Re: how much boost can i run with 10.5~:1 compression? (BlackRado)
high compression and boost are a decent combination for an extremely responsive engine... the only problem is your margin of error is extremely reduced... by that I mean that your chances of detonation, pinging and knocking are drastically increased, which means that your air/fuel ratio must be spot on, and you can't ever lean out while trying to run the gears out...
higher compression will result in faster spool time, lower boost threshold, better off boost performance, and better gas milage while tooling around out of boost.
untimately it's more of a matter of how much abuse your pistons, cylinders and crank can take ... the end result is all that much more pressure at the point of compression of the air ...
a little information ... you have to consider the resultant total compression when considering the engines potential. If you're at a 10:1 compression ratio that means that if stoic is 14.7 pounds per square inch, then at full compression the air is compressed to 147psi ... when you add forced induction and lets say you're boosting to 10psi, then the engine is compressing the air in the cylinder to a 10:1 compression ratio to what is being put in ... so at 10psi of boost, the air is actually at 24.7 pounds per square inch, once the piston pushes up against the closed valves and the head, you've got 247psi at full compression...
this is why lowering the base compression ratio helps on FI applications ... you can shove more air into the piston, because the resultant TOTAL compression is lessened... off boost power will also be reduced, but your able to supply more air while in boost ... it's a trade off for more power later, rather than sooner.
