[p4msi1]

Originally Posted by john marcella

Not nearly as simple as advancing or retarding a given Cam . Ivo depends on pressure in the manifold versus pressure in the cylinder left over from the exhaust cycle . Ivc depends on how close your cylinder pressure is to your Intake pressure.
Evo is dependent on how much residual pressure there will be in the cylinder when the Pistons coming up on the exhaust stroke after blowdown occurs ( pumping Loss). Evc will depend on the pressure in the combustion volume during overlap versus Inlet pressure versus exhaust back-pressure on the hot side of the turbo.
See complex.

How in the hell are you supposed to figure this out!!!! Does all this take into account velocities at different RPM points? I guess you would use probes to gather the info needed? Vaught and Wilkie I am not.

[john marcella]

Originally Posted by p4msi1

How in the hell are you supposed to figure this out!!!! Does all this take into account velocities at different RPM points? I guess you would use probes to gather the info needed? Vaught and Wilkie I am not.

You can't there is no math for it , that's kind of the point. Well I take some of that back there is math for it but it's so circumstantial on so many different things dynamically that it's almost impossible to come up with calculations.
You have to try stuff notice Trends and follow the data path. The problem is is you can't get fixated on one part of the system. It doesn't work because that part of the system is dependent on another part of the system and so on.
One of the biggest things that I see in this thread is people want to refer to a boosted motor as such a boosted motor. Shouldn't do that it's a turbo motor or a blower motor , 2very different approaches as well as requirements.

[john marcella]

Originally Posted by p4msi1

John, as I was degreeing in the cam I was thinking about all the events and an N/A IVO would want to be open earlier than a boosted motor because a boosted motor has forced induction. On the other hand an N/A motor may need the EVO sooner to help blowdown and evacuate the exhaust gasses BUT could a boosted motor benefit from a little later EVO to take advantage of the high cylinder pressure at that point and maybe produce a little more HP. You are right about the massive tug-o-war going on in there. I was wondering about the specific cam I will be using. Right now I degreed it as specified on the card and even called the manufacturer and he said to do it to the cam card. I'm not trying to break records BUT if I can take full advantage of this cam then that is what I want and doing it now is what I will do because once it is in the car it will not come back apart.

A blower motors Ivo realistically should be able to be open earlier than NA because it has more pressure in the intake manifold vs NA.

Now on a turbo motor could be just the opposite. Because of the back pressure on the hot side of the turbo connecting to the combustion chamber by way of overlap. Can't open the intake valve until the pressure in the cylinder is lower than the inlet pressure!
On a blower motor the back pressure on the exhaust system connected to the combustion chamber through overlap is at atmospheric pressure.!!!!!!!

[p4msi1]

Originally Posted by john marcella

A blower motors Ivo realistically should be able to be open earlier than NA because it has more pressure in the intake manifold vs NA.

Now on a turbo motor could be just the opposite. Because of the back pressure on the hot side of the turbo connecting to the combustion chamber by way of overlap. Can't open the intake valve until the pressure in the cylinder is lower than the inlet pressure!
On a blower motor the back pressure on the exhaust system connected to the combustion chamber through overlap is at atmospheric pressure.!!!!!!!

OK, so I am learning something here and it does make sense, can't thank you enough. I will keep this cam 4* advanced.

[john marcella]

Originally Posted by p4msi1

OK, so I am learning something here and it does make sense, can't thank you enough. I will keep this cam 4* advanced.

Ivo is only 1 event. Just sayin.
Usually the two Alphas are ivc and evo.
Whats the cam like ? Blower ?

[john marcella]

If you want to spin yourself out degree the cam and find out where .001 of valve lift is on ivo ivc evo and evc. Then look at where the Piston is in the bore at those numbers. Bet you will think you screwed up, but you didnt. Lol

[Tom Vaught]

Originally Posted by john marcella

You can't there is no math for it , that's kind of the point. Well I take some of that back there is math for it but it's so circumstantial on so many different things dynamically that it's almost impossible to come up with calculations.
You have to try stuff notice Trends and follow the data path. The problem is is you can't get fixated on one part of the system. It doesn't work because that part of the system is dependent on another part of the system and so on.
One of the biggest things that I see in this thread is people want to refer to a boosted motor as such a boosted motor. Shouldn't do that it's a turbo motor or a blower motor , 2very different approaches as well as requirements.

