Bleach

Sounds like you know where the power really comes from... not the exhaust!

I think 0.080 inches... or eightly thousandths is a typical shave for the head to add compression in the 10.2 to 10.5:1 range. That assuming you use a closed chambered head like a P79 or P90 on flat top pistons. As for the earlier heads with dished pistons... I'm not sure if the compression gains are more or less when shaved that much.

If you're not going to shim up the cam towers to keep the timing chain timed correct, advance the cam to the #2 position on the sprocket or even #3 would be fine if you have a really long duration cam. (use all new timing components) and change the chain out more often. Every 75K to 100K at least.

zguy36

If you shave your head, then the valve timing will be off.
-jeremy-

ZChief

I pulled this from another site. I'm in the process of picking the right combo for my 240.

Heads Up on Cylider Heads
an excerpt from the ZCCW Newsletter
Compiled by: James Lux

Here's a nice background piece on cylinder heads from Z aficionado Carl Beck.

OK lets talk heads - Just like model years, you have to ask - best for what? So first lets consider using a basically stock head, with a good valve job - i.e.: you just want to get the best stock head for your application. Most of the people that I talk to about this are putting an L28 in an early Z. ( I did notice that one person on the list wanted to keep the L24 block, but this isn't too common yet)

The basic casting on the E31, E88 and N42 (early 280Z, 75-77) head is the same. The only major differences are the size of the combustion chambers, and the valves. Some late 280 (78) heads have the round exhaust ports, and these don't have the flow of the rectangular port heads. The N42 has the notched intake ports for the fuel injection.

The early Z's (70 & 71's) had the E31 head. You can identify this head, by the part number cast on the head (E31). The number is on the passenger side of the head, just above the block, in between the first and second spark plugs. This head has 42.5cc combustion chambers, 1.65 inch intake and 1.30 inch exhaust valves, 1.5 inch intake ports, and rectangular exhaust ports. (NOTE: if when you look at the letter and numbers, the bottom of the E and the 31 aren't clearly visible - you can bet that the head has been milled - this becomes important later).

The E88 head as installed on the 72/73 Z's is basically the same as the E31, only it has a larger combustion chambers - 44.7cc with larger 1.38 inch exhaust valves.

So the (design) tradeoff that Nissan made in 72 was compression for flow - the larger exhaust valves allowed better flow, and the reduction in compression allowed them to meet the 72 emissions standards, and got them ready for lower octane fuels (i.e.: Lead Free was coming!). All three years 70-72 were rated at 150bhp.

So why do I say the E88 is the best - well there are two main reasons. (remember we are talking about using basically stock heads on street cars). First, with the additional cost of six intake valves, I can install the 1.73 inch intake valves from the 280Z. (With the E31 head, I have to replace BOTH the intake and exhaust valves). Second, is the consideration of "margin". If I start with the E31 head, I have a higher compression ratio, which I have a hard time getting good enough gas to maintain, but then I blow a head gasket (common), and warp the head. Now I have to mill it, to get it straight again. So the compression is increased, now it pings, and then I have to reduce the timing advance, and lose power and response. If I start with the E88 head, and have to mill it later, then I still have a drivable car.

Another consideration is what pistons are you going to use? Dished, Flat Top, Turbos? You would NOT want to put the E31 head, on a L28 engine with flat top pistons. A slight mill to assure that it's straight and flat, and you wind up with a 11.+:1 compression ratio - not much fun on the street - you can't buy gas for it. Octane booster, is expensive and a pain in the neck to carry with you all the time. (I know, I have several older muscle cars with 11.+:1 compression ratios - fun to drive once in a while, like 1/4 mile at a time!)

So for a basically stock L28 with the flat top pistons (to pick up the compression again) I maintain that the E88 head with the bigger intake valves gives you the best all round trade-offs (this is what I have on my Z). If you use the dished pistons, then the E31 can be used, but you'll have to change both the intake and exhaust valves, and you will still have to be concerned about how much you can mill it.

Now lets say you are going to spend the big money, and do extensive head work. In this case you can start with almost any head. Most shops do recommend the rectangular exhaust ports however.- Carl Beck

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And an expert-Andrew Levy in fact-did indeed add some info. He responded with this post:

"The best cylinder head is one that is flat, with no cracks and little corrosion. The E31 and the 72 E88 have a better combustion chamber shape then the 73 E88. The E31 and 72 E88, use the smaller exhaust valves (1.30"). The E31 and E88 are based on the same casting and the port geometry is the same. The effects on the compression ratio, from the combustion chamber volume difference, is small, less than 5:1.

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To which Carl replied:

Hi Andy:

I stand corrected, and your right on the money related to Flat and no Cracks. I would only add, one that hasn't already been milled once!

As per Jerry's question, how do you tell the difference between a 72 E88 and a 73 E88? (other than measuring the exhaust valve size), or "other than you've just seen enough of them to know!" What you refer to as the 73 E88 went into production 8/73 from my records. Is this the same head as used on the 260 engine or did they only use this head for a few months?

My intent in pointing out the difference between the E31 and E88 was to make people think of the "stacking of tolerances" effects when changing from the stock head on a 280 block (compared to the N42, N47, P79, P90-turbo etc.). You'll increase compression with either the E88 or E31 because of their smaller cc volumes, (lets say .5 - .7) then add the .5 for the E31, then add the .5 for a head that has to be milled, and we go from a drivable car, to one that's not so drivable.

As compression goes up and baseline octane numbers go down (which they did over the years), aside from pre-ignition, you also begin to have problems with engine heat! (I did at any rate-I live in Florida). For a street car today, I don't believe that you really want to get much over 8.5:1 - 9.0:1 max. From what I read, and from the race teams that I've talked to over the years (Bob Sharp Racing and Local Guys that run at Daytona/Sebring), the E31 head, milled a little with flat top pistons, and place on a L28, yields around 11.0 -11.5:1! With dished pistons it's still in the 10.0:1 range. Not too streetable.