I have an E31 cylinder head laying in the shop and was wondering if it offers any performance advantages over the E88 casting that is currently on my '73? I plan on removing the flat tops in favor of a pair of 4 bolt roundtops. My roundtops are mounted on a manifold with the casting number E41. Can anyone tell me what year Z this intake setup would have come from? Even though I haven't had a Z for many years I've been hoarding parts for a long time in hopes of finding another one to play with. I've had this head and intake for so long now that I can't remember what year car I took them off of. Thanks in advance. Cheers, Scott

My understanding is that there were four major variations of the soi-disant "E88" head for US cars. In my mind, I call them: Early; Small chamber; Large chamber; and Big valve.

• Early - used on late '71 cars, from maybe 6/71-8/71 (give or take). Had a small chamber with high squish very similar to the E31.
  
• Small chamber - '72 cars, mostly. Chamber volume not much bigger than the early E88 & E31, but reshaped for emissions with much less squish.
  
• Large chamber - most '73 cars. Larger chamber for lower compression than the previous. Otherwise much the same as the Small chamber.
  
• Big valve - '74 260Z. Same as Large chamber, but larger exhaust valves.

If it is original, I'd suspect your '73 head is what I call the Large chamber.

Would the E31 give better performance? Maybe a little over the Large chamber or Big valve. The E31 will give higher compression (about .5 point) over the two larger chamber heads, yet be resistant to detonation due to the increase in squish.

An E31 will have similar compression to a Small chamber head, but will be less prone to detonation.

For street use the E31 would be about the same as an Early E88.

But for a normal street motor, the maximum difference will not be very big, regardless. If the E88 you have on the engine now does not need rebuilt, I wouldn't spend the time, money and effort to change it. If it needs a valve job anyway, sure, might as well use the E31 instead.

But don't expect a big difference either way.

Edited February 16, 201114 yr by Arne

The E31 head would have come from a 1970 or 71. Are you sure the E41 is the casting on the intake manifold or is it on the balance tube? The 1970-72 have E46 intake manifolds. I'm not sure about a 1973, or later intake manifolds.

-Mike

Thanks Arne and Mike. The manifolds and the balance tube both have E41 cast into them Mike, so the mystery deepens on the intake front. The E88 that's on the engine is the original 123,000 mile head and seems to work just fine. I also have 2 spare E88's. One of them came off a friends 260Z. The other one was given to me by a guy who was going to throw it away, so I've no idea what year car it's from. Cheers, Scott

If the manifold is specifically a 4 screw manifold it's 70ish. 3 screws were 72ish

My understanding is that there were four major variations of the soi-disant "E88" head for US cars. In my mind, I call them: Early; Small chamber; Large chamber; and Big valve.

Agreed - there are at least 4 heads with casting marks E88. I believe that Arnie has them a little confused.

Late 71 E88:

6/71- 8/71 42.4 cc Combustion Chamber is the same volume and combustion chamber design is the same as the E31.

72 E88

9/71 through 7/72 44.7cc Combustion chamber design is the same as Late 71 E88 & E31. Castings around the exhaust valve were improved, intake and exhaust port runners reshaped slightly.

73 E88

8/72 though 7/73 47.8cc Combustion chamber redesigned for emissions. This head has a raised quench area {meaning it sits higher in the combustion chamber} - that increases chamber temperatures for improved combustion. {improved for emissions reduction not performance}.

74 260 E88

8/73 through 12/74 47.8cc Combustion chamber design is the same as the 73, exhaust valve increased from 33mm to 35mm.

The only way to tell the Late 71 & 72 E88's from the emissions 73/74 E88's is to look at the combustion chamber shape. The Late 71 & 72 E88's have the same combustion chamber shape as the E31's which have a rounded or slightly hemispherical quench area a little deeper than the E31. You can see the "notched area" around the spark plug on these heads, its missing on the later 73/74 heads.

See: http://www.zhome.com/ZCMnL/tech/E31andE88Heads.htm

FWIW,

Carl B.

I have an E31 cylinder head laying in the shop and was wondering if it offers any performance advantages over the E88 casting that is currently on my '73?

It "could". It depends somewhat on how much money you are willing/able to spend. If both heads were in the same "as new" condition - the E31 swap would give you a slight increase in compression ratio, from 8.8:1 to 9:1.

The trouble is that not too many 40 year old E31 heads are in "as new" condition. The E31's suffered from very small cracks in the castings around the exhaust valve seats. So the first thing you want to assure is - that isn't a problem with the E31 you have. Secondly, not too many E31's are straight, and most of them have been milled at least once. If you have to take more than a few thousands off them to assure that they are flat - you could be getting into compression ratio's that todays pump gasoline won't support.

Unless you are willing/able to spend hundreds if not thousands of dollars on custom head work - I wouldn't recommend that swap.

FWIW,

Carl B.

My general information notes on intake manifold numbers are:

E46--68-71 4 screw SU

E88--72 3 screw SU

N33--73 flat top

N36--74 flat top

Notes also said the N36 were the ones that had a little more volume, and flowed a little better. No true numbers were given to verify though.

Bonzi Lon

Agreed - there are at least 4 heads with casting marks E88. I believe that Arnie has them a little confused.

Thanks for clarifying, Carl. But considering I was writing from memory in a motel room 900 miles away from my Z docs, I was close...

Thanks for the info Guys... Regarding the head swap, sounds like a classic case of 'if it ain't broke, don't fix it". Regarding the intake, there are 3 bolts that attach the roundtops to the E41 manifold and the carbs have 4 screws that hold the dashpot covers on. The manifold has water fittings and the vacuum fitting comes out the top. I am so pumped to have this car, and through your helpfulness and expertise you all are firing me up all the more... Cheers, Scott

3 bolts? I'm pretty certain that Z roundtops have 4 bolts to the manifold.