High Compression K-Series builds??

4 posts / 0 new
Last post
Grant Dryburgh
Grant Dryburgh's picture
Online
Last seen: 10 min 1 sec ago
Joined: 24/10/2019
High Compression K-Series builds??

Just been having a look at various High power K-Series builds pondering options for later down the road maybe building a high power 1800K for my 7 Smile 

Got me wondering about CR ratios, most I've seen seem to be around 11.5:1 like the R500K. I've seen piston options for 12 and even 12.5:1 so has anyone come across a K running 12:1 or more and any thoughts regarding fuel octane and detonation with that much comp in a K ? Pros/cons?

No plans for anything just a topic for discussion/thoughts? 

oilyhands
Offline
Last seen: 3 hours 46 min ago
Joined: 17/04/2014

Longer duration cams need and tolerate higher static compression ratios, but generally there is not much to be gained from going higher than 11.8:1, certainly very few of the engines I have built have had static CRs higher than that, there is always the danger of detonation with resultant destruction of the engine if you go too high or if the octane rating of the fuel is not high enough or of the timing is a little too far advanced, I would sooner go a little too low and sacrifice the odd lb/ft of torque and have the engine's safety margin a little wider.

Oily 

Grant Dryburgh
Grant Dryburgh's picture
Online
Last seen: 10 min 1 sec ago
Joined: 24/10/2019

Thanks Oily, 

I know actual compression would depend on the cams etc but would yous say for something around R500 kind of power with cams like 1444s and required headwork etc pistons advertised as 12:1 compression would be ok ? Or better to play it a bit safer with 11.5:1? 

oilyhands
Offline
Last seen: 3 hours 46 min ago
Joined: 17/04/2014

You could probably go to 12:1, but compression alone isn't the only factor to consider, squish, chamber shape and finish these will have an impact on how well the engine tolerates the CR. Beyond 11.5:1 it's diminishing returns and increasing risk. 1444s dont have a lot of duration compared  to the 1227 R500 cams, just a very rapid lift ramp.

Oily