crcain

Hi Ted... so you are making two distinctions...

There is cylinder pressure which is created by a higher mass of charge air, which is then compressed on the compression stroke, and then when ignited there is more air to burn, so peak cylinder pressure is increased from more charge air all things being equal. More mass charge air is what you call "mechanical" cylinder pressure?

Then there is cylinder pressure created by advancing ignition timing so ignition occurs earlier, which means that the flame front will create peak pressure nearer to the optimum point in piston travel. But the advancing of ignition timing does not necessarily create more pressure, it just changes when peak pressure occurs. However, if peak pressure is moved to happen earlier, is there not less room in the combustion chamber as the piston is higher up. And less room means more pressure? When you add timing, you get closer to det. Why does the car det? Because more pressure (therefore heat) is being created.

Now I'm still back to my basic question... it seems to me from my basic understanding, both are valid ways of making more power. Why does the move to the "better" intake manifold yield more power safely than the adding of timing? There must be some inherent physical charecteristic of the system that has been improved besides "more air" right? Somehow more air is better than more timing. Why is that?

Ok now I'm upset at myself for not figuring this out yet. I know it's simple... generally more boost means more air... and adding boost and retarding timing makes more power. But I just don't understand why because it seems they both increase cylinder pressure.

I guess the answer must be the following... the increase in cylinder pressure, and the movement of the peak of this pressure towards the optimum piston position, yields more power, however, the increase in cylinder pressure achieved by more mass charge air yelds greater gains than of what ignition timing can yield. Also, the increase in pressure from more charge air is less prone to detonation because.... (this part I don't understand quite yet).

crcain

To simplify all the babble above...

We are in a situation where, we add timing and the car dets. Presumably we det because cylinder pressure has been increased. Yet we add the intake manifold, which provides more mass air for the same boost level, and this in turn creates cylinder pressure, yet we don't det, and make more power.

Why didn't we det with more air.

crcain

SWOLN... what about the new intake manifold makes the system more efficient apart from more air at same boost?

PVD04

iTrader: (23)

Before you think about power/pressure from the ignition, think about what is happening in the cylinder. You have a certain amount of air and fuel which provide a certain amount of stored energy. The better intake manifold provides more stored energy than the original manifold. In this situation, regardless of your ignition timing you have more stored energy available. Because of this, if you keep your ignition timing the same your peak cylinder pressure will be slightly higher. If you retard the ignition timing slightly, you can keep the peak cylinder pressure the same while making more power due to more energy provided by the original charge. Hopefully I didn't get too wordy and confusing in the way I typed this.

-Paul

crcain

I think what your saying is, peak cylinder pressure is not the only measure of power. Meaning you can keep the peak the same, but the overall energy used to push the piston is greater. This might be the answer I was searching for. I was only thinking of peak cylinder pressure as the only measure of power generation.

So you can have X amount of energy, and tweak the timing so you get as good of a peak as you can get, but when you have X + 1 energy, you can retard timing to get the peak back down to where it was, but your overall energy measured against the piston is greater?

crcain

And it's those cylinder pressure peaks which get you to detonation.

PVD04

iTrader: (23)

Correct, because the fuel can only take so much pressure and temperature before it spontaneously ignites (detonates).

PVD04

iTrader: (23)

What you're looking for is not maximum peak pressure, but maximum average pressure after TDC. You can create the highest maximum pressure by igniting the mixture early enough that it is nearly completely expanded by TDC, but this will severely hurt power and probably destroy the engine. What you need is enough ignition advance to allow the pressure rise to come while the piston and rod have their greatest mechanical advantage.

crcain

Yep it was just that peak versus average notion that I just wasn't understanding. It makes total sense that more air will facilitate greater average pressure. Thanks for setting me straight!

crcain

Ok I should be installing the HKS inlet tomorrow.

Since you guys helped me get over my retarded notion of only thinking about peak cylinder pressure as making power, I wanted to discuss further how a new intake manifold will effect the tune.

I'm swapping my Magnus + 63mm TB for HKS Inlet + q45 TB.

Now let us assume the HKS will make more torque everywhere. This means that for the same boost pressure, more air is filling the cylinders. Now if more air, this means, if I keep ignition advance the same, peak cylinder pressure will rise. Therefore, it seems reasonable that I will need to take a degree or two of ignition out of the map on boost probably?

But the increase of air will allow for a greater amount of work to be done against the piston over the entire power stroke which will offset the loss of the degree or so of advance?

Am I on the right track? Practically I will simply make sure I have sufficient margin from the car det'ing but I want to understand the theory before I go for it.

Ted B

iTrader: (6)

Don't get bogged down with static parameters like manifold pressure and ignition advance. So long as there is increased mass airflow, all else being equal, whatever ignition setting is required to reach the same margin with respect to the detonation threshold should yield more power.

crcain

Yes I understand thanks for the advice Ted.

JC evo1

what are you using to detect detonation?

crcain

Use det cans that my tuner showed me how to make a couple years ago. Pretty simple stuff... consists of copper pipe bolted to the cylinder head, and then a rubber hose stuck in the copper pipe, leading to two holes drilled into a pair of ear defenders. Partial pic here of the ones I made:

http://clubctrl.com/headphones.jpg

JC evo1

so you just use the cans when tuning but what about when driving, do you have aem?