burn slots in squish area ?

[automotivebreath]

Cammer, I appreciate your understanding.

Almost every thing that I accept as beneficial is based on results, primarily
with drag strip testing. Back in the 70s I had 2.02" valves replaced in my set
of 1.94 valve 461 castings. The results were disappointing to say the least.
The machinist installed new guides, screw in studs and did a beautiful three
angle valve job, how cold this thing not run? Little did I know there was so
much material under the seat in the valve bowl area, the bigger valve hurt
more than help. Armed with a drill, one carbide bit and a book from Smokey
Unick I "ported" my first set of heads. The car picked up six MPH in the 1/4
mile. I didn't need a dyno or a flow bench to determine that I liked the results.

It's much the same with grooved cylinder heads, no I didn't gain 6 MPH, but
I did realize a state of tune that I had never seen before in my 30 plus years
of tuning. May be I was wrong, perhaps others would not see the same
benefit. I cut grooves in 50+ sets of heads for other people, for the most
part they confirmed what I was seeing. Communicated with hundreds of
people here and around the world that say the same.

So whats the scientific reason that this simple modification brings on results?
I have my theory's but don't have the desire to spend time proving them.
Instead I'm spending my time learning as much as I can about combustion,
this much I can say: The more I learn the more I realize how little we know.
As for combustion as we know it, it's far from ideal, not even close. If our
engines were efficient we wouldn't need these big radiators, we would instead
use the wasted energy to power our cars.

[seattle smitty]

For the manufacturers to add grooves to their heads, they would have to add another machining operation, one which is in a different plane from the other operations. This would be expensive, and get the bean-counters' unsympathetic attention. Maybe it already has, or maybe the engineers edit their own ideas because they know ahead of time what they can get permission to do and what would be a wasted effort.

But now with the government making noises about very tight CAFE requirements to come, the engneers will gain some clout, relative to the bean-counters. So who knows what groovy technologies we will see . . . .

[Cammer]

We must remember the differing ways increased performance is obtained from parts such as cylinder heads. While I am looking for quiet, another may try to induce swirl or even turbulence to reach their goals.

The race track will sort out the winners!
_____________________

GFN will continue to produce great cylinder head articles and we will be able to post our thoughts as this all unfolds.

I do not know about trying to get David to grind grooves in cylinder heads but you are welcome to try!
________________________

Do we have members grinding grooves or other shapes on piston tops?

Anyone changing squish angles?
____________________________

[Calypso]

Originally Posted by Cammer

We must remember the differing ways increased performance is obtained from parts such as cylinder heads. While I am looking for quiet, another may try to induce swirl or even turbulence to reach their goals.

The race track will sort out the winners!
_____________________

Do we have members grinding grooves or other shapes on piston tops?

Anyone changing squish angles?
____________________________

Have to agree on different ways to accomplish similar (and, well...different) results. Engines seem to be filled with different interconnected inefficiencies. Intake induced swirl may in some cases trade flow for improved combustion, but if you can get the same combustion quality without swirl, you just pontentially got some more air in the cylinder.

It may be that some of the backyard methods may be worthless for highly R&D'd racing engines, but they may still give 80% fix for one particular process with 20% effort for most of us deadly, who may not be able to get to the root cause or "the best" solution.

Squish angles are interesting as it would seem to the naked eye that they may have, not only impact to the squish flow direction during compression, but also cylinder filling. The shadetree mechanic approach could be to use slight dome on the piston to deflect squish and roundings on the chamber edges. Maybe. No proof it would work.

[automotivebreath]

Originally Posted by Calypso

This is probably one of those areas where there are many ways to skin a cat.
SAE 1999-01-3664 is about benefits of directed squish

SAE paper 1999-01-3664 describes a bowl in piston squish jet combustion
chamber used with a flat cylinder head, here’s the results of that testing:

Compared to the engine with the bathtub combustion chamber, the
experimental investigation shows that engine with the squish jet turbulence
combustion chamber gives better comprehensive performance. The
combustion process shortens, the lean burn limit extends. At WOT speed
characteristics, the maximum power output increases by 25.7%, the average
specific fuel consumption decreases by 12.9% and the average emissions of
HC, CO and NOx decrease by 31.4%, 91% and 5.6% respectively

[tommurphy73]

I know of one person who machines his cylinder head to add a small amount of angle in the squish area to push the mixture towards the centre of the combustion chamber. This modification is included along with many others so it is difficult to determine the advantage from this one modification. However the complete solution works very well. He is achieving 115bhp per liter so from a 30 year old head design so not bad.

