ESE's works engine tuner

[oldjohnno]

I'm curious about transfer flow, specifically at times when the transfer is partially open (piston above BDC) and would love to hear any comments.

Obviously, at any point other than BDC the piston forms part of the short side radius of the transfer. There'll be a ledge on the bottom of the port window and then from there a sharp internal right angle up the side of the piston and then up to another sharp turn across the top of the piston crown. Only at BDC will the short side of the port be nicely shaped and at other points there must be a massive amount of turbulence around this turn.

There's not a lot you can do about it I guess - short of putting a huge radius on the edge of the piston crown so that it forms the short turn of the transfer. But this I guess would affect combustion terrribly and you'd have to run the top ring quite low on the piston.

Does it even matter? Does most of the flow occur at or around BDC any way? Does managing the flow in a partially open transfer warrant any attention?

[wobbly]

Adding a small radius to the piston and reshaping the squish to suit gave about 1 Hp in high 40s when dynoed by VHM.
But that was with a billet machined piston, so the power change could be just as much be caused by that.
There is more pressure above the transfers when they open than is in the duct, so reverse flow occurs - this is how port stagger works to affect the scavenging regime.
And the pressure differential created at the exhaust port around BDC by a correctly dimensioned diffuser,is way way more than that created by compressing the case due to piston movement.
Thus the flow regime as the piston approaches, then dwells at BDC, then starts to move upward is the critical period for the inner radius and the approach angle
of the port floor to be optimized.

[TZ350]

I'm curious about transfer flow, specifically at times when the transfer is partially open (piston above BDC) and would love to hear any comments.

It has been talked about on here before, from memory a small radius (with matching squish profile) on the edge of the piston is beneficial, And the trick with pipes is to get them to suck hard at BDC. Hopefully someone will be able to find the original posts.

Wob beat me to it, anyway the top of page 1500 has a very helpful post about ways to search this thread.

[bjorn.clauw.1]

It has been talked about on here before, from memory a small radius (with matching squish profile) on the edge of the piston is beneficial, And the trick with pipes is to get them to suck hard at BDC. Hopefully someone will be able to find the original posts.

Wob beat me to it, anyway the top of page 1500 has a very helpful post about ways to search this thread.

Page 1271

Searching the forum with google custom search, it even shows pictures

https://cse.google.com/cse/publicurl...90:5pd9xdluxce

[Frits Overmars]

I'm curious about transfer flow, specifically at times when the transfer is partially open ... Obviously, at any point other than BDC the piston forms part of the short side radius of the transfer. There'll be a ledge on the bottom of the port window and then from there a sharp internal right angle up the side of the piston and then up to another sharp turn across the top of the piston crown. Only at BDC will the short side of the port be nicely shaped and at other points there must be a massive amount of turbulence around this turn.
There's not a lot you can do about it I guess - short of putting a huge radius on the edge of the piston crown so that it forms the short turn of the transfer. But this I guess would affect combustion terrribly and you'd have to run the top ring quite low on the piston.
Does it even matter? Does most of the flow occur at or around BDC any way? Does managing the flow in a partially open transfer warrant any attention?

A radius on the piston edge greatly improves inflow from the transfers into the cylinder and it hardly improves any unwanted flow from the cylinder into the transfers.
And this radius doesn't need to be huge. I use 5% of the stroke as a radius. Of course the combustion chamber shape must be adapted to this radius.
It not only helps flow from the transfers into the cylinder; it also helps flowing washed-through mixture from the exhaust duct back into the cylinder.
Remember, when in the right rpm range, at transfer closure the exhaust port should stop being an exhaust port and should turn into a transfer port.
A radiused piston edge also helps to conserve energy during the supercritical first part of the blowdown phase because it lessens turbulence; especially in combination with a radiused top edge on the exhaust window.

[Frits Overmars]

Adding a small radius to the piston and reshaping the squish to suit gave about 1 Hp in high 40s when dynoed by VHM.... the flow regime as the piston approaches, then dwells at BDC, then starts to move upward is the critical period for the inner radius and the approach angle of the port floor to be optimized.

My approach: in BDC the extended transfer floor direction touches the piston tangentially.

[bjorn.clauw.1]

My approach: in BDC the extended transfer floor direction touches the piston tangentially.

Hi Frits, so when we take the piston out to turn this radius, would it be wise to make a small radius on the bottom of the piston skirts? Found in a book this helps to keep more oil on the bore wall (in that the sharp edge of the skirt acts as an oil scraper).

[richban]

I have been playing around with the exhaust port on the 300 cylinders. I have added some side angle to the port. Not much as the casting is very thin there and could easy pop out into the water jacket. But some has got to be better than the none it has.

Now there is quite a bit of space between the port and the power valve sides. Especially when fully closed. Also you will see the space in the centre beside the bridge is quite large. I am thinking I should weld up and reshape the PV. Is this worth the effort? My gut says yes. Any advice appreciated. Cheers Rich.

[wobbly]

Honda A kit setups have exactly the same approach Rich, but the slanteye festerers weld the PV with tig, and make it fit the bridge
and the side cutaway perfectly, in the up and down position - easy to do, but takes time to grind at to get it to fit.
Also when the valve is up, the whole thing should seal around the cavity, again a run of tig around the blades bottom face is easy to fill and grind..
I did the welding on a CR125 PV to make it fit the bridge exactly and picked up 1.5 Hp at 9000.

