siteunseen Posted July 8, 2014 Share #1 Posted July 8, 2014 I got this a couple of years ago and am ready to get the cam kit for it. I've read go wild not mild to prevent detonation problems, but cam specs are all over the place so advise me please. Can't decide whether to put it on top of an L28 with flat pistons or the L24. It's got the big intake valves and steel seats, also teal colored valve seals. All new a few years ago, never been bolted down. maybe I should use the N47 I have. Link to comment https://www.classiczcars.com/topic/49602-e-31-head-whatchall-think/ Share on other sites More sharing options...
Arne Posted July 9, 2014 Share #2 Posted July 9, 2014 Big intakes on the L24 will likely require fly-cutting the block, unless it has already been bored .040" over. Save it for an L28. Link to comment https://www.classiczcars.com/topic/49602-e-31-head-whatchall-think/#findComment-451248 Share on other sites More sharing options...
LeonV Posted July 9, 2014 Share #3 Posted July 9, 2014 Besides the bigger valves, it looks like it might be ported. Are you sure the installed cam is stock? Link to comment https://www.classiczcars.com/topic/49602-e-31-head-whatchall-think/#findComment-451249 Share on other sites More sharing options...
madkaw Posted July 9, 2014 Share #4 Posted July 9, 2014 Look familiar:) Except mine is a E-88. Sure the exhaust wasn't upgraded also. I'd see if those aren't 35mm. Clearance would need to be checked for sure, or just unshroud everything including the cylinder bores. I would mic the cam to see where it comes in at. Maybe you do have something there too! L28 block would put you at about 10.25 I think. That's my next step. I already have the flat top block sitting on a stand Link to comment https://www.classiczcars.com/topic/49602-e-31-head-whatchall-think/#findComment-451251 Share on other sites More sharing options...
Zed Head Posted July 9, 2014 Share #5 Posted July 9, 2014 You might measure combustion chamber volume to see what your CR will be. You might find the flat-top L28 puts you at 12:1 or something. Link to comment https://www.classiczcars.com/topic/49602-e-31-head-whatchall-think/#findComment-451253 Share on other sites More sharing options...
Walter Moore Posted July 9, 2014 Share #6 Posted July 9, 2014 It looks to me like the exhaust valves are oversized also. Those are the ones that hit the block on an L24. I have big intake valves with stock exhaust valves on my engine, and they didn't cause any problem on my stock diameter L24. Somewhere here there is a thread where madkaw (Steve) shows a view from the bottom of the cylinder that illustrates the problem with big exhaust valves better than it could ever be explained in words. Link to comment https://www.classiczcars.com/topic/49602-e-31-head-whatchall-think/#findComment-451258 Share on other sites More sharing options...
madkaw Posted July 9, 2014 Share #7 Posted July 9, 2014 Not sure what pic you are refering to Walter, but the one above shows how I clearanced the bores. My block is .040 over , but I did it for breathing reasons.I'm pretty sure the engine calculator shows 10.25:1 with stock chamber size on a L28 flat-top. Link to comment https://www.classiczcars.com/topic/49602-e-31-head-whatchall-think/#findComment-451267 Share on other sites More sharing options...
siteunseen Posted July 10, 2014 Author Share #8 Posted July 10, 2014 I'd like to run SUs now and a Weber triple 40s set up I have for later. If it was your car which would you get? Stage iii or the competition? F54 with flat pistonsType intake exhaust durationstage iii .490 290° 242° competition .530 306° 264°Information from here, http://www.iskycams.com/pdfcatalog/2004-05/page176.pdf Link to comment https://www.classiczcars.com/topic/49602-e-31-head-whatchall-think/#findComment-451360 Share on other sites More sharing options...
Diseazd Posted July 10, 2014 Share #9 Posted July 10, 2014 (edited) I have the Isky Stage III in all of my Z's. It's a really nice regrind......good duration....no ping, but I run the P79 heads. When you install a regrind, install new rockers (IMO) and you'll have to geometry the cam ( wipe patterns centered with the correct lash pads). If you run flat top L28 pistons (P79), your compression ratio may be high enough to ping with the early E31.......not sure about that, but if you over bore, it'll be even more of a potential problem. The Isky Stage III makes nice power for me......I love it and Isky is great to work with. Sounds really nice at idle too.....that's important. Edited July 10, 2014 by Diseazd Link to comment https://www.classiczcars.com/topic/49602-e-31-head-whatchall-think/#findComment-451362 Share on other sites More sharing options...
Jarvo2 Posted July 10, 2014 Share #10 Posted July 10, 2014 On a related note, I'm in need of new valve seals, and probably could use a clean-up and valve job on my 72 240z (E88 head). Would it be worth me just purchasing a $400 head from Datsun Parts LLC which is already reconditioned, or should I take my existing head to a machine shop to have it rebuilt? Also, what is everyone's opinion on valve seats...should the be replaced to accommodate unleaded fuel? Link to comment https://www.classiczcars.com/topic/49602-e-31-head-whatchall-think/#findComment-451364 Share on other sites More sharing options...
siteunseen Posted July 10, 2014 Author Share #11 Posted July 10, 2014 (edited) Everything I've read says get the bronze out and replace with steel. If you can find a local machinist that is familiar with our engines I'd go that route, Datsun Parts LLC, from what I've read isn't too concerned about quality control, it's more about moving products. Start at post #44,http://www.classiczcars.com/forums/misc-s30/52438-steam-powered-z.html#post459944The full monty, http://www.classiczcars.com/forums/engine-drivetrain-s30/51401-bronze-valve-seats.html Edited July 10, 2014 by siteunseen Link to comment https://www.classiczcars.com/topic/49602-e-31-head-whatchall-think/#findComment-451365 Share on other sites More sharing options...
madkaw Posted July 11, 2014 Share #12 Posted July 11, 2014 Valve guide seals can't be stock with that size cam so check that.Unshrouded combustion chamber will lower CR a bit.So the competition cam will clear pistons okay? Link to comment https://www.classiczcars.com/topic/49602-e-31-head-whatchall-think/#findComment-451380 Share on other sites More sharing options...
Yarb
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