Porting the 361 Big Bore

[Stihl 041S]

Saws are like guns, operater makes a big difference

Why don't you build us one out of stainless or titanium, Rob

Haven't run a mill or a saw in 5 months. Family matters clear up in 2 weeks and I can have a life again. Like give out Christmas presents.
Anyway, with dynos, you got to blow the saw up to see what it will REALLY do, otherwise there will always be a question.....................

 

[blsnelling]

Here's the results of the bored out carb on the BB vs the OEM ported saw. It had a 11% gain on it before. Thant's now 24% with the best times from both saws. If I average all cuts from both saws it's still a 18.5% gain. I was tweaking the tuning as I made cuts and took the fastest from each saw. The BB seems to like to run a little leaner than the OEM. Enjoy.

 

[brncreeper]

Time for a dyno? That would give you all your data and then some.

I bet you could make more $ with this thing then the payments would be.



http://www.land-and-sea.com/kart-dyno/kart-dyno.htm

Interesting, the torque arm appears to be nothing more than a load cell.

 

[Cowboy Billy]

Awesome Brad Lots of food for thought there. If I thought I could do it and not destroy my saw I would try it:jawdrop:

Billy

 

[yo2001]

sounds like you can lean on that BB saw pretty hard. Nice work

 

[volks-man]

refresh my failing memory.

is there much difference in the mufflers on the two saws?
oem ported has a deeper tone than the bb.
they still sound like 361s though!

 

[blsnelling]

What you're hearing is the higher RPMs of the BB. The BB saw has the factory muffler port opened with an additional hole with the Husky deflector. OEM has slots added in the front of the muffler. The cage is gutted on both.

 

[Lakeside53]

Here's the results of the bored out carb on the BB vs the OEM ported saw. It had a 11% gain on it before. Thant's now 24% with the best times from both saws. If I average all cuts from both saws it's still a 18.5% gain. I was tweaking the tuning as I made cuts and took the fastest from each saw. The BB seems to like to run a little leaner than the OEM. Enjoy.

What did you do to the carb?

 

[blsnelling]

I opened it up, probably close to 2mm. I first had to remove the brass nozzle, then replaced it after the bore was increased.

 

[mtfallsmikey]

:yourock:

 

[mtfallsmikey]

Stupid Question Friday

Brad; In your HO, would it make sense to do the BB rebuild/mods on a busted361 that could be had cheep, vs. buying a 440/441 assuming same bar length?

 

[blsnelling]

There's no replacement for displacement. A ported 440's going to walk on a 361BB. Now if you're just looking for more power in a lighter weight package, then sure, build the 361. If the 361 is cheap enough, I'd jump on it. I don't think you'd be disppointed in a stock 361BB and a muffler mod. A port job will just give you that much more. If you don't like it and want a 440, you can always sell it.

 

[parrisw]

I opened it up, probably close to 2mm. I first had to remove the brass nozzle, then replaced it after the bore was increased.

Did you have to make a bigger throttle plate?

 

[Lakeside53]

I suspect he bored the venturi portion only

 

[parrisw]

I suspect he bored the venturi portion only

Ok, that makes sense.

 

[blsnelling]

I suspect he bored the venturi portion only

That is correct. I'm using the same throttle and choke plates.

 

[yo2001]

So there is no ill effect from not having a venturi?

 

[wkpoor]

Brad, you are long over due for a log stand or racing stand and cants for testing!

 

[blsnelling]

So there is no ill effect from not having a venturi?

I do get a little run on at times when coming off WOT. But that's usually not an issue when cutting with it. Occasionally it will just die when you come out of a cut. One pull and it comes right back to life. So if it's your only saw and it's only for work, I don't recommend this mod. It's been recommended to try increasing the popup pressure and see if that helps. I haven't had a chance to do that yet.

 

[treefrog359]

brad have you had time to work on your 361 carb yet? did you adjust the pop off presure yet?