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| Engine Technology From the novices to the pros, talk about engine technology. Moderated by David Vizard, professional engine developer and well-known technical writer. |
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09-30-2007, 02:20 PM
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I just received a head prepared by Mike Holler for a turbo charged street car.
Mike used all of his tricks in attempt to generate maximum mixture motion; these include power linz in the intake ports, port bias to enhance swirl, rounding of all edges in the chamber and dimples in a dead area of the chamber. Here's a few pictures of the work:   
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09-30-2007, 02:59 PM
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Very interesting discussion!
I am curous as to how much mixture homogenation and fuel droplet size plays into this as it relates to pockets, wet-out, and layers in different chamber designs. How much is bore diameter an issue (especially in lower swirl 4-valve designs)? How much does this change from a 500+ci V8 to a small diameter shallow pent roof 4 valve chambered engine? Are these factors more important in drag racing than in road racing engines? What about highly loaded marine performance engines? What trends continue across all chamber designs and shapes? How much does fuel (various gasoline types, octane, SG, and burn rates) alter this? What about methanol or ethanol fuels? What about NA -vs- FI chambers? Variables out the Wazoo! What ones should we be concerned with most, and why? As for squish and quench... years ago, I took a piece of Pyrex glass and ground a chamber in it for a small bore two-stroke engine. I played with chamber shape, and squish clearance, %, and angles with it on a running engine. Very interesting, but more fun than informative until chamber pressure and crank angle could be logged. I find it interesting that many things that are common knowledge for two-stroke engine building seem to be "new" in some four-stroke circles. This may be even more true with current exhaust development, and especially the interest in square tubing. Quote:
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09-30-2007, 03:05 PM
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Quote:
Quote:
In cylinder Turbulance and Combustion Dynamics
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10-07-2007, 07:55 AM
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Hey fella's
In Cylinder Turbulance and Combustion. part three is in the works and well on the way to complete. DV
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10-07-2007, 04:03 PM
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Quote:
 Mike
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10-07-2007, 04:25 PM
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The article just came live. Though for me it raises more questions than answers.
 Dang it, now I can't concentrate at work!!Edit: I posted a question at the end of the article, but maybe it would be more appropriate to put it here, since the article should be more of an article and less of a discussion (that's what these threads are for). Excellent set of articles thus far. Thank you very much, Mr. Vizard!! The part about the red-hot intake valves hit me hard, though. Just to clarify, I'm generally more interested in the subject of lower BSFC's and better fuel efficiency than getting extra horsepower. A guy on the 'net known as Metric Mechanic grooves the face and back side of the intake valves to aid in fuel vaporization. Consequently it also has an effect on the boundary layer that can increase low-lift flow by about 5%, but that doesn't seem to be the predominantly positive factor. An engine with the "Surface Turbulence" valves installed needs as much as 20% smaller jets (when installing the ST valves, they also reduce the main's by that much). The engine acts like it's running rich if the fuel isn't cut back. I would assume that the increase in surface area on the chamber side of the valve would cause it to pick up more heat from the combustion process, while the grooves on the intake-side of the valve would help the valve dump more of that heat into the incoming air/fuel charge. The required ignition lead is reduced and detonation limits are stretched. Assuming this is true, could the 20% reduction in fuel be due to a 20% reduction in VE? In other words, the air is a full 20% less dense, and therefore needs the same reduction in fuel. Horsepower goes up, though. I would be forced to assume that this is due to better fuel vaporization and therefore a more efficient burn (causing less ignition lead to be needed and less detonation experienced). Following this theory, a "normal" valve wouldn't have as much of a fuel vaporization advantage as the ST valves due to the reduction in surface area (the ST valves can "catch" the fuel better, allowing the fuel to absorb more heat and less being lost into the air itself). Taking this a step further, a "normal" valve with a thermal barrier would have the advantage of not heating the air, much like the ST valve would be shielded from the air by the fuel. However, the ST valve should vaporize the fuel and therefore hold an advantage. Waddaya think??? Last edited by Pinhead; 10-07-2007 at 04:28 PM.
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10-08-2007, 06:21 AM
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Pinhead,
It is often dificult to comment on other peoples 'experiments' as the full charactoristics of the engine can be pretty much an unkown. I like the idea of the dimpled valves but the real question is - does the engine like the dimpled valves. As for atomization/vaporization I am inclined to think that the dimples produce- by whatever means - more mechanical break up of any wet streams rather than just adding vapor capability due to extra heat transfer area. In all I have not tried the dimpled valve deal but I just have a gut feeling it has sufficient merit to work. As for the carb re-cal with much smaller jets I am not really sure what to think of that. It could be that a better combustion process is producing a better scavenge wave from the exhaust and thats the reason for the smaller jets but really - at this stage - who knows? DV
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10-09-2007, 12:33 PM
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Jim Rowe (Metric Mechanic), has a patent on his theory.
Apparatus for the generation of turbulence in internal combustion engines - Patent 4976248 Notice he machines grooves in pistons as well as in valves. I can not see great value in this process other than for experimentation. Someone want to prove efficacy of this process? *********************
__________________
___________ Cammer
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