Ms461 saw design

[MustangMike]

Randy, good point.

Brian, not just long, but the design. That is a wild picture, what engine is that? Usually when you add more carbs you shorten the runners. Very interesting.

 

[MasterMech]

Nope long runners not new at all early 60's mopars came with them .......

Small block Ford too, remember the 5.0L HO in Fox body 'stangs? Exceptionally Long runners on that manifold and that was a pretty strong little motor for its time/displacement.

Again, wading in a puddle a little deep for me but that MS360/361/362 do-hickey that Chris posted states the improvement in emissions and more efficient cylinder scavenging with less loss of the incoming fuel charge. And there was no quasi-Strato marketing mumbo jumbo mentioned. Perhaps the smaller quad transfers and the "stuffed" crankcase of the 461 make for higher charge velocity through the transfers, further improving scavenging especially at less than peak RPMs. Hasn't it been said the 461 feels like it has a broader power and and more nut down low?

 

[Trx250r180]

Randy, good point.

Brian, not just long, but the design. That is a wild picture, what engine is that? Usually when you add more carbs you shorten the runners. Very interesting.

That is an early 60's 413 mopar cross ram ,factory part came on the cars back then

 

[J rod]

Longer intake runners usually means more HP in the upper rpms and less torque down low,shorter runners more torque down low with HP peaking at less rpms,

 

[J rod]

Just wondering but are the carbs any bigger on the 461? Will the carb interchange at all with the 460 or vise a versa to compare differences?

 

[MustangMike]

I thought it was shorter and bigger diameter for hi RPM and smaller diameter and longer for torque.

 

[MustangMike]

That is an early 60's 413 mopar cross ram ,factory part came on the cars back then

It is very cool.

 

[Chris-PA]

I'm pretty sure resonance tuning has nothing to do with the transfers in this case.

chris........post that stihl emission .pdf up, if you still have it.

-omb

Joe - here it is (I never tried uploading a PDF before):

 

[MustangMike]

Chris, That is great, thanks.

 

[Chris-PA]

Chris, That is great, thanks.

I'm pretty sure I got it when it (or a link) was posted by a member here previously.

 

[Brush Ape]

That is an early 60's 413 mopar cross ram ,factory part came on the cars back then

Wedge and them are probably singe feed double pump dual 620's. Just like the Kennedy Imperial.

 

[Brush Ape]

I don't pretend to know the answers, but I also don't believe that Stihl became the company they are by manufacturing technology that does not work..

Corporations don't manufacture technology, Technology manufactures corporations.

 

[tacomatrd98]

Longer intake runners usually means more HP in the upper rpms and less torque down low,shorter runners more torque down low with HP peaking at less rpms,

You have that backwards chief...The shorter/larger the intake, the slower the charge will be, but it is capable of flowing more resulting in higher theoretical rpm/power. A smaller/longer intake results in higher charge velocity creating better low rpm torque with a sacrafice in total volume of flow, resulting in a theoretically lower working rpm. As always, if other changes are not made to accommodate a larger/smaller intake/carb, actual results may vary.

 

[Bilge Rat LT 20]

You can use max volume runners or more of a slightly tapered venturi type runner design. Length, volume, carb size, bore, stroke, rod length, crank throw, valve size, cam lobe ramp speed, piston speed,park time, vacuum strength and duration, etc. all make the motor gulp the fuel/air mix. Then throw in the exhaust side of things. Makes my head hurt!!!

Spent a few minutes looking at a flow bench and long sheets of graph paper. Lots of ways to make the wheels go round.

 

[tree monkey]

the epa only cares about hydrocarbons (unburned fuel) and in parts per million.
caterpillar put an air pump pushing fresh air into the exhaust pipe to reduce the parts per million reading, they were cheating.
fresh air strato does the same thing.
4 port transfer scavenge better the 2 ports, witch mean better performance, on less fuel, and lower emissions.
the long transfer tunnels hold more volume (fresh air or exhaust gas).
the 461 has a larger case volume then a 460.

stihl and husky have spent millions developing the fresh air strato engine, it's not going away anytime soon.
delayed scavenging is very new, and I feel it will be the way in the future. simple, lighter, fewer parts, cheaper to make.