Marcella is correct on this one.

The Math just gives your general concepts. You have to do a SYSTEMS approach on the specific engine and typically every system is different. So you look for what the engine is trying to tell you, not some math equation.

A boosted Engine just means that it has a pressure ratio higher than 1.0

There is a world of differences between how a belt driven supercharger and a Turbocharged engine operate and how fast they can make torque and horsepower.

But a guy who understands how the engine works can move between one system and the other because the physics does not change, the math changes but not the physics.

Just saying. Corky Bell wrote books on both Supercharging and on Turbocharging and they are very good because he understands the physics and can explain it very well in his books.

Tom V.

[john marcella]

Originally Posted by john marcella

If you want to spin yourself out degree the cam and find out where .001 of valve lift is on ivo ivc evo and evc. Then look at where the Piston is in the bore at those numbers. Bet you will think you screwed up, but you didnt. Lol

Then after you do this you can get fixated on trying to get the same or more area under the curve and trimming up those 4 events. Become obsessed with valvetrain component weight so you can maintain control with more valve acceleration.

Or just wish you had a 4-valve motor after calculating its curtain area versus time/ crank degrees vs A2 valve motor. 4 valve motor is a turbo best friend because of this. !

[Stan Weiss]

Originally Posted by john marcella

If you want to spin yourself out degree the cam and find out where .001 of valve lift is on ivo ivc evo and evc. Then look at where the Piston is in the bore at those numbers. Bet you will think you screwed up, but you didnt. Lol

While not a blower cam this graph shows a cam install by the card, 6 degrees advanced, and 6 degrees retarded and the piston position. I could not find the graph that showed the valve relief position as well.

Stan

[p4msi1]

Originally Posted by john marcella

Ivo is only 1 event. Just sayin.
Usually the two Alphas are ivc and evo.
Whats the cam like ? Blower ?

@.050 238- 246 LSA 112 ILC 108
io 11
ic 47
ec 27
eo70

Blower is a D1SC procharger which this motor will outgrow.

[p4msi1]

Originally Posted by john marcella

If you want to spin yourself out degree the cam and find out where .001 of valve lift is on ivo ivc evo and evc. Then look at where the Piston is in the bore at those numbers. Bet you will think you screwed up, but you didnt. Lol

What really gets me is how fast a piston moves just by spinning it by hand verses 7500 rpms and more, then the air column has to stop at the intake valve then accelerate into the bore. I know there is an inertia effect going on but the fact that these defining moments are there, are mind boggling.

Brings me to another question, do heads need to be flowed to to come up with the best cam design. I have very close approximate numbers on my heads but never actually flowed. The car in question is in my signature and I think it should run mid to low 9's. current cam is 264-270 @ .050 740 lift on 110 lsa. 11.9 comp. Tiger heads was said to flow 440 cfm and I don't know at what lift but probably 850-900 lift. It is still street driven with occasional trips to the track.

[Stan Weiss]

John,
Just to go off on a tangent a little here. The top lines in the attached graph shows the shows the same valve lift curves as my last graph. The second line is the vertical valve drop for a head that has a 14 degree valve incline angle while the third line is the vertical valve drop for a head that has a 24 degree valve incline angle. How much if at all does the actual valve drop come into play?

Stan

[johnta1]

Interesting old thread on Speed Talk, with UD Harold.

Cam and Airflow

[john marcella]

Originally Posted by Stan Weiss

John,
Just to go off on a tangent a little here. The top lines in the attached graph shows the shows the same valve lift curves as my last graph. The second line is the vertical valve drop for a head that has a 14 degree valve incline angle while the third line is the vertical valve drop for a head that has a 24 degree valve incline angle. How much if at all does the actual valve drop come into play?

Stan

Vertical valve drop?? Explain

[Stan Weiss]

Originally Posted by john marcella

Vertical valve drop?? Explain

John,
I do not know what the technical term is or if there is one.

What I mean by vertical drop is how far down the bore the valve moves verses the amount valve is off of its seat.

With a zero degree valve incline angle. vertical drop = amount valve is off of its seat.

With a 90 degree valve incline angle vertical drop will always be zero.

Stan

[p4msi1]

Originally Posted by johnta1

Interesting old thread on Speed Talk, with UD Harold.

Cam and Airflow

That was a good read.!