Have to write this down before I forget it. Has there ever been any studies done on the affect of dimples on a piston top and or combustion chamber dome? How does a boundary layer affect combustion?
I have no idea where that thought came from.
Have to write this down before I forget it. Has there ever been any studies done on the affect of dimples on a piston top and or combustion chamber dome? How does a boundary layer affect combustion?
I have no idea where that thought came from.
If you search around speedtalk there might be some answers for you.
Poor example:
The BMW engine shop Metric Mechanic has done a lot of work with dimples in the cylinder heads and ports. They used to have a bunch of information about it on their website but I can't find it there now, so I don't know if it's something they still do nor not. It has been a controversial subject with some people in the BMW crowd as to whether it works, but I recall they cited some studies that had been done by independent testing authorities.
Ha - yes there was, probably 25 years ago in a magazine i was reading....maybe Hot Rod or Car Craft at the time - not sure, but it was dimpling combustion chambers and the result was positive. its been a while and cant recall the specifics but i think that impacted the A/F suspension, a more unified burn was reported.
I remember there was an engine feature in Popular Hot Rodding for an Engine Masters Challenge Pontiac 400 and the builders randomly dimpled the combustion chamber as an experiment. The engine had hundreds of dyno pulls on it, and the pistons and chambers looked they had never been run, they were absolutely spotless
I read an article in a circle track magazine one time about dimpling piston tops, but only in certain areas, to move the flame front around and get more even combustion. It was a very clever guy who only revealed in after they passed a rule in the series that mandated stock pistons after a teardown when he was kicking ass. Apparently he went through dozens of sets of pistons until he figured out what worked. It was fascinating.
Ross provided the forged pistons that Johnston and Milano modified in-house. “We did dimple the tops of the pistons and the combustion chambers to help atomize the fuel,” he says. When asked about any empirical evidence that the dimpling did anything to actually help, Johnston referred back to a 409 Pontiac he built for a previous EMC competition. They tested that engine with stock-type chambers first. “It looked fat in areas and the combustion chamber had wet spots where it would puddle in there. I thought, ‘You know what, I’m gonna try this.’ Because I’ve seen some articles done on this but I’ve never seen any testing and nobody knows where to put these things, so I just kind of randomly made it look like a golf ball in the combustion chamber. We didn’t do anything to the pistons on that motor.” Between just the dimpling of the chamber and also changing the spark plug depth where the electrode would protrude slightly into the chamber, that engine picked up almost 40 hp and Johnston was sold. With the dimpling done to this 455, the pistons and chambers looked like fuel had never touched them. They were also able to run significantly less timing for best power.
https://www.hotrod.com/articles/0912phr-dci-455-pontiac-engine/
I would hotlink the photo too, but the Hot Rod Mag picture viewer sucks and won't let me.
EDIT: Kinda got them to hotlink, but they're tiny, because terrible picture viewer is terrible.
This thread made me think of the Somender Singe grooves that a lot of people got excited over.
I would think dimples could increase flame front speed but wouldn't they also cause hot spots/detonation if you're not careful?
In reply to NickD :
that's the article!! LOL!!
If it really worked the OEMS would be all over it on lean burn engines but its interesting for sure.
wearymicrobe said:If it really worked the OEMS would be all over it on lean burn engines but its interesting for sure.
Unless it turns out to be a case of "it helps, but not enough to justify the costs in a mass production environment" kind of thing. Especially if significant care is required to avoid creating hot spots and detonation.
rslifkin said:wearymicrobe said:If it really worked the OEMS would be all over it on lean burn engines but its interesting for sure.
Unless it turns out to be a case of "it helps, but not enough to justify the costs in a mass production environment" kind of thing. Especially if significant care is required to avoid creating hot spots and detonation.
Also, at least in the instance I shared, it's trying to crutch a 50 year old combustion chamber design. Modern heads/fueling designs may not need that assistance
wearymicrobe said:If it really worked the OEMS would be all over it on lean burn engines but its interesting for sure.
Having worked for OEMs, this just isn't the case. Tried and true usually wins. They'll spend money on direct injection or (back in the day) FWD or other promising things, but anything that might cause them emissions trouble is a non-starter. Direct injection had been proven to reduce emissions so they jumped all over it, but spending millions on R&D for an unknown is not something they typically try. They'll plug it into a computer sim and it spits out a range of possible outcomes that range between fail and panacea and skip the prototypes.
Myth Busters dimpled a Taurus.
stuart in mn said:The BMW engine shop Metric Mechanic has done a lot of work with dimples in the cylinder heads and ports. They used to have a bunch of information about it on their website but I can't find it there now, so I don't know if it's something they still do nor not. It has been a controversial subject with some people in the BMW crowd as to whether it works, but I recall they cited some studies that had been done by independent testing authorities.
Everything I've ever read by actual owners of MM engines is that they are usually noticably weaker than claimed when put on the Dyno.
Did Dan Paramore do anything along those lines? For some reason I'm ringing a bell there, but maybe not.
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