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Old 04-26-2009, 01:56 PM   #1
zex97
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possible sticky cylinder heads 101

This could be a good sticky or maybe for FAQ section if there is one. Got this from another site several years ago and I can't remember the name of it. It might be shut down now but here you go.

I've been asked on several occasions to do something like what you're going to read here by more than one member or moderator of the SOHC Forum. And that is, do a monthly/bi-monthly tech article for the SOHC guys. Call it newbie information, call it guru enlightenment, call it me just talking out of my ass, or even call it something to read and think about. Just take what I say with a grain of salt, take what everyone else says with a grain of salt, and take your own grain of salt, and put them all into a shaker. A salt shaker only works when it's full of a lot of pieces. Now, with that said......

Here's Cylinder Head 101:

"What's a Head?"

Cylinder heads are easy to explain if you're a NASA scientist that plots Moon orbits for a living, it's something you'll understand in a few seconds. If you're not, then you'll have no idea what it is, what it does, or what to do to it until you THINK it's time to do something to your cylinder head. But everyone forgets to ask the first BIG question. WHAT IS IT? WHAT DOES IT DO?

Here it is in a nutshell. It's a piece of metal with holes in it that makes the engine breath.

When I say "breath", I mean that in a very articulate way. A cylinder head's job is to let the intake air and fuel charge into the engine, let exhaust gasses out, and give the gasses a place to burn as well as house the thing that makes the burn happen (called the combustion chamber/spark plug). That's IT. That's ALL it does. If you try to get more complicated than that, you're missing the point. The point is simple. Cylinder heads like to be treated like they're simple machines, not overcomplicated and not over thought. But at the same time, you need to remember that they are very PRECISE machines that need to be kept within tolerances. So... What have we LEARNED here?

We've learned that a cylinder head is a piece of metal with holes in it, that is a simple, precise machine that allows intake air and fuel into the engine, lets exhaust gasses out, and houses the combustion chamber and the spark plug.

"The Cam's Job"

Now this is where cylinder heads get really simple. The camshaft. What does the cam do? It times the valves opening and closing, and tells it how far to open. THAT'S IT!! All the cam does is "time" and "lift". The time we call "Duration" in degrees of rotation. 360 degrees of crank duration is equal to 1/2 of the cam's rotation. The reason for this, the crank has to make 2 trips around for the cam's 1 rotation. Thus, we have a "4 Stroke Engine". Up, Down, Up, Down. One Cam rotation. The lift we call "Lift" in inches or millimeters. We multiply the "Cam Lift" times the rocker ratio to get the "actual valve lift". I'll explain this later.

So far we've got...

A cylinder head is a piece of metal with holes in it, that is a simple, precise machine, that has a device in it that times the lift and the duration of the valves by rotating at 1/2 the speed of the crankshaft, that makes the engine breath the fuel and air charge in and let the exhaust gasses out, and also houses the spark plug and the combustion chamber.

See how easy these things are?

Wow, it's such a simple device that I think I'm ready to go ahead and grab a dremel tool and port and polish it, order up a replacement cam, put a new set of valves in it, and get some high dollar springs and retainers! I Know all there is to KNOW about cylinder heads now!!

They're just a piece of metal with holes in it, that is a simple, precise machine, that has a device in it that times the lift and the duration of the valves by rotationg at 1/2 the speed of the crankshaft, that makes the engine breath the fuel and air charge in and let the exhaust gasses out, and also houses the spark plug and the combustion chamber!

So what to do NOW?

Simple. If you so far understand what a head is, what a head does, and what a head's role in life as we know it is... Then you're NOT ready to go build one, you're JUST getting ready to start learing about them.



"So far we've got...

A cylinder head is a piece of metal with holes in it, that is a simple, precise machine, that has a device in it that times the lift and the duration of the valves by rotating at 1/2 the speed of the crankshaft, that makes the engine breath the fuel and air charge in and let the exhaust gasses out, and also houses the spark plug and the combustion chamber. "

If we're all still on the same page, let’s start getting technical.

