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CYLINDER HEAD 101
Lance M Wolrab
December 29th '04

BACKGROUND
In our search for power, at the heart of every engine's inherent ability to make torque is the cylinder head. Why? Because no matter what else you do to an engine, if it is going to make more power, it has to move more air. Of course there are a number of givens that must be addressed before we get to modifying the head. It is understood that the bottom end must be built to withstand the power we expect to make, and that the fasteners holding the head to the engine are up to the task. Not to mention the tuner must ensure that the right amount of high octane fuel is mixing with the air we are moving, and the ignition system must be up to the task of lighting off the charge at precisely the right timing. But these things are all in support of the one thing that separates powerful engines from not powerful engines: the ability to move large amounts of air efficiently through the intake and out the exhaust.

SO WHERE DO WE START?
Conventional wisdom says buy the fastest thing you can afford, then modify it. Since you are here, I will assume that you are working with a 2JZ-GTE, which is certainly a good choice. I will also assume that you are a true power junkie, and that big power is your goal. Toyota has built a powerhouse in this engine, and to say that they did a wonderful job of over-engineering it is an understatement. But there is room for improvement.
Once we remove the head from the engine, there are a number of things that become obvious. Most important is that for some reason, Toyco decided to point all the exhaust ports toward the stock turbos. The ports from #1 and #6 are long and steeply angled toward the engine center. The ports from #3 and #4 are angled slightly toward #1 and #6. This is unique. In combination with the OEM log manifold, there is little more that Toyco could have done to choke the engine. Why they chose this route is specifically known only to them, but I would hazard a guess that they were very concerned about packaging, and wanted to squeeze the set up as much as possible. They succeeded in that.
After a cursory look in the ports, we move on to the factory valve job. From what I have seen so far, the OEM valve job is pretty good for a production job, and they did take a little extra time to blend the valve seats into the ports. This is uncommon in other engines, and negates a great deal of the expected gains from a "street port" job. The bulk of the improvements on a so called street port are from blending the valve seats into the shape of the ports. Toyco has already done most of that for us. Any porting to be done at this point is going to have to be carefully planned with specific goals in mind. Preliminary testing of a Supra head showed me that the intakes are very nice, and respond nicely to increased valve lift, a clear sign of a good port design. On the other hand, the exhausts are diabolical. Japanese engine theory bases exhaust port design on thermodynamics, not airflow. It is not uncommon for an American tuner to see large gains in performance by just opening up the exhaust ports on Japanese engines. This is not simple or easy with the 2JZ-GTE. The stock exhaust ports fail to flow any more air at about 8mm of lift (0.317"). Increasing high lift flow is the first thing on the mind of the man holding the die grinder. Still there is not a lot to be gained.
For these reasons, staggered cam sizes seem to work well in the Supra. A longer duration exhaust cam combined with a shorter duration intake cam can yield surprising results. Never forget, your cams must compliment the engine. Part of that is recognizing that valve lift over 8mm on the exhaust only promotes valve spring failure. For that reason, I don't recommend exceeding stock lift on the exhaust side. There is no advantage except in the driver's mind.
Once we have the cams chosen, the next item in the head that needs attention is the valve springs. The OEM springs are just about soft enough to collapse with a thumb and forefinger. Well, maybe not quite that bad, but you get the picture. The OEM springs have a 40 lb seat pressure. With adequate boost, it is theoretically possible to actually blow the valves open, and if you are running 30+ psi on race gas, you are getting into the marginal performance area for stock springs. It used to be that the only stiffer springs available were around 80 lbs seat pressure. While that is a nice thought, it is very hard on the valves and the seats. There are now, fortunately, springs in the 60 lb range available. They provide enough seat pressure to positively close the valves without hammering the seats, valve stems, retainers, and keepers to death. Valve cooling depends on good closure, the heat from the valve head is transferred to the cooling system through the valve seat, so good contact is a must.
Before we move on to cutting the seats, retainers and keepers need a moment of attention. You will see titanium retainers touted as the gnat's eyebrows for keeping your valves happy and safe from valve float. If you have a lot of money to spend, they won't hurt, but titanium does have a shorter service life than steel. Titanium will tend to fret where steel is a little more resilient. The reason I bring this up is because the 2JZ-GTE is not known for floating its valves, in fact, even with the wimpy stock springs there have been some really powerful engines built that lasted quite well. I would call titanium retainers completely optional in my build up, and leave it to the customer's discretion whether he wanted to spend that money on retainers with a marginal performance increase, or spend that money somewhere else where it might have a more significant effect. That said, I would HIGHLY recommend them on ANY race engine. There is an insurance factor that comes with them that is appropriate for a competition engine, but I would be expecting to disassemble and inspect that engine at least every season.

