Anyone buy into this theory?

I'd think if this was an effective way to increase efficiency, you would see it in modern day OEM engines. Efficiency aside, would there be any performance benefits to a turbulent design?

It all sounds good on paper, but I'm skeptical. Some companies are now adding CNC turbulent designs etched into the CC, Ports, Pistons, etc...

Runners

Dimples
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Ridges
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CC Chambers

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Pistons


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That's weird...

I know companies usually leave the CNC tooling marks on the intake side so air/fuel tumble to mix better. I've never ever seen it on the combustion chamber or piston.

 

They do it in oem applications but not in the form of tooling but in the form of rough casting. From what I hear it mixes the air fuel better.

 

I guess I have 2 topics in the pictures above. I understand a turbulence layer on the intake runner could be beneficial. I'm more interested in its effects inside the CC.

Thanks all..

 

Combustion Chamber design is pretty specific for a given engine.

What a Carburetor Engine "wants" vs a Port Fuel Injection engine "wants" can be totally different in the combustion chamber.

For a while the catch word was SWIRL, then the catch word was TUMBLE, now the catch word was DIRECT INJECTION.

All of those holes in the combustion chamber do something. Deal is, Is it good or bad at a given point in the combustion cycle vs the engine's rpm point.

SWIRL is not good at some rpm points. TUMBLE is not good at some rpm points. Camshaft events at one rpm point may not be right vs a different set of points.

That is why OEMs have VCT devices on their engines. Why they have variable CHARGE MOTION DEVICES.

So to assume that a fixed rough finish or some golf ball dimples work everywhere might be a bit premature. JMT

Tom V.

 

Thanks for the input Tom.

I stumbled across this article today. They are using some “grass roots” testing methods, but it was interesting they suggested dimpling the head to assist with the “concentration of fuel wash and lack of movement”. They then go on later and suggest dimpling the pistons to "further assist in mixture quality."

http://www.hotrod.com/how-to/engine/ctrp-0309-race-engine-airflow/



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These were also relevant for anyone interested. The drop in EGT temps in the second link was note worthy for a FI application.

http://www.hotrod.com/how-to/engine/...uench-pistons/

http://www.revsearch.com/grooves/grooves.html

 

A guy named larry Widmer was big on the Dimple Deal in the combustion chamber about 20+ years ago.

Tom V.

 

I always relate swirl to runner length. I do know that it does create a swirl effect causing better combustion. Coming from a long runner intake with 11" runners to 3" runners was a huge difference in timing curve. With long runners I run 10-11* advance and with the short I find myself running 30* at idle to keep egt's down.

 

Swirl is basically the air flow rotating in a circular fashion around the piston top.

Too little swirl and the fuel drops out of suspension. Too much swirl and the winds up on the combustion chamber walls prior to arriving at the top of the stroke.

Tumble is basically air flow doing summersaults in the combustion chamber. High tumble works at some rpm point but not at others.

What you were seeing with your short runner vs longer runner experiment was Ram Tuning. With the very short runners there basically was no Ram Tuning.
With the 11 inch runners there was tuning at some parts of the induction cycle.

The OEMs have used Charge Motion Devices that fit in the runner and direct the air given ways for improved combustion. Some were to improve Swirl, some were to improve Tumble.

Most things are like installing a 1.00" camshaft lift in a gas engine. When you have all of the other pieces it works pretty good. Put it in your little street/ strip car and you probably will have to change
a lot of other things to make it work.

Rarely does one concept buy you very much. The OEMS deal in 1% to 3% gains as a big thing. They have all of the other stuff already figured out.

Boosting being an exception. Big strides there because a lot of people were not doing it in a big way correctly. Ford did boosting in 1979 on a 2.3L Mustang.
Ford is doing boosting on a 1 liter 3 cylinder engine today that is the best in the game the last 3 years of international voting. Takes money but also takes time
to get all of the pieces tou need to make a concept work. Swirl or tumble is one small part of the pie.

Tom V.

 

I understand with a properly designed port that something like dimpling wouldn't be needed. Looking at the nascar/indy/etc shows this to be true. But if I were to add dimples to an OEM 6.0 liter LS casting head many tests have shown repeatable gains with the use of dimples in NA applications. CAn anyone think of a reason these gains wouldn't also apply to a forced induction setup? Any reason they could cause problems?

I plan on running an untouched 317 casting this year on a very mild 6.0 LS engine at around 20-25lbs of boost. Should get me in the ballpark of around 900 flywheel. Unless someone can think of a reason not to dimple the head, I had planned on trying it.

Larry Meaux had some positive thoughts on this subject.

http://hotrodenginetech.com/pipemax-creator-larry-meaux-on-race-engine-head-porting/

 

https://www.v6mustang.com/threads/my-current-build-head-work-etc.278414/#post-4832158

This guy is talking about dimpling. Read it the other day.

 

Thanks for the link.

I think I decided to try it. I could care less abut the tiny drop in compression. I'm already higher compression wise than I'd like my build to be. I see no reason a few dimples in the CC would cause my detonation threshold to change. (though I could be horribly wrong). And I'm not concerned about damaging my $120 "race heads". I'll have nothing for comparison really, but I'll post up some pictures before and after and report any odd looking combustion when I have the heads off next.

