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"Dimpled" combustion chambers?

Posted By: BradH

"Dimpled" combustion chambers? - 11/20/09 10:12 PM

Anybody who does this stuff for a living think there are benefits to be found from applying dimples to the combustion chamber as shown in this PHR article link ?

The builder also did this to certain areas of the piston tops , too.
Posted By: neonic

Re: "Dimpled" combustion chambers? - 11/20/09 10:17 PM

Call Keck Machine, Brian has played with this in the past. He will be able to tell you what kind of results there was if any. 712-445-2248
Posted By: Bigcube

Re: "Dimpled" combustion chambers? - 11/20/09 10:59 PM

Here's a little bit of info I heard from a local guy many years ago when he was experimenting with it. Think about a valve like a spray nozzle on a hose. The less you squeeze it, the wider the water spray is. At very low lifts the intake charge will be a wide spray. The fuel can have a tendency to come out of suspension and return to liquid form as it travels past the chamber around the intake. The dimples around the intake valve help to agitate the mixture and return the fuel back to a gaseous state by "stirring" the mixture back up. His findings on the dyno was it didn't make any more power but strangely the motor did not need as much timing to make the same power. This was tested on a BBC and was probably back in the late 80's. I think if there was any real benefit from it you would see it much more.
Posted By: Sport440

Re: "Dimpled" combustion chambers? - 11/20/09 11:21 PM

I dimpled my first engine, both the head and the piston back in 1972.

So Im the true Pioneer of it My testing of its results wasnt very scientific though.

I judged the results by the Sound and Shake of the engine. And boy did it sound mean and had plenty of shake. A success for sure!


BUT, I was only 12 years old and the said engine was a 3.5 hp lawn mower engine. The theory then was if I make more room for gas and air to fill then any explosion of that fuel and air would have to be bigger. In reality All I did was lower its Compression.

Ok , Sorry for the story, it is true though.





On the Dimpling shown, I can only speculate on its possible advantages or disadvantages.

One fact I can state is that a dimpled surface will allow air to flow more smoothly over it.

On the head where its dimpled it may slightly improve the intake charge flow.

The dimples on the Pistons , hey if it keeps the pistons cleaner for improved heat reflection, that could be a good thing.

Would any of these two things be enough for any noticeble improvement, I dont know. mike
Posted By: Bob_Coomer

Re: "Dimpled" combustion chambers? - 11/20/09 11:35 PM

Wouldnt then make more since to dimple the intake runner on the intake, and the head intake runner? I mean by the time it reaches the face of the piston and chamber how much more does the mixture gotta go?
Interesting read but IMo if it was worth its time and effort it would be conman practice by engine builders, and dimple tools would line the catalogs of Jegs and Summit Racing.
Posted By: 67_Satellite

Re: "Dimpled" combustion chambers? - 11/21/09 01:10 PM

I believe it's done to keep the boundary layer of air next to the chamber wall in motion.Golf balls are dimpled for the same reason.Lots of people will suggest building a "quench" chamber or leaving the intake port "rough" to accomplish the same goal.Got to keep the air and fuel in motion and mixed,large liquid droplets don't burn as well.
Posted By: ahy

Re: "Dimpled" combustion chambers? - 11/21/09 01:18 PM

There was a builder of BMW engines that used small steps instead of dimples in the intake port and bowl. I believe it was patented. As posted, the idea was to keep the boundry layer agitated and fuel mixed. I believe strategically placed steps also improved port flow. With the fuel better mixed there was less tendancy for detonation also. He did a lot of testing, both flow bench and engine to get it right.

I can say that the engines ran well... fairly high CR, low timing requirement and good power with simple parts.
Posted By: dizuster

Re: "Dimpled" combustion chambers? - 11/21/09 01:29 PM

Are you sure they aren't carbon deposite buildup holders to increase detonation?....

Posted By: 340Cuda

Re: "Dimpled" combustion chambers? - 11/21/09 03:48 PM

Funny I was just thinking about this the other day after a Myth Busters show (you would have to have seen it). I have always found the dimples very interesting, especially since Jim McFarland was a proponent of it and I have a lot of respect for him.

However the clean piston tops on the 455 really make me wonder. Any engine we have ever had that had much clean area on the pistons did not run worth a crap! As in it was slow.

Bill
Posted By: rowin4

Re: "Dimpled" combustion chambers? - 11/21/09 04:13 PM

Quote:

Wouldnt then make more since to dimple the intake runner on the intake, and the head intake runner? I mean by the time it reaches the face of the piston and chamber how much more does the mixture gotta go?
Interesting read but IMo if it was worth its time and effort it would be conman practice by engine builders, and dimple tools would line the catalogs of Jegs and Summit Racing.