The FIRST thing that I do with any head is decide what it's going to do for a living. Is it a drag only head, a street only head, an autocross only head, an SCCA road course head, or is it going to do double duty or all 4? The use is the most important feature of the design.

Drag heads need to produce ALL of their power up top. Autocross heads need to make all of their power in the mid range. SCCA heads need to be reliable as all hell, and make power AND torque up top. Street heads need to do all 3, but also need to have well idle characteristics AND fuel economy. Get this through your "head" right now. Nothing can do ALL of the 4 without having to compromise SOMEWHERE. Compromise is for the weak. Only those who LOOSE, compromise. Ask Jeff Gordon if he'd drive his NASCAR heads on the street... No.

So: Let’s start with MY most popular request. The "street head" that does "EVERYTHING" OK and "NOTHING" perfectly.

On a street head, being conservative is the best approach. Conservative Cams, conservative ports, conservative valve cuts, and conservative intake and exhaust matching. Do nothing in excess and you'll get more power all over the place than you started with, BUT less of a gain in ANY ONE area. I usually retain the stock valve angle, retain the stock port angles, and retain the stock seat depth and installed height with a pretty conservative valve and seat face cut. Usually just a single angle cut (45 degrees/45 degrees) and a conservative cam to bring it all together.

NOW: The term "port and polish" needs to get out of your mind completely right now. There is no polish, just like there is No spoon. Let’s think about what the air has to do here. It's going to be going through the intake runner at about 240 mph, and out the exhaust runner at about 620 mph. Do you think it CARES if the surface it's going past has a nice finish on it? No. Not at all. Also, on the intake side you have to remember that the surface is "wet", or "has fuel in it" Any completely smooth surface will puddle the fuel flying past it and make the intake charge leaner. Try this one. Dump a dixie cut of water on your paint. Dump a dixie cup of water on concrete. What evaporates faster? Same idea on the head. The air going 240 mph through the intake only cares that the "shape" is correct, and that there is little restriction in the runner. So long as the valve is open, the air is going to go through it by default. The only thing you're trying to do is let it get there easier, with the least amount of effort possible.

The stock Honda head for all D series are pretty much "street" designed. Very little change needs to be made except for "clean up" work. By "cleaning up" the port passages, cleaning up the bowls, cleaning up the runner entry, and cleaning up the intake match, you're going to get the air in EASIER. NOT GET MORE AIR IN. You're just reducing the work the engine has to do.

In cylinder heads 103, you'll learn more.......



QUOTE(HumanResource)
Single Cut Valve job for STREET...interesting


Most certainly. There's absolutely no benefit to having multiple angles on a cylinder head that's not intended to make maximum power. As a matter of fact, I've found that some of my best flowing head have flowed best with only one angle on them at peak lift. Now, the low lift flow takes a little hit, but if you're looking for that type of performance number, then you're also not looking to get 30 miles a gallon and have the thing hold together for 100,000 miles.

For the most part, a single cut on each side holds up best, lasts the longest, seals the best, and takes the most general abuse. Remember, the seal surface on the valve is only about .8mm. Any more than that and the surface area would be too high to disperse the load and hold the thing closed!


Ok, you're all getting it. Let’s get to the important part.

The bowls.

Yes, the bowls. The part of the head where the intake air and exhaust gasses have to TURN nearly 90 degrees to get through the ports. The biggest single restriction in a cylinder head, and most commonly the last part anyone plays with.

Yes, port matching can help you smooth out the air flow. Yes, opening up the port openings CAN improve overall flow. But the bottom line is this: Unless the bowl is good, you can throw 100 million cubic feet at it, and only get 100 down the hole.

