Reggie_ghee Posted April 7, 2014 Report Share Posted April 7, 2014 (edited) wanna do up a 4k engine N/A any ideas? wondering how the 3k heads hold up and the difference in the compression? Edited April 7, 2014 by Reggie_ghee Quote Link to comment Share on other sites More sharing options...
B.L.Z.BUB Posted April 7, 2014 Report Share Posted April 7, 2014 http://www.rollaclub.com/wiki/index.php?title=Tech:Engine/K_Series/How_to_build_a_tough_K_motor Quote Link to comment Share on other sites More sharing options...
altezzaclub Posted April 7, 2014 Report Share Posted April 7, 2014 3K combustion chamber is about 29ml, 4K about 31ml. You'd have to measure them yourself to be accurate. Quote Link to comment Share on other sites More sharing options...
styler Posted May 8, 2014 Report Share Posted May 8, 2014 altezzaclub is that for flat top heads? I also have figures of 36cc and 40cc for 3k / 4k flat top heads from a while back, did you measure these yourself with the ol' burette and perspex plate by any chance? I know the twin squish are much smaller with herron style pistons to suit on some 4k / some 5k, and then there's the other 5k style is shallow dish -8cc or so, not sure on head cc on it. Quote Link to comment Share on other sites More sharing options...
altezzaclub Posted May 8, 2014 Report Share Posted May 8, 2014 I also have figures of 36cc and 40cc for 3k / 4k flat top heads from a while back, Funny, I was going through this with Steve last night.. if you back-calculate the 4K head volume from the comp ratio of 9.1 : 1 it should be 34.5cc. If you use a compression ratio of 9.4 to one then the head volume has to be 32.6cc. I measured mine with a lab pipette & plastic sheet and got 31cc on a stock (I assume!) head. This is on KE70 4Ks. That was working with the published bore and stroke, flat-top 4K pistons and a head gasket of 79mm diameter and 1.1mm thick. (which I measured off a used one last night, don't forget the gasket is larger than the cyl bore) So maybe the factory measure in some technical way rather than just having whatever spark plugs and valves in there. Richo and I measured his brand-new shallow dish 5K pistons a month back and the dish was 5point something cc, I can't remember offhand, he wrote it all down as we measured his 4K and 3K head volumes. Basically, in a 4K block the dish removes the extra compression from having 5K pistons, so you still have to skim something to raise the CR. I'd be tempted to deck the block and the top of the pistons to remove some dish!! He's using the 3K head to raise compression, so a 3K head, 4K block and 5K bore. I'm dying to see it going! Quote Link to comment Share on other sites More sharing options...
altezzaclub Posted May 8, 2014 Report Share Posted May 8, 2014 Here's what I reckoned. You guys can check the figures in case I've made a cockup... We could back-calculate from the 3K being 1166cc and CR 9.1:1. Head gasket plus combustion chamber can be 'X'. 1166/4=291.5cc per cyl. So (291.5+X)/X=9.1 or 291.5+X=9.1X or 291.5=8.1X so X=36cc, gasket about 5cc so combustion chamber 31cc. For the 4K, 1290cc with a CR of 9.1 to 1 1290/4=322cc So (322+X)/X=9.1 or 322+X=9.1X or X=322/8.1 or 40cc. Gasket is 5.4cc (being 79mm by 1.1mm, larger than the bore, I just measured it) so 4K stock is 34.5cc It all depends on what CR you use, the 69-77 plain 3K and the 4K-C both have 9.1 to 1 in Wiki. If you use the 9.4CR then the 4K becomes (322+X)/X=9.4 or 322/8.4=X so X=38cc stock. knock off the 5.4 gasket for 32.6cc combustion chamber. The 3K becomes (291.5+X)/X=9.4 so 291.5/8.4=X or comb chamber is 34.7cc minus 5.4cc gasket for 29.3cc. Quote Link to comment Share on other sites More sharing options...
styler Posted May 9, 2014 Report Share Posted May 9, 2014 Hey altezzaclub, I use this online calculator, just scroll down for the results once entered... http://www.csgnetwork.com/compcalc.html I think the head gasket is around 75mm for 4k std, 80.5mm for 5k? Yeah there are a few combos of k motor parts haha, trying to get the compression right for NA Quote Link to comment Share on other sites More sharing options...
styler Posted May 9, 2014 Report Share Posted May 9, 2014 I think one major factor that is giving us the run around is measurments from pre skimmed heads and also rough syringe measurements. Need to import a cylinder head burette kit at some point... Quote Link to comment Share on other sites More sharing options...
styler Posted May 9, 2014 Report Share Posted May 9, 2014 Yeah -6cc for 5k shallow dish seems familiar, instead of -8cc. Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.