Mase

actually, you lose power under detonation.

kpt4321

Please explain why then.

On the edge of detonation, which is presumably where he is since the car has been running like this for a while, you're very close to the maximum power production for a given setup.

Especially since we're only talking about timing advance here, and not A/F ratio.

kpt4321

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Mase &raquo;</TD></TR><TR><TD CLASS="quote">actually, you lose power under detonation.</TD></TR></TABLE>

So, uh....

Are you planning on explaining this anytime soon, or can we just assume you were joking?

That's one hell of a generalization.

kpt4321

Hey tough guy! What's the matter? You're afraid to answer the question here, but you can bring it up in other threads like you're some kind of badass, and pretend that you know it all even though you never answered the question?

kpt4321

Since Mase is too cool to talk about this, I'll give you my take on it.

Power is maximized when you have the most pressure in the best places during the power stroke. Of course, that last sentence sounds a bit silly, but I put it like that for a reason. In a lot of cases, people will say you make the most power when you have the most pressure; however, due to the dynamics of an engine, it's actually more comlex than that.

Since the rod is a moving lever, there is a certain point at which you want to exert as much of the pressure as possible. In general this is going to be around 15 degrees after top dead center, which is generally the point where you will make the most power if the pressure curve peaks there. However, you obviously can never exert all of the force of combustion on the crank at one point. As such, it's not just the peak pressure that matters. Not only does pressure under the curve matter to some extent, it matters where on the stroke that pressure occurs. This means that not only will the highest peaks pressure not necessarily make the most power, but the highest pressure under the curve will not necessarily make the most power either.

A good example of this is preignition (which is NOT the same thing as detonation. It can lead up to and often causes detonation, but the end result of a preignition event is very different from the end result of a detonation event that occured without preignition). When you have preignition, the cylinder pressure skyrockets through the roof, but you definately won't make more power. This is because the vast majority of the pressure occurs at a time when the piston and rod do not have a good mechanical advantage on the crank.

I'm rambling again, my apologies.

Anyway, about detonation.

Detonation on pump gas occurs primarily when the pressure and temperature of the mixture in the cylinder get high enough such that the flame no longer propigates linearily from the spark plug; as you light the mixture with the plug, the temperature and pressure of the mixture is being increased due to the compresion stroke, AND due to the quick expansion of the burning gasses. If the gas reaches it's autoignition point at a time earlier than desired for proper flame front propigation, you get detonation.

So, when does mild detonation occur? In a lot of cases, mild detonation will occur around or shortly after the pressure peak. This causes a slight oscillation of pressure after the pressure peak, and will also cause the remaining materials to be combusted faster, and end earlier.

The average pressure during these oscillations will generally (again, this is a case of mild detonation) be around the same or slightly higher than the pressure that would have been generated had the flame front continued through the cylinder smoothly. In addition to that, if the materials combust faster, you move the pressure curve a little bit higher and a little bit closer to the power peak, and in addition you move it "up" the power stroke to a lesser crank angle after top dead center. The combined effects of this possible higher average pressure (during detonation) and the force being moved to a point of a higher mechanical advantage could be more power.

When you start having serious detonation (of the type that explodes motors), the peak cylinder pressure gets much higher, and the curve on either side of it gets much steeper. In a lot of cases, the peak pressure will also move to a point earlier in the crank's rotation, which makes for less power and more motor parts shooting through your block.

Mase

you're a tool bag. seriously. i didnt even read your post.

im not gonna sit here and waste my time, anyone can search the internet, just like u did, and find all of that out.

plain and simple. right before detonation occurs, power drops off. its very simple, go take your hunk o junk car, put it on the dyno, start adding ignition timing, power will go up and up, then all of the sudden, it wont make anymore power, actually lose a little, then here comes your detonation.

if you think im gonna sit here and argue over this ****, you're crazy. you think youre big and bad that i dont answer to you? im actually tired of proving people like you wrong, i have much better things to do w/ my time, so go ahead and think you're smarter and bigger stunna.

now, do yourself and all of us a favor, go out and do something with your life. quit wasting banwidth with your garbage.

kpt4321

A dare you to find that on the internet. You won't because I didn't.

Why is it that people just assume that since someone has good information, they found it online? Maybe (gasp) they actually learned it somewhere?

I explained why it's true. Unless you can prove otherwise, I stand by it.

kpt4321

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Mase &raquo;</TD></TR><TR><TD CLASS="quote">now, do yourself and all of us a favor, go out and do something with your life. quit wasting banwidth with your garbage. </TD></TR></TABLE>

From someone with 4 times as many posts with me, I think this comment is a little hypocritical.