Determining the correct valve opening and closing points

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justanothermelvin
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Determining the correct valve opening and closing points

Post by justanothermelvin » Wed Apr 03, 2019 2:24 pm

Can anyone explain how they determine what the best valve opening and closing points should be for an engine. Feel free to use any engine combination. Is there some kind of formula?

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Re: Determining the correct valve opening and closing points

Post by PackardV8 » Wed Apr 03, 2019 8:42 pm

How high is up?

Your question is a multi-variable regression analysis. Intended use? Displacement? Bore? Stroke? Number of valves? Pushrod or OHC? Carburetion or EFI? Auto or stick? Gear ratio? Vehicle weight? Emissions compliant? There are many more considerations which determine correct valve action.
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Re: Determining the correct valve opening and closing points

Post by cjperformance » Wed Apr 03, 2019 9:56 pm

6.66 x SCR for IVC then work backwards from there :P
Craig.

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Re: Determining the correct valve opening and closing points

Post by racin69z » Wed Apr 03, 2019 9:57 pm

I am curious of the effects of how the individual events effect the whole package. I started out on stock motors with RV cams, and slowly worked up into building race engines with high compression over the years as my involvement in the hobby has increased. I consider myself a decent novice at best.

I always pick the duration at .050 for the rpm range I needed and then the lobe separation based upon what I am doing with the motor. I have always picked tighter 106-110 lobe separation when building an a N/A motor that needs good torque at launch, and wide lobe sep 112-114 for a nitrous motor or a fuel injected motor that needs low overlap. By changing the lobe separation it is effecting the individual events, but I've never really understood why.

I think earlier intake closing increases trapped cylinder volume and that can increase low rpm cylinder pressure and torque production.

Later exhaust closing can help pull in the intake charge, but too late and I guess you get reversion back into the intake port diluting
the intake charge.

I suppose intake opening is connected with exhaust closing. Earlier and you use the kinetic energy of the exhaust to pull in the intake charge. Too late and you do not get flow going until well into the intake stroke.

Exhaust opening, not really sure on that one I guess if you open too early you loose pressure on the power stroke.

Lynn

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Re: Determining the correct valve opening and closing points

Post by steve cowan » Wed Apr 03, 2019 10:39 pm

i think Jack summed it up in a modest way,its a can of worms at best.
Craig was having some fun :D
only advice i can think that might remotely help-
what ever motor sport and or engine family (GM, FORD,MOPAR etc) you are interested in you need to research and try and test for yourself,you might be lucky and know people that dyno and race etc,over time with a lot of data there are positive and negative trends that will show in the real world,hear say is everywhere and you will have to sort through that yourself.
it has been said on this forum before- cylinder heads are way more important to make potential power than a camshaft,i doubt anyone in the whole world has this engine stuff completely worked out.good luck and be careful of information overload :lol:
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Re: Determining the correct valve opening and closing points

Post by cjperformance » Wed Apr 03, 2019 11:14 pm

Yes i was just having a luagh !

Pipemax and some other good engine programs may give you so.e help understanding the dynamics of the components V's valve timing. Especially where you can alter some stuff and see a different result.
Talking to people about a more specific combo is best.
Even camming a Ford Cleveland with small port vs big port factory heads on a basic engine takes some carefull and often trial and error learnt thoughts on valve timing to suit/do what you want.

Id suggest to pick on a SBC or SBF , pick a capacity , a fuel, and an end use , maybe even pick a cylinder head and or a hp or rpm goal and ask from there .

You will get good info and then maybe try peoples patience and alter something in the combo and go again!
After a while you will begin to see some patterns even without any computer programs.
Really basically you can then start to think, well this combo will run ?CR so closing the intake valve at Xdeg will make it lazy or have too much cylinder pressure, you can say well that much duration is going to make it a pig with the convertor i have, or closing the ex valve that late is no good with my restrictive exhaust etc etc.

Start specific then expand from there.

P.s. i think my formula is pretty good though :lol:
Craig.

