Jump to content
Email-only Log-Ins Coming in December ×

IGNORED

Cylinder head numbers


Recommended Posts

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

Link to comment
Share on other sites


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.

  • Like 2
Link to comment
Share on other sites

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.

  • Like 1
Link to comment
Share on other sites

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 by EuroDat
Link to comment
Share on other sites

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

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
×
×
  • Create New...

Important Information

By using this site, you agree to our Privacy Policy and Guidelines. We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.