ESE's works engine tuner

[Jannem]

Has anyone tried putting a fin to the exhaust port roof to help with the pressure distribution and reduce the secondary flow to make the port more efficient? The attached CFD picture shows pretty well, what the situation typically is. I've seen it work with compromised intake ports using my flowbench.

[Frits Overmars]

Has anyone tried putting a fin to the exhaust port roof to help with the pressure distribution and reduce the secondary flow to make the port more efficient? The attached CFD picture shows pretty well, what the situation typically is. I've seen it work with compromised intake ports using my flowbench.

Jannem, that fin may indeed reduce secondary flow and make the port more efficient. But what your flow bench does not tell you, is how much heat the fin will transfer from spent gases to washed-through fresh mixture.
Any fin is a heat exchanger. Or, as I used to say when I was younger and more sarcastic: "I'd rather have my cooling fins at the outside of the exhaust duct" .

[Jannem]

Jannem, that fin may indeed reduce secondary flow and make the port more efficient. But what your flow bench does not tell you, is how much heat the fin will transfer from spent gases to washed-through fresh mixture.
Any fin is a heat exchanger. Or, as I used to say when I was younger and more sarcastic: "I'd rather have my cooling fins at the outside of the exhaust duct" .

It indeed is a compromise, as is the single ex-port. Cut and try will tell, or braze in this case. Just thought if someone has tried and would be willing to share findings.

Edit: perhaps another fin on the roof of the port, inside the water jacket could compensate some...

[136kg136ps]

Frits,seeing the words outside cooling above,would it be helpful to have external water cooling on the first few inches of exhaust?I was thinking brass,copper or stainless tubing tightly wound or possibly welded to the header for better heat conduction.Inexpensive and simpler to figure out vs welding up the cylinder to add water passages it would seem.

[Frits Overmars]

perhaps another fin on the roof of the port, inside the water jacket could compensate some...

It would compensate some, but not nearly enough.

Frits,seeing the words outside cooling above,would it be helpful to have external water cooling on the first few inches of exhaust?I was thinking brass,copper or stainless tubing tightly wound or possibly welded to the header for better heat conduction.Inexpensive and simpler to figure out vs welding up the cylinder to add water passages it would seem.

The first few inches? I have no idea what those are, some new unit of measure maybe?
OK, joking apart, cooling the first part of the exhaust duct is highly commendable. It should be done over a length that can contain the cylinder capacity. Cooling further downstream will only be beneficial if the exhaust pipe is too short.
Winding tubing around any pipe won't do much good for cooling. If you must cool a pipe, welding a water jacket around it is a hundred times more effective.

[F5 Dave]

Port is now 28mm, so there is room. Don't have extra rings to test. Piston is Italian GPM, and appears much more decent quality than the typical far east choices. Rings do not have a coating and look decent, but are magnetic.

It's an AM6 cylinder with Suzuki piston. Stock the transfer timing is at 130deg and blowdown will not be staggering even with raised exhaust. Will see how it all pans out after we get it on the case, but expect to machine the lower end of the cylinder as the piston is little shorter than stock.

The aggregate angle of the piston with the flat at the edge is ~15% and the 44mm is 4mm overbore with 39mm stroke. So the angles may be reasonably close after all. Basic trigonometry says 2mm per side you'd use 3 deg less angle for the new bore with original type piston.
I appreciate the oversquare by boring out is not ideal with the implications to transfers. Two wrongs usually do not equal one right, but in this case higher dome and overbore impact to transfer angles may actually fit somewhat together. I'm however building a angled porting tool to adjust the transfers.



I wholeheartedly agree. I would have liked to use another piston which has much shorter compression height and 10mm longer rod, but it's out of the question because of the budget constraints. Without going into lengthy personal history, I can dedicate much more time than before and very little funding to my kids at the moment. Used to be vice versa. Life has it's surprises and the bad ones may be good ones as well. My 15yr son paid for the bike out of his own pocket and got much better one than he expected, because we could buy one previous owner didn't know how to fix and we did it together.

I have a lot of experience in the 4-strokes, decent tools and even a crude flowbench which can be used to test basic wet flow, but 2-strokes are a learning curve.

