661 muffler mod progression w/thermocouple

[huskihl]

From the test I have seen done it looks like the baffle removed and maybe enlarge the existing exhaust port a little (maybe not even at all)….

Also this is a stock saw so it’s not ported….i was watching redbulls videos and seems like a little back pressure seemed to do better…

He has hundreds (if not thousands) of hours doing R&D testing on the 661, but his findings mostly apply to his ported saws.
Anytime you open up a hole or add more deflector area, you’re allowing the engine to rev and make power higher in its RPM range at the cost of some forgiveness. It’s not like there’s a one size fits all muffler mod. What works best for a short bar isn’t going to be the best with a long bar. It’s all about the happy medium

 

[Khntr85]

He has hundreds (if not thousands) of hours doing R&D testing on the 661, but his findings mostly apply to his ported saws.
Anytime you open up a hole or add more deflector area, you’re allowing the engine to rev and make power higher in its RPM range at the cost of some forgiveness. It’s not like there’s a one size fits all muffler mod. What works best for a short bar isn’t going to be the best with a long bar. It’s all about the happy medium

Pretty sure the one video I watched was only a stock 661, but yes he does have many videos….

You would think that just opening the existing port a little (on any saw), would be beneficial if not only for getting some excess heat away…I have modded all my saws (modestly), and never seemed to loose anything wether using a long or short bar….

Of course if you start making huge ports and/or multiple ports you would start changing things…

 

[tree monkey]

The ports u add are the same size when u do one or two?
@tree monkey

yes

 

[Woodslasher]

Pretty sure the one video I watched was only a stock 661, but yes he does have many videos….

You would think that just opening the existing port a little (on any saw), would be beneficial if not only for getting some excess heat away…I have modded all my saws (modestly), and never seemed to loose anything whether using a long or short bar….

Of course if you start making huge ports and/or multiple ports you would start changing things…

I had a pair of stock 395's put in my care once, one was a basically new unit that I couldn't touch and the other was a used unit I had free reign over. Being me I gutted the muff on the one and opened up the factory outlet till it was the size of the deflector. Out of the wood sitting on the ground when I blipped the throttle on the stock one it took 1-2 seconds to get to top speed, the modded one was almost instantaneous. It was barely noticeable in the wood, but the stock one had a wee bit more grunt. The modified one was obviously quicker off the line, though.

It was kinda interesting having two basically identical units to compare because I'd have never noticed the difference with just a before and after run. I've opened up all the outlets on all my other saws (except saws I got pre-modded) and I never noticed the speed vs torque difference. I'd always felt them get quicker without realizing that anything else had changed.

tl;dr, unless you have 2 saws to compare, you probably won't feel all the differences.

 

[Khntr85]

I had a pair of stock 395's put in my care once, one was a basically new unit that I couldn't touch and the other was a used unit I had free reign over. Being me I gutted the muff on the one and opened up the factory outlet till it was the size of the deflector. Out of the wood sitting on the ground when I blipped the throttle on the stock one it took 1-2 seconds to get to top speed, the modded one was almost instantaneous. It was barely noticeable in the wood, but the stock one had a wee bit more grunt. The modified one was obviously quicker off the line, though.

It was kinda interesting having two basically identical units to compare because I'd have never noticed the difference with just a before and after run. I've opened up all the outlets on all my other saws (except saws I got pre-modded) and I never noticed the speed vs torque difference. I'd always felt them get quicker without realizing that anything else had changed.

tl;dr, unless you have 2 saws to compare, you probably won't feel all the differences.

Ya makes ya wonder about having some back pressure…

 

[bwalker]

Ya makes ya wonder about having some back pressure…

For what?

 

[tree monkey]

 

[singinwoodwackr]

Muffler? We don’t need no stinking’ muffler, lol

 

[singinwoodwackr]

Ya makes ya wonder about having some back pressure…

Maaaybe….

 

[huskihl]

Wait. I thought saws wouldn’t idle if the muffler opening was too big

 

[jacob j.]

Wait. I thought saws wouldn’t idle if the muffler opening was too big

They will, but they're annoyingly loud and obnoxious.

 

[singinwoodwackr]

They will, but they're annoyingly loud and obnoxious.

WHAT?

 

[huskihl]

They will, but they're annoyingly loud and obnoxious.

+ scary

 

[bwalker]

Ya makes ya wonder about having some back pressure…

I didnt have time to respond yesterday in depth so Im doing it now.
A muffler outlet is like any other port. The bigger you make it the less it flows at low rpm and the more it flows it high rpm. Torque is a measure of cylinder filling efficiency, so its no stretch to see why a smaller muffler outlet is more forgiving than a larger one. The trick is to find the right balance that meets your needs just as it is with the transfers, intake and exhaust ports.

 

[legdelimber]

Take gawk at the exhaust on those longtail boats even the two cylinder ones would have them. About 2:20 we get a fairly good view of the motor and exhaust

Couldn't find many of the older vids now, but the two cylinders ones were just scary fast. 2:10 in this vid

 

[bwalker]

Take gawk at the exhaust on those longtail boats even the two cylinder ones would have them. About 2:20 we get a fairly good view of the motor and exhaust

Couldn't find many of the older vids now, but the two cylinders ones were just scary fast. 2:10 in this vid

Those style exhaust have a one way pulse vs a two way pulse for a tuned pipe. IE a tuned pipe provides for negative pressure to scavenge the cylinder and then positive pressure to ram fresh charge back into the cylinder. The pipes pictured just provide for negative pressure to scavenge the cylinder.

 

[Khntr85]

I didnt have time to respond yesterday in depth so Im doing it now.
A muffler outlet is like any other port. The bigger you make it the less it flows at low rpm and the more it flows it high rpm. Torque is a measure of cylinder filling efficiency, so its no stretch to see why a smaller muffler outlet is more forgiving than a larger one. The trick is to find the right balance that meets your needs just as it is with the transfers, intake and exhaust ports.

Yea that’s where haveing 2 of the same saws and multiple exhaust to play with would be nice….like the things redbull does which are awesome!!!