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Originally Posted by SupraTT/Iceland
yes I was on pump gas but this car has always been driven on pump gas it?s a daily driven car.
How much Octane do I need to be safe ? here in Iceland you can buy 98 and 99 octane gas at pumps I think in you standard that would be 94-95 octane...
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Unfortunately, I can't give you that answer unless you first tell me your maximum boost level. In theory, if you want to be totally safe for all boost levels no matter what,
and you're on an unlimited budget, you could simply run pure
VP-Import 120 octane fuel. Of course, that'll probably cost you $20/gallon (USD) or so. For the rest of us that don't have $$$ to waste, the full-time VP-import option really isn't practical. To determine the most cost-effective option, you
first need to determine the
maximum boost level that you plan to run (eg. 20psi? 24psi?)...and from that figure...(and the ignition timing curve in the ecu that you're running (I assume it's a bone-stock oem ecu))...you can then determine the approximate minimum
motor octane level you need in the your fuel to be 'safe'. After you have that minimum motor octane number, you have to determine where you can get race fuel locally, and what brands/octanes are available, for what prices.
For 20psi (or possibly a little more), I'd guess that
pure 100 (motor) octane fuel would be sufficient. This is but one option, and not necessarily the most cost-effective option in your area. For example, it might be more cost-effective to purchase c16 leaded race fuel and mix it about 1:3 with pump gas (i.e. 34% c16 and 66% 'premium' pump gas). You can also consider using Toluene (instead of c16) at approximately the same ratio, if that's easier for you to obtain. Yet another way to supplement your octane level is methanol/water injection.
Another fact you might also find interesting is that you don't have to guess at any of this boost vs. octane stuff, or even take my word for it. If you monitor your ecu's knock and timing retard function, you will see yourself when your engine starts detonating with your chosen boost+fuel combination...and then you can react by (immediately) reducing your boost, or by increasing your fuel's 'net' motor octane level. For example, on a US-spec '93-'95 Mkiv Supra turbo, you can monitor your oem ecu's knock function and your oem ecu's timing with a device called a
Techtom MDM-100. For US-spec '96-'98 Mkiv Supra turbos,
this OBDII Scan Tool works well.
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Originally Posted by SupraTT/Iceland
...How long can the stock pistons handle 20 psi? how many miles?
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Do you mean 20psi on pump gas, or with race fuel?
If you're asking about 20psi on pump gas, when your engine starts detonating, NO brand/model of piston can handle it. In other words, (again) detonation will damage ANY piston. It will also damage your spark plugs and the metal in your (aluminum) 2jz-gte head. Fwiw, I've personally seen missing chunks of metal from the inside of a 2jz-gte combustion chamber.
If you're asking about 20psi with enough octane to match that boost level, then the stock pistons can handle 20psi for many, many thousands of miles of 'spirited' driving.