Porting question.

[JeremyEdge]

How do you determine what shape the porting should be on a sleeve.

Thanks,

Jeremy

 

[Jim Allen]

"How do you determine what shape the porting should be on a sleeve."

Look at & study very carefully the transfer porting shapes used on present day high performance two cycle engine such as the Aprillia, Rotax, Suzuski & the Metkemeijer 35,000 RPM .40 speed engine. You will discover that present day technology, dyno testing & actual testing has proven that Gordon Blairs tea cup handle shape is not the best. Transfers that have the correct inside & outside radaii, which can take advantage of the Coanda effect have been proven the best, especially for the high flow rates necessary in any high HP, high RPM engines.

Jim Allen

 

[dwilfong]

Jim you as always have opened up my mind. Found some papers on Coanda flow theory.

Going to be a long night.

http://www.wseas.us/e-library/conferences/2007athensmech/papers/565-373.pdf

David

 

[JeremyEdge]

Thanks for the info Jim,

David I just read some of that material.

It is some really cool stuff.

 

[Jim Allen]

It is the inside radius that is very important. There has been an attempt at using this technology in the gas engine world, but the selection of to small of a radius did not produce the desired effect at higher RPMs. Finding the correct radius can be difficult, but it is not impossible. You want to provide an easy path for gas flow with very little turbulence & pressure loss.When combined with the type of exhaust duct technology found in the MB4o engine, a domed top piston, plus a toroidal head design, the HP that can be developed at very high RPMs is significantly increased over present day stuff.

The toroidal head that is use on my 26 cc gas engine allows the flat electrode of the spark plug to be .017" away from the piston crown at TDC. With a chamber volume of 1.3 cc & a deck clearance of .003", there is no detonation, even when then engine is aggressively leaned. The top edge of the exhaust port & the pistons top edge are radiused to take advantage of the De Laval nozzel effect. Since this engine is piston ported, there is also a radius on the bottom edge of the piston & the bottom edge of the induction window. I do not know the exact timing of this engine, but I am sure of the effect these type changes can make because of the HP developed at WOT.

Jim Allen

 

[chunk t]

The toroidal head that is use on my 26 cc gas engine allows the flat electrode of the spark plug to be .017" away from the piston crown at TDC. With a chamber volume of 1.3 cc & a deck clearance of .003", there is no detonation, even when then engine is aggressively leaned.

Jim Allen

sorry, not to derail the thread. I'm curious about the squish area on the head with this type of porting. Is it typically parallel to the piston face or tapered; and what is the squish area (%) relative to the area of the piston face?

 

[Jim Allen]

Many dyno tests have shown me that a squish band area larger than 50% of the bores area, always reduces peak HP. In engines that are over square (1.339" bore X 1.102" stroke or 1.125" bore X .902" stroke) it becomes difficult to design a chamber, with this number, when using hemi type chambers.

The best relationship between whatever angle is on the piston crown & the squish band appears to be a 1 deg steeper angle on the squish band when compared to the piston crown. Deck clearances should be closed down until the piston & squish band just begin to touch at their outer most edges, when running at the engines maxium RPM. This gives a high squish velocity. When combined with a very sharp edge at the junction of the squish band & the head's bowl, the incomming gases will be tumbling instead of swirling.

The toroidal head design easily allows a 50% squish area, even in big bore situations. Its placement of the ignition source in the middle of the chamber promotes the rapid burn needed for high HP, high RPM engines. The design of the toroidal button allows very efficient cooling in the area of the bowl as well as in the area surounding the plugs threads. This helps to further reduce the possibility of unwanted detonation.

Jim Allen

 

[Mark Leyde]

What does this toroidal head shape look like? Would you happen to have a picture or drawing of one?

Thanks,

Mark

 

[lohring]

You need enough port area to flow enough mixture to produce the power you want. This concept is called time area or the "average" port area as the piston opens and closes the port. There are empirical numbers that relate the needed time area to power for exhaust, blowdown, transfer, and intake areas.

You also need a transfer layout that will flush the exhaust gas out as much as possible without loosing too much out the exhaust. See

.
Lohring Miller

 

[Jim Allen]

"What does this toroidal head shape look like? Would you happen to have a picture or drawing of one?"

Google, Vinceracing.com or TSS500LC & TSS500GP cylinder head inserts.

