[eschaider]

Like the song says, "don't worry, be happy".

If it's your money, your parts then its your call. Once you start to supercharge 8psi will get old very fast and you will begin to increase boost. Shortly after that bad things will begin to happen.

There is a reason some manufacturers can successfully use 12:1 and 8 psi of boost. Most high octane gas can handle an effective c/r in the neighborhood of 11 or 12:1 even somewhat higher for a short periods of time. It is possible to get away with an effective or if you will operating compression ratio of 15:1 and with race fuels as high as 17:1. Pump gas at usually 93 octane or in some places as low as 91 octane is looking more like a 12:1 c/r limit for very short periods of time

When you boost an engine you raise the effective (or dynamic) c/r by the number of additional atmospheres you add to the intake. At 8 psi you are adding 8/14.7 or 0.54 additional atmospheres. A 0.54 atmosphere increase in manifold pressure means you increase the unmodified effective compression by 1.54 times. That makes a 12:1 compression ratio looks like 18,5:1 compression.

You can not run pump gas at 18:1 compression and MBT (maximum brake-torque timing) without killing parts — in any production engines.

In the case of the Coyote, Ford has several tools they use to mitigate the detonation potential at these thresholds. The ECU will take two steps to prevent detonation. The first will involve stretching out the intake valve closing point with the variable cam timing the way a long duration cam would do. By stretching out the intake valve closing point the engine's dynamic (read effective) compression is dramatically decreased. Unboosted or lightly boosted you still have a very responsive high compression essentially n/a engine.

In addition to the delayed intake valve closing point the ECU begins to pull timing until it can no longer "hear" the detonation. The effect is to produce a lower compression, detonation free but still supercharged (at low boost) engine with better than n/a performance. The other manufacturers who offer high compression lightly supercharged engines take very similar steps to protect the engine and manage warranty exposure / expense.

When you buy a supercharged Coyote crate motor directly from Ford it comes with 9.5:1 compression not 12:1 and has a Ford ECU with the VCT logic to stretch the intake valve closing point and the knock detection to pull timing at the first sign of detonation. Even the Edlebrock supercharged Coyote's on the Ford website come the same way with 9.5:1 compression.

Encouraging someone to build a 12:1 supercharged engine is sending someone down an expensive path of broken parts they do not deserve to experience. There are guys on this site who may want to experiment with supercharging and they do not deserve to be steered into destructive engine combinations.


Ed