Importance of Valve Events

442 · Post by **442** » Thu Mar 09, 2006 2:51 pm

I first want to say thanks to all the great minds that post on this site and the knowledge I have found that now makes me just dangerous enough to……..Well I’ll stop there.

As I view this and other sites I have come across several well known cam grinders who look at certain valve events in a very different fashion. Does anyone else find this to be true? Is there no standard by which certain valve events are considered higher priority than others?
Now let me step back and say that maybe cam design is so mystical that it can be looked at in several different ways. I became confused when I came across some comments and wondered why they differed so. I understand there are programs that allow one to plug in numbers to come up with a particular cam for the engine at hand but would not the theory behind the importance of the events then affect how that particular grind was made?

I guess it will never really matter that much for my purpose and that some things are best left to those who know what they are doing but what are your thoughts?

One designer says:
The LEAST important is the exhaust valve opening.
The next least important timing point is the exhaust valve closing.
A somewhat more important timing event is the intake valve opening.
The last timing event is the most important, and the most critical to engine performance - THE CLOSING OF THE INTAKE VALVE.

Another says:
The least most important in the cycle is the intake valve closes ABDC
The 3rd thing to consider is the exhaust closing
The 2nd thing to consider is the intake valve opens
And the 1st event that happens in a cam cycle is that the exhaust valve opens.

Thanks in advance.

pastry_chef · Post by **pastry_chef** » Thu Mar 09, 2006 3:34 pm

I know yet another school of thought from another well known designer.

1) Intake and Exhaust opening tied for number one importance.
2) Intake closing is next in importance.
3) Exhaust closing least important.

He also will concede that the engine sees valve timing as more of an area, rather than a discrete series of "events".

I like his thinking, but I think ANY "event" being off a few degrees will make or break everything.

Ape · Post by **Ape** » Thu Mar 09, 2006 5:06 pm

There is a very very good paper on that subject by the former mercedes R&D chief W.D.bensinger, you might want to see if english reprints are available, but from his perspective intake closing point is the most important since it´ll dictate the rpm range, and thus Ve etc.
Lobe separation will be a byproduct of the other events.

highVE · Post by **highVE** » Thu Mar 09, 2006 7:02 pm

Only dealing with a few cam grinders my self, i have my own personal opinions as and engine builder. #1 first and foremost event is the closing of the intake valve!! I don't care what anyone says, you can't convince me otherwise. "When do i close it???" well keep it open long enough to get as much mixture in as possible, but yet get it closed so we can start compressing the snot out of it, to take advantage of what is there. I would have to think all the Gurus on this forum would have to agree it's the most important. and if it's really not, well i haven't learned a thing at all about engines.

Just my thought.
Mike Theroux
www.mikesportingservice.com

Joe Mendelis · Post by **Joe Mendelis** » Thu Mar 09, 2006 8:57 pm

pastry_chef wrote:I know yet another school of thought from another well known designer.

1) Intake and Exhaust opening tied for number one importance.
2) Intake closing is next in importance.
3) Exhaust closing least important.

He also will concede that the engine sees valve timing as more of an area, rather than a discrete series of "events".

I like his thinking, but I think ANY "event" being off a few degrees will make or break everything.

Exhaust opening is more important than intake closing?

Who is this well known designer?

MadBill · Post by **MadBill** » Thu Mar 09, 2006 9:05 pm

Anyone who disputes that IVC is the most important valve event is farting against thunder.
For what it's worth, all my engine simulation programs, from Dynosim and Dyno 2000 through The Engine Expert to Dynomation are in rare agreement on this: Optimize all four events for a narrow RPM range, then reduce each in succession by say 5° and there is a far greater loss in estimated power from the IVC change.

pastry_chef · Post by **pastry_chef** » Thu Mar 09, 2006 10:41 pm

Exhaust opening is more important than intake closing?

Who is this well known designer?

http://www.chevelles.com/forums/showthread.php?t=97864

MadBill · Post by **MadBill** » Thu Mar 09, 2006 11:05 pm

Well, whoever he is, I think he's part of a tiny minority. (Poll, anyone?) Of course you can build great parts even if your theories are wrong, so long as they point you to the right design. So if he gets all four valve events exactly correct for the application, he'll have race-winning cams regardless of what he thinks about the relative importance of the events.

