Yeah I think unless you're already having problem boiling your coolant (esp if running all water for racing), increased pressure rating at the radiator cap valve isn't going to change anything. Anyways, check this out:
I checked on my car, my stock radiator cap is labelled 137kPa, which is 19.87 psi. Our service manual gives the following values under "radiator" (units are kPa (psi)):
Cap relief pressure: Standard 122.3 - 151.7 (18 - 22)
Cap relief pressure: Limit 107 (16)
Leakage testing pressure: 157 (23)
I'm interpreting that to mean that the stock system was designed ideally for a cap that opens in the 18-22 psi range, and that any cap that opens at less than 16 psi should be replaced (faulty). Additionally, leak-testing the rest of the system (the radiator and hoses, etc) should be done at 23 psi, so we know it can handle that much pressure, but who knows how much beyond. The stock cap rating is right in the middle of this "Standard" cap relief pressure range.
Now over at:
The Z Store, they're selling an increased performance Nismo radiator cap that they claim works on all kinds of older Z's as well as our new 370Zs, offering increased pressure, blah blah. Their description says:
Quote:
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This performance/racing radiator cap from Nissan Performance (NISMO) is rated at 18.2 lbs. O.E. caps rate around 12.6 lbs. for non turbo and 16.8 lbs. for turbo.
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So the "performance" radiator cap they're offering to us for the 370Z is actually a lower pressure rating than our stock caps (although still within the "standard" range). On the other hand, the PIAA one you linked is 186kPA, which is well above the leak test pressure for our stock cooling system. If something goes bad enough to cause those pressures in our stock system, I think I'd rather have the cap let loose than blow a hose (or worse).