Intake closing

[Tom68]

I've always considered this the single most important event in valve timing.

The rest matters for a host of things but for power output with other rational numbers Inlet closing seals the deal.

I felt Power Nations latest test on their high comper test backs my belief ???


https://youtu.be/1mY5Z9r49xY
,

Cam.jpg

[Biteme]

They never optimised ignition timing on pump fuel, so it’s not a fair comparison

[Tom68]

They never optimised ignition timing on pump fuel, so it’s not a fair comparison

Yer, and putting race gas in I would have gone straight to 30 degrees then started adding.

[Walter R. Malik]

I've always considered this the single most important event in valve timing.

The rest matters for a host of things but for power output with other rational numbers Inlet closing seals the deal.

I felt Power Nations latest test on their high comper test backs my belief ???


https://youtu.be/1mY5Z9r49xY
,

Cam.jpg

The exhaust opening can be very important. especially with a deficient exhaust system.
I have actually seen engines pick-up top end power by "advancing" the camshaft, which points directly at the exhaust opening.

[F-BIRD'88]

Intake opening... Everything else follows that.

[Ks Fats]

The opening and closing points of both the intake and exhaust are application specific and to say one takes precedence over another (as a generalization) is nonproductive. I think Harrold (and a few others) just rolled over ...

[David Redszus]

The most important single valve event is IVC, followed by EVO.

But merely advancing or retarding a cam is poor practice since both events are affected.
And then we do not know which event was more productive.

Properly, IVC and EVO, must be altered independently to determine the optimum valve event timing.

In the video, the selection of fuels, a/f ratios, and their properties was casual to say the least.

A real automotive lab would chuckle and giggle at such practice.

[F-BIRD'88]

I built a 350 with 12.65:1 cr. It ran fine on 94 pump gas as long as spark advance was 27° btdc or less.

A whole nother story on 110 unleaded and 36° btdc spark timing.

[F-BIRD'88]

In the real world where most of us have to work with what we got, advancing/ retarding. the cam you got on hand can be very effective to getting the most performance from your engine/car combo.
Max what you got. There is no downside other than time spent tuning.

[hoffman900]

On a single camshaft engine, advancing / retarding the cam from installation changes all 4 events. I wouldn’t read too much into these tests.

[F-BIRD'88]

On a single camshaft engine, advancing / retarding the cam from installation changes all 4 events. I wouldn’t read too much into these tests.

A gain in car performance is a gain.
Observing a gain or a loss in * car* performance
is important, and informs, either way.

"Everything. effects Everything"

Especially if the ET slip matters.
Ignor that if you want.

[CamKing]

Intake Opening:
Too soon, and the port velocity will be too low.
Too late, and you won't have enough time to fill the cylinder.

Intake Closing:
Too soon, and you won't have enough time to fill the cylinder.
Too late, and the pressure below the valve overcomes the pressure above the valve, and you lose cylinder fill.

Exhaust Opening:
Too soon, and you lose efficiency of the power stroke, and reduce the velocity over the exhaust valve.
Too late, and you won't have enough time to evacuate the cylinder.

Exhaust Closing:
Too soon, and you won't have enough time to evacuate the cylinder, and the pressure in the combustion chamber will be higher then the pressure in the intake port, and cause reversion.
Too late, and the velocity past the exhaust valve will be too low, and reduce the pull on the intake during overlap. This can also cause reversion.

All are important, and all effect the others.
What's optimum for one RPM, will not be optimum for a different RPM.

[hoffman900]

On a single camshaft engine, advancing / retarding the cam from installation changes all 4 events. I wouldn’t read too much into these tests.

A gain in car performance is a gain.
Observing a gain or a loss in * car* performance
is important, and informs, either way.

"Everything. effects Everything"

Especially if the ET slip matters.
Ignor that if you want.

Well, yeah, but if you want to understand how things work so you can move beyond that change, you need to isolate variables to figure out WHY it did what it did. That's how engineering and science works.

[ingram]

Intake closing determines the dynamic compression ratio, pretty important to know.

[F-BIRD'88]

Cylinder fill is dependent on how much stuff gets in by the time the intake valve closes. Nothing starts to happen before the intake valve begins to open.
Every thing good happens at points (*soon*) after that.