 

[dwilfong]

http://www.rusengines.ru/ also check out Cyclon.

 

[Jim Allen]

Sectional view of type of toroidal head that I'm presently using.

 

[dwilfong]

http://lup.lub.lu.se...&fileOId=574803

I have read a paper on the emission out put of a small glow Eng done by a person writing his Doctoral Theseus.

He put a camera in the combustion chamber as it was running to get a pic of the combustion kernel as it developed.

In his findings he stated that the pan cake style chamber was the most efficient at burning the fuel.

When looking at the info on the Coanda flow. It seams that a flat surface will attract the flow toward it.

It is all theory with no actual data to back it up. but I think it would be worth a look at.

With this style chamber it is possible to get a 50% squash to bore ratio with strait sided chamber. this makes it possible to use the area in the chamber to its full volumetric advantage.this makes it possible to bring the electrode as close as possible to the piston top and maintain a flat toped chamber that is very shallow with sharp 90 deg edge as the entry in to the chamber tumbling the fuel air mix.

It also makes it possible to slam down the squash and still maintain a reasonable CR.

Just a theory.

Lots of stuff here

http://www.lunduniversity.lu.se/o.o.i.s?id=12683&search=link&author=vok-vtm

David

 

[RodneyPierce]

I have read a paper on the emission out put of a small glow Eng done by a person writing his Doctoral Theseus.

He put a camera in the combustion chamber as it was running to get a pic of the combustion kernel as it developed.

In his findings he stated that the pan cake style chamber was the most efficient at burning the fuel.

When looking at the info on the Coanda flow. It seams that a flat surface will attract the flow toward it.

It is all theory with no actual data to back it up. but I think it would be worth a look at.

With this style chamber it is possible to get a 50% squash to bore ratio with strait sided chamber. this makes it possible to use the area in the chamber to its full volumetric advantage.this makes it possible to bring the electrode as close as possible to the piston top and maintain a flat toped chamber that is very shallow with sharp 90 deg edge as the entry in to the chamber tumbling the fuel air mix.

It also makes it possible to slam down the squash and still maintain a reasonable CR.

Just a theory.

David

Isnt this what we (me and you, and im sure a few others) are currently doing in our custom buttons anyhow?

 

[dwilfong]

I have read a paper on the emission out put of a small glow Eng done by a person writing his Doctoral Theseus.

He put a camera in the combustion chamber as it was running to get a pic of the combustion kernel as it developed.

In his findings he stated that the pan cake style chamber was the most efficient at burning the fuel.

When looking at the info on the Coanda flow. It seams that a flat surface will attract the flow toward it.

It is all theory with no actual data to back it up. but I think it would be worth a look at.

With this style chamber it is possible to get a 50% squash to bore ratio with strait sided chamber. this makes it possible to use the area in the chamber to its full volumetric advantage.this makes it possible to bring the electrode as close as possible to the piston top and maintain a flat toped chamber that is very shallow with sharp 90 deg edge as the entry in to the chamber tumbling the fuel air mix.

It also makes it possible to slam down the squash and still maintain a reasonable CR.

Just a theory.

David

Isnt this what we (me and you, and im sure a few others) are currently doing in our custom buttons anyhow?

Just thinking out loud. The recipe changes as new info is obtained. not sure if this is a perfect scenario. always good to get input to Ideas to progress.

David

 

[lohring]

Below are pictures of the core patterns and the cylinder used in the Profi 40 engine. The pictures are courtesy of Frits Overmars. Note the similarity to the Aprilia core patterns pictured above. Otherwise, as far as I know, you need to get into at least 50 cc engines before anyone uses this style of transfer and exhaust design.

Lohring Miller

 

[dwilfong]

Here is a little souvenir from my 1988 Cagiva WMX 125. burned up the original cly with the high tec coating on it and had LA sleeve make this one for me. Used Pro X , KX 125 pistons in this set up.

Had a man by the name of Albert Bold fit this in the jug. This eng used the knife valve on the ex port. 25 year old tec. the bike was a replica of the world champion ship wining bike. Only a few where made for static display in select dealers show rooms. Got the bike at the yearly action of left over inventory. No one bid but the shill. found out why later. Dellorto would not release the needle jet to keep it alive for three years.

This is the mother of the Aprilla.

David