Intake/exhaust port CFM flow? Porting the heads? Tech babble.

[merlot566jka]

Had my heads off last week and valves out. Looking in the ports, I was curious about the flow on them. Has anyone ever flow benched a head?
Also noticed there is a ton of metal there if anyone were to port them...

Looked around some other diesel forums out of curiosity to see if porting yielded the same effects as it does on gas performance engines. From what I saw, there wasn't much scientific data, but tons of "lowered my EGT..." "Bunch of turbo lag..." "Can't tell a difference..."

So I analyze it a bit. A compression ignition engine uses no throttle plate. So every intake stroke, the engine is trying to suck in as much air as the port will let in. Add a turbo, and the engine is being force fed air. That means (if) the turbo is appropriately sized, the volume of air should be the same, just increased pressure... If you increase pressure, volume stays the same....air speed increases?
Would a better flowing port actually do anything at the level we use the engine? The only thing I see is a decrease in pumping loss, which I believe is more than equalized with a turbo.

This leads to more thinking...
If you had ports on the multifuel that flowed (example) 200CFM and that was adequate for the engine from factory, would there be any benefit to a port that flowed 300 CFM? Aside from amount of time it takes to fill the cylinder and efficiency of cylinder filling, what are we accomplishing with better ports?

Now if we INCREASE the amount of air being forced into the engine (higher volume turbo) then I could see where a head that flowed more air in/out would be helpful. But to port a stock engines' heads, why?

To bring this all back around, what does the deuces heads flow on the intake side? Is it more or less than the engine uses at 2650rpm?

If 100% efficient, we need 360cfm for the entire engine at 2650rpm. 360/6= 60cfm per intake port

If 70% efficient, we need 250cfm for the entire engine. 250/6= 41.667 CFM per intake port.

I haven't measured anything, but just looking at those ports and the size of the valves, they should easily flow 60 CFM.

 

[SCSG-G4]

Re-do your calculations. You have an error! The actual displacement of the 465 engine is 478 cu/in. Sorry!

 

[merlot566jka]

Crap. I knew that.

6cfm difference anyway. Drop in the bucket!

 

[patracy]

Ummm, unless you have a NA LDT, your VE can exceed 100% in a forced induction system.

 

[merlot566jka]

Yup. But I was going on the VE of the engine itself to see if the ports were designed to allow enough air in the first place.
Of course, you can exceed 100% VE completely NA (in a certain rpm band)
With Helmholtz theory, it's been shown to go as high as 115% NA.

But I think that's outside of the realm here. That's why I mentioned an "appropriately sized turbo", meaning it flows close to or the same CFM the engine requires. That way we don't start thinking about big honkin' hairdryers.

Also, I chose 70% VE cause that's fairly low, and what I would expect from an engine designed in the 50's, before the addition of the turbo. Technically, the turbo should just feed in pressurized air, with or without the turbo, the engines port flow would remain the same. The turbo is icing on the cake.

 

[VPed]

I do not think 60 cfm is right. You only have a small timeframe to get the air in there so flowrate during that period needs to be higher. It would be 60 cfm if you have a full minute to fill the cylinder.

 

[gimpyrobb]

You guys are talking about things that are over my head, but 60 cubic foot of air sounds like a lot!

 

[merlot566jka]

Vped,

You're exactly right!
Time is a very large factor here. But usually disregarded when calculating flow on cylinder heads.

Why?

Reason being, most engines have different camshaft profiles, rpm limits, etc.

To successfully calculate how much the engine flows during an event you need much more information. Things like;
Effective cam duration
Valve size
Port flow at .050" lift intervals (up to max lift I suppose)
Speed of sound at testing temp
Speed of sound at operating temp
Flow velocity of intake system
Effective valve closed duration
Reflective (wave) value
Runner diameter
RPM

And probably more that I can't remember. It gets pretty complicated when you try to factor in how much air can flow while the valve is opening, opened, and closing.
The industry standard is to measure CFM at a pressure drop of 28" of water (1psi) using a MAF hot wire, vane, pitot, laminar element or pressure drop across an orifice. This tells how much air can flow through (by telling you how much it restricts)

The theory is that if you can say a cylinder head can flow xxx.xx cfm at 0.xx" of lift, you have a baseline for performance (power/mpg) modifications or just a mark for capability (in the case of the LDT/S)

With this information you can now calculate how much air can flow through that valve, on average, over a period of time. That period of time depends on how long the valve is open, how far it opens, what rpm you are running at, and how fast the air moves.

