20 deg blowdown is about the least I would go on the 4 port huskies, any less and they start to feel weak on the top end. 2 port stihls with tighter bases can go a little less than 20 deg if built for torque but not much less. Looking at about 23 deg blowdown on this one.

Wow! Ok, thanks.

On the Last 395 I did, it was all I could do to get 20°, I didn't raise the transfers at all, but raised the ex up some. Do you think I'm ok to raise the ex up some more on this 395 to get more blowdown? I think I had it at 160° dur. Compression is at 195psi now.

Thanks for the tips. Sorry though, don't want to clutter up your thread too much.

 

[timberwolf]

On that sized saw I think you could raise the exhaust a bit, compression is up there at 195 and it will likely get stronger at the top of the powerband if you can find a little more area in the top of the exhaust port. Sometime it does not take much to give it enough blowdown so that cylinder pressure drops below base pressure when the transfers open.

 

[parrisw]

On that sized saw I think you could raise the exhaust a bit, compression is up there at 195 and it will likely get stronger at the top of the powerband if you can find a little more area in the top of the exhaust port. Sometime it does not take much to give it enough blowdown so that cylinder pressure drops below base pressure when the transfers open.

Great thanks allot for the tips!

 

[timberwolf]

Turned down the base and made a popup piston for it.

Videos on doing that stuff here if you haven't watched it before.

http://www.youtube.com/watch?v=t3Q6OsmMXEU
http://www.youtube.com/watch?v=oyuhi12zlp8

It cutting about 2 seconds flat now, I feel it should be a bit better, so going to run a tank of gas through it and see where the compression settles.

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[parrisw]

Turned down the base and made a popup piston for it.

Videos on doing that stuff here if you haven't watched it before.

http://www.youtube.com/watch?v=t3Q6OsmMXEU
http://www.youtube.com/watch?v=oyuhi12zlp8

It cutting about 2 seconds flat now, I feel it should be a bit better, so going to run a tank of gas through it and see where the compression settles.

DAM!! That's really awesome!

What's the chain on it? Anything special?

 

[timberwolf]

Just factory chain, not super sharp either.

Compression at 195 psi.

I richened it up a hair and made another few cuts, cutting in the mid 1.8 range now.

 

[parrisw]

Just factory chain, not super sharp either.

Compression at 195 psi.

I richened it up a hair and made another few cuts, cutting in the mid 1.8 range now.

Nice! Looks like the same compression tester that I have.

 

[MS390]

carb

1. What to do??

2.How many RPM does your saw run?

TW...... :yourock:

 

[timberwolf]

On this carb I just took out the venturri 1mm and cleaned up some rough edges on the carb and the intake. 15k RPM or a hair less WOT no load seems about where it cuts best.

E 160.0 deg
T 116.6 deg
I 156.4 deg

 

[Metals406]

Brian, what elevation are you at? There should be a 3% modifier per 1,000 feet of elevation for comp.

 

[timberwolf]

Just a few hundred feet here so I don't bother counting that.

 

[Metals406]

Just a few hundred feet here so I don't bother counting that.

I was just curious. . . So that's be around 185 here for me. A guy would have to be mindful building a 200+ comp engine here, and then shipping it to sea level.

 

[parrisw]

On this carb I just took out the venturri 1mm and cleaned up some rough edges on the carb and the intake. 15k RPM or a hair less WOT no load seems about where it cuts best.

E 160.0 deg
T 116.6 deg
I 156.4 deg

Do you do your carb work on a lathe or by hand?