rjenman Posted October 23, 2005 Report Share Posted October 23, 2005 I understand that K heads are interchangeable between K blocks... Is there any issue with heads that are designed for blocks with a smaller bore going onto bigger-bore blocks? example: 3K or 4K head on 5K. Is there more to it than just bolting it on with a new gasket? :harhar: Quote Link to comment Share on other sites More sharing options...
Felix Posted October 23, 2005 Report Share Posted October 23, 2005 all engines (k/3k/4k) have the same bore size (75mm) apart from a 5k and 7k(both 80.5mm), which have dished pistons. if you bolt a k/3k/4k head on a 5k (7k has extra headbolts and isn't interchangable) you will lose compression. Quote Link to comment Share on other sites More sharing options...
rjenman Posted October 23, 2005 Author Report Share Posted October 23, 2005 ok i knew all of that except you gain compression, thats the idea Quote Link to comment Share on other sites More sharing options...
Felix Posted October 23, 2005 Report Share Posted October 23, 2005 ok i knew all of that except you gain compression, thats the idea huh? skimming your existing head gives more compression. putting an earlier head on a bigger bored 5k will lower the compression ratio. ok for forced induction. Quote Link to comment Share on other sites More sharing options...
rjenman Posted October 23, 2005 Author Report Share Posted October 23, 2005 ok now I'm confused, i was referring to heads like a 3K bigport, which gives 10 to 1 compression? Quote Link to comment Share on other sites More sharing options...
Felix Posted October 23, 2005 Report Share Posted October 23, 2005 ok, let me get this right. you are talking about putting an early 3k head on a 4k? if so, yes it will increase the compression. both have the same bore size..... stroke is different. Quote Link to comment Share on other sites More sharing options...
rjenman Posted October 23, 2005 Author Report Share Posted October 23, 2005 no no i'm talking about a 5K block :harhar: Quote Link to comment Share on other sites More sharing options...
Felix Posted October 23, 2005 Report Share Posted October 23, 2005 well a 5k has about a 16cc dish in its pistons in standard form. you will drop the compression ratio to about 8.0:1 with an early 3k head. attached is a pic of a 5k piston. Quote Link to comment Share on other sites More sharing options...
Dan Posted October 23, 2005 Report Share Posted October 23, 2005 both have the same bore size..... stroke is different. Ok. So you are saying that stroke made up the 100cc difference between the 3k and 4k. So, if i fit a 4k crank into my 3k block, I will then have a 1300? If so, if I fit a 5k crank into a 3k block, will I get the same result (1500cc)? So there was no changes in bore sizes, only stroke and compression? Sorry to move in on your topic rjenman Quote Link to comment Share on other sites More sharing options...
Felix Posted October 23, 2005 Report Share Posted October 23, 2005 3k = 75mm bore x 66mm stroke 4k = 75mm bore x 73mm stroke 5k = 80.5mm bore x 73mm stroke if you put a 4k crank in a 3k and changed nothing else, the pistons would hit the head. a 4k and a 5k crank are identical. in both the 5k's i have had they have "4k" cast on the crank in raised lettering. Quote Link to comment Share on other sites More sharing options...
Super Jamie Posted October 23, 2005 Report Share Posted October 23, 2005 7k block with earlier head apparently does work, you just use an earlier head gasket with a sealant (hylomar, permatex, silicon, etc) over the pushrod side and there's enough there to make it not leak. at least that's what i've seen on japanese starlet webpages Quote Link to comment Share on other sites More sharing options...
Felix Posted October 23, 2005 Report Share Posted October 23, 2005 you'd at least need a 5k head gasket, otherwise the firing ring would overhang the bore. Quote Link to comment Share on other sites More sharing options...
Super Jamie Posted October 23, 2005 Report Share Posted October 23, 2005 ahh! the guy in question used a 5k head he had from his last engine, so that would make sense Quote Link to comment Share on other sites More sharing options...
mikeys toy[RL] Posted October 23, 2005 Report Share Posted October 23, 2005 but isn't the 4k block about 3/4" taller to make up for the stroke? Quote Link to comment Share on other sites More sharing options...
cookie Posted October 24, 2005 Report Share Posted October 24, 2005 if I recall somewhere I read an article mention how to increase a 4K engine compression ratio to 10.1:1 the author use a 3K head + 4K block and porting plus polish the head :D Quote Link to comment Share on other sites More sharing options...
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