066/MS 660 port #'s. Please share your stock #'s

[Deets066]

This is some good stuff!

I will make a few cuts off each log that I posted in the vids, bar and chain hasn't been touched. Here to learn and try new things. Great thing about this is that I can take it away if I don't like it.

 

[Deets066]

I will say that, with less intake timing in a ported 046 I did notice less fuel consumption. The 046 with the low intake was very snappy and fast with a 28"

 

[drf255]

OK,

So by raising the intake floor, you increase case pressure but lower volume a bit because overall duration is decreased and you should be getting less case filling because of an earlier closing point. So you'll get a higher pressure but slighter lower volume charge. The opposite with closing later. If engine design allows intake port raising, one can get both increased volume and pressure.

So with a higher pressure but lower volume charge, what do you feel that allows you to do with transfer placement?

If the transfers are tighter, I'm imagining you could keep them lower cause they'll have a lot of velocity and fill quicker. On bigger transfers (quads) it seems that keeping the intake higher wouldn't have the same benefit as with a dual port as they have more total transfer area (tunnel and port) so they need a more volume and lower pressure to do their thing.

Am I off here to suggest that keeping an intake higher for more case compression is more beneficial for dual port than quad port motors?

On a dual port Hybrid (ie 046/044) I'd imagine you'd want the intake lower to compensate for the lower case volume with the bigger transfers.

Am I way off here?

 

[Deets066]

You can't put anymore charge in the case when it's full. With a lower you "could" be try to overfill the case and getting spit back, this doesn't hurt anything except fuel consumption. I think I will still fill the case with the higher intake because of widening.

The transfer height should probably stay where it's at, yes I'm increasing velocity but I don't think it's enough to change transfer height because of it.

 

[drf255]

A case fills by vacuum, very much like a 4 stroke car engine intake manifold.

We've all seen the effects of inertia supercharging on a race car with a tunnel ram.

What I'm saying is that at high RPM, when charge is flowing, you should fill a case more with more duration. But you'll get spitback at the point when the case pressure overcomes the incoming charge pressure. When the air speed and pressure exceeds a certain point, I think you'll get little to no spitback with even very low intakes.

I know there's a equations for max case volume/engine displacement. I remember Treemonkey stating it.

I'm sure there's some volumetric efficiency of case design formulas as well.

 

[mdavlee]

I like the raised intake on the KS cylinders in the 660. Haven't tried it on a Mahle yet.

 

[drf255]

Where does the extra fuel go on a saw with a low intake. is it burned, lost out the exhaust?

 

[Moparmyway]

Ok, I'm liking this a little better

That right there is where mine is at .....................
I know running "exotic" fuel changes things slightly, but if yours runs anything like mine does, you might be looking for some 385's at GTG's ............. you know, just give them 385's a little different perspective !

 

[Moparmyway]

Am I off here to suggest that keeping an intake higher for more case compression is more beneficial for dual port than quad port motors?

Where does the extra fuel go on a saw with a low intake. is it burned, lost out the exhaust?

Lost out the exhaust

 

[drf255]

Lost out the exhaust

So how does that occur?

Less case pressure. Mixture adjusted at carb. You get better cylinder filling and exhaust scavenging with a lower intake?

If its leaving the exhaust port, its as unburned charge.

 

[Moparmyway]

So how does that occur?

Less case pressure. Mixture adjusted at carb. You get better cylinder filling and exhaust scavenging with a lower intake?

If its leaving the exhaust port, its as unburned charge.

Unburned out the exhaust is correct

Transferrs push the spent gasses out, they are also pushing out raw fuel and combustible gasses.

More primary compression and less case filling seems to be a great combo for the 90cc dual port Stihls.
It could also be that the additional vacuum signal created in the case by the lower intake helps to fill the case more efficiently

 

[drf255]

Hmmmm.....

So sounding to me like a lower intake fills the case better at high rpm. Would allow a lower upper transfer because will fill faster/better, but low end torque would suffer.

Higher intake, more secondary compression at lower rpm, less at high rpm, higher transfers, worse on the top end.

So maybe this is why 046/044 Hybrids run so well with high transfers. Lower intake, but increased case compression because of a smaller volume at the same time. Bigger transfer tunnels.

 

[Moparmyway]

Hmmmm.....

Higher intake, more secondary compression at lower rpm, less at high rpm

Why would there be less secondary compression at higher RPM and more secondary compression at lower RPM ?

 

[drf255]

Earlier Closing Intake. Less Duration.

More pressure at low RPM. At HIGH rpm, less ram effect from charge inertia because less duration in time.

Why do you think a longer intake duration causes more cylinder filling?

 

[Moparmyway]

We are only talking 3-4 psi at most for primary compression.
I dont believe secondary compression is effected to the point that there is less secondary compression at higher RPM.
Sometimes a longer intake will not cause more cylinder filling. There comes a point where its full, and you begin to go backwards if you give more time/area to the intake.

You can only get in so much mix to the upper cylinder with the transferrs and exhaust open at the same time .............. it just goes out the exhaust if you try to get more in there before the exhaust closes

Let me just state that I am in NO WAY an expert here, and I may very well be wrong. The more that I think that I understand, the more I see that I dont.

 

[drf255]

Thoroughly confused am I.

 

[Mastermind]

Closing point on the intake is what y'all need to be thinking about. You can't transfer what you didn't trap. Over filling the case just makes more spitback, and is why a velocity stack works so well on a race saw.

 

[drf255]

Closing point on the intake is what y'all need to be thinking about. You can't transfer what you didn't trap. Over filling the case just makes more spitback, and is why a velocity stack works so well on a race saw.

So why does a lower intake cause increased fuel consumption and unburned fuel out of the exhaust?

 

[Mastermind]

I can't see it sending any unburned fuel out the exhaust. I can see it wasting fuel due to excessive spitback.

Raising the transfers will send raw gas out the exhaust though. That is one reason newer saws have lower transfer ports.

 

[jmssaws]

I've got a cylinder that has had the intake lowered a ton and it will soak everything under the filter cover spitting back not out the exhaust.