head shaving and increasing compression

[JBRoc01blaster]

Aright I just had a quick question about a chart that was posted in here in a " Head Shaving " thread ... First heres the chart



-.010" off = 10.20:1= 139 psi = 21.20 cc's
-.020" off = 10.58:1= 144 psi = 20.35 cc's
-.030" off = 11:10:1= 150 psi = 19.49 cc's
-.040" off = 11.47:1= 156 psi = 18.65 cc's
-.050" off = 11.98:1= 162 psi = 17.77 cc's



So if this chart is accurate then you get the greatest gain in terms of cc's when you only take .010 off even tho your psi will be greatest at .050 off ? I am going to have my head lapped and redesigned soon and I was probably going to have .030 shaved off so I can have the greatest gain in cc's without needing to run higher then 93 octane. If my greatest gain in cc's comes from only .010 off as stated in the chart then why would I have any more taken off ? I would think that your cc's would continue to increase as your psi increases but this suggests otherwise. I would like some more knowledge on this topic so I can be confident in my decision before moving forward and getting my head done. If anyone can accurately clear this up for me I would really appreciate it !

 

[Awk08]

the small cc increases from boring, or the decrease in cc's from shaving the head, are next to neglegent in performance gains or losses
a well designed combustion chamber and increased compression add far more power than the small loss in cc's

 

[best]

If I understand the question it is a case of diminished returns, as most power gains are.
For everything gained there is often something lost, so the trick is to find balance.
The greatest gain may come with the first 0.010" you shave off the head, but you will still continue to gain with each 0.010" cut off, but less, and each 0.010" will put you closer to problems like overheating and the need for critical jetting to avoid detonation. If you are redesigning the combustion chamber I would suggest you can go big as the hemispherical chamber with 50% squish has proved quite detonation resistant.

A limiting factor for doing a head shave is there is only a 0.050" lip around the stock chamber, so any more than that and you have to cut the squish area too, which is an angled cut. The squish angle is wrong on the stock head so don't just copy it.

 

[JBRoc01blaster]

Cool thanks for the info guys, I was hoping someone with your experience and knowledge would reply ! I just got an e-mail back from Ken this morning and he's gonna be lapping and redesigning my head on the blaster. Now that I have the whole psi/cc gain and loss cleared up, I'm gonna have .020 - .030 taken off. I'm split between .020 and .030 taken off, would having only .020 shaved off be noticably more forgiving on my motor ? If there is no real difference in terms or ware on the motor between .020 and .030 off then I would have .030 shaved off. Any input in that matter ?