Ms461 saw design

[Mastermind]

The issue with two strokes and the EPA has always been raw, unburned fuel escaping the cylinder during scavenging, at least as far as OPE is concerned. It's how/why engines like the 4-mix came about. From a pure performance standpoint, we don't really care if a little fuel/air charge escapes as this means the cylinder is completely purged of exhaust.

Forgive me for going into territory of which I am no expert, but is it possible that the differences in transfer port design between the 460 and the 461 are the key to the reduced fuel usage? If the cylinder scavenges more efficiently with less loss out the exhaust port, fuel consumption for the given power output would also decrease. Regardless of any "delayed stratification" or other marketing phenomena.

Brian, I have a feeling you've been in a 461.......

The design of the transfer ports on the 461 are designed in a way that introduces that fresh charge into the rear of the jug better than on the 460....

Come to thing of it, they are designed in a way that I remember looking at the first time and thinking WTF????

Off to search for a pic.

 

[Mastermind]

Transfer flow is from the front, upward to the rear. Also, the outside of the transfers open before the center. Which I thought was odd.

 

[KG441c]

Transfer flow is from the front, upward to the rear. Also, the outside of the transfers open before the center. Which I thought was odd.

pros or cons of the design vs the 460? Sorry just boggling my mind!! Im learning!

 

[Mastermind]

The MS460.....

 

[MustangMike]

Thank you all for that excellent information.

I probably should not bring up this "sore topic", but me being me I will. The purpose of any exhaust, no matter if it is holes in a tin can, headers, or straight pipes, on any engine (4 cycle or 2 cycle) in not simply to create "flow" but to create a pulse that will be in sync with the engine at a certain RPM range.

The pulse will alternately help to stop unburned gasses from escaping and then evacuate burned gasses. (even a 4 cycle with a cam has overlap)

Experimentation over time have likely led to the recommended percentages quoted on this website.

As an engine is made to be more aggressive (a cam or porting, etc) the exhaust will have to be enlarged accordingly to remain in sync. That does not mean that an engine will not work w/o this feature, but it will work better with it.

 

[KG441c]

Also Im wondering and lost as why the intake transfer is on bottom of base of cylinder 0n the 461 but inside the cylinder of the 460?

 

[Trx250r180]

Tried to get some pics off stihls demo vid ,shows the airflow of a 461 ,don't know if will help or hurt this discussion ,may help explain the airflow differences ,i do notice the front of the piston skirt is windowed at the bottom ,not sure if just for timing of the front transfers or if that helps airflow

 

[Ron660]

The MS460.....

Ports on the 460 look larger than the 461.

 

[blsnelling]

But there are 4 transfers on the 461.

 

[blsnelling]

I don't see any evidence of stratofication in those pics.

 

[Ron660]

But there are 4 transfers on the 461.

OK four smaller transfers on the 461 and two larger ones on the 460. I couldn't see the entire circumference of the cylinder. Are the transfers the same on the 460 as the 046?

 

[Ron660]

What do they go through to get EPA certified in CA????

Yes CA is more stringent. States can pass more stringent air emission regulations but not less than federal (EPA) standards. A lot of States are restricting watercraft 2-cycle engines. Get ready, more stingent air index quality regulations are coming! Especially were cities are in non-attainment for non-compliance of ozone standards (usually based on a 3-yr. average).

 

[Ron660]

I have no idea how it could work........but the 661 is built on the same ideas.

They are getting them past EPA somehow.....

When emissions are concerned at least these two parameters are measured to be compliant: LEL (lower explosive limit) and CO (carbon monoxide). A constituent of LEL are VOC's (volatile organics). Their goal is to "burn off" the impurities. By returning these impurities, back into the transfers if that's the case, they will be burned by combustion. An example of burning off or "flaring" VOC's are when oil refineries do this practice.

 

[Mastermind]

Ron, it sounds like you are well versed in EPA speak.......

 

[Mastermind]

Brian, I watched that whole video.......nary a hint at any type of stratification.

 

[Chris-PA]

I don't see any evidence of stratofication in those pics.

Unfortunately that animation is just more marketing fluff, there is nothing to see. You're just supposed to see the pretty animation and think it means something. They show all the gas in the same green so you can't tell anything about what is supposed to be happening - but it's green, so that must be good........

As for how they pass with this design - I don't think the 460 had Mtronic? If not they've gotten a big reduction in emissions and fuel loss just from that. Then they've gone to quad trasnfers which does reduce scavenging losses somewhat as well. Here's a Stihl document describing the progression but including a piston ported strato in the explanation. Nowhere in the document I took this from does it mention this exhaust stratification system at all, but it is from 2010.

 

[Mastermind]

The 461 is not M-Tronic either Chris.

 

[Chris-PA]

The 461 is not M-Tronic either Chris.

Ok, sorry to muddy the waters. Also, that page I posted is from 2012 (as it says right at the bottom), not 2010, but they don't mention this technology at all.

 

[Mastermind]

It think when describing this unit, using the word "technology" is overkill.

 

[one.man.band]

maybe way over thinking this, folks.

treemonkey already alluded to the answer in his posts a couple pages back.

good posts man.

-omb