 

the dimples are basically a continuation of the same concept you are already familiar with in the intake port, a precisely roughed surface doesnt create "turbulence" it creates a boundary layer. rough slower moving air is navigating these pockets or ridges or coarse sanded surfaces or dimples, and in effect creating a smooth surface for fast moving air to ride along. the dimples you did on your heads are an extension of that same process in the combustion chamber...

in regards to Tom V's quick name drop about larry widmer, it seems hes given up that design philosophy and is still pretty hardcore about tumble... see his website at endyn or theoldone and look closely at the heads and matching pistons in his "roller wave" (read: lots of tumble) designs... they claim that utilizing their specific engineered designs, they dont even bother calculating static compression anymore because no one would believe they are running (and i almost hesitate to say this) 17:1 and oftentimes alot higher static compression ratios with these setups... on pump gas.... in street cars... the combustion chamber modifications we are talking about here are all just evolutions of the singh grooves, and like Tom said, work on some motors, some times, somewhere in the rpm band. on an advanced cylinder head design like the LS motors have i dont think you will see the gain that dr singh did on his two stroke TATA motors scooter bike junk box heads.

another thing to point out, in relation to your question about using these with boost... is the possibility not of lowering your compressin ratio, which is no real big deal considering the size of the holes were talking about, but you should consider the effects it has on the surface area of your combustion chamber, how that equates to combustion efficiency from a heat and cooling aspect.

personally, if youre going to do some experiments before you get your thugged out aftermarket heads in a few months, i recommend you try some sort of ceramic thermal barrier coating on your valves (face and stem) and see the kind of improvements that nets you. i am willing to bet your 4 lug front runners itll be more quantifiable than the dimples.

all we ask of you, forcefed, is to take good notes and document your findings to try to answer all the questions you and everyone has been asking to best of your abilities... obviously we arent scientists and this isnt mythbusters, just have a good record of what you did and how it effected change!

 

I think the dimples will have a greater effect in the CC because they will be exposed to raw fuel. Should have the 'spoon under a faucet' effect and help eliminate areas where fuel concentration/puddling are a concern with OEM castings. (especially at low engine speeds) As said above with a race oriented port design I don't see dimples having a positive effect.

In my case I would be glad for any reduction in compression. If I had purchased my short block parts new, I would have targeted 8.5:1. Picked up my short block cheap though, so I had to roll with what the previous owner picked out. (around 9.8:1) With boosted engines I prefer low SCR's. The added heat one additional point of SCR produces is crazy when compared to a pound of boost. Lower SCR's provide a large tuning window and are more engine friendly in general. Being an amateur shade tree hot-rodder, having a large margin of error in the tune is always a plus! I build tons of boost on the line before the car ever starts moving, "off-boost" performance isn't a big concern.

I don't have the time/resources to play with coatings in the CC. I only did this because it was an easy free 'mod' I could do myself with minimal time/effort. Unfortunately I'm a poor candidate for any kind of good data. New engine, new cam etc. I'll have no before/after comparisons on drivability/performance. I'll only be able to look at the CC for cleanliness as evidence of a cleaner more efficient burn. I took many pictures of my 5.3/4.8 piston faces and CC's last year for comparison. With the ethanol and water/meth injection The CC's already looked pretty darn good. So I may learn nothing from this experiment.

Hoping for improved idle and ideally improved burn/flame travel at big boost levels with less ignition advance. It may turn it into a knock happy monster... I've never see the dimples tested on a FI engine.

On a side not my 4-lug front runners happen to be for sale. Shoot me a PM if you want a deal.

 

you know if you have the same bolt spacing as my 280zx? and i hear you 100% on all counts, lower compression isnt necessarily a bad thing, and im no professional car builder guy either, atleast 50% of my knowledge was read in a book at some point so this is all theory were talking. as far as coating the valves, i dont think it would be too expensive you should look into it... the temperature of the intake valve is probably significant, having a large portion of its surface area exposed to the combustion process. think of the effect that has on the fuel air mixture as it has to whip off the valve and valveseat into the cylinder... a thermal barrier there would probably be worth its weight in gold for ease of tuneability and detonation resistance and REAL LIFE wet flow improvement.

you have to take everything measured on a flowbench, including wet flow testing, and only compare it to what others have observed on flowbenches under like conditions. two things in life ive never seen before is a UFO and whats goin on in the combustion chamber when its business time. all the cold non dynamic measurements we take are merely indicators to what may possibly occur... there are not representative of whats actually going on in there.



ken, i never read that patent before that pretty interesting, i must have been explained "the fisher price version" of whats happening there. thanks for the heads up.

 

I can't believe the intake valve temp. will have a large effect on the CC temps as a whole. I'd think it would be a drop in the bucket when compared to something like adding a point of compression to the mix. I'd guess a little water injection would be much more effective at dropping intake valve temps.(just a guess though.) I agree every little bit helps, but I don't feel a slight drop in intake valve temp is going to change your detonation threshold a noticeable amount.

Here's a cool article about a 'new' type of wet flow bench. Uses ultraviolet light and dyed fluid so they can see vortexes and all. After reading this article the 'dimple theory' continues to make sense to me. Sure wish I could see a pre and post 'dimple' flow on the bench they are using!

http://rehermorrison.com/tech-talk-40-wet-flow-revelations-the-monsoon-inside-your-motor/

 

We do massive amounts of computer analysis, single cylinder testing, and multi-cylinder testing (as related to Swirl and Tumble and other fluid/air and what is happening in the intake manifold and combustion chamber).

I will say that few flow concepts work everywhere in the rpm range or cylinder head concepts. You can have too little swirl, too much swirl (causing fuel holes in the mixture), too much Tumble, too little Tumble, etc. Direct injection at very high pressures seems to work but even on that deal there is debate on where you put the DI Injector in the cylinder head (Near the spark plug, near the block and head gasket, etc).

Tom V.

 

regarding the valve temperatures, theres some anecdotal evidence that the temperature of the valves can be lowered by atleast 100* temp drop when you coat it, vs uncoated in a hard run street strip combo naturally aspirated. thats no small potatoes.