Compression of an E88 head

[guy_geo]

I'mo looking at the compresison ratio of the head I have on my engine..

10.5:1 ???

[Jeff G 78]

If all else is stock, you should have 8.3:1 CR. If the head has been milled it will be slightly higher.

[guy_geo]

E88 was not a high compression's head?

[Arne]

Not by today's standards, no. Actually, I think the highest compression for any of the L-series engines here in North America was 9.0:1.

There were at least 4 major versions of heads which carried the E88 casting number.

1. Late '71 were very similar to the E31 combustion chamber, but slightly lower compression, had a CR of 8.7:1 or so.
   
2. '72 had a different combustion chamber shape, and a CR a bit lower yet, about 8.3:1. (Sometimes called "small-chamber" E88.)
   
3. '73 changed the chamber shape yet again, CR about the same as the '72, maybe a touch lower. (Sometimes called "larger-chamber" E88.)
   
4. '74 was much the same chamber as the '73, but had larger exhaust valves.
   

[Jeff G 78]

Only if used in conjunction with flat top pistons from a '81-'83 ZX. If an E-88 is installed on an F54 block for example ('81-'83 ZX), it would net around 10:1 CR.

[guy_geo]

Looks like I have flat top pistons....

[Carl Beck]

Hi Guys:

I'm not sure where Jeff/Arne got 8.3:1 CR for the 1972 Model Year L24. The Factory Service Manual says it's 8.8:1.

After gathering statistics from several engines, most of the engine builders agreed that it actually comes out to the following.

L24 E-31 Head

Swept volume = 398.9cc

Combustion Chamber = 42.4cc (E31 Stock)

Gasket volume = 7.61cc

Deck Height = - 0.174 cc

42.4+7.61-0.174 = 49.836

49.836+398.9 = 448.736

448.736 / 49.836 = 9.004:1 compression ratio

L24 E88 Head (72 Model Year)

Swept volume = 398.9cc

Combustion Chamber = 44.7cc (E88-1972)

Gasket volume = 7.61 cc

Deck Height = -0.174

44.7+7,61-0.174 = 52.136

52.136+398.9= 451.036

451.036 / 52.136 = 8.65 : 1

Note: Deck Height is as measured, not published in the service manuals. Nonetheless Nissan seems to have included the deck height - as they reported 9:1 c/r for E31 Heads. But then Nissan reports 8.8 : 1 for 1972 Model Year, although it calculates out to 8.65 : 1

As you can see - if you play with the numbers - taking a few thousands off an E88 to assure it is flat, or un-shrouding the valves, or adding larger valves - - will all change the C/R to a great extent. As they can all increase/decrease the total combustion chamber volume.

With the pump gas available in most parts of the country - and lacking a modern engine management system - you really don't want to go much over a 9:1 CR for a street engine. If you do, you have to run 93 Octane, and have your timing spot-on at all times. It also leaves you no room for any possible future over-heading/blown headgasket episodes if that head needed to be milled again...

FWIW,

Carl B.

[Carl Beck]

Looks like I have flat top pistons....

If you have a stock L24 - you should have flat top pistons. But you don't have L28 size flat tops. So you won't have 10+ : 1 compression ratio's on your L24. (unless you over-bore the block an install larger pistons, or lengthen the stroke etc.).

FWIW,

Carl B.

[Jeff G 78]

Aww crap. Sorry about the bad info. I forgot that the 240 pistons are flat and that the CR is higher than in a 280.

[guy_geo]

OK, I'm trying to figure out what the previous onwer did on the engine's car...

I bought the car from Carlos Motorsport in California and brought it back here to Mtl.

Lost a good deal of info on that car...

[guy_geo]

OK.

I'm trying to fond out the + side or - side of the combo engine I have..

280ZX block

240Z head E88

OE cam

Headers

Anything special???

Why did the previous onwer told me I have a special engine???

[Jeff G 78]

Depends which 280ZX block it is. If it's a '81-'83, then you have the flat top pistons. Those with an E88 head should give you around 10:1 CR (depending on other work it could be a bit more or a bit less). If you have a '79 or '80 ZX block, then no, it's just a 2.8L with 8.3:1 CR.