staggering port heights

[harleyracer59]

I have a cylinder that was on my cruiser motor a couple years ago. it was one of my first attempts at porting. it is a piston port with no boost port. so 2 transition ports and an exhaust port. that cylinder would rev like no tomorrow. hit 50-52mph a couple times with a 44 tooth sprocket. which would put the rpms 10,000+ plus. according to a calculator I used somewhere. it had shmedium take off from 0 and didn't really have a powerband just steadily climbed. I didn't have a chamber on the engine at the time, just the stock pipe with the cap removed and a Harley k model muffler clamped on to it. I did put a piece of hose in the end to reduce the exit size.



the ports were atleast .5mm maybe 1.25mm off as far as height goes. you can tell with the naked eye when looking at it.



has any one else experimented with staggering port heights? im talking left to right not transition to boost. although im interested to hear about those experiments too. Could thes staggered ports explain my having a little bit of take off even though the cylinder pushed to 10,000 rpm. its usually a trade off, low end or top end, 1 or the other. im thinking of trying this on an extra AF05 cylinder I have to see if theres anything to be gained. would love to hear from my fellow tinkerers abot there experiences and or their thoughts on this subject. what do yall think?

[190mech]

There is tons of info on the web about staggered transfer ports for the A,B,&C ducts,but none on staggering the timing between the 2 A ports..The theory is to have both flow exactly the same,that way the mixture columns meet in the center of the bore and flow up into the combustion chamber,pushing the residual exhaust gasses out of the Ex port..With the cylinder in a sink and running water thru each duct should give you an idea how it flows...

[ryan_ott]

Checking flow with the water flowing in the sink is how I check mine.

[190mech]

Jan 2, 2019 6:14:24 GMT -5 ryan_ott said:

Checking flow with the water flowing in the sink is how I check mine.

"Poor mans flow bench"!!

[harleyracer59]

I check mine with the water hose. my mom would kill me if I tried to use the kitchen sink... lol
like I said this was one of my first attempts at porting a 2 stroke. I was using my 4stroke knowledge and still didn't completely understand the whole port timing thing. I was on the bigger better kick, when in doubt hog it out thought. even though I knew that even with 4strokes its a matching game. like, a tunnel ram is better on square port than oval port heads. and a huge cam is a dog on the street with out a stall to get you to the rpms.
I now mark the cylinder using a marker against a ring and check with a caliper while cutting.
but if staggering A to B or C is done commonly, with steep port angles and low port volume, staggering A1 and A2 might push the spent gasses out while also dropping pressure before A2 opens combining to then fill the void or vacuum created by the initial high pressure blast from A1? or am I wrong in that thought?
I understand it wont work like that in every situation but in a small port volume high pressure situation, could it possibly do as I described? possibly giving you a little more on the low rpms before hitting the powerband to the high rpms? instead of just being a paperweight till 4000-6000 rpm when you finally get to the beginning of said powerband or on the pipe?
I understand theres almost always a trade off, but maybe it would be a tolerable trade if it gave you even a little more in the lowers for a little less in the highers while still being able to achieve original peak rpm? I know with our cvt scooters that might not be a good thing, but on a single speed, in/out clutch like my bike motor, it might be acceptable?
im just thinking out loud here, and asking for thoughts and opinions from you guys. I am in no way saying I am correct or right and I agree with you. im just saying, what if?

[jackrides]

Would someone please provide background or refs. about designating ports by letters? I'm ashamed to have skipped those classes.

[pitobread]

It may work. Similar to why you stagger your a b c port openings. The first port to open has combustion gasses forced down creating reversion. Perhaps by a slight stagger it allows one charge to be built up in the other runner instead of both being acted upon. But it will 100% mess up your flows. But if it's an old inefficient motor perhaps that isnt the limiting factor in that case.

[harleyracer59]

Jan 2, 2019 14:35:35 GMT -5 jackrides said:

Would someone please provide background or refs. about designating ports by letters? I'm ashamed to have skipped those classes.

Were talking about transfer ports and multiple transfer ports. Som cylinders have one set ( left and right) transfer ports (A) plus a boost port ( center opposite side of exhaust) for a total of 3 ports. Some cylinders have 2 sets of transfer ports (A&b) and a boost potent for a total of 5 ports. Some have 3 sets (A,B,C) with a boost port for a total of 7. Some cylinders have multiple boost ports or no boost port at all.
Basically transfer ports are fed from the sides and boost ports at fed from center back. We’re not saying exactly the orientation of abc we’re just using the letters to designate a single set or multiple sets. Hope that clarifies this for you.

[harleyracer59]

Jan 2, 2019 15:19:46 GMT -5 pitobread said:

It may work. Similar to why you stagger your a b c port openings. The first port to open has combustion gasses forced down creating reversion. Perhaps by a slight stagger it allows one charge to be built up in the other runner instead of both being acted upon. But it will 100% mess up your flows. But if it's an old inefficient motor perhaps that isnt the limiting factor in that case.

I never thought of that.  just like am expansion chamber, sort of.   that would totally mess up flow. especially on the first opening side because of the reversing flow multiple times.   but I also had a non orthodox  exhaust on it.   but that cylinder was one of my highest rpm cylinders not my fastest acceleration but a lot higher rpm and faster than a stock cylinder.   
 I was thinking more of the toilet bowl effect.  instead of colliding in the center I envisioned  one side pushing and the other side joining in to ad volume when the initial high pressure was starting to fade.  mind you this all in a 1000h of a second.    
  and while I could agree with you as it being of archaic design,  I wouldn't call a small single cylinder single speed engine that could propel 350 lbs to 50 mph and pull up a moderate hill without pedal assistance,  inefficient.