Home Head Work Thread

[seang]

A properly ported head is a good thing, and an improperly ported head can actually reduce engine efficiency/performance compared to stock. This doesn't mean that the idea should be forever shelved, and shyed away from - as much as it may seem this isn't voodoo (sorry, fans of voodoo).

Maybe you would like to share with us any experiences you may have with home head porting, or any head work (engine related).

[seang]

Here's a few links I thought tasted good

Popular Hot Rodding Article on Head Porting:http://www.popularhotrodding.c....html

Another one from Popular Hot Rodding that deals with porting mistakes:http://www.popularhotrodding.c....html

List of terms regarding head work:http://alaniztechnologies.com/headterms.html

CCing the chambers:http://www.cosworthvega.com/cc_an_engine_GEC.html

StockCarRacing Tutorial:http://www.stockcarracing.com/....html

A simple Google search of "cylinder head porting" turns up alot of articles/sites.
Modified by seang at 1:21 PM 1/21/2010

[sleekster]

How much do the stock heads flow and what have you done that is simple and how much flow increas . I am new to this board but i do know that head flow is where all the power is then friction then weight

[seang]

Head flow is importnant, and you should read all the links I posted, too.

I haven't done any of this to any cylinder heads. I'm new to this, too, that is why I started this thread so people could share info. I do have an example of some stock ka24e flow numbers vs ported.

ka24e stock intake = 208.3 cfm / port & polish intake = 239.6 cfm

ka24e stock single valve exhaust = 144.3 cfm / port & polish = 181 cfm

Scroll down this page for the actual flow charts:http://home.att.net/~MabuhayCarlos/TurboHead.html

^ link used to be good

[raremotive]

Hmm,

All talk about flow and not weight on velocity.

What about initial velocity when the valve opens and the piston moving down?

You can have two water pipes, one really big and one really small. If you were to look at a constant volume to observe what is going on. Sure, big pipes move more water, but slower compared to the smaller pipe with same applied force. This can be a problem when you have a limited window of time. Also the effects of increased flow without accounting for air velocity shifts the power band to the higher rpms. So basically turns your lower to medium rpms very sluggish. But it will open up the higher rpms for more power.

That's because you increased the area. Remember air has mass, and with mass you have inertia effects. Means F=ma applies.

So to put things in conception, lets for now hold acceleration as constant for easy viewing, increased area means you increased mass flow rate which means it requires more force to move it. So in power band perspective, lower rpm less air being moved, and higher rpm's less restrictive and more air moved because there's enough force to move it quickly. It's like the concept of a water pump, if you want more water out of a hose, you need a bigger pump because it has more force to move it.

Now we understand what happens with increased area happens. Now hold area. Let acceleration vary over time. More acceleration means more force to move the air. Especially if you have a greater initial velocity which allows you have a better draw vacuum. Vacuum is pressure. Pressure is force over area, (F/A). For our example, constant area, means more force acting on the air. The effects in the engine? You will see increase in entire rpm range.

But in the real world, mass flow rate is not constant because it's inertia.

The real trick about the engine is to imagine the engine as a air pump. The more air you can get in and out. The more power you have.

Porting tricks:

It's about allowing the air move with less change in direction while maintaining the same cross-sectional areas. This allow you to maintain inertia and overall air velocity.

Unshouding the valves, again allowing air to move with less change of direction.

You see where this is going? If you can change the port to move air without changing direction as much and changing the area, you have more power in all bands of rpm.

Why flow # are useless to me?:

The setup is to put suction on combustion chamber of the head, and crack open the valve. A constant suction is a steady state flow problem.

My problem with it, it doesn't measure changing velocity. And it's steady state. It doesn't take account for VE or air reversion (where air bounces off the valve and heads out of the runners in reverse direction). By the time air get it's maximum flow rate is when the valve is closing.

I can carve open that port like no other, plug it into that bench and it will report a massive flow gain. In real applications, I will see little power in the low to middle band of rpm, I would constantly need to stay in the higher rpm to have any useful power.

Which brings me to my final point:

Does flow matter?

Yes if you are talking about getting the most air in the shortest amount of time. A big pipe will always flow more, but it's harder to move in such short time.

But if you are talking about increasing the area, especially for higher rpms...

You can shrink the intake port and shorten your intake runners to reduce high rpm restriction and you will make more power. This is because the combustion chamber makes only so much suction power, or pressure. Pressure is Force/Area. The smaller the area the larger the force is, therefore you are going to have a greater initial velocity, which yields a higher final velocity. Or greater suction force, better VE, more power. And hell'of'a responsive motor!
Modified by Rare_f8 at 7:08 AM 2/5/2010

[seang]

You aren't the first person to bring up the emphasis on velocity.

Is there such a thing as too much velocity? Do you want to keep it below the speed of sound, or doesn't it matter if it breaks mach 1?

