Now that my 240 restoration is complete (well largely complete - is it ever complete complete?) I'm trying to clean up my garage.  I knew I had two spare heads, but find that I actually over the past decade have accumulated four.  Three are N42s while the other is E31.  I have an N42 on the car.  

The only difference I can see is that the valves are a bit larger on the 42.  I haven't measured the combustion chamber size, and don't know what differences there are in cams.  I'd like to know which head is correct for my '71 HLSS30 28726,and what differences there are in terms of performance.

Many thanks

I don't know a lot about the fine details, but the E31 was used on the early E31 L24 block upto around Oct/Nov 1970.

Your 240Z should have a P30 L24 block with an E88 head.

The N42 was on the early L28 in the 280Z leaded fuel version. They changed to the N47 when unleaded was introduced.

I know the early E88 had the same chambers as the E31 until somewhere around Aug 71 I believe. Not sure where that lines up with the Vin numbers. The later E88 heads had larger chambers and the E88 on the L26 got the bigger 35mm exhaust valve and the less desired emmision chambers.

The valves in the E31/E88 were 42mm inlet and 33mm exhaust. The N42 has 44mm and 35mm.

Chambers on the E31 and early E88 smaller than the N42.

9 hours ago, EuroDat said:

I don't know a lot about the fine details, but the E31 was used on the early E31 L24 block upto around Oct/Nov 1970.

My Dec 1970 car has the E31 head. 

Pictures tell a lot...............................

Just for reference, I know of an all original 3/71 with an E31. Also has the side drain oil pan, but on a p30 block.

1 hour ago, w3wilkes said:

My Dec 1970 car has the E31 head. 

That is why I said around Oct/Nov. Vin numbers would be a more accurate means of identifying the transition. There are so many points where things change.

14 hours ago, Richard McDonel said:

The only difference I can see is that the valves are a bit larger on the 42.  I haven't measured the combustion chamber size, and don't know what differences there are in cams.  I'd like to know which head is correct for my '71 HLSS30 28726,and what differences there are in terms of performance.

Many thanks

The chambers in the E31 and N42 are very similar. The N42 does have a little more capacity which will lower your compression ratio a little.

Depending on head gasket thickness and overbore you would expect roughly the following compression ratio.

E31 = 42.4cc chambers  C/R 9.0:1

N42 = 44.6cc chambers  C/R 8.5:1

 

Edited March 22, 20204 yr by EuroDat

Wow, you guys know your stuff!  

You remind me of something I witnessed at Pebble Beach Concours 2018.  I was standing next to an OSCA (low production Italian sports car mid 1940s through early '60s) when the judges came around.  A sign next to this car said that it had won the 1 litre class in the 1951 Mille Miglia.  One of the judges spent an inordinate amount of time peering under the hood.  Finally he stood up and pointedly asked the owner, "Is this the original cylinder head for this car?"  

"No" the owner answered, "but it IS the head that was on the car when it won the Mille Miglia."  You could see the judge pondering and puzzling , looking at his clipboard, as in "Do I dock this guy a point for an incorrect cylinder head, or let it go because this is the head that helped make the car famous?"  

I guess with an incorrect head on mine, I dare not enter it in a concours.  

Thanks All

I remembered a excellent website in Australia that might be some help. You can play with all the combinations.

http://www.ozdat.com.au/ozdatonline/enginedesign/

 

My 5/71, HLS30-30855, has the E31 head, as well as my 2/71, HLS30-23305.

Edited March 23, 20204 yr by Galaxybj
Added info

My 240z feb.'71 has a E88 head Original.. HLS30-26074

My early 71, 08750 has an E31.