This has probably been asked in this long thread. I talked to a speed shop about this they said will probably fail California emissions ? is this true. Second Cal has expensive gas does this tune require higher than 87? , the person I talked to at Ford said yes. $10 more a tank sounds like a bad deal for 30 more HP and some tweaks to shifting.
Just so you understand - running anything except the highest octane fuel you can buy,
in a turbo vehicle, is stupid.
"grades of gas don't matter!" is the cry of a naturally-aspirated car owner that does not have ignition timing/compression that takes advantage of, or
needs high octane fuel.
What do I mean? Here's the long and short:
- High octane fuel helps suppress the conditions for pre-detonation of fuel, or "knock" (A turbo engine piston can be
obliterated by knock instantly).
- This "knock" condition is more prevalent with hot air, which turbos produce (even Intercoolers produce 'hot' air, just cooler than from the turbo itself).
- The "knock" condition is also more prevalent when the air/fuel mixture is more lean
- Advanced timing, high boost (higher=hotter air), etc factor into your knock equation.
To counter the possibility of destroying your engine, there is a "knock" sensor which basically detects
when you are experiencing pre-detonation,
not before it. So what happens when the sensor fires? Your engine is actively de-tuned to relieve the stress on the motor.
I'll say that last part again:
Your engine performance instantly decreases to safeguard the engine.
That's right, the factory tune, and any other, takes an instant nosedive when "low-grade" fuel/environmental conditions cause your engine to imperceptibly knock.
The short version:
If you run a turbo vehicle with an ECU, no matter what tune - even stock, always run the highest octane fuel you can buy.
As a bonus, when your vehicle is running at peak performance, when you are not jumping all over it, you can increase gas mileage (a
little bit) - that's because with better fuel, you can run
more lean without knocking. (A good tune does this even more, and even the Ford Performance tune does it,
which is why it requires high octane fuel)