wardy18 33 1 Cars Posted October 23, 2007 a couple of head gasket questions are there different thicknesses to go for, or is there a standard?! im asking because like me at the moment im looking to a couple of head skims on 2 different 8v heads, one skim is to match what piper say for their 270 cam (its a mates 205 so not wantin to go too mental and jus stick to what they recommend), and the other is my hillclimb 205 which i will be skimming as much as possible as advised hopefully by Catcams when fitting one of their cams but surely i also need to take into account the thickness of the head gasket as this will affect the compression ratio i am going for?! so is there a standard thickness i can work with so i can include it in my calculations when workin out how much needs to be skimmed or do i have to choose?! thanx for your time simon Share this post Link to post Share on other sites
DamirGTI 327 Posted October 23, 2007 Hello ! Well me thinks that thick or thin head gasket will affect the squish clearance much more than actual compression ratio Id use standard head gasket thickness , or if needed then a little bit ticker something like 1.50mm .. but not more than that .. Cheers ! Damir Share this post Link to post Share on other sites
wardy18 33 1 Cars Posted October 23, 2007 cool so if i work with 1.5mm in mind i can work out the amount to skim off the head what is squish clearence?! Share this post Link to post Share on other sites
DamirGTI 327 Posted October 23, 2007 Hi ! You must calculate the compressed thickness of the head gasket Squish clearance/height is the small clearance between the opposing (flat) regions of the piston crown and flat region of the head designed to give added compression and thus vortex-generated turbulence to the charge to mix it better and increase the burn rate - squish area serves to push the air-fuel mixture from the cylinder walls towards the spark plug . Swirl turbulence is the end result, sometimes called, in this case 'squish-induced swirl turbulence' to distinguish from port-induced swirl. There is of course also huge turbulence during the compression stroke anyway, especially at high rpm, generated by the piston shearing the charge off the cylinder walls. This creates very high speed vortices that improve the charge mixing.. It's best to keep the squish clearance between 0.035 and max. 0.045mm to assist combustion and cylinder scavenging . Cheers ! Damir Share this post Link to post Share on other sites
wardy18 33 1 Cars Posted October 24, 2007 thanx for the reply mate so the squish clearence u stated above of .035-.045mm is the distant from the very peak point of the piston to the very flat of the head, so i assume this distance including the compressed thickness of the head gasket?! how much does the gasket compress then, it must be quite alot, because if the above is correct then the 1.5mm gasket will compress to less than .35mm as obviously there will be a very small space between the top of the piston and the bottom of the head before adding the compressed gasket thickness!! is this correct mate?! sorry if its a little confusin how do you know how much a gasket will compress by?! i assume this all has to be takin into account when working out compression ratios and how much to skim from the head?! thanx again Share this post Link to post Share on other sites
DamirGTI 327 Posted October 24, 2007 (edited) Hi ! It's a bit tricky , yes you must calculate measurements of the compressed thickness of the head gasket but how much will this 1.50mm gasket compress i really don't know - if you have old gasket try measuring him and then buy new gasket of the same thickness ... Anyhow don't bother yourself too much with this as the worse thing you can do here is to increase the squish clearance , stick to OE setup where possible and reduce it maybe, never increase it.. - increasing it too much is power loss ! Heres a few pics (blue area on the piston crown and head/combustion chamber is the squish surface ..) : Cheers ! Damir Edited October 24, 2007 by DamirGTI Share this post Link to post Share on other sites
wardy18 33 1 Cars Posted October 24, 2007 ok sound, so pretty much stick to the 1.5mm head gasket and just work out how much can safely be skimmed from the head using the page you scanned for me a while back ie use the figure the page shows you scanned and work out how much has been skimmed of previously by measuring teh actual head compared to this standard figure then skim off any more thats needed to gain the correct compression ratio or settin you have been given!! thanx mate, its all falling into place now Share this post Link to post Share on other sites
DamirGTI 327 Posted October 25, 2007 (edited) Hi ! No probs always on service to help Heres some more to keep you awake : http://www.rbracing-rsr.com/squishcalc1.html I wish all the best results for you Damir Edited October 25, 2007 by DamirGTI Share this post Link to post Share on other sites
wardy18 33 1 Cars Posted October 25, 2007 ah nice one, that makes things a lot more clearer, i must say its gettin very technical so using a thinner head gasket will reduce the Squish Band and increase power but you run the risk of bending valves if you go too far and havent accounted for rod stretch and carbon build up very interesting and maybe a good thing to look into Share this post Link to post Share on other sites