[richban]

Honda A kit setups have exactly the same approach Rich, but the slanteye festerers weld the PV with tig, and make it fit the bridge
and the side cutaway perfectly, in the up and down position - easy to do, but takes time to grind at to get it to fit.
Also when the valve is up, the whole thing should seal around the cavity, again a run of tig around the blades bottom face is easy to fill and grind..
I did the welding on a CR125 PV to make it fit the bridge exactly and picked up 1.5 Hp at 9000.

Cheers for that, As I figured after seeing an RS250 barrel, the valve fits very well indeed. Time to get the tig out. Also I have checked glens cut up barrel and it looks like I can take another 1mm or so out to get a little bit more angle depth and curve out of the sides.

[bjorn.clauw.1]

Had some time this morning to finish my cast iron "wet" liner. (credits/thanks to Makr and everybody on this forum actually). This will go on the mule engine when the dyno is finished.



I acid etched the ports in the liner and transfered the port geometry to the inside of the liner. I then milled the ports on a conventional lathe. Very time consuming. I wonder if anybody made a jig (much like a wood copy carver) to copy the ports from another cylinder onto the sleeve?

[seattle smitty]

Yes Sir!!! THAT is one way you can get improved heat transfer out of an iron sleeve!!

Have you got a way to promote a forced directional flow of the coolant through and around the slots in the sleeve? Like maybe with the coolest incoming water flowing over the exhaust side first??

Incidently, since I can't tell for sure from the photos, does the sleeve positively seat into the barrel at some point, or are you just retaining the sleeve with the interference fit? Does it seat at the bottom of the water jacket? IF so, is it just metal on metal with some kind of goop-sealant, or was there room for an O-ring?

[bjorn.clauw.1]

I forgot to take pictures with the sleeve out. Here's an artistic rendering of the fitment.


o-ring is the same one that seals the combustion chamber.

interference fit is 0.12mm. A lot, the idea behind this is that it will help the heat transfer. Also the bore size of the sleeve shrunk from 54.04mm to 54.01mm. so I hope it will expand a little bit faster than cast iron in general because it is under compression from the aluminum cylinder. So when the cylinder expands the sleeve will follow. (tests with a hotplate seem hopeful).

Cooling fluid comes up from under the exhaust port, then around the outer cylinder wall. This is blocked now (not in the pictures) so it is forced through the cast iron slots (left 2 small bleed holes, one on either side). Then the coolant exits the sleeve above the intake port where it goes over the cylinder head and flows back (over the cylinder head) to the exhaust side where it exits the cylinder head cover.

Sleeve is pulled/fixed onto its shoulder by the cylinder head. No provision to keep the sleeve from rotating. To install the sleeve I turned down an aluminum tube that has a slipfit with the sleeve bore. I then welded both sides and installed a water in and out connection. So during the fitment the sleeve is cooled from the inside with running tapwater through the aluminum pipe. (did not block until I turned the water off)

[lodgernz]

Please forgive me if this post is too far off-topic for this thread.

I may be misreading things, but it seems to me that the 125GP class in NZ is dying a slow death due to the increasing cost and difficulty of maintaining the engine of the only competitive unit, the RS125, long since abandoned by Honda in any useful context.
There appear to be no foul-strokes that can make the grade, even given their huge capacity advantage under the current MNZ rules, and no competitive 2-stroke alternatives are jumping out of the woodwork.
As far as I know, the only 125 2T left in current manufacture is the KTM SX125. I'm wondering, would it be possible to coax the 45 or so HP required to make this engine a viable substitute for the RS125 if developed sufficiently and shoe-horned into the RS frame?
If a 2T substitute is not found soon, I can see corrupt FIM legislation will eventually trickle down to NZ and we'll be stuck with a poxy 4T class, inevitably of 250cc and dominated by Honda.
Are there any competitive kart engines that could be modified to fit the RS frame?

Opinions?

[wobbly]

There used to be a class in karting here called 125 National.
We won 3 titles in a row and still have the lap records at every track we raced using a TM125MX engine.
This was ( is ) way cheap to maintain, REAL easy to tune,and if you wanted to get smart all the ratios from the other TM kart engines will fit.
That engine ended up with 50.2 Hp,at the sprocket on Avgas ( 10 years ago,I would get way more now ) and as the PV was converted to be driven by a cable servo, it had WAY
more power down at 10,000 than any RS125 ( our main competition ).
The problem with the dedicated kart engines is that the carb is out the front, but having the pipe under the seat is an advantage power wise.
Its common knowledge that the Aprilia RSA125 didnt handle as well as the RSW125 due to the engine having to be moved back away from the front tyre to increase carb clearance.
But take a TMKZ10 kart engine and replace the 30mm carb with an SPJ38 and fit an Ignitech and that is well over 50 Hp at the sprocket without touching a thing.
Bore one to 60mm,giving 152cc and its over 60.
But as a side point we get 41.5 Hp at the sprocket from a 2002 CR125 dead stock except for the reeds and the pipe for SKUSA racing, throw on a 2004 cylinder with cable PV,do some porting
and your RS125 will get blown away easy.
A complete SKUSA engine parts kit is still available from HRC for under 2000 USD,and I bought a siezed 2004 cylinder,to fit on an old NSR250 MC21, here in NZ
the other day for $200, they are available new on line for around 400USD complete.
The CR125 may be wet clutch, but fit Hinson alloy/kevlar plates and you would never know, and they last forever.
Cheap as chips the whole thing.