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Speedy Squirrel Speedy Squirrel is offline
Rocket Scientist
Join Date: Jun 2008
Location: Detroit
Posts: 898
I see this chart come up from time to time. There is one important thing missing, ignition timing.

You can run a high effective compression ratio, even with no intercooler. To do so you will run max power timing around 10 to 15 BTDC. With this timing, most of the combustion energy is released AFTER TDC. All it does is make the exhaust real hot, no power increase. Burns the exhaust valves, even our cool, sodium filled ones. At the other extreme, you can run low effective compression ratio, and lots of timing, but after you get to 28 BTDC or so, you are not making any more power, and you are still far from the detonation limit.

Optimising boost, compression ratio, and timing really comes down to choosing the maximum boost that the engine can structurally stand, and then raising the compression ratio and adjusting the timing until you reach the exhaust temp limit.
Old 04-07-2009, 07:12 PM
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