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Old February 19, 2013, 17:07   #151
Tim Dreas
FALaholic #: 17255
Join Date: Apr 2005
Location: York,PA
Posts: 898
Originally Posted by Cava3r4 View Post
another automotive analogy for you:
YOu build an engine with 10 to 1 compression with ALUMINUM heads. (the Alum heads supposedly will allow you to RUN ONE more compression point VS. cast iron heads due to the additional "cooling". So 9 to 1 with cast iron, 10 to 1 with Alum).
Okay, so you build a 10 to 1 engine. (pick your favorite brand.. 454 Chevy, 428 Ford, 440 Mopar).
With the CRAP gas you have today, SUPPOSEDLY 91 octane with SUPPOSEDLY only 10 percent "ethanol" you are going to PING.
PING or Detonation is when the flame front violently explodes. This is described as a force equal to hitting your piston with a sledge hammer.
Cast pistons are going to SHATTER.
FORGED pistons might survive but not for a LONG time!!
It's not only due to the reduced heat using an aluminum head that allows a higher static compression ratio, but the valve seats are ground on a cold head using the valve guides as centers. When an aluminum head heats up and expands the valve guides and valves usually go off center from the valve seats a bit, reducing their sealing and reducing the cylinder pressure. The valves just don't seal as well in an aluminum head resulting in lower cylinder pressures.
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