I want to start by saying something that is on every page on this website. I am not an expert. I do not know everything. I have a really good working knowledge of what I have been in contact with, however, I have not seen everything. I ask that you are take everything I say with a grain of salt, from my stroker information, to this head page. Remember, you get what you pay for, and all of this information is free. I am not trying to discredit myself, or my information, but all to often, over the first year I had these pages up, I found people taking what I wrote, and making it gospel. Sure, I have lots of information on this page, and I have made every effort to ensure the accuracy of what I wrote. However, I do not do this for a living. While I used to be a mechanic, I am no longer, and never worked exclusively on Datsuns. If you want someone who really knows what they are talking about with Datsun motors, go to the Don Potters or Dave Rebellos. These people make their living working on the L4 and L6 motors, and have done so very successfully. But they will not just give away what they have learned in all the years they have worked. You must pay for that service. If ultimate performance is you goal, go to them, don't do it yourself. I guarantee you will not be able to extract the performance or reliability that they can. Period. Now that I have discredited myself, here is what I have to say!

I have had so many questions e-mailed to me about performance questions for heads, that I needed to rewrite this page. My original intent was to focus entirely on the Stroker motor. And the emphasis on the P-90 and P-90A was in line with that. It is an excellent head for two types of motors. Any forced induction, such as a turbo or a supercharger, or a big inch motor, like the 3.1L. What I hope to do is outline what each of the heads are, dispel some myths that even I helped to perpetuate, and maybe give the average Joe and idea of what head is good for their application.

So what heads are out there?

Lots.

It helps to understand some of Nissans development timeline on their motor and heads. While this is not 100% accurate, it helps give a basic understanding.

When Datsun designed the L6 motor, they combined what they had learned from their highly successful L4 motors with a lot of design cues from the durable Mercedes L6 of that era,(as a matter of fact, bought the patent for it). And in typical Japanese fashion, they kept all the good parts, and improved most of the bad ones. With 7 main bearings for the crank, they are for the most part bullet proof.

But what about the heads!?!!??

First, you must find out what head you are looking at. You can tell by glancing on the passenger side,(U.S. models) of the head,(spark plug side), in-between the # 1 and # 2 spark plugs. Near the base of the head,(where aluminum stops and iron starts), there will be a letter and number combination. The early 240Z heads had an E-31 cast there. This head is a performance oriented head, with high compression, and as far as I know, was only built through 71. In 72, the E-88 replaced it, but for all purposes, is the same. It has a slightly larger and redesigned combustion chamber, which will lower your compression, (ever so little). But both these heads are impractical for any big-inch motor buildup. With a 3.1 stroker, the compression just gets to high, and other steps must be taken. Even for a 2.8, these are really too much compression and too poor design in the chamber.

But on with the time line. The E-88 head gained a larger exhaust valve as it was put on the 260. The E-88 gave way to the N-42. Up to this point, all these heads had round intake ports, and square exhaust ports. Some N-42's have notches for fuel injectors, some don't. For anything but all out performance, (ie full on race motor) the notches make virtually no difference if running carbs.

Then, with the 280Z, and fuel injection, the N-47 was introduced. This had round intakes, with notches for the fuel injectors. But more importantly, this was the introduction of the Exhaust liners. The exhaust port was now round, and lined with a metal "liner" whose purpose was to heat up red hot and in a glow plug effect, burn off unburned gasses, lowering emissions. It is interesting to note that this liner, sometimes referred to as the Evil Exhaust Liner, has been often lambasted, even by me, is actually very good. Paul Ruschman took the time to write me and give me some excellent background on the exhaust liners and their effect on performance. He actually did some extensive flow testing with many heads in various states of modification. Here is what he said:

Your claim that the round liner actually hurts flow is incorrect. In fact it outflows the STOCK square port by a noticeable margin. The Intake is a different matter though. On all heads utilizing the round exhaust port, N-47 and P-79, the Intake port has been recast with a straight wall on the side closest to the center of the cylinder so the port has a the shape of an upright "D". This port flows slightly less than the E-88, N-42, P-90. The slightly less flow is not a prob. as it will support approx. 230 HP of air flow on a naturally aspirated engine and this smaller intake port has much BETTER swirl characteristics due to the casting revision. That was the purpose in this casting revision. As any knowledgeable engine builder/tuner knows, swirl is very important when making consistent power, (better Volumetric efficiency in most engines, depending on the design of the port of course), as it promotes more complete combustion.