I see that the xxx four stroke motor has slots machined in the cylinder head on page #1 of that thread. It also seems to go quite well.

Regards
Tom

[MAP]

Greetings,

I'm trying to understand the physics of what may be at work here. I can see that the one-dimensional-like feature of the groove can pose a barrier to transverse flow, hence the reversion benefit. Is that the thinking here?

But this near one-dimensionality can also accentuate longitudinal flow. If so, then is the groove intended to "accumulate" squeezed-out charge from the quench area as the piston nears TDC, and then eject it in the direction of the spark plug?

If so, then its efficacy would seem limited. In general, from a minimal-energy condition, it would seem that most of the compressed charge in the quench area as the piston nears TDC, would take the shortest geometrical route into the chamber volume proper. From the picture, it would seem that the majority of the charge would thus actually bypass the groove, and instead make a beeline into the chamber. If this thinking is correct, then why not create a system of grooves, somewhat akin to the typical tread pattern on wide tires to eject water, so that a greater fraction of the compressed charge in this area is guided toward the main groove, thus accentuating the strength of the ejected stream headed toward the spark plug?

I know that adding grooves reduces the overall quench/squish action given that this increases the average height of minimum compression in this area, but perhaps a better optimization than currently known, or practiced, exists?

Best regards,
Mark

[Calypso]

Originally Posted by MAP

Greetings,

I'm trying to understand the physics of what may be at work here. I can see that the one-dimensional-like feature of the groove can pose a barrier to transverse flow, hence the reversion benefit. Is that the thinking here?

But this near one-dimensionality can also accentuate longitudinal flow. If so, then is the groove intended to "accumulate" squeezed-out charge from the quench area as the piston nears TDC, and then eject it in the direction of the spark plug?

If so, then its efficacy would seem limited. In general, from a minimal-energy condition, it would seem that most of the compressed charge in the quench area as the piston nears TDC, would take the shortest geometrical route into the chamber volume proper. From the picture, it would seem that the majority of the charge would thus actually bypass the groove, and instead make a beeline into the chamber. If this thinking is correct, then why not create a system of grooves, somewhat akin to the typical tread pattern on wide tires to eject water, so that a greater fraction of the compressed charge in this area is guided toward the main groove, thus accentuating the strength of the ejected stream headed toward the spark plug?

I know that adding grooves reduces the overall quench/squish action given that this increases the average height of minimum compression in this area, but perhaps a better optimization than currently known, or practiced, exists?

Best regards,
Mark

I think those are fair questions, but answering them satisfactorily without backing of serious research is not going to be easy. It's all half speculation before that.
Starting from jet formation: It would seem that the efficiency of narrow groove would not be that good forming a jet versus the effect from regular squish. Is more always better? Could there be something more there than meets the eye considering increasing area groove? How does the normal squish effect begin in detail? Does the fuel in the area have something to do with how the groove works?
Jet effects could be easier to speculate: having a jet (flow vs. pressure) at low lift, near intake valve short side, at overlap could suck mixture from intake. Pressure recovery at other side could block some reversion from exhaust.
Effects during compression then are probably topic of their own.

[big block fiero]

Originally Posted by Calypso

Intake induced swirl may in some cases trade flow for improved combustion, but if you can get the same combustion quality without swirl, you just pontentially got some more air in the cylinder.

good post and well stated.

[big block fiero]

Originally Posted by MAP

If this thinking is correct, then why not create a system of grooves, somewhat akin to the typical tread pattern on wide tires to eject water, so that a greater fraction of the compressed charge in this area is guided toward the main groove, thus accentuating the strength of the ejected stream headed toward the spark plug?
Best regards,
Mark

Another interesting idea.