a_z_story Posted April 5, 2020 Share Posted April 5, 2020 Hello, I am trying to understand why my E31 cylinder head might have a "H" stamped camshaft from a 280zx L28E in it? After scouring the web, I've found one comment stating that it performs like a stage 1 upgrade, but it seems like the lift and duration specs are less than a L24 and L26 camshafts. Is there more to it than that? Segue into my build plans... I'm looking at mating this cylinder head to a N42 block with flat top pistons. I'm exploring all sorts of combos using parts from the two motors I have in my possession (L24 with E31 head mentioned above, L28 with N42/N47 combo) . I'm interested in a high compression N/A carbureted motor build to put into my 10/70 240z. Michael Quote Link to comment Share on other sites More sharing options...
JMortensen Posted April 5, 2020 Share Posted April 5, 2020 (edited) Any stock cam is simply too small for a high compression NA build. WAY too small. WAAAAAAAAAY too small. Most people find the Schneider cams online. Their Stage 4 would be my minimum for a build with SUs, that's .490/290. I had a similar .490/280 regrind on my car with stock compression and SUs. Worked GREAT, but wasn't quite enough cam when I switched to 44s. Then I screwed up the crank (balancer came loose, broke the keyway, rounded the end of the crank) so I built a higher compression bottom end. Ended up 11:1 with E31. Pinged like a mofo, had to severely retard timing to prevent that and was way down on power. Was looking to upgrade the cam again, and then I gave up and went LS. There are a couple on the market from ISKY and Erson I believe that run about .540 lift and 310 duration, that would be the one to use for a hot street motor with triples based on my experience. In order to run a big enough cam to make it worth the effort to install it you will need springs and retainers and shorter valve stem seals. Despite not liking their cams, the Schneider springs and retainers work great, and you can use off the shelf Ford 2.9L valve stem seals and that will allow for ~.600 lift without any problems IIRC. Edited April 5, 2020 by JMortensen Quote Link to comment Share on other sites More sharing options...
NewZed Posted April 5, 2020 Share Posted April 5, 2020 (edited) The old cam probably flattened a lobe so it was repaired with that one because they had it in stock. Odd timing coincidence... Edited April 5, 2020 by NewZed Quote Link to comment Share on other sites More sharing options...
a_z_story Posted April 5, 2020 Author Share Posted April 5, 2020 @jmortensen - Thanks for the insight - I should have been a bit more clear, I'm targeting 10:1 so nothing too outrageous as far as I can tell. Would like a reliable street engine that can run on higher octane pump gas. Does that change your camshaft suggestions at all? My initial thoughts are to use the N42 block, L28 crank, rods and flat top pistons with a 1.3mm head gasket, and then the e31 with the N47 valves, mild porting and combustion chamber work, and an aftermarket camshaft (put my $ into the head). Thought behind using the e31 head is to have the smaller combustion chamber with the flat tops to increase compression, and to also allow the use of my SUs (triples someday) and square port header. I entered this mix into a website engine calculator and came back with 3.0L (manually adding the combustion chamber volume to the cylinder volume) and ~10:1. I've seen several threads discussing similar builds, so I think this is somewhat on track... I still need to see if my cylinder head and and the block have been decked at all. I'm also curious to know what boring 1-3mm over would do? I also spent some time reading about a theory of using an L24 crank and rods with l28 flat top pistons to make a "unstroked" bottom end, which was an interesting idea but I'm not sure it ever came to fruition. Seems like you'd loose torque, but reduce the rotating mass? Tradeoff? Seems like there's a lot of ideas on the internet, but people never build em out! @newzed - That makes sense. It's an internally oiled cam, so does that get supplied oil through the e31 cam towers? I thought I read the origional e31 cams were solid and oiled with the spray bar. Mine looks to have both systems in place. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted April 5, 2020 Share Posted April 5, 2020 (edited) No change on cam recommendations. Again, that .490/280 cam worked really really well with SUs at 8.3:1 compression. It dwarfs all of those stock cams. If you look you'll probably see that I have hundreds of posts telling people to go bigger on the cam, no exaggeration. I am very biased, but it's because of my own experience. I've related this all before, but we're in quarantine, so what the hell... I built my L28 dished E31 combo and ran it, then added a small cam that my friend (a Nissan master tech and autocrosser) recommended. It was a high lift short duration cam, would make any of those stock cams look small. Aside from slightly changing the way it sounded at idle there was no noticeable change. Later I read online somewhere, probably on the old zhome.com mailing list, that people tended to use cams that are way too small. My friend had that .490/280 cam that he had accidentally ordered, and it was just sitting in his shop. He was afraid to install it. I bought it and he warned me how I was going to hate it, lose a bunch of bottom end, etc. but I went ahead and installed it anyway. It was probably worth 30 or 40hp, and there was no loss of bottom end at all, everywhere in the rpm range was so much better. I brought it by and let him drive it, and he immediately bought a .610/320 or some huge cam for his L18 with 44s in his race car. LOL. When I switched to the triples it was again probably 40 hp gain over the SUs, my wife was scared to drive it at first, but I really felt it could use more cam at that point. Then of course when I built the flat top bottom end it desperately needed more, but as I said, I gave up on it. 10:1 is pretty high compression for the crappy combustion chamber designs on the L heads. That's about what you get with an N42 and flat tops, and if you look, you'll see plenty of threads about pinging at that compression ratio with that combo. You can solve this with the cam, but it has to be big enough to compensate. That .540/310 cam would work great with triples and there are a lot of people running something around that size, so you don't have to take my speculation about it as your only guide. I don't know about SUs haven't tried them in a high compression build, but I suspect the same would be true. I think Greg Ira (gira) is selling a cam in about that same size range that was an old Don Potter grind. He would have more info on what to do with SUs if you're going that way, as he races EP and they are mandated. He is a member here, but I'm not sure how often he checks in anymore. You can also find him on FB. Edited April 5, 2020 by JMortensen Quote Link to comment Share on other sites More sharing options...
