Mastermind Meets The MS500i

[Mastermind]

So.....as *s-wordty as I've felt, and with the power going off twice, I got all four jugs roughed in and the epoxy poured.

I'm done for today.

 

[Stump Shot]

I think the faster piston speed is the reason they like more BD. It makes sense.

Wouldn't a little more transfer duration compensate for a little less blow down time when trying to fill the cylinder at high rpm rates?

 

[drf256]

Wouldn't a little more transfer duration compensate for a little less blow down time when trying to fill the cylinder at high rpm rates?

Not sure what you are asking Steve, but I think we are talking about 2 different things here.

At 54mm bore and only 79cc, the 500i must have a stroke comparable to an 036 which is 17cc smaller. It’s actually slower piston speed, I wrote it wrong.

So when one considers that piston speed in any saw is not constant (speed is a sine wave throughout stroke) and the fact that a shorter stroke saw moves the piston less physical distance per * of crank rotation, it makes sense to me that these short stroke saws want more blowdown. The physical distance between the Ex roof and the transfer roof is a lot less at 20* BD than it would be in a longer stroke saw.

Not sure if I’m explaining my thoughts correctly.

 

[Jimmy in NC]

My guy is telling me .... tacos!

Walking or standard?

 

[Jimmy in NC]

Not sure what you are asking Steve, but I think we are talking about 2 different things here.

At 54mm bore and only 79cc, the 500i must have a stroke comparable to an 036 which is 17cc smaller. It’s actually slower piston speed, I wrote it wrong.

So when one considers that piston speed in any saw is not constant (speed is a sine wave throughout stroke) and the fact that a shorter stroke saw moves the piston less physical distance per * of crank rotation, it makes sense to me that these short stroke saws want more blowdown. The physical distance between the Ex roof and the transfer roof is a lot less at 20* BD than it would be in a longer stroke saw.

Not sure if I’m explaining my thoughts correctly.

I think you are doc.

 

[smokey7]

Makes total sense to me doc and mm

 

[Mastermind]

What makes sense? Two strokes? No way.

 

[drf256]

What makes sense? Two strokes? No way.

11.5* of BD factory and 7* taper is a bit mind boggling for a quad I’d say. Even for a dual port.

 

[drf256]

What’s your thoughts on the combustion chamber assymetry?

 

[Mastermind]

What’s your thoughts on the combustion chamber assymetry?

I'm not sure what to think of it really.

 

[Stump Shot]

Not sure what you are asking Steve, but I think we are talking about 2 different things here.

At 54mm bore and only 79cc, the 500i must have a stroke comparable to an 036 which is 17cc smaller. It’s actually slower piston speed, I wrote it wrong.

So when one considers that piston speed in any saw is not constant (speed is a sine wave throughout stroke) and the fact that a shorter stroke saw moves the piston less physical distance per * of crank rotation, it makes sense to me that these short stroke saws want more blowdown. The physical distance between the Ex roof and the transfer roof is a lot less at 20* BD than it would be in a longer stroke saw.

Not sure if I’m explaining my thoughts correctly.

You're are explaining things just fine, so maybe I am not. Let me try going around the fence post and give it another try.
If the blow down was shortened a little bit, will make the transfer stay open longer.
Will not then the increase(in time) of the incoming charge offset the slight loss of having less blow down?

 

[Mastermind]

I wish I understood this stuff.....but in all honesty I dont. I have ideas and theories, but then a new design or model comes along and completely destroys them.

So....I take a good look at what the designer is doing, and merely try to enhance the design.

 

[Fruecrue]

You're are explaining things just fine, so maybe I am not. Let me try going around the fence post and give it another try.
If the blow down was shortened a little bit, will make the transfer stay open longer.
Will not then the increase(in time) of the incoming charge offset the slight loss of having less blow down?

I don’t know one way or the other, but if blowdown allows time for the combustion gases to escape via their own pressure differential to atmosphere, couldn’t there be a problem with mixed fresh and spent gases that is causing the benefit of added blowdown, not simply a transfer duration or feeding the top end problem?
Run on sentence.....
Surrry.

 

[MG porting]

Not sure what you are asking Steve, but I think we are talking about 2 different things here.

At 54mm bore and only 79cc, the 500i must have a stroke comparable to an 036 which is 17cc smaller. It’s actually slower piston speed, I wrote it wrong.

So when one considers that piston speed in any saw is not constant (speed is a sine wave throughout stroke) and the fact that a shorter stroke saw moves the piston less physical distance per * of crank rotation, it makes sense to me that these short stroke saws want more blowdown. The physical distance between the Ex roof and the transfer roof is a lot less at 20* BD than it would be in a longer stroke saw.

Not sure if I’m explaining my thoughts correctly.

What about case volume by the looks of the 500i the crank looks like it's nice and snug in there. If that means anything?

 

[Mastermind]

I don’t know one way or the other, but if blowdown allows time for the combustion gases to escape via their own pressure differential to atmosphere, couldn’t there be a problem with mixed fresh and spent gases that is causing the benefit of added blowdown, not simply a transfer duration or feeding the top end problem?
Run on sentence.....
Surrry.

Well......

They increased the length of the transfer tunnels on the 462, and the 500i by casting part of them into the case. It's my understanding that allows the transfers to be back fed by exhaust gasses without them getting all the way into the crankcase. This then is used to purge the spent gasses from the combustion chamber with the back fed gasses in the transfers.

Yeah?

Nope?

GFY?

 

[Mastermind]

On the 461 I couldn't see this actually working as advertised because the blowdown time was too long. Now we are seeing both longer tunnels (like the 5 series Huskys) and really short blowdown time. (Again, like the 5 series)

 

[Mastermind]

So.....color me confused.

There's no way at this point that I can pretend to really know that any of this is based in fact. As soon as I start to think I'm gonna kick a field goal, they will move the goal post.

 

[Mastermind]

What about case volume by the looks of the 500i the crank looks like it's nice and snug in there. If that means anything?

Think of air as an elastic material. The more open the case is, the more the "air" has to be compressed or stretched to start moving. So....a tighter case equals a more responsive transfer event.

 

[MG porting]

Think of air as an elastic material. The more open the case is, the more the "air" has to be compressed or stretched to start moving. So....a tighter case equals a more responsive transfer event.

Is this why the blow down numbers work for this stile of saw? Just curious. Now you got my brain in full throttle and the smoke is starting to get bad!!.

 

[Mastermind]

Is this why the blow down numbers work for this stile of saw? Just curious. Now you got my brain in full throttle and the smoke is starting to get bad!!.

I think the blowdown time on this engine has more to do with emissions than performance.