The objective of a "perfect" bowl is to allow the air to make a smooth transition. The more angles, the more disruption, the more turbulence there is in the bowl, the worse the head will flow. The smoother the bowl, the better. Now, don't confuse "smooth" as in surface texture, I'm talking "angles". You want to make the bowl angle work BEST with what you're setting the head up to do. Exactly how to shape the bowl depends on what the set-up is, and how fast you want to go, AND how much work you want to put it the head.

From here, I'm going to link over to "the Old One" so you can see how HE does some of the bowls on his heads. The one he's got on there is a D16, and it's almost amazing to me how I never really looked at his porting as compared to mine, but it seems that over the last few years, we've developed "similar" techniques.

My "god knows how many pics" need hosting, so to give you the idea, (and to drop a plug for a guy who I still say is better than me...) take a look at the Endyn page and have some fun reading what he says there.

http://www.theoldone.com/articles/d16a%5Fhead/



(taken directly from Larry's page at Endyn. A good cheap plug. If you're lost and don't want to get out the grinder, another option to me, is HIM. He is the "Doo Doo")

Now, looking at his heads, I'm amazed to see how similar our styles are. Now, I MUST admit that looking at his heads remind me of some of my simple stage 1&2 packages (especially the fact that he leaves most of the guide and guide step there), but our styles and stems for testing are fairly similar. I find that a lot. MANY of the guys who I work with, compete with, race with, build with, all look at my heads and say "damn, that looks just like one of mine", or vice versa.

I DO however disagree with his statement of "the guide in the way doesn't do much." I've found MUCH different results (in the 30 plus CFM area), but I also have found much different longevity issues too. If you take down the guide, you're taking the mileage off at an ASTOUNDINGLY huge rate. Each 1mm I knock the guide takes about 30-40% off the heads life. The BEST flowing B series I did only took about 300 miles to eat the guides right out of it and beat the seats all to hell. She ran like a raped ape till she instantly lost 30 plus % HP all at once. I knew what happened, and she's STILL down getting repaired now as we speak. But when all you're doing is tossing 1/4 mile runs, it's WORTH the power to lose the reliability. If you want reliability, then leave the guides there. If you want the flow, get out the grinder and reform the top of the bowl COMPLETELY. AND make sure that you don't JUST take the guide; you have to make the WHOLE BOWL work together. That means for each little bit off the guide step, you need to appropriately take out MORE bowl volume to compensate for the additional valve stem area you've unshrouded! If you're lost, make SURE you don't try. That is for the SERIOUSLY heavy head porters ONLY. Not advised for ANYTHING that needs to get you to work on time.

Most cylinder head guys have a basic understanding of what needs to be done and why. Some have little tricks they use. Nearly ALL know about the main route to flow being in the bowl. It's easy enough to spot an amateur at work when you see a bowl that looks like it was either done with a round bit and has enough ripples to be a small ocean, or has the short side taken to a near flat angle.

I tried flowing a few scrap head with the short side (the floor of the port, or the small angle) cut all to hell just to see where and how the flow was disrupted. What I learned, you don't need to know. Just trust me; the stock short side turn is about perfect. The bowl however....

The Bowl needs your love!

Last edited by zex97; 04-27-2009 at 10:03 PM. Reason: Combined all topics under one for ease of reading
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Old 04-27-2009, 07:40 PM   #2
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99.75% of people have no clue what they are reading......
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Old 04-27-2009, 08:08 PM   #3
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Why did you feel the need to break this into three sections?
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Old 04-27-2009, 09:56 PM   #4
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It was broken up this way when I found this several years ago. A moderator could combine them all into one post if they want.
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Old 04-27-2009, 10:04 PM   #5
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There I combined them all into one.
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Old 03-09-2012, 04:02 AM   #6
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awesome read! Thank you so much! What is the interchangeability of d-series cams? is there a way to get cam specs on what comes from the factory? (I've been searching) Specifically interested in d16y7 cam specs vs d15z7 (3 stg) ... Thanks
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