a_z_story Posted April 6, 2020 Author Share Posted April 6, 2020 Really appreciate the thorough responses Jon. I just picked up the L28 today and spent the afternoon getting it down to just the bottom end. Was interesting to remove the oil pan and see that the crank appears to have been lightened and balanced previously. Cylinder walls are smooth. No surprise flat tops already in there though... ha! I think the N42 block will be a nice foundation for what I hope to build. 8 hours ago, JMortensen said: 10:1 is pretty high compression for the crappy combustion chamber designs on the L heads. That's about what you get with an N42 and flat tops, and if you look, you'll see plenty of threads about pinging at that compression ratio with that combo. You can solve this with the cam, but it has to be big enough to compensate. That .540/310 cam would work great with triples and there are a lot of people running something around that size, so you don't have to take my speculation about it as your only guide. I don't know about SUs haven't tried them in a high compression build, but I suspect the same would be true. It seems like folks have the ping problem with the non-high quench heads more often in the 10:1-11:1 realm...would you say that's accurate? You mentioned your 11:1 build pinged badly - was the head or block decked on that? and did you try a 2mm headgasket? This is the output from that calculator I mentioned previously. Doesn't seem like the combustion chamber volume is taken into account in the total displacement value. It would be slick to slap that .540/310 cam into the e31, do the larger valves and run SUs for now and be able to transition to triples in the future with no downside from a conservative cam choice. I'll try to seek out Greg Ira and get his input...hell, maybe his cam? If you care to follow, and are on instagram, I made an account dedicated to the build. @a_z_story Quote Link to comment Share on other sites More sharing options...
JMortensen Posted April 6, 2020 Share Posted April 6, 2020 I cut the head just enough to make it flat, and replaced the valves with ones that didn't have any dish in the head. Stock gasket. It was just under 11, like 10.95:1 as I recall. I also ground out the extra spark plug threads, smoothed the chambers and cc's them, rounded the valve edge. It was pretty well optimized to not ping. The E31 has a better quench design than the E88 or N42, but not as good as the P heads. 2mm headgasket eliminates any benefit that you get from the better quench on the E31. Quote Link to comment Share on other sites More sharing options...
NewZed Posted April 6, 2020 Share Posted April 6, 2020 13 hours ago, a_z_story said: Doesn't seem like the combustion chamber volume is taken into account in the total displacement value. You must be thinking of total cylinder volume at the bottom of the stroke. The combustion chamber is not included in displacement. Because "displacement" is, literally, the volume that is displaced, or moved, by the piston during its stroke. You could call it "swept volume", for example. Compression ratio is the displacement volume divided by the combustion chamber volume. All of that displaced material is packed in to the tiny combustion chamber. Quote Link to comment Share on other sites More sharing options...
a_z_story Posted April 6, 2020 Author Share Posted April 6, 2020 (edited) @newzed Yep, I totally was. I now see how it's not a factor in displacement. However, I would think the compression ratio calculation is total cylinder volume at BDC (combustion chamber+head gasket volume+deck height+piston volume+displaced volume) / total volume at TDC (combustion chamber+head gasket volume+deck height+piston volume). Essentially the biggest volume/smallest volume. The combustion chamber, head gasket volume, cylinder head dome or dish all being part of that volume of air being compressed into the combustion chamber. Is that incorrect? We might be saying the same thing too...Lots of learning going on right now, so thanks in advance for the willingness to share the tribal knowledge. Michael Edited April 6, 2020 by a_z_story Quote Link to comment Share on other sites More sharing options...
NewZed Posted April 6, 2020 Share Posted April 6, 2020 (edited) That's a good point. I might be wrong on the second part about CR, haven't had the thought in my mind for quite a while. The displacement part is right though, and that's how engines are described. Size. My mistake. https://engineeringinsider.org/basic-definitions-used-engine-terminology/3/ Edited April 6, 2020 by NewZed Quote Link to comment Share on other sites More sharing options...
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