He went on to say a great deal more, which I am very grateful for, and has given me permission to share some of it with everyone.

What about a 2.8 motor?

This was one of the most common questions I received over the first years my web page was up, (and continue to receive). While the 3.1 motor sounds really cool on paper, it is downright expensive, and can be impractical for most people. So what head is the best for a higher performance 2.8? Ask 10 engine builders that same question, and you will get 10 different answers. As I have tried to stress, you need to look at the engine as a WHOLE. But since I talk about the engine as a whole on the 2.8 page, I will get straight to my thoughts on head selection. I agree with Paul about the N-47. It is an excellent all around head that offers great performance with some minor work. The N-47 head is also found on some early 80's Maximas. There is one important difference on the Maxima N-47 vs the Z N-47. One, the combustion chamber is significantly smaller than any previous L6 head, cc'ing between 39 and 40cc's. But more importantly, it has the squish combustion chamber design of the later ZX engines, or the P series heads. This allows great performance, with the appearance of a stock head. It has the smaller combustion chamber because the Maxima motor is a 2.4L motor. However, realize that drastic measures will need to be taken to use this head on a 2.8 motor. First, you at a minumum need the 2mm HKS head gasket to help lower the compression ratio. Second, the Maxima head has smaller valves similar to the E-31 and E-88 heads. To get the most from the heads, you need to fit the larger valves,(from the later heads), and unshroud the valves so they are not limited in the larger 2.8 motor. I would leave that to an experienced head machine shop. I am not about to go around grinding on the combustion chamber itself.

But what do you do to get the most out of your N-47, (non-maxima head)?

Again, I will defer to Paul, who says this better than I can:

In fact the N-47 series heads have approx. 75%-80% intake to exhaust flow ratio just by blending in the casting just behind the exhaust seat into the liner. This is the theoretical perfect flow ratio for a naturally aspirated engine. The liner has a much more generous short side radius and is MUCH wider at the turn/bowl which helps the air flow out of the port by not constricting it. This allows the air to slow down a little, (thus helps the air flow make the turn much easier so the air doesn't slam into the back wall of the port).

So what is he saying? He is saying that because the heads with liners have a larger radius coming out of the cylinder, and a larger area at the turn, the air has an easier time making that 90 degree turn to exit the head. Some minor work needs to be done to the bowl area to see the full benefit of the exhaust liner heads. The bowl area is immediately above the valve, and appears, well, like a bowl! It is where the air has to turn to make the entry into or out of the cylinder. The idea is to enlarge that area so the air can slow down, and has an eaiser time making that turn. When I get a chance, I will scan an excellent diagram from a book about porting chevy heads. It clearly illustrates what we are trying to say. Again, here is Paul:

We are familiar with fluid flow, and it takes the path of least resistance. If it must change direction dramatically, it slows down and loses energy. Now in a stock vs stock configuration, the square ports flow better. But with some minor bowl work on the liner heads, they really shine. When I port Datsun heads this is the main thing I do: I unshroud the valves by bringing the chamber wall out to the gasket and under cutting the chamber walls immediately around the valves to aid in air flow. Any work in the ports themselves will yield no performance benefits as the ports themselves already out flow the region in the chamber around the valves usually by 2 fold, depending on the head of course.

Right here, I need to say something about working on your head, either in the runners or in the chamber area. There are people out there who have worked on Nissan heads for longer than some of us have been alive. And they, who are "in the know" as I call it, are still learning stuff about the Z heads. What does this mean? It means that those of us with little to no knowledge of porting Z heads should leave it to the professionals. You can expect to spend anywhere from 300-1500 to get a Z head ported, and the more you spend, the better it gets. If you attempt some of the things Paul or I talk about, do so carefully, and be prepared to lose a head, or lose much of the performance you may have gained thus far. BE CAREFUL ABOUT GOING TO A CHEVY PLACE TO GET YOUR Z HEAD PORTED!!! Find somewhere that knows and understands Z heads. Otherwise, you will may be sorry in the long run. What commonly happens is someone works on the ports or chamber of a head, either you or someone who doesn't know Z heads, and ends up with less power than a stock head! If you are really interested in porting and doing it yourself, I recommend buying the following book. It offers excellent information on porting/polishing, and all the magic involved. It explains it in easy to understand terms the lend themselves to learning. The book is called (I'll put it here as soon as I find it, I misplaced it!! - it is a book about porting chevy cylinder heads).

