Everyone knows camshafts are a critical aspect of putting together a good engine combination, and can drastically affect the characteristics of an engine in terms of power, driveability, and even reliability. I've personally witnessed advancing the cam in an engine just 1 degree result in an increase of 25 peak HP, and at least 10 ft-lbs everywhere else, all under 6000 RPM. I like to ask this question a lot because it almost always envokes some really interesting discussions, so I hope you don't think I'm trying to "test" anyone like I understand some members would do in the past.

Pertaining specifically to naturally aspirated combinations, what valve event do you think is more critical to engine performance and why?

1) Exhaust Opening
2) Intake Opening
3) Exhaust Closing
4) Intake Closing

 

Our cylinder heads are largely effected by overlap due to the pentaroof chamber. I would say that exhaust opening is a very large contributor to the shape of the powerband as it will play a large role in how the intake and exhaust manifolds work in conjuction with eachother. Maybe intake closing is really more important though. I will now spend the day hypothesizing the effects that the motion of the valve has on the flow conditions through the port.

 

saying what event is most critical is not right, "all four events are important", and they all need to be paid attention to.

 

x2. You can't say one is more important than the other. Without all 4 working as a unit the motor wont run well, if at all. Optimizing all 4 to the point of maximum performance without hampering any of the others function will get you peak performance.

 

I think he is trying to start discussion on the specific details of the timing events.
its fairly obvious and ambiguous to state that "all 4 need to work together"
what if someone had examples where varying the intake valve opening resulted in a change of 1hp/degree where as varying the intake valve closing results in changes of 2hp/degree. Now can you say one event is more important than the other? How do you find the balance between total duration, cam centerline, opening and closing event timing etc.
its not really possible to make 100 camshafts with 1 degree changes to actually run comparison tests, so through discussion hopefully we can gain some understanding which would better help us choose the correct camshaft which is the ultimate goal it would seem.
IMO the valve events that overlap are more critical than the other two but i think another very important aspect is the timing relation between peak lift and peak piston speed.

 

group cam shaft buy? jk.

idk...intake would let all the fresh air in but too much would be bad and not enough. but if you don't have a well timed exhaust opening it would leave too much burnt unusable air in there. or also piston kissing. and continue on the possibilities of good bad and best.

but idk if it could come down to just one. i'd say when the intake closes is definately one of the highest. or how long its open for i guess is the important part since it can't measure the amount of incoming air. and when the exhaust closes for how much or little burnt air gets out.
in staying with yours but changing the idea a little i'd say when valves close is more important.

 

On my phone, so ill have to elaborate later, but IVC is by far the most important.

 

Intake valve opening/closing (in relation to the piston) I would say has the most effect...This is the main factor of how much air comes into the cylinder. The "entrance door" if you will.
Of course the exhaust valve events are important too, but the first step to combustion is getting the air into the chamber correctly. If you dont start out with the correct amount of air at the correct time, it really wont matter as much about the exhaust cause the combustion event is already destined for misfire...

I think the car manufacturers have proven this by all of the "variable intake timing" systems out. I-vtec, VVTL-I, MIVEC, VANOS, Vario-cam, etc...They all do basically the same thing. Advance the intake cam at various throttle positions/loads to improve efficiency/torque. I think only Nissan has variable valve timing on both intake AND exhaust, dont they? Someone please correct me if Im wrong...I think BMW might also be doing it with their "double vanos" technology.

 

i think vhp is the most important. valve hitting piston.

 

yep, You nailed this one!!
valves hit pistons create more sparks burning the mixture much more efficently makes the total performance everyones looking for!!

VHP ftw!!!!!!! j/p

 

Still waiting

 

I'd agree completely.

As far as making power is concerned, the goal of a naturally aspirated build is to take advantage of the inertia the air has as it enters the chambers to build more pressure and trap more air mass. I think the internet has coined the term "Interia Supercharging" for this. So if you close the valve too soon, that energy is wasted as it crashes into the back of a closed valve rather than in the chamber and you aren't trapping as much air as you potentially could with a latter valve closing. Keep the intake valve open too long, and you get reversion as the air tries to make its way back into the intake passage.

Since fuel has energy, and you need air to burn that fuel, trapping as much air as possible in order to burn as much fuel as you can is the utmost priority to make power. The exhaust valve events are only secondary...in a naturally aspirated engine.

 

question is: if we all agree that IVC is most important.

how do you want it to close, would you want peak lift as long as physicly possible and close as quick as possible or do you want a gentle closing ramp?

given that the spring could keep up...

 

There is much less flow resistance when the valve is fully open, so ideally it would remain near peak lift as long as possible, aggressively move down the closing flank, then gently close. However, with an aggressive closing flank, you need stiffer springs to prevent float/bounce at higher speeds.

For what it's worth, I also agree that IVC is by far the most important. Not only does it have a large effect on your VE curve due to the inertial ramming phenomenon mentioned earlier, but it affects your dynamic compression ratio and has a large influence on how high of a static compression ratio you can have before knocking becomes a problem.