ESE's works engine tuner

[Frits Overmars]

I keep looking at the bridge between the ports and wondering it this should be cut lower... I suppose I am wondering if cutting this down (red line) and adding a radius instead of the sharp edge currently, would aid flow into both ports?

Attachment 309463Attachment 309464

It would certainly help the flow into the A-ports more than it would hurt the flow into the B-ports (if the latter would be hurt at all, which I can't tell).
So the bulk flow would improve. But sending more mass through the A-ports might upset the scavenging balance, so there are no guarantees here.

[Frits Overmars]

Transfer passage entry obstruction

This is a picture of a TM KZ10B cylinder with the piston at BDC. The transfer cut out in the piston protrudes around 4.5 mm below the level of the side entry into the cylinder. Surely this must create a significant flow disturbance and loss of flow.Attachment 309469
1. One could modify the piston a bit by blending, but there is a limit, particularly under the A ports, where only a mm or so of material removed will expose the aux exhausts to the crankcase at TDC.
2. Lower the level of the side entry into the cylinder so that it matches the level of the cut-out in the piston, ie adding a nominal 4.5 mm of material,
3. Fit a longer rod in conjunction with a piston with a correspondingly lower compression height.

Option 1 seems like a good bet.
Option 2: neaa... You should take Wobbly's advice instead.
Option 3: what would that change at the bottom of the cylinder?

[RomeuPT]

Well I do like the chamfer/flat top on the piston edge ( ha hah,I showed Harold that idea when I designed the BSL500, and it ended up in the Swiss Auto,Pulse, as well ) but it also appears to have a radius,that now, we have
VHM using to make better power from KZ2 engines.
But if Harold copied a certain Honda cylinder, then it for sure wasn't a late model A Kit as they ALL had very a oval Exhaust exit shape at the cylinder face that transitioned
into a round within the flange to mate with the header - no step = alot more power.
Honda even issued a tech bulletin that said you would loose alot of power if you ground the cylinder round to match the very old design spigot on the 125 customer bikes.
The best power I have ever got from a T port 125 cylinder was with a 41 wide by 32 high oval, and that was tested back to back starting at 40 round and progressively inserted/
welded and ground smaller and smaller in the cylinder and spigot.
The final design with the 41 by 32 dimensions used as cast in the cylinder - and CNC machined in the spigot made another Hp over my welded test pieces.
But shit Harold, every dumb arse could see that shaping the tang below the boost port was worth some power, allowing better flow from the reed cavity into the case area.
But no - so just maybe Mr Fishers sarcasm, and Frits tacit agreement are worth noting.

Hello. What you mean by "chamfer/flat top on the piston edge"? This kind of piston top: http://www.mitaka.co.uk/YAMAHA%20PISTONS/PT.05YZ125.htm ???

I seen somewhere that the chanfer on a flat piston improves power before peak? But the head must have this shape also for the result to happen. So, with this kind of flat top on the right head shape we will have more power everywhere compared to a domed top on a Honda Cylinder?!

Thanks

[ken seeber]

Option 3: what would that change at the bottom of the cylinder?

Frits,
By increasing the rod length and reducing the compression height of the piston, but leaving the crown at the same level relative to the cylinder (ie, its TDC and BDC positions would remain unchanged), the transfer cut out in the piston could be raised by the same amount, thereby better matching the cylinder. Should have explained this better. Another side benefit might be the less side thrust. A negative might be the fact that the piston pin and bearing might get hotter.

[Frits Overmars]

1. One could modify the piston a bit by blending, but there is a limit, particularly under the A ports, where only a mm or so of material removed will expose the aux exhausts to the crankcase at TDC.

By increasing the rod length and reducing the compression height of the piston, but leaving the crown at the same level relative to the cylinder (ie, its TDC and BDC positions would remain unchanged), the transfer cut out in the piston could be raised by the same amount, thereby better matching the cylinder.

But the amount that the transfer cut-outs can be raised, will be limited according to your option 1 just the same. The minimum required piston length here depends on the distance from TDC to aux exhaust floor, irrespective of con rod length, doesn't it? I'm afraid I'm going to need a drawing to understand you on this.

