Correct way to obtain IVC

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Oct 17, 2006 | 01:16 AM

Beast96Z

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From: Shreveport, LA

Correct way to obtain IVC

Let's say that a givin intake tract loved a 47* IVC @ .050". We have a few diffrent ways of changing IVC, such as duration, LSA, and IVC, but more importantly, which of these ways would make the most logical way of getting to 47*? If I have a bigger N/A motor, should I run a smaller duration cam and no advance to get the IVC were it needs to be, thus leaving me on the intake biased side of TDC, or run bigger duration and advance the cam to get the IVC, thus leaving me exaust biased of TDC, but a bigger duration. Being intake biased should have a better effect on a N/A application, but since I lowered my duration to get there, did I loose HP over the bigger duration/advanced cam? I guess in a nut shell, I'm asking does adding duration out weigh intake or exaust biased ICL's? What about adding duration and getting further away from the intakes "sweet spot" IVC? Can the added duration overpower the sweet spot?

The reason I ask, is because alot of people here run alot of diffrent sized cams with the same intake. Durations and ICL's can range from stock to extreme, HP can to. I've seen IVC's out of the sweet spot of these intakes make huge power, and I've seen cams in the sweet spot make big power. Just something I was pondering in my head.....

Oct 17, 2006 | 09:41 AM

Adrenaline_Z

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From: K-W, Ontario

Quote:

Originally Posted by Beast96Z

I don't know the process of custom grinding lobes, but I would think you can
spec a lobe to be ground with your ideal IVC and not change the lobe separation.

Quote:

Originally Posted by Beast96Z

If I have a bigger N/A motor, should I run a smaller duration cam and no advance to get the IVC were it needs to be, thus leaving me on the intake biased side of TDC, or run bigger duration and advance the cam to get the IVC, thus leaving me exaust biased of TDC, but a bigger duration.

Not too sure about your description of valve timing here, but based on what
I'm reading:

I think moving the overlap region more on the exhaust side of TDC is going
to totally kill the engine's ability to scavenge the chamber. It may end up
pulling exhaust gas back into the chamber during lower to mid range RPM
as the piston begins the intake stroke. The exhaust valve should begin to
close fairly soon after TDC to allow the intake charge to be drawn in.

Quote:

Originally Posted by Beast96Z

Being intake biased should have a better effect on a N/A application, but since I lowered my duration to get there, did I loose HP over the bigger duration/advanced cam? I guess in a nut shell, I'm asking does adding duration out weigh intake or exaust biased ICL's? What about adding duration and getting further away from the intakes "sweet spot" IVC? Can the added duration overpower the sweet spot?

I would suggest selecting some cam profiles to clarify the question.

List the valve events, along with ICL to make your statement. Maybe link
a few cam cards. That would probably help everyone answer your needs.

Oct 17, 2006 | 11:54 AM

Beast96Z

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From: Shreveport, LA

Your right, that is kind of a word jumble to get through. I'll put it like this:
Cam 1. 230* at .050" with a 112LSA/112ICL = IVC of 47*
Cam 2. 236* at .050" with a 112LSA/108ICL = IVC of 47*
Cam 3. 252* at .050" with a 112LSA/112ICL = IVC of 58*

Cam 1 is in the intakes sweet spot and is intake biased.
Cam 2 is in the intakes sweet spot, but bigger on duration, and exaust biased.
Cam 3 is completly out of the intakes sweet spot, but intake biased, why do they still make power?

Is there a point when adding duration outweighs maintaining a correct IVC? At which point does advance become intake or exaust biased? I'd like to get a good understanding of getting the IVC in the correct way, then I'll move on to EVO.

Oct 17, 2006 | 12:28 PM

Adrenaline_Z

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From: K-W, Ontario

Quote:

Originally Posted by Beast96Z

Quote:

Originally Posted by Beast96Z

Cam 1 is in the intakes sweet spot and is intake biased.

Many things to consider here, and a short list would be:
- lobe shape
- other valve timing events
- other engine parts
- which RPM range and Peak is to be tuned?

If everything is truly optimized for this motor at a specific RPM range, then
changing any of the above items will result in a decrease of averge power
and/or peak RPM.

Typically, a cam designed with more duration and later IVC will help make power
at higher RPM.

As RPM increases, the time that the valves stay open decreases. If the cam
allows for the valves to stay open longer at a higher RPM, there is more time for air to
enter the cylinder.

If the valve timing continues to work with all the pulses and engine parts, the
added duration benefits the horsepower curve. There will likely be a loss in
lower range power (in a non variable timed valvetrain), and/or a shift in torque
peak (higher up the band) as a trade off.

Quote:

Originally Posted by Beast96Z

Is there a point when adding duration outweighs maintaining a correct IVC? At which point does advance become intake or exaust biased? I'd like to get a good understanding of getting the IVC in the correct way, then I'll move on to EVO.

IVC is RPM dependent. Later closing IVC's work better at high RPM. COuple that
with more duration, more overlap, SCR, etc. and you're tuning toward higher RPM
power.

Keep in mind, this only works if the other engine parts can flow well enough
to support the valve timing and the engine is built to spin at higher revolutions.

Last edited by Adrenaline_Z; Oct 17, 2006 at 03:51 PM.

Oct 17, 2006 | 01:05 PM

gun5l1ng3r

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From: Laguna Niguel, CA

Quote:

Originally Posted by Adrenaline_Z

IVC is RPM dependent. Later closing IVC's work better at high RPM.

Is this generally because there will be more duration as well, or does the actual valve closing later in the stroke advantagous at higher RPMs?

Oct 17, 2006 | 04:18 PM

Adrenaline_Z

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From: K-W, Ontario

Quote:

Quote:
Originally Posted by Adrenaline_Z
IVC is RPM dependent. Later closing IVC's work better at high RPM.

Quote:

Is this generally because there will be more duration as well...

In a case where a later IVC point allows for more duration, then generally yes.

In a case where the same lobe is put on a wider LSA, keeping a similar duration, then it's tough to call because overlap changes and then centerline
may also change.

Quote:

, or does the actual valve closing later in the stroke advantagous at higher RPMs?

If the later closing valve allows for more charge to enter the cylinder before
the pressure changes cause the charge to push out, then all is well.

The RPM, or mutliple RPM (harmonics) at which this occurs is based on how the pulses are
moving, how long of a period (time) is required to revert the pulse (inertia),
incoming mixture velocity (force).

Typically as piston speed increases, so does the incoming intake charge.
This can help overcome slight opposing pressure changes ABDC which allows
IVC to occur later as RPM increases.

Again, there's always a trade off. With a weak incoming pulse at 2000 RPM,
a late IVC is going to cause some of the charge to push out and reduce VE.

Oct 19, 2006 | 11:29 AM

gun5l1ng3r

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From: Laguna Niguel, CA

Quote:

Originally Posted by Adrenaline_Z

If the later closing valve allows for more charge to enter the cylinder before
the pressure changes cause the charge to push out, then all is well.

Can the charge continue to fill the cylinder while the piston is on its way to TDC?

I bet that the answer has to do with the speed of the incoming charge and that piston velocity (a highly debated topic lately) has a lot to do with the velocity of that incoming charge.