Air Flow / CFM's

[AZMIDLYF]

Block V angle?

[Chaz]

Don't over think it .. Think Briggs + Stratton ... LOL

People that want air to go one way ( small chamfer to big bell ) on the feed side .
And some type off stand off to keep it going back the other .



The one's that really have a handle on it put a little roll (ditch ) for the air to turn away . The same way a cutting tool rolls the chip out and away ...
Mercury ... ahhh ... not so much ..

[powerabout]

How to incorporate that in rod slot?
Problem is the air has to move sideways to get behind the liner asap

Maybe glue sealskin in there so it stands up when the air goes the wrong way.lol

Of course maybe with the ram air effect of the incoming and half the rod going into the crankcase the air doesnt go back in just the pressure wave from the piston that pushed the fuel back out as we know?

[AZMIDLYF]

Reversion?

[Chaz]

Unless you are capturing air while at speed or something to generate pressure , then there is no such thing as "ram air" . The inlet lives in the same 14 psi sq/in that you and I do.

So freeze frame the crank at BDC . Nothings moving (btw that's where the reeds get beat up ) OK start again , the piston starts moving away from BDC and creates a "low pressure" environment . There are two leaks , the reeds open to the crankcase , the air in the crankcase moves into the lower cylinder area . That's 1
( Is this when you think the air goes 90* out to the transfer windows ) ????
OK , I'll give ya that if the exhaust pulse is still strong enough , it might pull some air and fuel that way , but for the majority , it's going to be open for aprox another 55 * and hinder the signal to the reeds . Now that they close for the next 125* the reed will get the full signal and the transfer feed will just a pocket of dead air . The charge wont run there without a reason . OK , TDC , as the piston starts moving down it generates a high pressure area and with the reeds closed the only place for it to go is out of the transfer windows once they open .
See , no magic turns in mid air ....
I relies that above and below the rod slot is all the same crankcase , but if your gonna go thru the trouble of splitting it in half , ya might as well do what ya can to keep what ya got , rather than knowing it's playin ping-pong back and forth .

Coming back down to BDC :
Ever been in a hurricane and watched what the wind did to the neighbors shingle roof ... ?
Made them flutter until it just ripped them off sending them crashing into your house .
What-cha think that rod does to the reed when it come's zippin by at 7-9 K RPM ??
Kinda makes that idea of clippin the front half to move the reed closer to the storm look like a pretty ******* stupid idea ...

[AZMIDLYF]

Chaz, the piston moving downward is compressing the crankcase and forcing the intake charge up the ports. What prevents the suction on top of the piston from pulling from the exhaust ports?

[RBT]

I love your last last line. Never understood why people cut the front half. I suppose you might get a cc or two of stuffing only to move the valves closer to your hurricane.

[Chaz]

If you follow the chain of events from TDC , there is a big boom followed by a rapidly expanding ball of energy that's looking for a way out . Arpox 90* the ex port opens and sends a wave or column away . It uses the next 30* or so blowing down the chamber before the transfers begin to open .
If the battle then becomes the 5 or 6 psi push from the crankcase or the vacuum left in the wake of the hi-speed exhaust , I would have to say the exhaust pulse would win and the piston slowing for it's turn around at the bottom becomes of little consequence of what's happening above it ...

A good read is Gordon Jennings "So you think you want to build expansion chambers"
or something close to that . He speaks on the importance of the head pipe and the first (divergent) cone and what effect their length and taper have on the exhaust pulse .

[FMP]

As the piston is on the upstroke about 35*+ - before the ex port closes some of the fresh charge from the transfers is spilling into the ex chest. At that time the leading cyl ex pulse is hitting the ex port and stuffing the spilled fresh charge back in against the flow of the compressing cylinder volume and raising cyl pressure as the ex port closes. This timing is important, and is dependent on ex port height, crank pin angle, distance between ex ports as well as temp. As the rpm increases the pulse arrives closer (later in degrees) to the port closing. Crank rpm , rotational speed gets more and more ahead of the pulse.

[AZMIDLYF]

Thx Chaz. I will look into Mr Jennings.

[powerabout]

So how does the fuel get spat out of the inlet at certain rpm as your theory doesnt allow for that especially carb engines.
All bulk flow but no pressure waves which is the key to a 2 stroke

[powerabout]

Did we solve the sharp and blended sides of the rod slot?

[powerabout]

What is interesting with this and then what porting we then do to fit our theorys was Racer said he had 3 drag engines on his dyno that made almost same power yet he said 3 different ideas on porting. Bsfc all different as well

[AZMIDLYF]

Did we solve the sharp and blended sides of the rod slot?

Post #62 above

[dwilfong]

The scavenging effect of the ex tuner has a lot to do with any timing changes. If you do not change the tuner the timing changes will not make as much of difference.
The ex tuner is what helps keep the flow in transfer ports moving in the right direction as the piston comes off BDC.