So on with the heads. For a buildup of a 2.8 motor, or even the smaller 2.4 and 2.6 motors, the Maxima N-47 offers amazing flexibility, and keeps the compression up there. With the 2.8 and a Maxima head, the compression needs to be watched closely, for it is easy to end up with 11:1 or even higher compression. By juggling piston heights, gasket thickness, etc.. A streetable compression can be found. It is the "squish" design on the Maxima head offers greater protection against detonation, or pinging as it is sometimes called, so you can get away with a little higher compression than the earlier heads. But take into account what Paul and I said earlier. You really need to re-shape some of the combustion chamber to realize the potential of this head. Not something for the faint hearted! Besides, those heads are hard to find.

I haven't really talked about the later heads yet, so let me get on to them. The P series heads were introduced on the ZX motor. With the improved combustion chamber design, and flat top pistons, the Z now had more power than it ever had,(although it also weighed more than it ever had!). When I can get some pictures, I will put them here, but for now, you can go to the DATSUN GARAGE and look on his head page to see the dramatic difference in chamber design. The later style heads have a "quench" area, which squishes the fuel mixture around the spark plug. This promotes better combustion, and as a nice side result, more power, more mileage, etc.. Granted, these are small gains, almost unnoticeable, but there nonetheless. The first turbo motors had the N-42. I feel the primary reason was Nissan needed an exhaust port which didn't have the steel liners, for the turbo would cause this metal to overheat. However, they had no recent head designed for such, except the old N-42. They were quickly switched, (during the first year, so not many have it), to the newer P-90 heads.

The P-90, the P-90A and the P-79 all have the same combustion chamber, in both design and size. The advantage of the "turbo" heads, or the P-90 and P-90A is that they have the squish combustion chamber of the P-79,(better power, etc...), and the same size SQUARE exhaust ports as the earlier, E-31, E-88, N-42 heads. Again, take into account Paul's comments about the benefits of the exhaust liners. I found the square ports eaiser to work with for my knowledge on porting.

The P-90A was introduced in 82 and has hydraulic lifters instead of the former solid ones. Both P-90 heads are covered on my P-90 page.

As a side note, the first turbos were not available with a 5 speed because Datsun deemed that their existing 5 speed was inadequate for turbo use. So after adapting the stronger Borg T-5 to work with the L6, the turbo was available with the 5 speed. However, many people will tell you they shift horribly compared to the NA 5 speeds. Balky, poor shifting, and vague. Almost completely opposite of the NA boxes. This is a bogus myth circulated by those who haven't driven them. By something as simple as replacing the shifter mechanisim with a Hurst shifter on the T-5 trannys' they shift far more precise than the NA 5 speeds, and are stronger to boot. However, their gears may or may not be advantageous for your application.

To the best of my knowledge, the valve lengths are all the same on the later style heads,(P-79, P-90's), for I used some new valves I had laying around from an E-88 in my P-90A,(the E-88 had been fitted for the later, larger valves). As always, you should have a machine shop check the length before you order any valves or try any mods, like the one listed on The Datsun Garage homepage, written by Bryan Little, where he talks about using longer valves on the P-79 head, and shaving to get higher compression. I see no reason why you can't do this on the P-90 heads.

At this point, I need to make an important point again. Unless you are going to do Bryan Little's,(actually , the Z Doc in Roanoke, VA) mod,,(which is only good for the 2.8L) or are running a large displacement motor,(3.0 or 3.1), none of the three above mentioned heads,(the P- series), are for you. They simply have too much chamber area for any good application in a smaller motor. Your compression will be too low. On a 240 or 260 motor, I would recommend the N-47 from the early 80's maxima. Sure, with the mods to a P-series, your compression will be near stock, but we are looking for more performance, right! More compression generally equates to more power. If you are unsure of where you stand compression wise, take a visit to my compression page, and calculate your compression. There is an excellent program that was written by Walter Fath in the Sydney Z car club, and it was posted on the web. I had it e-mailed to me, and will post it on this page when I can. It is an interface program which lets you see what different combinations of heads, blocks, pistons, etc.. will produce. It is called Lengine, and I am currently asking permission for its use.
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