Is backpressure from muffler needed.

[rolloman]

I'm building a stock appearing saw from a Husky 359. Is backpressure from a modded muffler with holes required to run good or would a modded muffler with a straight thru tube all the way thru that is the same size and shape as the exhaust port create more power etc.

 

[timberwolf]

No, not needed. However if you are going to essentially what will be a tuned header it will need to be designed with the saw RPM and port timing in mind in order to get the most out of it. If the header is not tuned to work with the saw it could be worse than nothing at all.

Often getting a saw to idle and run at low speed will be tricky with very low back pressure exhaust designs. But poor idle and low speed is an acceptable side effect if it is for racing.

 

[troutfisher]

I have made a saw slower by going too far. It is a 2100 husqvarna, I modded the muffer and got good gains, then a year later I went back and added two more tubes. I should have left it alone. There were some pretty good holes in it to begin with, so I don't think it was holding any pressure. I'm not sure what happened.

 

[rolloman]

Thanks guys. I should be done with the build in a couple weeks, and I'll let you know how it turns out.

 

[rolloman]

Finished the saw.

Got the saw finished yesterday. The first thing noticed was the awesome fast revving (spoolup) that it now has. We cut with it, and it was a significant improvement over stock. We didn't have a good poplar log though. That will be the next test as soon as we get one. I am considering just one more change to the lower transfers, possibly, or maybe getting the exhaust and transfers back to their stock height because they were lowered due decking the cylinder base for squish adjustment. If I'm correct this will up the rpm slightly. Will this be worth taking it apart again? The roof of these ports will be raised by .030" in order to get back to stock. Will I lose any tourque if I do this? Still learning so please excuse the elementry questions. I'm hooked now with this new hobby after hearing this thing run that I ported. Can't wait to watch it being used in competition this spring. Looking into other Husky and Jonsered saws for different classes now. Any suggestions for saws that work out good? Sorry for rambling on guys.

 

[troutfisher]

What are your port timing #'s?

 

[rolloman]

It will be monday before getting to the saw and posting the numbers for you.

 

[troutfisher]

It will be monday before getting to the saw and posting the numbers for you.

That's fine, timing numbers will tell these guys a lot more about the saw. .030 is pretty big, could change timing 10* or more and that's huge.

 

[rolloman]

Got the port timing #s. This was my firs time doing this so let me know if anything is strange and I can remeasure.

Exhaust opens 105*
Exhaust duration 151*
Transfers open 123*
Transfers duration 112*
Blowdown 20*
Intake opens 275*
Intake duration 160*

 

[timberwolf]

All depends on what you want from the saw but 105 on exhaust is low and with transfers at 123 you only have 18 degs of blowdown. Fine for low RPM, but if you feel at all that the saw is weaker at the top of the bowerband it may well do better with a little higher exhaust.

 

[rolloman]

Thanks and Sorry. I just realized that I had previously started a thread on the porting and squish band questions, so I'm gonna move back to that thread since I did get all my muffler questions answered in this thread. I'm kinda new at using these forums so I'm still learning.