[Half-Inch Stud]

Sooo, the question was "what do you think?" About dimples on a piston top. So i tink it means more surface area, like an +060 overbore. What say you!

More HP with less ping. No dowside.


Pontiac Engine Design Theory FB group

[Half-Inch Stud]

Ohoh, i failed physics for that moment. Larger surface area being acted upon, but the sum of the downward forces is "theortically" the same as a flattop.

I wonder about all the angled forces aimed partially at the sidewalls, well those angles have a proportion downward that Trig angles, or integration shows add to the flat, but not more.

Uh, sorry.

[Formulas]

Use a pencile to put 5lbs of force on a scale use a 4x4 piece if wood to exert 5lbs of force on the scale

you get 5lbs of force on the scale no matter how wide the force is applied

scale represents a piston, 5lbs of force represents combustion pressure

[Skip Fix]

I had seen an article by Jim McFarland years ago in Circle track about doing that more to create a little more turbulence in the flame front over the piston. Showed some piston tops before and after and a more even burn

[Formulas]

There was some work in the past to dimple combustion chambers like a golf ball about the time the Singe ? "spelling" groove was being batted around, dont recall it getting much traction

[Half-Inch Stud]

Fuel-air burn chemistry is amazing to figure the hydrocarbons can find the oxygen is short time.

Fuel dropout into the top ring+land is (should be) the dominant loss. Fuel wets the Top ring land upon inhale and Compression. The dimple don't come close to salvaging ring-land fuel. Tight Piston-head to Wall is the most effective, higher Top ring too. Hot Ring re-vaporizes the fuel too.

[PAUL K]

I gave up on that theory when they flipped flopped the reasoning for it. It can't work both ways. There might be something there but it's going to be awfully small.

[misterp266]

I saw that posted somewhere else too. From SEMA. I believe it’s a motorcycle application but that really doesn’t matter. The claim is a more controlled flame front and more complete burning. Not sure they claim more power. I see it as just another gimmick. So many other things could be way more productive in adding 1/10th of a horsepower per cylinder!
Looks pretty though doesn’t it?

[Scarebird]

If it worked the OEM's would be doing it.

[johnta1]

I'd be more inclined to believe the Somender Singh grooves that Formulas is talking about (I think).

The dimples may work some but well enough?

The rough grinding on the ports and intake ports will also probably work better?

[Half-Inch Stud]

Originally Posted by johnta1

I'd be more inclined to believe the Somender Singh grooves that Formulas is talking about (I think).

Go for it. R&De ! I admit to not being brave-enough to try it, not even to a 1-CYL.

[mgarblik]

Darin Morgan did some development work on piston heads, intake tract, and combustion chamber dimples. Quite a bit of wet flow testing as well. This was for Pro Stock drag racing where they will gladly spend 60-80K for 1 HP. Nothing significant or verifiable there. Does look kinda cool. Another "trick of the week" IMO.

[wolf]

More surface area = more heat transfer = less power and efficiency.

Dimples = potentially more turbulence (depending on other geometry) = better charge mixing = faster flame speed = potential for higher efficiency (depending on other factors).

So, my 2 cents, if the dimples help, it's likely because you had a bad chamber/piston/port design in the first place.

[Tim Corcoran]

Originally Posted by Scarebird

If it worked the OEM's would be doing it.

Exactly what I was thinking.

[sdbob]

Don at DCI were talking years ago and I mentioned dimpling the piston and ports like a golf ball for increased flow. He showed me pictures that Smokey had done years ago for exact same thing. Hmm must not have been a big enough advantage or was kept secret.

[Half-Inch Stud]

Originally Posted by sdbob

Don at DCI were talking years ago and I mentioned dimpling the piston and ports like a golf ball for increased flow. He showed me pictures that Smokey had done years ago for exact same thing. Hmm must not have been a big enough advantage or was kept secret.

Seems to me if Smokey tried it, then the PMD engineering got to hear the results, whether thru formal or informal channels.

[steve25]

In terms of the chambers in the iron D port heads and combustion efficiency it’s imperative that this machine lip is NOT blended out.

It can be polished over lightly so that it does not develop into a hot spot ( rolled over .008” )but if you blend it out then the pressure drop and the fuel shearing action that accompanies that pressure change is lost!

If your running a low comp ( 71 and later D port ) and over .400” lift then un-shrouding work as in my last two photos is helpful, but note how I ground a fuel sheer lip back during the un- shrouding work.

[misterp266]

More dimples . . . .

[Half-Inch Stud]

Originally Posted by misterp266

More dimples . . . .

So ah, on paper, them dimples increase port area.
In practice them dimples reduces port area, by creating causing a thicker "boundary layer" than the smooth surface would have.

Such a layer is defined here, as not having the air velocity of the bulk flow.

[steve25]

DIvouts are a excellent way to help shred up any rivers of wet flow back into a burnable state of mist, but there still needs to be a pressure drop taking place around the short turn to get the fuel to the back side of the valve andthen out.

Many many times a short turn shape that works great on a flow bench to get air around it and move big numbers will not get the needed fuel in to make use of those CFM numbers.

This is especially true on Intake ports that have minamal short turn height in relation to there minimum valve bowl diameter.

In cases like this the short turn is layed back so much to reduce or get rid of flow turbulence that there's little to no pressure drop and then not enough fuel gets into the chamber.

If your heads have intake ports with this much short turn height then you have nothing to worry about.