Joe Mendelis · Post by **Joe Mendelis** » Thu Mar 09, 2006 11:11 pm

pastry_chef wrote:
Exhaust opening is more important than intake closing?

Who is this well known designer?
http://www.chevelles.com/forums/showthread.php?t=97864

"I think of the dynamic compression ratio as the amount of air/fuel trapped in the cylinder at intake valve closing, and then compressed"
I think he is confusing the above with volumetric efficiency.

I'll never go there again.

Jay Allen · Post by **Jay Allen** » Thu Mar 09, 2006 11:58 pm

Just to say what event is the most important is wrong. Let's say you want an IO of 10* BTDC. The last time I checked there was an INFINATE number of ways to get there. The same can be said by just looking at any of the single 4 cam events (IO/IC, EO/EC). I cannot believe that ANYONE who has been around cams for any amount of time would concentrate on any 1 given event. Thus.......I can assure you that LOBE AREA plays into this. I try to identify how much area I need for a given application. I then move all of my events around in an attempt to achieve what I am doing for a customer. All 4 events have their place. All 4 need to be paid attention to. Not just any 1.

Good Luck.

Racedad · Post by **Racedad** » Fri Mar 10, 2006 9:22 am

Doe's anybody have a computer dyno program they trust to predict optimal valve timing to maximize VE for given combo and RPM.I have Pipemax and using it will help me optimize sizes of things,but you input VE.I have dyno2000 and it can be used to select vave timing to optimize VE but I don't really trust it.We have a chassis dyno but not enough time or money to try many combinations,I'd like to start with a predictably good setup and fine tune from there.

Ron E · Post by **Ron E** » Fri Mar 10, 2006 9:24 am

Jay Allen
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Man, that's a tough neighborhood.

442 · Post by **442** » Fri Mar 10, 2006 9:24 am

Thanks for the responses.

Pastry_chef hit it right on the head.

I had found that particular thread he referred too......http://www.chevelles.com/forums/showthread.php?t=97864

When the resident cam expert was explaining valve events a gent that had worked for another cam company spoke up and a pseudo debate began.

It made for good reading but it was contradictory. That's why I became confused. This statement in particular was one that was used to try and prove the point he was trying to make about the importance of certain valve events.

Here is a little thought for the most important vs. the least important valve opening/closing events.
If you can get to a dyno, get yourself 2 cams, with the same intake and exhaust profiles, but a 2° difference in LSA, say 110 vs 112, or 106 vs 108. The only difference is really the valve opening and closing timings.
Dyno both cams with the intake installed to the IDENTICAL intake CenterLine. The intake opening point and the intake closing point is identical in both dyno tests.
Why does the dyno show 2 different power curves? Both cams had the IDENTICAL opening and closing points on the intake. They only differed on the exhaust opening and closing points, and yet they produced different power curves.
Notice, I didn't say one was better than the other, only different. Each of them is best for some application, and that's why you talk to your cam grinder.
I know why they produce different power curves, and what effects the opening and closing points have on the power curve.
I still put the intake closing point as the 3rd most important in the cycle, beating out only the exhaust closing point.

442 · Post by **442** » Fri Mar 10, 2006 9:40 am

Darrin Morgin or Larry Meaux,

Do you have any input or thoughts on this matter?

SStrokerAce · Post by **SStrokerAce** » Fri Mar 10, 2006 10:32 am

I agree with Jay that there is a not really a priority. I think all of them are. Then again if you had to pick one, IVC is the most important. If you don't tie the cam to the compression ratio then you are not doing something right.

That guy on the thread is talking about overlap as being the most important, which to a degree it really is. If you can't get the exhaust system to help the intake system then you really are missing out on some good cylinder filling.

So that leaves you with exhaust valve closing as the event that's left out.... which in priority it is the least important, but it is closely tied to exhaust tuning events.

As for the Lobe Area.... ummm yeah, but wouldn't valvetrain stability be more important than that? In theory the Lobe Area is important, but when you can't control the valve you can't make the power.

Bret