Yer making me cry, but only for those poor sweet lost horseypowers. On my Suzuki having finally changed to KX60 43mm piston, after years of dreadful Suzuki pistons, and having to destroke to do so it was still a big improvement. . . and they come in 1mm oversizes.
Skim the base if you can't afford the longer rod ATM.

[Jannem]

Yer making me cry, but only for those poor sweet lost horseypowers. On my Suzuki having finally changed to KX60 43mm piston, after years of dreadful Suzuki pistons, and having to destroke to do so it was still a big improvement. . . and they come in 1mm oversizes.
Skim the base if you can't afford the longer rod ATM.

No need to cry for the HP that never was there to begin with.

Skimming the base is in the plan. Gotta see where all the timings exactly fall first.

Curious how much you gained from the long rod, short piston route?

[F5 Dave]

Thats the thing. They were there. They just escaped through poor ring control. Just jumped out of shower thinking better warn you, Std Kawi rings eat iron bore. Wiseco should be fine.

TZR rodkit allowed 13000 rpm peak with rev on, whereas suzuki parts were already at (past) limit at 12, so not one change at a time.

[136kg136ps]

Thanks for the humor and reply Frits.

[Jannem]

Std Kawi rings eat iron bore. Wiseco should be fine.

TZR rodkit allowed 13000 rpm peak with rev on, whereas suzuki parts were already at (past) limit at 12, so not one change at a time.

Is that bore eating because of the differences between rings meant for nikasil vs. iron bore? I'm unfamiliar with coated bores...

Wouldn't destroking impact the timings as well? How much did you destroke? Did you increase the bore at the same time?

[F5 Dave]

Yeah they had soft rings which on placed bore was no problem, but soft on soft is like rubbing two blocks of cheese together. I plated the bore and sidestepped the issue. Most rings can handle either.

I had to destroke quite a bit to get back into class limits 53cc max, something like 37.6. Started with a new barrel. As we've learned here not an ideal configuration.
But even with that disadvantage the better components win out.

[Jannem]

Yeah they had soft rings which on placed bore was no problem, but soft on soft is like rubbing two blocks of cheese together. I plated the bore and sidestepped the issue. Most rings can handle either.

I had to destroke quite a bit to get back into class limits 53cc max, something like 37.6. Started with a new barrel. As we've learned here not an ideal configuration.
But even with that disadvantage the better components win out.

Interesting, and new stuff coming all the time. Thought those rings were harder... 😂

I'm probably committing a forum suicide, but I was thinking about using a chainsaw piston that is fully open from sides and practically see through. This with single exhaust and opening transfer entry to the bore all the way to the cylinder base.😄

[190mech]

I looked at chainsaw pistons for a build a few years back,the skirt was too short and would open the exhaust to the crankcase at TDC and also the skirt width would allow exhaust to bleed thru the sides also..Found a good quality motocross piston instead!

[guyhockley]

Well - I didn't mention any names but you instantly knew my train of thought ?
Thanks for the (french) article - pity my schoolboy french is too many years ago - although I can pick up some interesting thoughts - the pork chop thing would appear to be an easy way to gain some case volume - although as Wobbly says - full circle is better - it may be possible to slim the flywheels (on the inside face) to the crank pin depth - and regain balance weight with heavy inserts - although more research needed there to understand whether it's possible to add enough weight in the space available...

I find it interesting that lots of the 125 kart engines seem to use flywheels of around 90mm diameter and 18-20mm crankpins, as does the X30 Super Shifter 175 (63.5 x 54.5 bore and stroke, from memory). Hydroplane racing motors seem to like flat disc disc wheels with a bolt on balance weight.
http://www.grmracing.com/125-parts
Scroll down to G1020 and G1028.
Wonder what the plate is made of?

[Jannem]

I looked at chainsaw pistons for a build a few years back,the skirt was too short and would open the exhaust to the crankcase at TDC and also the skirt width would allow exhaust to bleed thru the sides also..Found a good quality motocross piston instead!

Thougt about the sides, but missed TDC entirely.😬😂