361 Shootout

[Trigger-Time]

It may be here and I missed it, but what is the sq inches
of stock cylinder exhaust port?





TT

 

[timberwolf]

Stock exhaust port area (flat plane) is .563 in2 so that make the muffler restriction about 16% of the port area.

I'll get some port maps up later.

 

[timberwolf]

Here are the stock port maps.

BB is wider on intake and exhaust, but lacking on transfers, also I don't like the shape of BB transfers much and they are not very even side to side.

 

[timberwolf]

Durrations then are:

361BB
E 156.4
T 108.6 to 115.4
I 140.6

361 Stihl
E 160.6
T 109.6 to 113.6
I 149.6

 

[mtngun]

Thanks as always for the hard data, TW.

If I may pick your brain a little -- and I'll understand if you don't want to reveal all your knowledge -- I assume, based on some of the HP charts you have posted in previous threads, that you are using MOTA, which I recently obtained and will soon be playing with. How do you determine the correct ignition timing numbers that MOTA requires?

I haven't figured out how to hook a timing light and degree wheel and then still be able to start the darned thing, not to mention the degree wheel prolly wouldn't appreciate being spun 13,000 rpm.

 

[timberwolf]

I have timed saws off fly wheel from idle to WOT and found that none of the saws I looked at had any fancy timing advance curves. So I just use the book spec, what ever it is 23 or 26 BTDC. Mota does not show a big difference with changes to timing, not sure it is 100% accurate in that aspect. Also, as I don't mess much with ignition timing on work saws it really does not matter much for the software.

Couple muffler pics. For this on just one 3/4 in pipe and will open up the existing outlet a little more.

 

[Trigger-Time]

Couple muffler pics.

For this on just one 3/4 in pipe and will open up the existing outlet a little more.

Nice bead!

With my 8th grade math I come up with, the 3/4 pipe is about 72% of the
exhaust port.......is this correct?

I apologies for such a simple question, but I do want to know.


Thanks
TT

 

[timberwolf]

That sounds about right but there is a good .20 in2 in the back so should take it up to about 110% or so. It took quite a bit of ajustment on the low speed and a little on th HS to bring it back to tune. Running about 15,000 RPM now.

Cutting about 2.3 seconds which works out to a 22% improvment over stock.

Sorry, video is dark, was getting late.

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[timberwolf]

Caps off for a trim, top cap trimmed, bottom still has limiter tab.

 

[mtngun]

Thanks for the timing info, TW. The lack of advance makes sense, since saws run WOT all the time.

 

[Zombiechopper]

Well I got mine tuned up pretty well with the stock carb today. I got it tuned nice with 2.5 out on the low and good reliable idle and good restarts. I'm really curious if the carb is holding this saw back? Brian, am I way out to lunch needing that much low jet?

 

[timberwolf]

On this stock saw with MM I am out exactly 1 3/4.

We'll see just how nuch the carb is holding it back.

 

[timberwolf]

By the computers numbers the stock 361 was just over 4.3 hp @ 10000 and MM was 5.1 hp likely just slightly higher peek HP RPM if I ran a longer calculation with closer RPM intervals it would show. But this matches pretty well with the in the wood gain. More torque right across and it was easy to feel the difference.

 

[mtngun]

By the computers numbers the stock 361 was just over 4.3 hp @ 10000 and MM was 5.1 hp likely just slightly higher peek

Thanks for the MOTA data, TW. 19% gain in power just by a MM, pretty impressive. Or a reflection on how bad the stock muffler is ?

I'm surprised it's making peak torque at a mere 6500 rpm, but then it has pretty sane port timing numbers.

 

[Zombiechopper]

TW, do you plan on tweaking the venturi, boring out, or a carb swap? Or does it depend on what you find? I really think I have a carb issue with how mine is ported. Timing is all stock but seriously wide ports and fairly aggressive transfers. Squish at .018 with no popup. It has quite good throttle response but not as good as my ported 460 nor as good as a stock 200T so I think it needs something more. It also revs up to about 13k real quick then takes a couple of seconds and bursts to 15500. Four strokes nice there but the funny lag and jump to rev out is unlike other saws I have.

 

[gemniii]

By the computers numbers the stock 361 was just over 4.3 hp @ 10000 and MM was 5.1 hp likely just slightly higher peek HP RPM if I ran a longer calculation with closer RPM intervals it would show. But this matches pretty well with the in the wood gain. More torque right across and it was easy to feel the difference.

Finally NUMBERS that look like they could be repeated!

Now do you have anything like that in a 660 w/ regular muffler and the same 660 w/ DP muffler like at https://www.baileysonline.com/itemdetail.asp?item=QS+1122+140+0800&catID=1981 ? Just wishing

Thanks TW for your work.

 

[timberwolf]

Here are some predictions for the 361s.

Bottom set is the stock, second up standard work port, next up hot work port with more carb and intake work and higher compression and top set BB taken about as far as I figure I can and keep it a work saw.

Something to keep in mind with software design though is it does not look at some things like flame speed friction or piston/component mass nor does it easily look at fuel delivery curve and that results in seeing some values out at high RPM that won't be seen in real life. These saws won't cut at 12-13k in the wood though looking at the graphs it would be easy to think they should.

 

[timberwolf]

I have all sorts of numbers for 066s and 660s, in general a muffler mod takes them from just over 7 hp to about 7.7 hp with DP cover and a little over 8 if opening them right up.

New 660 produced in last year or two are not ported as well factory as the older 660s and 066s. They produces same peek HP but at a slightly higher RPM, the torque peek though is not as high or wide. Trouble is exhaust durration is up around 180 deg or a little more stock. One thing for sure is you don't want to raise the exhaust port further when porting these as work saws.

 

[timberwolf]

Torque is dotted line, hp solid.

So at opperating RPM looking at more what it does in the 9500-11,500 range.

 

[2000ssm6]

That dyno graph is awesome, takes alot of CAD to build one of those.

Opps, not a dyno. Intresting none the less.