Can too much intake lobe area decrease performance?

[CamKing]

Nitro, what's the pressure you see in the cylinder and port from BDC to 90 degrees after BDC ?

[nitro2]

Nitro, what's the pressure you see in the cylinder and port from BDC to 90 degrees after BDC ?

Port pressures on something half decent at high rpm would be +3 at BDC and +10 peak somewhere approaching the (0.050") IVC. Port pressure > cylinder pressure for 30-40 (50) ABDC then port pressure and cylinder pressure are pretty close for quite a few degrees after that, then at the very low lift before seating the cylinder pressure >port pressure. As rpm varies the magnitude and location of the peak pressure varies some, getting higher and later as rpm climbs. Way into the overrev it mostly just gets later.

[CamKing]

Nitro, what's the pressure you see in the cylinder and port from BDC to 90 degrees after BDC ?

Port pressures on something half decent at high rpm would be +3 at BDC and +10 peak somewhere approaching the (0.050") IVC. Port pressure > cylinder pressure for 30-40 (50) ABDC then port pressure and cylinder pressure are pretty close for quite a few degrees after that, then at the very low lift before seating the cylinder pressure >port pressure. As rpm varies the magnitude and location of the peak pressure varies some, getting higher and later as rpm climbs. Way into the overrev it mostly just gets later.

How about with the valve removed?

[Roadknee]

In Camking's example posted above where a more aggressive cam reduced VE and output what was the cause?

(1) The valve opened too fast and disrupted cylinder filling during the first half of the induction cycle that could not be made up on the second half
(2) The cylinder was "overfilled" during the first half of the induction cycle, and the port and cylinder pressures equalized well before IVC increasing reversion and reducing VE
(3) Other?

[nitro2]

Nitro, what's the pressure you see in the cylinder and port from BDC to 90 degrees after BDC ?

Port pressures on something half decent at high rpm would be +3 at BDC and +10 peak somewhere approaching the (0.050") IVC. Port pressure > cylinder pressure for 30-40 (50) ABDC then port pressure and cylinder pressure are pretty close for quite a few degrees after that, then at the very low lift before seating the cylinder pressure >port pressure. As rpm varies the magnitude and location of the peak pressure varies some, getting higher and later as rpm climbs. Way into the overrev it mostly just gets later.

How about with the valve removed?

Without a closing valve there is no way to artificially boost the pressure going into the cylinder beyond the naturally occurring port pressures, so you can forget getting +10, think +5 or +6 as a peak. As you know the way the valve closes (not just the IVC number) will have an effect on the way the pressure rises in the port relative to crank angle and the resultant VE.

[CamKing]

As you know the way the valve closes (not just the IVC number) will have an effect on the way the pressure rises in the port relative to crank angle and the resultant VE.

Shhhh. Not so loud.

[nitro2]

As you know the way the valve closes (not just the IVC number) will have an effect on the way the pressure rises in the port relative to crank angle and the resultant VE.

Shhhh. Not so loud.

[nitro2]

The closing valve converts kinetic energy of the flow to pressure which is pretty obvious, and in addition to that a pressure pulse is supposed to be coming down the intake runner into the port/cylinder at about the same time, but what might not be so obvious is that in addition to the aforementioned, the closing valve also boosts the local magnitude of the pressure pulse as it gets pinched at the valve. It's pretty easy to take a very high VE and make it worse because several parameters have to be aligned just right to get the very high VE in the first place. It's easy to get moderately high VE because only some of the parameters have to be aligned right.

[Enigma]

The closing valve converts kinetic energy of the flow to pressure which is pretty obvious, and in addition to that a pressure pulse is supposed to be coming down the intake runner into the port/cylinder at about the same time, but what might not be so obvious is that in addition to the aforementioned, the closing valve also boosts the local magnitude of the pressure pulse as it gets pinched at the valve. It's pretty easy to take a very high VE and make it worse because several parameters have to be aligned just right to get the very high VE in the first place. It's easy to get moderately high VE because only some of the parameters have to be aligned right.

This sounds an awful lot like "the lift curve of the valve controls power, and too much (or too little) rate of opening (or rate of closing) can negatively affect power output." It's a shame that it took 5 pages of augmentative posts to get to what was posted on page one, which is: you can lift a valve quick enough to hinder power and torque.

[MadBill]

I'd summarize by saying that for most situations (not all, someone could likely build a 'square lobe' that opens too fast for any engine's gas dynamics), opening the intake as fast as mechanically possible (with matching adjustment to IVO angle) followed by a significantly slower closing rate designed to best utilize the kinetic energy of the low lift 'jet' is the hot ticket. Coincidentally, that's just how most of Mike's solid roller intake lobes are configured..

FWIW, Dynomation does a poor job of predicting power, absent 0.050" flow data...

[nitro2]

The closing valve converts kinetic energy of the flow to pressure which is pretty obvious, and in addition to that a pressure pulse is supposed to be coming down the intake runner into the port/cylinder at about the same time, but what might not be so obvious is that in addition to the aforementioned, the closing valve also boosts the local magnitude of the pressure pulse as it gets pinched at the valve. It's pretty easy to take a very high VE and make it worse because several parameters have to be aligned just right to get the very high VE in the first place. It's easy to get moderately high VE because only some of the parameters have to be aligned right.

This sounds an awful lot like "the lift curve of the valve controls power, and too much (or too little) rate of opening (or rate of closing) can negatively affect power output." It's a shame that it took 5 pages of augmentative posts to get to what was posted on page one, which is: you can lift a valve quick enough to hinder power and torque.

Hmmm...... to the best of my knowledge I have not provided any answer whatsoever to the question "Can too much intake lobe area decrease performance" question, not to mention the OP's question in the thread title itself, is worded in a peculiar way.

I have indicated that -1psi is not a relevant value, I have answered CamKing's questions, and I have tossed out the little tidbit about the closing valve also boosting up the local pressure of the incoming pressure wave. Hopefully someone found some part of that useful.

[RevTheory]

I tend to wonder what Kaase might have to say about this topic with his aggressive lobes on a 92 ICL

[Erland Cox]

Please explain to me what I'm missing. If you are experiencing the above scenario isn't it because you opened the valve too soon, not to fast?

It can actually be either, in most cases it's from opening it too soon, but not in all. I was working on a Pro Stock project a few years ago, and we had the cam working very well. It was well developed, and one of the fastest engines out there. On the spin-tron, the cam was good, well past where we were turning, so we decided to get more aggressive. I designed a cam with the same duration and lift, but wil more area. It was fine on the spin-tron, but lost 100hp on the dyno, and the CFM's were way down. I opened and closed the valve at the same spot, but I opened it too fast.

How did you correct this? With less duration or with less area?
And what is the reason for that?

Erland

[CamKing]

How did you correct this? With less duration or with less area?
And what is the reason for that?

We reduced the duration, and kept the velocity/acceleration rates the same.

[Erland Cox]

Did you reduce the duration only on the opening side if this was the side where you made the cam more aggressive?
Is the reason for this that the depression in the cylinder drops too fast and then picks up again as the piston speeds up?

Erland.