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Re: Determining the correct valve opening and closing points

Post by modok » Thu Apr 04, 2019 1:11 am

justanothermelvin wrote:
Wed Apr 03, 2019 2:24 pm
Can anyone explain how they determine what the best valve opening and closing points should be for an engine.
NOPE!
It's an impossible riddle.
what is "best", and how it's determined are both highly subjective and intertwined
Then we ad
AN ENGINE
Which, is complicated also
You ALMOST broke the internet man, careful!!!
Glen Urban

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Re: Determining the correct valve opening and closing points

Post by digger » Thu Apr 04, 2019 2:24 am

First you need to decide the objective(s)

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Re: Determining the correct valve opening and closing points

Post by modok » Thu Apr 04, 2019 2:58 am

whirled peas
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Re: Determining the correct valve opening and closing points

Post by plovett » Thu Apr 04, 2019 7:31 am


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Re: Determining the correct valve opening and closing points

Post by cab0154 » Thu Apr 04, 2019 7:59 am

so many variables in engine combos, let alone combinations of cars and intended use it is hard to say. at the end of the day you have to start somewhere. which is why i spec'd my own stuff. i look at the whole combination, try to determine how much lobe area/duration/lift i think it will take. then i start with where i think the intake closing event will work best and that determines my IO and thus my ICL. then on the ex do the same but start with EO. the centerlines and thus LSA end up where they end up.
"Anyone who thinks the low RPM engine will be faster just does not have as much experience as the rest of us" -The late, great Joe Sherman.

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Re: Determining the correct valve opening and closing points

Post by CGT » Thu Apr 04, 2019 9:43 am

Even if there was a way of determining "perfect" valve events for an application(outside of the perfect cam first time internet stuff), that perfect set of events would and is only perfect for a moment across a few hundred rpms, a literal snapshot.

Then a new set of events would become "perfect"...thus the move towards variable valve timing, cam phasers, cam actuators and solenoids etc.
"If you pick up a starving dog and make him prosperous, He will not bite you. This is the principal difference between a dog and a man"

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Re: Determining the correct valve opening and closing points

Post by cab0154 » Thu Apr 04, 2019 10:02 am

CGT wrote:
Thu Apr 04, 2019 9:43 am
Even if there was a way of determining "perfect" valve events for an application(outside of the perfect cam first time internet stuff), that perfect set of events would and is only perfect for a moment across a few hundred rpms, a literal snapshot.

Then a new set of events would become "perfect"...thus the move towards variable valve timing, cam phasers, cam actuators and solenoids etc.
excellent point!
"Anyone who thinks the low RPM engine will be faster just does not have as much experience as the rest of us" -The late, great Joe Sherman.

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Re: Determining the correct valve opening and closing points

Post by CamKing » Thu Apr 04, 2019 10:08 am

CGT wrote:
Thu Apr 04, 2019 9:43 am
Even if there was a way of determining "perfect" valve events for an application(outside of the perfect cam first time internet stuff), that perfect set of events would and is only perfect for a moment across a few hundred rpms, a literal snapshot.

Then a new set of events would become "perfect"...thus the move towards variable valve timing, cam phasers, cam actuators and solenoids etc.
Agree. It's all a compromise. The best events to get you off the corner, will not be the best events to carry you past the flag stand. If I'm designing a cam for a circle track car that runs from 4,500-7,600rpm, if they can hook it up, I'm going to focus more on making the cam efficient at 4,500, then at 7,600rpm. If they're tire limited, I may go the other way. It's all a compromise.
Now, if you're designing a cam for a steady-state industrial engine, then you can have the perfect events with no compromise.
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Re: Determining the correct valve opening and closing points

Post by Orr89rocz » Thu Apr 04, 2019 2:14 pm

Now, if you're designing a cam for a steady-state industrial engine, then you can have the perfect events with no compromise.
I think the op would benefit from knowing the basics of how you determine duration and lift and centerlines based on a less complex situation like a fixed speed stationary motor

Or even something simple like a 350 inch v8 looking for a peak power at 6000 rpm. If it needed to make 450 hp, what would it need for a cam with assumptions on optimal intake runner length/size/area and flow numbers assumed are correct to support this goal, cuz thats a science in itself. Ignore everything else like power band, usage and other parameters. Just need to make 450 at 6000.

I think some calculations can be used to determine air flow required to support then look at the induction on what its capable of supplying. Cam/engine simulation software are capable of ball parking this.

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