Valve Events (intake open) - camshaft

[Guest]

This is going to be a broad topic, but do you prefer to open the intake valve before top dead center or after top dead center?

I'm dealing with an LS1 (intake restricted. And alot of the intake opening events of the camshafts being sold are negatives (after top).

Would it be wise to open the intake valve before top dead center to get a jump on the restricted intake pull?

[Guest]

might add, i was looking mainly @ .050 specs

hopefully that might keep everyone on the same page.

[speedtalk]

If I was going to focus on just one timing event, it would be the intake close - that's the most critical.

[Sticky Bumps]

Thanks. Why aren't the IO & EC as important?

The two most important would be the IC, EO, correct? Pairing the events up.

[learner]

Its not uncommon for smaller cams to have valve events at negative numbers at .050". Intake closing is the most important event for naturally aspirated applications because for the most part is controls cylinder filling, reversion levels,etc.

[buddy rawls]

I have found out thru my work that the overlap activity is of incredible importance. this is where the port cross-section and flow capability and residual pressures are all working against low piston speed. An incorrectly timed EC and IO can throw the whole combination off very quickly. this is where you will get into all the flow exchange per unit of time, and how the overlap angle becomes extremely relative to the specific motor flow capability.

I used to follow the IC importance, but in the past 8 years of developing my own models and calcs, I am sticking to all 4 events as important. Focusing on IC only tends to look at the cylinder pressure issue, which is a 'THE' key issue. However, by omitting the importance of starting the cylinder fill and exh sign-off, makes IC less important, and focuses on TDC overlap activity. The EO becomes extremely important on the Exh side capability and low lift E/I ratio. It all works to form a single picture, they are all equal team players.

[Darin Morgan]

I used to follow the IC importance, but in the past 8 years of developing my own models and calcs, I am sticking to all 4 events as important. Focusing on IC only tends to look at the cylinder pressure issue, which is a 'THE' key issue. However, by omitting the importance of starting the cylinder fill and exh sign-off, makes IC less important, and focuses on TDC overlap activity. The EO becomes extremely important on the Exh side capability and low lift E/I ratio. It all works to form a single picture, they are all equal team players.

YEA! What he said. DITO

There is not one event more important that the other. Your trying to isolate your variables and you cant do that. The dynamics are far to complex to try and relate to one specific variable and manipulate that one without regard for what's happening to the others. Its a delicate balance, a dance if you will. If you change your intake closing for instance ( close it later ) You could manipulate the overlap duration, cross flow dynamics in the chamber or other related variables to dynamically fill the cylinder to higher VE. Not to mention the other dynamics involved with camshaft tuning now days. Tuning a cam is a major effort. Its not as simple as duration lobe centers and overlap. The cams we use are tuned on a spin fixture to loft a certain amount and gain an incremental amount of duration per rpm increase. Our power band is from 8000 to 10000rpm.. At 8000 the cam starts to loft and gains an initial 8 degrees of duration and at 10000rpm it has gained 15 degrees of duration. I know I have gotten a little off track here I just wanted to point out that's its getting harder to keep track, document and manipulate all of the variables and there are a lot more than just intake closing.
.
.
Darin Morgan
R&D-Cylinder Head Dept.
Reher-Morrison Racing Engines
1120 Enterprise Place
Arlington Texas 76001
817-467-7171
FAX-468-3147
Visit our web site at http://www.rehermorrison.com

[Sticky Bumps]

Thank you for your responses guys.

I appreciate your share of knowledge.

[learner]

Darin, if i started another post would you answer some connecting rod questions?


Thanks

[Darin Morgan]

Darin, if i started another post would you answer some connecting rod questions?


Thanks

I am not the person you should be asking but I will try. Any questions I can not answer I will pass on to Mike Giannone and see if he has the answer. I respect his opinion more than anyone else in the industry.

[rmbuilder]

Darin,
A couple of questions on the loft you mentioned in your post.
1. When the follower lofts does it go “light” over the nose or is there actual lobe/follower separation?
2. Is there more than one point of separation in the valve train besides the lifter/lobe interface (assuming there is actual separation)?
3. Where is the point of lifter rebound on the lobe and how do you control it?
4. How does the loft/rebound upset the valve spring?
Thanks in advance.
Bob