[seattle smitty]

Hah, Ken, I have an old racing outboard with a waaayy uglier mismatch than that: 1977 Yamato RB-5 350cc flat-four piston-port. Pretty good bore/stroke (47.4X49.4) and long rods (because the engine was sleeved down from a 500cc), but the rest of it was pretty sad . . . partularly that mis-match. The piston skirt had to cover the piston-port, and the factory handled this by leaving half of the skirt hanging well over a centimeter into the path of the A/F charge that was supposed to flow into the single transfer port at BDC. I forget what Yamato was claiming for this 350, but somebody put a new one on the dyno and made about 58 hp . . . on methanol!!

Wobbly, evidently Ken knows what you mean, but I'm a little confused about the "ball-nose." Rotary-file? End-mill? In any case, the idea is to end up with a constant rolled edge, a smooth radius over the piston cut-out and the transfer entry, right?

I would think one possible step Ken could take in that direction is a longer rod, using the same piston and a spacer under the cylinder. Then he could make a good radiused entry . . . as well as probably having less unwanted shrouding of the transfers by the crankshaft wheels. There's a lot of that shrouding to be seen in my crappy old outboards.

(EDIT) Aw Dang, I didn't see that we'd got to P. 1128. Oh well.

[jonny quest]

what is the ideal BDC piston transfer case opening scenario? The big radius entries from cyl bore to transfer duct would seem to be counter intuitive if piston travels below this opening at BDC.

The KTM and RS have sharp cyl bore to transfer duct shape. would they improve with a big radius like the Aprilia?

[richban]

It would certainly help the flow into the A-ports more than it would hurt the flow into the B-ports (if the latter would be hurt at all, which I can't tell).
So the bulk flow would improve. But sending more mass through the A-ports might upset the scavenging balance, so there are no guarantees here.

Interesting. I went back through my photo's to try and find some early piston wash images. Would that give and indication of how the A and B ports are balanced? I'm sure I have a pic.

[husaberg]

Interesting. I went back through my photo's to try and find some early piston wash images. Would that give and indication of how the A and B ports are balanced? I'm sure I have a pic.

http://www.kiwibiker.co.nz/forums/at...8&d=1409608613

[richban]

http://www.kiwibiker.co.nz/forums/at...8&d=1409608613

Husaberg, keeper of the digital realm. Thanks for that. I am interested as to what the eyes of experience would read in it.

[jonny quest]

Problem with reading that piston is at one time, probably prior to that piston it was detonating. How much time is on that piston... because if you're not familiar with reading that type of fuel... it can be deceiving a bit. It doesn't look like that piston has more than two hours of run time... but transfer balance looks good.

[wobbly]

Yes, the YZ125 has a small chamfered edge on the piston, with a flat top - and this has been reported as being quite superior to a simple dome.
The KTM had a slightly wider chamfer,and some of the heads had a proper toroid, but in both cases the head shape follows the piston to get constant squish height.
In my original design the chamfer angle was the entire squish width, then a flat top, and this combined with a toroid chamber made better power than a dome
with a bathtub.
The ballnose shape on the transfer duct /bore wall entry was flow bench and dyno developed by Mr Thiel.
See pic.
The radius on the piston cutout has been around for years, and as Mr Savard at SavTec is doing this to his KZ10B engines, I will be trying it soon
when I test a batch of new lightweight piston designs, that also have thinner rings like an A Kit Honda ( more damn copying going on - its everywhere ).

[jonny quest]

I thought I read in the Pit Lane forum that Frits/Jan tried a radius on bottom of piston with worse results. I definitely could be mistaken. And if my memory is correct, did it not work because of the already rounded edge of cyl/transfer duct opening.

[richban]

Problem with reading that piston is at one time, probably prior to that piston it was detonating. How much time is on that piston... because if you're not familiar with reading that type of fuel... it can be deceiving a bit. It doesn't look like that piston has more than two hours of run time... but transfer balance looks good.

Can't remember the hours on that one but quite a few maybe 10hours. Yes big air leak got it rather cooked. It's still in the engine that has now done a full race season. Time to replace. Also we have never really looked at the piston at BDC in the barrel. I will be doing that today. Surely a Honda 250 bottom end with a 150 barrel a running a Kawasaki KR150 wiseco piston might be in need of some sort of match up. We will see.

[wobbly]

Rich, what is the deck height and ring pin position on the KR150 piston.