SEAT CUTTING
Here's where we touch on a little religion. In the time I have been working with cylinder heads (about 20 years now), I have found that there are two distinct schools of thought on valve contact seat width. Some prefer wider, some prefer narrower. The wider guys claim longer valve life through better heat transfer, the narrower guys claim better heat transfer through crushing the carbon on the face of the valve and seat with a higher psi on the narrower seat. Some flow guys like wider seats and claim that narrow seats cause unwanted turbulence, other guys think that narrow seats can be used to induce useful turbulence. On street heads that won't see a lot of very heavy duty use, I prefer narrower seats. On race engines I always go wider. Typically, I use the manufacturer's spec, and just apply the tight end of the tolerance for street and the wide end for race.
The other thing that I like to do is to narrow the valve contact face to suit the width of the seat. It does shorten the ultimate service life of the valve, but it gets the port open in a hurry at very small lifts. I typically set the contact face to 2.5 to 3 times the width of the contact seat, so it measures somewhere between 3 and 4 millimeters. I backcut the valve with somewhere between a 30 and 35 degree cut until I have the valve face width where I want it. I normally place the bottom edge of the contact seat about 1mm up from the bottom edge of the valve contact face. I also use a drill press and a die grinder with a coarse cartridge roll to smooth out the valve stem where the head is welded to it. At the same time, I am reducing the stem diameter to slightly more than the diameter of the keeper groove (the weakest part of the stem) to get as much material out of the port as possible. Finally, I finish the valve with a clean 45 degree cut. The books like to tell you to make a 45 degree seat and a 44.5 degree valve, but in my experience, if the seat is properly cut, the interference objective with the different angles doesn't help at all.
When the seats themselves are cut, you will need to address the technology the machine shop uses. Most modern tuners, myself included, swear by the Serdi carbide cutter technology. This method provides the most consistent and concentric seats from valve to valve that can be had. The other method still in use involves abrasive stones cut at various angles and used in sequence to cut the valve seats one angle at a time. It is challenging, and sometimes very difficult to do really good work with this method. It requires a skilled and patient operator to do nice work with stones. I have done many, many, heads with stones. It is still a viable technology, but given the choice between the single cut carbide method and the abrasive stone method, I'll take the cutters every time.
When you choose the cutters, you will probably be asked questions like:"Do you want multiple angles or full radius?" "How many angles would you like; 5, 7, or 9?""Will you be using the stock valves or do you want to go oversize?""Will this head be ported?""Would you like us to remove the guides for your port work, and reinstall them after porting is complete" "Would you like the guides counterbored, cut off square, or left alone after they are installed in the port?"
Now we get to the meat of the port work. All of these questions are going to depend on your budget and ultimate power goals. They will also depend on your port artist's view of how to get air molecules moving through that port. I have seen ports where the guides were completely blended in to the roof of the port, and others where the guides were practically untouched. The truth is, it will all depend on where the gains (if any) can be made. Typically the biggest gains are in the last 1/2" of the port before the valve. The blending work of the seat and the shape of the port floor are the two areas I typically work on first. The port floor should not have any radical angle changes, the idea is to convince the air that it wants to follow the port's inherent shape, and not argue with the direction of the port wall. Angular changes will most certainly discourage the molecules and they will tend to form little pockets of undesirable turbulence.
The same is true for the roof and sides of the port, but generally these are not where big improvements are made, unless there are significant increases in overall size. Typically, I just knock down the casting flash and provide a finish that makes sense for what is happening next. If the exhaust ports are going to be coated with a thermal barrier coating, I will leave a rough finish, if not, they are easier to clean with a polished surface. Polishing does little to enhance flow, but certainly makes clean up at the next rebuild much easier. In fact, some tuners use polishing to hide the flaws in their work, so if you do have the ports polished, examine the work carefully, and last but not least NEVER polish intakes. A slightly rough surface actually works much better on the intake side. I usually finish intakes with a 150 grit cartridge roll. It's a smooth surface, but not glassy smooth.
Back to port sizing. You are fighting a battle between making the port large enough to flow the amount of air that you want but still maintain enough velocity to promote good cylinder filling AND good scavenging. This is where the art comes in. The man with the die grinder has to be able to think like an air molecule and create a shape that will give both volume and velocity. The biggest complaint I have with the 2JZ-GTE head is the exhaust ports are very small for very big power. This is really good for velocity, and velocity is good for boost, but by the same token, you have to be able to evacuate the exhaust manifold reliably, or you will have exhaust bleeding back into cylinders that are at the end of the power cycle. This causes a natural EGR effect because the cylinder that you wanted to have empty and ready for a fresh charge is now contaminated with inert end gases that will dampen the combustion process on the next cycle. This is why positive pressure is so desireable. Positive pressure is when your manifold pressure is greater than your exhaust pressure. With the OEM twins, this pressure ratio is negative, sometimes as much as 3:1. Yes, that means when you are seeing 20 psi in the intake manifold the exhaust manifold is seeing 60 (!) psi. With the bigger turbos like the TO4R, this isn't nearly as big an issue, and negative pressure ratios are smaller, so we are looking to improve flow without sacrificing too much velocity.
I like to see port area between 80% and 85% of the valve area in the exhausts. I will typically take a junk valve and grind down the diameter to use as a guide, especially in exhaust ports, to make sure that my walls stay somewhat round and not wavy, and to let me know when I have gone far enough. It is possible to go too big, although I don't think there's enough wall thickness with the GTE head to get into size trouble without getting into very serious wall thickness trouble. As I mentioned before, the intakes are really quite nice straight from Toyota, and need little if any attention. There's not a lot to be gained there.
Another area that needs attention while we are here is the combustion chamber itself. You will notice a sharp edge on either side of the chamber where the squish area begins. That edge needs to be rounded and smoothed. It is also a good idea to puy the head on top of the block with the dowel pins installed and check the rounded parts of the combustion chamber. If they are not flush with the cylinder walls, that edge needs to be rounded and smoothed as well. There should be NO sharp edges in the combustion chamber when you are done. HOWEVER, don't go crazy with this. The sealing surface between the cylinders is VERY small, about 8mm across. If you go overboard here, you could compromise the seal between the cylinders, and that will ruin a perfectly good head. All you are doing is removing the sharp edge to prevent autoignition.

