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1slow370

To answer the second part of your question, running low compression and high boost vs. high compression and low(or no) boost makes more power due to consumption vs. efficiency. With higher compression you increase the efficiency of the combustion process releasing more power from the same amount of air/fuel. Say you have a car with 11-1 compression and you increase it to 12.5(about the maximum for gasoline) and you see 40 hp gain. You made the engine ~14% more efficient. Now when you lower the compression to decrease the chance of knock to accommodate boost you allow yourself to run like +20psi(assuming your block and rods don't blow and all other things)so while the N/a horsepower would be lower because the reduced compression makes it less efficient so lets say like 255 whp, you are consuming over twice as much air and fuel so double that plus some(about 14.7psi atmospheric so you'd be at about 1.2bar) and you'd be seeing about 566hp. 9-1 compression correctly setup and tuned can go to over 35psi so around the 862hp mark. of course those are hypothetical hp numbers but you can see the point that while you increase efficiency with higher compression, you can burn a hell of a lot more fuel/air with lower compression and boost.

Denny McLain

Let me see if I have a simpler answer:

Detonation.

Can't speak for every motor made nor even for a Nissan motor, but the later model small block Chevys limit for safe boost using stock hypereutectic pistons is right around 6 psi. You can do water or alcohol injections to raise it some, but seen a ton of supercharged F-bodies break stock pistons when taken over that limit.

So.......the simple answer is you can safely run higher boost vs stock pistons/stock compression. The bottom line is if you're going to run a relatively mild amount of boost, stock pistons/compression is fine. Only an inexperienced fool would try to run high boost w/o proper block prep as your begging for almost instant trouble.

On a side tangent, the upper limits regarding N/A compression depends upon the particular motor. We put the wrong head gasket on my Corvette and unknowingly ran 13.3 to 1 thinking we were only 12.8 to 1.

Except for running a bit hot during Dallas 100 degrees days, the car ran perfect on 93 octane gas using timing tables higher than the stock. This was mainly due to the reverse cooling head design for the LTx motor.

The commonly held urban legend taboo is about 12.5 to 1, however that's how urban legends self-promote and propagate themselves as no one tries anything different.

Again, clueless regarding Nissan but it sounds like a moot point if increasing compression requires replacing pistons as I doubt there is much more to be had in power gains vs the hassle.

Demon Z

That makes a lot more sense. Thank you both for your input!