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ahem

Wiseco Piston Unleashed: Nissan's 370Z is a thing of beauty and power. Wiseco has the piston to give it the power it deserves.

:icon14: 9:1 compression? :icon14:

I't says its a FI piston.

Yeah, but if you can get 500WHP out of a turbo kit (they're coming out, some are already) - with the stock pistons...I doubt you'd get much more by swapping to a lower compression and increasing the boost pressure. I mean, swapping pistons won't get you to the 1000WHP range. $1100 or whatever for the pistons themselves, Probably around $1-1.5K to have them installed, plus a good chunk of money for a turbo designed around them and their lower compression...vs getting a turbo designed for the stock motor.

hmm.

Then there's the block limitations...

Why couldn't they come out with some set of 12:1 or higher for those that want to stay NA?

im still new to the compression ratio and stuff, slowly learning. What is a good compression ratio to be running a TT setup....say between 500-600whp?

anyone can claim the turbo is designed around a stock engine, but the fact of the matter is that no matter how strong a stock block may be, it's still a risk turbocharging (or supercharging) a car that was never designed for boost in the first place. Doing a built motor (aftermarket forged pistons and rods) goes a long way towards mitigating that risk.

First, no one really knows how high of compression you can go with a 370Z using 91-93 Octane gas.

Typically the next step is a thinner head gasket for a tighter quench and higher compression. Then it's milling the head for desired cc's to increase compression. You may have to cut deeper valve reliefs depending upon how these motors are set up but that is easier than you might imagine. (Honestly don't know that part)

More than likely you really don't need a high compression piston unless your building a true race motor using racing level octane and or just really want a forged piston instead.

Absolutely, positively correct. It's usually the pistons that go first.

If you keep the boost reasonable low (under 5 psi) you can probably get away with it on most any motor. However, everyone I know once they taste the power; the first thing they want to do is up the boost. Then what?? Ring lands usually and new pistons immediately after usually followed by a few rods.

Yeah they have kits for the stock motor but you would NEVER want to even aproach the 10 psi barrier with 11-1 compression unless you are running meth

you can neither do a thinner headgasket, nor mill the heads for increased compression on these engines, given that they use a 1 piece front cover that goes from the oil pan to the heads

if you want compression you either make the combustion chambers smaller, or you do it through the piston

Interesting. Well there goes a bunch of hotrodding stuff' learned thoughout quite a few years. Just shows.... just when you think ya know, ya probably don't.

if you're thinking domestic V8's, yeah different ball of wax. Pushrods make things way easier in this regard from a packaging perspective.

This is something I've been wondering about for a while but never got a definitive answer: Why is running low compression with high boost better than the opposite? What are the determining factors that make the former more desirable in high hp apps?

Detonation.

Boost creates cylinder pressure and what is referred to as "dynamic compression." Plus, intake temps are higher due to compression air which makes them more prone also and is why people run intercoolers. The big turbo guys running at a quarter mile or eighth mile track are running ice water in the intercoolers to get intake temps down. Also probably running 30+ lbs of boost. I'm sure there are people who are better able and are willing to go more into depth whom may chime in.

Not read his book ,but the Corky Bell whom did my supra wrote a book "Max Boost." Corkly is right up there with Detwhiller (sp) and da boys and I'm sure he answers it a thousand times better in the book.

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.

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.

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