N47 vs. E31

[Guest Anonymous]

okay stock to stock which head is better? the e31 or the n47. Non modified...this is going onto a l24.

[Dan Baldwin]

What's your intended usage? For a street driven L24, I'd go with the E31. It should give you ~9.1:1 compression ratio. The N42 would give you bigger valves, but CR would be more like 8.8:1. Also the N47 would require a different exhaust manifold/header, for its round exhaust ports.

[Guest Anonymous]

Thanks for the help, but heres one more question. Doesn't the E31 have to be reseated because they were made in the lead gas hay day?

[Synlubes]

Eddy,

 

If you don`t already have a head, I would look 4 a N-42!

 

You would not have to deal with valve seat issues as you would with an E-series head + as Dan said the N-42 already has the "big valves" and is a great stock, bolt on head that gives very good performance! They have the more common square exhaust ports + they can be found easily!

 

The N-47 is similar to the N-42(same size vavles) but has round exhaust ports. I did run an N-47 with a square port header 4 a while, I used 1 square & 1 round manifold gasket(back 2 back) and did not have any problems an the car ran well! It was only because I have nothing else at that time!

 

Just my opinion!

[Guest Anonymous]

okay lets say i have to rebuild the head i get (e31 or n47) then which one would be the best for my application (l24)

[Synlubes]

N-42

 

It would already have the big valves!

 

In my opinion, it is a very good head for bolt on performance!!!

[DAW]

Are you talking about a 280Z N47 head or a Maxima N47? They are very different heads.

 

With the availability of the Maxima N47 head, the E31 makes no sense on a stock 240Z shortblock; and the 280Z N47 head, while having bigger intake valves than the Maxima N47, has larger chambers which drop the c.r. lower to the point where performance compromise will definitely be felt.

 

The Maxima and 280Z heads both share the same size exhaust valves which matter the most on an L24 vs L28 (for a stock L24 you don't gain much from the larger intake valves vs a stock or modified L28). But it is also important that you realize that if you run these larger (44mm) exhaust valves on any head on a std bore (83mm) L24 you need to grind reliefs at the top of the cyl bore or the valves WILL crash into top of the cyl wall. The E31 and stock 240Z heads have 42mm exh valves that clear (although reliefs at exhaust side of bore helps flow even with smaller valves). Cutting the reliefs is easy even with the block in the car.

 

The Maxima N47, let's call it N47m, has a closed chamber design which seems to ping less than the E31 (about the same size chamber) at the same c.r.

 

All things considered, eliminate the E31 unless you are willing to put new hardened seats in it (and if you do this, you'll want to upgrade the exhaust valve size and maybe the intakes).

Between the N47m and the L28/280Z N47, let's call it N47z, both have provision for f.i. should you choose that route later, but the N47m is hands down the better performing head on a stock L24 due to the significantly higher c.r. produced and the closed chamber design. You do need to swap in a 240Z-280Z(X) cam and intake valve springs but that's trivial. DAW

[Synlubes]

DAW, I`m glad you jumped in here because I had foregot/didn`t remember to make the point about the cly wall knoch!

 

It sucks getting old!