I've got an E31 head on its way from Portland. It appears to be in pretty good shape and I was thinking of putting it on an L28, preferably with flat-top pistons. Are there any problems with having too much compression? Should I be thinking about bigger valves.

OR.... I currently have an E88 on my L24, would it be better to just swap the E31 onto it, rather than going with the L28?

I have a 1971 240Z with a build date of 12/70 and has most of the features of the first gen. Series 1 body, interior, etc., but the engine numbers don't match and someone has already swapped a 5 speed in, so doing a total restore to make it original is not what I have in mind. I like the early look with the hatch vents in back etc., but prefer the five speed and perhaps the greater displacement of an L28. Any ideas?

I'll attach a couple pictures of the head to show you what condition it is in now. Thanks, Gary

And what about porting? New valves springs? Different Cam? I'm lost, but only want to have to do all these things once. I'm sure most is just a matter of opinion. I've downloaded the engine calculator, and with some combinations of the L28 and E31 with flattop pistons it seems like the compression gets awfully high.

Here's another shot of the E31

One final question, any changes suggested for cam or should I run with the one that came with? I want good performance and reasonable fuel economy, not trying for a street racer, but want to be able to get out and pass when I need to.

One last pic:

Gary240z,

There is a possibility that the E88 on your 71 240 is the small chamber version...The early 88s had small chamber of E31 and are very desirable in the SCCA ITS class,in that may flow better... unmodified,different casting.

Easy check if you decide to pull head...31 and 88 chambers look the same.

Being that engine/tranny has been swapped around....won't know for sure without looking. No exterior marking to verify....that I know of

david

It looks to me like your E31 has been shaved at some point. Not too much room between the "E31" casting number and the bottom of the head. I know, it's not the most scientific way to tell but it has worked for me in the past.

If it has been shaved, your compression will be higher than you expect. IMO putting the bigger valves in is a must, if not you might as well go with a shaved P90 or just an N42, since they already have the bigger valves and compression you're after.

I expected my car to run on pump gas with a stock bore L28 with flat tops and E31 mildly cut, about the same as yours from the looks of it, with unshrouded valves (read bigger chambers) and it doesn't. I need about 95 octane. According to the engine calc I was supposed to come out at 10.2:1 compression. I think I have something more like 11:1. My chambers are polished, there are no sharp edges and I still can't run pump gas, even with the timing backed WAY off. I can't prove my compression ratio, but everyone else's stories makes me think my compression is high.

A BIG cam would help on the compression and octane too. More overlap allows more compression with less octane, but you'll lose some low end.

On the other hand, mine hauls butt, and it's not a daily driver anymore. So this was a good way to go for me, but certainly wouldn't be a good thing for everyone.

Jon

You definetly want to get the head checked out for straightness

Stock width from top (Valve cover) to bottom is 108mm any less and its been milled. The last head I pulled off would have had to have 0.025 shaved off to fix. It had the banana factor.

Also get cam specs checked.

What's the cam profile?

CT

Howdy,

Thanks for all the replies. I don't have the head where I can find out all the pertinent info, but when I get it I'll take it to the local shop where they work on them. I'll have to wait until the head makes it up here from Portland, and that will probably depend on when my friend makes a trip north to see his parents (which doesn't happen too often, gee I wonder why?) or I can meet him down there.

I have an E31 head that I'm thinking of selling to help fund my race season. Ported polished slightly milled,large valves, new seats.

Mild cam. It ain't cheap though:

GaryZ240,

I'd have to agree with jmortensen about that head having been faced. If you look at your "c" jpeg it appears that the #3 and 4 chambers are much larger than the others. Just lay a straight sheet of paper on your monitor with the c.jpeg and try to line up the edges of the chambers towards the in/ex face.

I would guess that both ends of head have had more material removed than the center. If this is true you will have various compression ratios on the different cylinders. The head may need cc-ing to operate properly.

I also would not use the cam or rockers if what appears to be rust actually is, and not some sort of reddish assembly lube. Also, if the head was milled to correct a bow'ed condition then the straightness of the cam towers is also a question area.

When the head is in your hands you will be able to access it's condition more accurately, and get estimates to correct any problems.

I hope I'm wrong (wouldn't be the 1st time).

GaryZ240,

I'd have to agree with jmortensen about that head having been faced. If you look at your "c" jpeg it appears that the #3 and 4 chambers are much larger than the others. Just lay a straight sheet of paper on your monitor with the c.jpeg and try to line up the edges of the chambers towards the in/ex face.

I would guess that both ends of head have had more material removed than the center. If this is true you will have various compression ratios on the different cylinders. The head may need cc-ing to operate properly.

I also would not use the cam or rockers if what appears to be rust actually is, and not some sort of reddish assembly lube. Also, if the head was milled to correct a bow'ed condition then the straightness of the cam towers is also a question area.

When the head is in your hands you will be able to access it's condition more accurately, and get estimates to correct any problems.

I hope I'm wrong (wouldn't be the 1st time).

Sorry guys, I hit my browser "back" button and it posted again. Tried the edit/ delete post and don't have privleges to delete the copy or origional.

All right guys, my e31 has been majorly shaved and the guys I took it to for the larger valves and a run through are concerned about clearance etc. The cam towers already have been shimmed but they think I should have a shim added for the entire head -- they don't think .020 is enough and recommend .040 or even .060 as better. I haven't been abled to find such a shim that thick. They usually go to Innovative Machine and Supply http://www.innomach.com/shims.htm, but they don't stock for the older cars. They will, however make me a custom one for $125 plus. Am I just wasting my money (something I have little enough of in the first place) or will the investment in the e31 be a good thing. I have two of these heads, but the other one has some major corrossion issues in the valve areas. Should I stick with the e88 I have? Does anyone else make a reasonably priced shim? Gary