Codeblack

no! don't shut up, lol.. I think that you are on the right track deconstructing what Jim was saying, both of you guys are (the post was for him btw, but i really liked your reply). I think i could speak for quite a few saying there are several fairly abstract guys around here. teheh[sm=wink_smile.gif]
and yea, I am also under the impression that dynamic compression is the average max pressure accumulated while revving

and thanks! well said UD, hopefully Jimmy will confirm semantics, lol... just kiddin'

SAVAGEJIM

SManMTB is correct, the phrase "dynamic compresion ratio" is not anything that actually exists in physics and real life. It was a phraseI inventd to try to express that more fuel-air being packed into th cylinder can produce more pressure and more bang at the point of ignition.

What SManMTB said about trapped compression ratio is correct. Our loop scavenging 2-stoke engines use the trapped comprssion ratio as far as the engine actually producing power and torque.

The typical whole compression ratio, which is called geometic compression by the way, is the compression ratio we all are familiar with: the compression ratio that uses the swept volume from piston at BDC to TDC.

ugly duck

Not even close. It's a phrase most engine builders use in the real world. You maybe developed the idea in your head, but believe me it's been used for YEARS.

Codeblack

aww.


can I ask a semi-off topic question? What is ABC, ABL and ABN sleeving? do all these vary greatly with port geometry or metals used for sleeves?

SManMTB

ABC, ABL and ABN indicates what materials are used for the piston and liner.
ABC means: Aluminum Piston, Brass Liner, Chrome plated
ABN means: Aluminum Piston, Brass Liner, Nickel plated.
ABL is basically OS's way of saying ABN since ABN has a bad rep.


ABN is not as durable as ABC.

Codeblack

you're my hero

SManMTB

OK, looked at wikipedia and yes the term does exist and from what I can see 'Dynamic Compression Ratio' = 'Trapped Compression Ratio' if you look at how it is defined.
So now we can move on but we should still use the terms in their correct ways to avoid serious confusion.

Now I got to go. I need to raise my compression ratio of the wing to get better lubrication down the straight. Otherwise the clutch bell will oversteer in the corners.

SManMTB

That goes for cross flow 2 stroke engines too.

ugly duck

lolz

Codeblack

ohh be nice....

SManMTB

LOL

SAVAGEJIM

Right then, since my use of this phrase has stirred you up, I decided to do some net research and found some useful info.

As the way I was using this phrase, referring to fluid dynamics increasing chamber pressure, this is not correct. I qoute from the following link: http://www.kennedysdynotune.com/Dyna...ion%20Tech.htm

"Note: there is some confusion about use of the term "Dynamic Compression Ratio". Some people use it to refer to the characteristics of an engine combo running at high speed. In that case, the engines volumetric efficiency will have a major effect on cylinder pressure. In this case, a larger cam will increase cylinder pressure when within its' rev range. Thus, more power and more cylinder pressure will be created. We prefer to think of this concept as "cylinder pressure" to avoid confusion. "

What SManMTB said is correct about trapped compression ratio, and as far as 4strokes, the true compression ratio at the instant all the valves are closed is what the phrase "dynamic compression ratio" refers to.

It would have been more useful if you actually said where you got this info instead of coming out so strongly with such a phrase as "Not even close."

Other useful links that descibe Dynamic compression ratio versus geometric compression ratio (what the indsurtry calls "Static compression ratio"):
http://www.empirenet.com/pkelley2/DynamicCR.html
http://www.hotrod.com/pitstop/hrdp_0...ion/index.html

There is even a neat calculator progrm to calculate compression ratios:
http://www.kb-silvolite.com/calc.php?action=comp

ugly duck

haha, I'm not stirred up at all. I'm only saying that you didn't invent the phrase because it's been used in many other circles for years. And again, like I said, you may have developed the idea by yourself and chose to call it "dynamic compression ratio" - I won't argue that - but by far you weren't the first to think along these lines or call it that. I'm not saying that you're using it wrong or trying to correct you in any way other than that.

I would appreciate a bit of credit, though - if I'm getting in your face, I'll let you know it. I've quoted what I needed to quote and commented on that - period. Don't take it personally.

SAVAGEJIM

No need to apologize fo correcting me or anyone here, afterall, we are all here to learn and pass on as much correct information as possible. And credit indeed you deserve for posting of how the industry uses the phrases "dynamic compression ratio" & "static compression ratio." But bear in mind we are people who will want some verification of information since we are of the inquisitive minds. So, referrencing a source or two or even the simple mention of "I am an automotive mechanic" or whatever would definitely help prevent alot of second guessing by many of us.

Regardless of how the industry uses these terms, they are of course confusing and by straight physics incorrect phrases. The way I see it, the industry should scrap these terms and do the following:
>>What the industry calls "dynamic compression ratio" should be called "true compression ratio" or "trapped compression ratio," either of these two phrases are correct in their description in what is happening.
>>What the industry calls "static compression ratio" should be called "geometric compression ratio" or "swept compression ratio," static implies the piston is not moving and it is at first intuition hard to imagine how it is possible for a reciprocating engine to compress anything when the pistion is not even moving.

Just a bit of advice concerning your use of the phrase "Not even close" in your post, you could have left those three simple words and your post would have sounded much more neutral and freindlier. Such phrases can risk a flame war (at the very least, leaving out such phrases will not put the other into any sort of discomfort).

dayglo

u guys may need to think about getting girlfriends. just a thought![)]

Codeblack

walk away before you get degraded big time

SAVAGEJIM

My girl actually is interested in my RC facination, call me lucky I guess. Whenever I'm out bashing or in with a dremel porting and modding my engines, she is inquisitive about the hobby

dayglo

don't worry, i ran away from this one. although i like being degraded, so let it begin please. just sayin some people in here are way to serious about this stuff, or should i say "terms" and it cracks me up. i think they just need to relax alittle. thats all. now degrade.