I think a big thing to consider is the flow rate of the engine aka (Cubic Inches x Target Peak Torque RPM % 3456 = flow rate in CFM). Then, you can take that number and multiply it into the volumetric efficiency. I can see where you are coming from on too much flow without velocity.

It seems nowadays that the auto makers are in such fierce competition that the heads from the factory already flow a million times better than they did 20 years ago. It's amazing how much power the late model cars make - they are leaving less on the table for improvement, because they are just so good stock. Anyways, there is still some old stuff out here that someone might want to improve on while they are at it.

[raremotive]

Fooking Badaxe write up! You aren't the first person to inform me of the emphasis on velocity.

Is there such a thing as too much velocity? Do you want to keep it below the speed of sound, or doesn't it matter if it breaks mach 1?

Doesn't matter even it becomes restricted/chocked, it still flows. Basically a normal shock develops. After the shock, the flow becomes subsonic, pressure, temperature, and density increase, total pressure decreases.

http://www.cycledoctor.com/Articles/JET.htm

Plus, if you are going to run that high of a rpm you ought to adjust your runner length. Which is calculated based on speed of sound. Air induction travels at speed of sound in your intake all the time whether you know it or not.

http://www.wallaceracing.com/i...h.php

http://www.velocity-of-sound.c...3.htm

Note: Induction waves are when the air bounces off the closed valve (because it has mass and inertia effects applies) and leaves the runner...

http://auto.howstuffworks.com/question517.htm

Remember, "inhibit" just means restricted. It still flows. But again I am not talking about making the hole so small that VE is affected too. But... somehow.. if you manage to shrink your runner length... the "inhibition" reduces.

Honda developed a short runner, long runner with a intermittent valve to open between the two. This is to try to serve a wider band of rpm. You can see the power curve on the normal RSX and RSX-s(equipped with that intake).
Modified by Rare_f8 at 9:20 PM 2/5/2010

[seang]

Sweet. I used that Wallace Racing calculator when I drew up my custom intake manifold idea last year:zerothread?id=445363

[raremotive]

sorry. I edited the last post. I added a new link after the first paragraph.

[raremotive]

So, why isn't everyone shrink-porting? Probably some builders are doing it, but traditional thinking stops many people from even considering such a move simply because it seems backwards. First, it's easy to assume that a big engine needs big valves and big ports. But although its displacement is big, a Harley isn't spinning at a NASCAR engine's 8500 rpm. So, the numbers show that the ports are oversized to begin with.

Second, when you put a Harley head on the flowbench and then get busy with the die-grinder, it's pretty easy to get more flow, because the stock ports aren't very streamlined. The man doing the porting feels good because he's getting bigger numbers, and the customer is happy because he sees smooth, shiny ports. After all, the whole idea of the flowbench is that more flow is supposed to translate into more power; but with a Harley, that relationship is weak.

This is exactly what I am talking about. Not just Harley, but ENGINES!!

[raremotive]

Good article:

http://www.motorsport-developm...h.pdf

[seang]

Cool. That PDF article is kind of tough to read, though. I will be furthering some points you made with these next tibits:

- We race cars, not flowbenches.

- Lots of people think that having the port walls smooth as glass is the best when actually it can hurt performance. Air flowing in the head is like a river. The air along the side of the wall of the ports moves very slowly while the air in the dead center of the port moves very fast. That's why the port wall finishes are very important. If done right, it forces the air in the center of the port to flow faster.

- It is possible to machine lots of metal out of the head to achieve higher numbers on the flow charts, but that is not always best. You could have a head that flows lots of air, but then when installed on the car, you find yourself unable to drive it. Which is why "We race cars, not flowbenches."

- Optimal flow is to have the Exhaust Side 75% of Intake Flow. On a flow bench, when the water flows out of the exhaust ports, it slows down as the water spreads out in space. Using an equal length individual runner header, it forces the air to keep its speed and produce a vacuum effect which will contribute an additional gain.

Note, I want to say that I did copy and paste the stuff in this post. If I have in fact stolen what is legally someone else's intellectual property, let me know. I just like the knowledge.

[seang]

I am bumping this thread because it was moved from the engineering forum.

[Rev_D21]

I wonder why it was moved. It's totally welcome in KA though.

[seang]

I mentioned earlier on in an above post something about the speed of sound. There is a factor here, and it is called "Mach Index." Here is a line from the link: "The Mach Index is a mathematical expression of the speed, in this case, of the inlet velocity, relative to the speed of sound."
http://www.rbracing-rsr.com/machcalc.html

On KA engines, sohc and dohc versions both run dual intake valves and have good induction designs--I doubt they have many problems with mach index. The naps-z head is a good example of a design that would sooner have issues after a certain rpm.