What modifications do in terms of tuning... Part 1: Intake Manifold
 

Just thinking about this lately... let me give an example.

Let us say we have a totally maxed out Evo Green setup, except he is running a stock intake manifold. Now let us assume his car is mapped perfectly.... and let's say his pump fuel map is always just a couple degrees from det and he runs 12.0 AFR at full load.

Now he goes and bolts on a "better" intake manifold. Let us say this means it makes peak torque slightly earlier and the torque and hp curves are raised by 30 ft/lb and hp each.

Presumably, if he is on a speed density system, his AFR's go slightly lean, and the car runs faster. A bit of fuel is added to the map, the AFR's are back down to 12.0 now.

Here is my question now... what has happened to his perfect and exact "2 degrees from det" safety margin? Naturally you'd think, hey, we just made more torque, cylinder pressures are higher, therefore we probably need to pull timing a bit to get back that safety margin. But I'm thinking this logic is probably flawed.

Now if the intake manifold had somehow relieved back pressure, or cooled the intake charge, I might say, well hey it may have actually helped fight det because of those attributes. But the intake manifold does neither, but I know it does other things but don't understand them well.

Would love to hear your guys thoughts.

bump this one time to see if i can get anyone to play along.

I was thinking maybe a "better" intake manifold would allow for a better mixing of the air / fuel mixture, and therefore this might bring down intake temps? Also perhaps it ultimately allows for a smoother burn?

Just trying to figure out this basic question... you have a car maxed out in terms of timing, and then you add the intake manifold and this allows for more charge air to get fill the cylinders (more power). This more charge air presumably means more cylinder pressure... so is it natural to think perhaps a degree or two of ignition needs to be taken out from adding the part?

Oh just thought of something else, if the "better" intake manifold creates more incoming air velocity through the intake ports, then what does this mean during scavenging on valve overlap. Hmm, maybe nothing really. But if you fill the cylinder with more air, presumably then more air in cylinder means more exhaust gas velocity, which means greater scavenging.

Hmmm :updown:

If the intake manifold changes mechanical efficiency in one direction or the other, anywhere in the usable rpm range, ignition timing requirements will change. Where the change results in greater torque, the ignition timing will need to be retarded. Where the change results in lesser torque, the ignition timing will need to be advanced.

Yes! I got Teddy B on the hook here to answer all my questions :D

If you say an intake manifold makes more horespower, this means torque has increased somewhere to account for the horespower correct?

And so if we say more torque was made by adding the intake manifold, is it safe to say, if you measure a before and after gain, without adjusting ignition timing, that the net gain might be over inflated due to the fact that ultimately ignition timing needs to be brought down to keep the same safety margin from detonation?

What confuses me a bit in all this, is that you have stock turbo cars at peak torque only able to run let's say 5 degrees advance at peak torque and making 400 ft/lbs, then you have stroker GT35R cars making like 600 ft/lbs and potentially can run the same amount of advance. But I guess the reason this is possible is a) less exhaust back-pressure, b) cooler intake charge, and perhaps c) the fact the torque peak is made at a higher rpm which allows for more advance just becuase things are happening more quickly?

And then of course it's a stroker too which automatically makes more torque because of the longer stoke crank?

Ok I've figured out the essence of my question... I think. :D

Before the intake mani, we are tuned to perfection, we simply cannot make more torque without running into det. This means more cylinder pressure equals detonation.

Now we add the intake manifold which ultimately just let's more air flow into the engine for any given boost level. Now more air means more cylinder pressure. But weren't we just a moment ago at the verge of detonation when cylinder pressure increases?

the increased airflow would lean out the mixture, and require more fuel. The resulting additional air and fuel would then increase cylinder pressures, this making more power. You are also forgetting that the ported manifold reduces pumping losses, thus improving efficiency.

An increase in torque at any rpm increase hp at that rpm. Hp is just torque with rpm considered.

The motor makes a certain amount of torque at a given rpm, at the detonation threshold. If the manifold delivers more VE, it increases cylinder pressure, which causes the air/fuel charge to burn more quickly, which reduces the detonation threshold. So, ignition timing comes down a bit, but torque (and hp) go up.

An engine that makes peak torque at lower rpm will use less ignition advance than an engine that makes the same torque at higher rpm. When the piston speed slows with respect to the flame front, the ignition needs to be discharged closer to TDC.

Aby has done this exact thing to his EvoGreen set-up (adding an aftermarket IM). Perhaps he'll see this thread and chime in.

Ok so I understand most of that I think.

But we can increase cylinder pressure before adding the intake manifold by advancing ignition. But we don't because the motor will det. Then we add the intake manifold and it increases cylinder pressure. So presumably we det or come closer to det, so we pull timing.

Why has increasing cylinder pressure by adding the intake manifold provided power while advancing timing didn't?

Is it because what Vapor mentioned about pumping losses? Meaning at a given boost pressure, the turbo does not need to work as hard to provide the same volume of air. Therefore the wastegate is more open, therefore less back pressure, therefore less chance to det?

Advancing the ignition timing does not get more air into the engine. It does not increase mechanical cylinder pressure. Don't confuse mechanical pressure with the pressure created by combustion. All it does is ignite the air/fuel charge earlier, which potentially creates peak combustion pressure before the optimum point in the piston's travel.

The size of the turbo (both compressor and turbine) is a separate matter.

Interesting theories.......................I think someone should post some logs from their testing of this, it won't be me though.

I think that explains it Ted. I never thought of the distinction between the two types of cylinder pressure. I'll think about this more and see how well I can digest the info you have given. Thank you.

Hi Dave... I'm just making my best effort to understand this stuff as I will be swapping Magnus inlet for the HKS soon.

:) just learned new things... great topic

Okay I'm in :updown:

2 things that I can see as maybe a flaw apart from where I see you are taking the discussion.

One being that, if you have a "better" manifold, one would tend to see the initial torque being shifted later in the rpm band, not earlier. I think we have seen this in DB's manifold tests. Every one was compared to stock and every aftermarket manifold lost initial hp and tq.

...but lets say hypothetically, one could achieve what you are asking for. Your map is still skewed because all the cells the were at peak tq and hp have now been shifted negatively(on the x axis, to the left) of your map. So, technically you need to recalibrate to a new map and take into conisderation your changes.

My take on your theory is this. As long as you can achieve cooler temps, through efficiency or cooler fuel or whatever you'll make better hp and therefor more tq. In your "better" manifold it would be efficiency that got you the torque increase, along with the extra air. The additional air would also help to absorb some of the heat, which helps make more torque.

Someone smack me if I'm talking out my butt.

Random thought occurs here: Anyone, use anything to cool their fuel?