So you are absolutely right, 60cfm is 60 cubic feet per minute, and we have a whole lot less than a minute to fill the cylinder.

At 2650 RPM we know the crank is spinning twice for every 1 rotation of the cam, and the cam opens the intake valve once per 720* of rotation, right?
So, 2650 rotations per minute divided by 2 is 1325 rotations per minute of the cam. So if we divide the minutes up into seconds we get (1325/60) 22.08333333333333 rotations per second. Crap, thats fast. Lets take the reciprocal and see if we can figure out how long it takes to make 1 revolution. 1/22.08333= 0.045283018867925 seconds. Woah!! We have 45.28 miliseconds to make 1 revolution of the cam! Eek.
Since the cam is round, 360 degrees, it takes (45.28ms/360) 0.125 per degree of rotation of the cam at 2650RPM. Say our cam has an intake duration of 150 degrees (I have no idea what it really is) that is 150x0.125=18.86 milliseconds.

By golly, we need to move 60cfm in 18.86 milliseconds! And that has to be done for the engine to be 100% volumetric efficient.

With some more math, I bet we could figure out how much air the head has to flow to allow the full 60cfm into the cylinder in just 18.86ms. I bet it's somewhere around 230-300cfm. No clue really.

If you think about it, the engines capacity is 478 cubic inches. How many cubic feet is that, if you were to move it once per cylinder, 1325 times in a minute?

Hmmm
CFM=(rpm x CID)/3456
RPM
CID (cubic inch displacement)
3456= constant to convert inches to feet and divide by 2 because we're only sucking air once every rpm

(2650 x 478/3456=366.5219907407407

So maybe I was wrong when I said 60cfm... Cause only one cylinder sucks in air at a time, and you want some more air available for the next one firing... Plus if the engine is 478 cubic inches, that's .27662 cubic feet, divide it by 6, 0.046103333333333 cubic feet per cylinder, maybe it's not 60cfm...

.0461033 per cylinder.
1325 times per minute...

.0461033 x 1325= 61.0868 cubic feet per minute
61.0868 cubic feet per min per cylinder x number of cylinders (6) = 366.5212 cubic feet per minute at 2650 rpm

I was a little off.

 

[merlot566jka]

Sorry. Day off work. Had too much coffee.

 

[w3azel]

**** bro, my day off I watch some TV or work on a project not do some math homework. Very interesting though. I'm convinced any engine can put out more power but to many here believe the MF is the worst thing ever invented and its a miracle if it runs and doesn't blow up on during normal use. Keep up the work and I hope you and some other smart guys can come up with something good.

 

[merlot566jka]

I havent owned a TV in 9 years. I do own books. Read all of them out to sea. Own a deuce.. took it apart... put book information to work on deuce engine.

Not too sure what I will come up with. But thanks!

 

[ICAT]

nobody said to be a member of SS that we would have to do math

 

[SCSG-G4]

nobody said to be a member of SS that we would have to do math

You only do math if you want to, a few want to, the rest of are just bumps on the log!

 

[merlot566jka]

No one does math outside of work except for weirdos like myself. No one is a bump on a log any more than I was today.

 

[VPed]

Sorry. Day off work. Had too much coffee.

I'd say waaaaayyy too much. But I did like your response.

 

[Tinwoodsman]

Isn't doing this type of stuff to a MF sort of like dressing up a pig?

 

[merlot566jka]

But...

I haven't done anything.

My pigs are as they came from the factory. Bacon.

 

[smoke]

hemichallenger is working on something like this. I think he may chime in or pm him.

 

[ducer]

When air pressure goes up air volume has to go up with it, this leads us to air density. Put a bigger snail on. Making the exhaust port flow to well will remove to much heat from the cylinder which will result in a loss of power. That is why even on the best racing heads with the best ports the exhaust only flows 80-85% of the intake port. These engines are a ticking time bomb from everything I have read on them. I will choose not to screw with mine until it blows up and then replace with something bigger. You can allways improve any stock engine's power output. At best a stock engine is a giant compromise between engineers, long service life, metalurgy and most importantly, the bean counters.

Denny

 

[Diecorpse]

I think you have a good idea. Getting more power out of a multifuel. If you found out exacty how much air the stock turbos force into the engine, couldn't you just install a larger turbo that produces the air flow you want without other modifications to the heads? I guess I'm still trying to understand this. Lol.