PUTTING IT ALL TOGETHER
Now that our hands are numb and frozen from holding the die grinder and making a big mess with aluminum chips all over the shop floor, we can clean everything up and get ready for assembly. I typically cheat. I get everything basically clean, then insert the buckets into the head and bolt on the cams. I mark each of the valves with a permanent marker so I know where they go, then I put in a shim on the valve I want to check and install the valve without the spring or retainer. I typically use a medium thickness shim, then I see how much I will need to shorten the stem to stay in a reasonable range. Sometimes this means having the thinnest possible shim available to check clearance. I do this without the retainer and springs so that I can measure the overall length of the stem (there is a minimum spec, DON'T ignore it or you will be dropping valves!) and trim the length to suit the shims I have on hand. If you have access to a complete set of shims in the full range of sizes, you don't need to do this, you can just pick out the correct shim and install it. Of course if you have a set of shims like that, I want to be YOUR friend! So we go down all 24 valves, and select the right shims and trim the valves where necessary.
On to measuring the chamber volume. For this drill, you will need a few typically not available tools. You need a laboratory burette, it should be accurate to 0.1 cc or better. If you can find one that is about 30cc, it will make the job much easier, since we are measuring somewhere around 55-60 cc. You need to do this to measure your compression ratio. So, get a piece of clear plexiglass big enough to cover one of the combustion chambers, drill two smallish holes in it, install the valves with a grease seal around the seat, then put the plexiglass over the chamber with another light grease seal. Now take the burette, fill it with solvent or some other convenient fluid, but not water, it doesn't seem to work well for this, and please don't use gasoline for the obvious reasons. Fill the sealed chamber with solvent, and measure the exact volume to 0.1 cc. This is your combustion chamber volume, and your engine builder really needs to know this number. Also, you will want to be sure that all of your combustion chambers are within 0.1 cc of each other. It can make the difference between a detonated and destroyed cylinder, or just driving home normally. Document this, and save that document in a safe place. It will become valuable down the road when you need to do this again.
Finally, we clean up the head one more time, maybe I forgot to mention, but NOTHING beats hot soapy water for getting engine parts clean. Solvent tanks do a wonderful job of removing grease, but there is always a film of dirt left after the solvent is gone, so I always do final prep with water based cleaners (avoid the temptation to use Castrol SuperClean on aluminum, you'll be glad you did, it has lye in it that makes aluminum ugly) like Simple Green or liquid laundry detergent that is properly diluted. Rinse thoroughly with the hottest water you can stand and blow out all the holes with air. I use Red Line assembly lube because it really works. My favorite test is to take a spot of Red Line's assembly lube and put it in a small container with some engine oil. Swish it around, watch it completely disappear. Try that with a lithium grease based assembly lube! I have also seen this same lube completely protect an engine that had the oil pump fail on start up. We ran the thing up and down the street twice, fairly hard, then realized it wasn't a bad wire, there really was NO oil pressure. The engine was perfect on disassembly, even the rod and main bearings were as new. It works.
At this point we are home free. Installing the seals, springs, retainers, and keepers is really a no brainer. Just don't forget to tap each of the valves with a plastic hammer to seat the keepers before you install the buckets and shims.

Got questions? Think I'm clueless and need an education? Send me an email.

Lance

The above article is copyright Lance Wolrab and TO4R.com and cannot be reproduced in any way without written permission from the author.

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