 

[MasterMech]

the epa only cares about hydrocarbons (unburned fuel) and in parts per million.
caterpillar put an air pump pushing fresh air into the exhaust pipe to reduce the parts per million reading, they were cheating.
fresh air strato does the same thing.
4 port transfer scavenge better the 2 ports, witch mean better performance, on less fuel, and lower emissions.
the long transfer tunnels hold more volume (fresh air or exhaust gas).
the 461 has a larger case volume then a 460.

stihl and husky have spent millions developing the fresh air strato engine, it's not going away anytime soon.
delayed scavenging is very new, and I feel it will be the way in the future. simple, lighter, fewer parts, cheaper to make.

So you're saying the delayed scavenging works and is not just marketing fluff or an overly restrictive muffler? Because of the larger case volume reduces primary compression and the longer quad transfer setup is more efficient at scavenging the cylinder of exhaust?

If that's true, then the muffler mods or dual-port conversions we are all so fond of on these saws defeats the system while providing measurable power gains?

Just my opinion but if delayed scavenging is for real, I still think fresh-air stratocharging is technically superior. The system can be utilized in an engine modified for increased output without significantly altering it's original function. Same as with emissions equipment on cars, what good is it doing if it's the first thing everybody rips off looking for better performance?

 

[Chris-PA]

the epa only cares about hydrocarbons (unburned fuel) and in parts per million.
caterpillar put an air pump pushing fresh air into the exhaust pipe to reduce the parts per million reading, they were cheating.
fresh air strato does the same thing.
4 port transfer scavenge better the 2 ports, witch mean better performance, on less fuel, and lower emissions.
the long transfer tunnels hold more volume (fresh air or exhaust gas).
the 461 has a larger case volume then a 460.

stihl and husky have spent millions developing the fresh air strato engine, it's not going away anytime soon.
delayed scavenging is very new, and I feel it will be the way in the future. simple, lighter, fewer parts, cheaper to make.

Fresh air strato is not just an air pump diluting the exhaust, rather it is also to delay the mixture's arrival to the combustion chamber. There is a document that Joe referred me to: http://www.tfd.chalmers.se/~hani/pdf_files/mikaelMasterThesis.pdf (it's a little too big to attach) that describes how the system works. Most of it is about setting up a computer model, but at the end are some good graphics that show the state of the flow at various crank angles. The fuel does not begin to arrive until after BDC.

The main thing I understood after going through it is that the primary function of fresh air strato is a time delay of the fuel entering the chamber, so the fuel spends less time there with the open exhaust port. The strato air ports become the main air entrance, and the flow through the case is just whatever is necessary to carry the fuel - as long as the fuel gets there in time to mix with the air before ignition that's all it needs to do.

Because there is not fuel in the air that is flowing most of the time you can optimize port timing to improve pumping efficiency without worrying about fuel loss, but you still don't want to lose much air out the exhaust port or you are losing pumping efficiency which would be counterproductive.

EDIT: Stihl has used both "Delayed Stratified Scavenging Technology" and "Delayed Scavenging Technology". The latter term is from their description of this system.

 

[Chris-PA]

I did an experiment porting a strato GZ4000 clone where I increased only the strato air port duration while leaving the normal intake alone. The intent was to increase air flow, based on the idea I expressed above that the case air flow was only to move the fuel mix to the chamber - so as long as I could adjust the mixture correctly and I improved total air flow I should have more power. http://www.arboristsite.com/community/threads/my-first-strato-porting-job.250199/ - page 3 is more interesting.

 

[Mastermind]

So Scott, are you saying that your take on the 461 is that by design, it is simply a more efficient engine? And since it is more efficient, it has less unburned fuel in the exhaust?

 

[MustangMike]

Very interesting discussion, I'm learning things. Unfortunately, I don't think any of us have the equipment to monitor pressure in the crankcase and cylinder throughout the combustion process to fully understand what is (or isn't) going on. It does seem a little similar to the debate between supercharges and turbochargers, the supercharger relies on fresh air and creates less heat, but is parasitic needing a pulley to drive it off of the engine, while the turbo gets "free" power from the expanded exhaust gasses, but there are numerous heat issues that must be addressed.

The supercharger (like using fresh air) is easier to get right, but is not as efficient as a turbo if you can work out the heat issues. It seems likely Stihl is trying to work out the heat issues on the 661.

Now whether the 661 is delayed stratified or just delayed, I don't have a clue.