Many years ago, at a seminar put on by Jack Roush, he stated you should leave the intake runners rough to break up the gas. Old technology? Why no blast the combustion chamber with course sand.

Posted By: BradH

Re: "Dimpled" combustion chambers? - 11/21/09 08:04 PM

Quote:

... I have always found the dimples very interesting, especially since Jim McFarland was a proponent of it and I have a lot of respect for him.



Speaking of Jim McFarland: http://www.pumpgastech.com/combustionlecture.pdf

Posted By: Sport440

Re: "Dimpled" combustion chambers? - 11/21/09 11:32 PM

Quote:

Are you sure they aren't carbon deposite buildup holders to increase detonation?....





Dimples = Carbon Anchors
Posted By: rt66jim

Re: "Dimpled" combustion chambers? - 11/22/09 02:54 AM

Back in the 80's when Ernie and Bill Elliott were the Fastest guys in NASCAR. This was suppose to have been one of their secrets.
Posted By: cheapstreetdustr

Re: "Dimpled" combustion chambers? - 11/22/09 04:54 AM

i had taken a jewlers dremel..and drilled holes in the valve seat just inside the throat ..
i pressed in small pieces of stainless wire..
to do the same....
we never got it wet flowed...but i still think it would work..

that and even putting stainless mesh over the intake gasket port opening...to keep things emulsified..?
i dont have the fixture to test it thoroughly..
cheapst
Posted By: ademon

Re: "Dimpled" combustion chambers? - 11/22/09 08:11 AM

I dimpled the plenum floor of my modified 71 stock 340 intake, also dimpled the floor of the runners about 2" in from where it meets the head. did it help any? not sure, did it hurt performance? bet not.
Posted By: BradH

Re: "Dimpled" combustion chambers? - 09/27/10 11:03 PM

back from the dead.
Posted By: vcummins

Re: "Dimpled" combustion chambers? - 09/27/10 11:31 PM

don't wast your time
Posted By: 70HemiGTX

Re: "Dimpled" combustion chambers? - 09/27/10 11:37 PM

Quote:

Wouldnt then make more since to dimple the intake runner on the intake, and the head intake runner? I mean by the time it reaches the face of the piston and chamber how much more does the mixture gotta go?
Interesting read but IMo if it was worth its time and effort it would be conman practice by engine builders, and dimple tools would line the catalogs of Jegs and Summit Racing.



My one friend works for a shop that does alot of sprint engines. They used to dimple the intake runners and intake ports of the heads. Don't know if they still do it or not. I'll ask him the next time I see him. Their theory was the turbulance would keep the gasoline in a gaseous suspension instead of it running down the bottom of the ports.
Posted By: BradH

Re: "Dimpled" combustion chambers? - 09/28/10 02:11 AM

Quote:

don't wast your time


V - Is this because you've tried it w/ no success, or because of what you saw while doing wet-flow testing, or ???
Posted By: dOOc

Re: "Dimpled" combustion chambers? - 09/28/10 02:27 AM

Let me add .....

Anyone do any mods to enhance swirl ? ... like maybe a direction-dam in the intake port ...??
Posted By: vcummins

Re: "Dimpled" combustion chambers? - 09/28/10 03:43 PM

Quote:

Quote:

don't wast your time


V - Is this because you've tried it w/ no success, or because of what you saw while doing wet-flow testing, or ???



I have experimented with this and it was A wast of time but I know that on A mopar head it don't work. so maybe not A wast of time if ya don't test things ya don't learn. The wet flow was horrible and was washing the chamber.and it looks like to me that it was doing the same thing on the poco chamber to..That head was cleaned (they claim they did not clean it) but it was cleaned by hand or it was fuel wash cleaned so it was running vary wet with fuel not good. the chamber should not look like that clean with black spots? I think not. looking at that chamber they stop the cut at the top of the plug. Not good I can see if the head was wet flow tested the fuel would flood the spark plug. the plug is to low (shrouded) Not good for flame travel and A big hole for fuel to puddle. the ground strap on the plug should never be by the intake valve.
The chamber should have A lite brown and dry.test like you would A spark plug shut off at the end of A run and pull plug go in and look at the chamber.

dorsal fins can help greatly to help swirl to direct air behind push rod junction. A stock mag head has one on the floor.

I know to much info sorry
Posted By: emarine01

Re: "Dimpled" combustion chambers? - 09/28/10 08:01 PM

It seems to me that fuel injection is the way to go..... Now having said that, I wont do it either.... Annular boosters seems to be an easy-er thing to test and fool with but when you think about it how do you atomize the pump shot from any carb any way, the dimples have some science behind it but the testing and results are hard to prove, then just think about the variables involved as per application... but it is a interesting topic
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