goethe6889

Each time I aggressively accelerate, I hear a rattling sounds which then immediately goes away...happens each time of spirited acceleration. Is this normal for a supercharged engine?

newmoon

I hope it is not engine knocking. That usually only happens if you use regular 87 octane gas. Need to use premium 91 octane or higher.

snagitseven

Today's modern high compression engines' computers are designed to handle regular 87 octane without knocking by retarding the ignition (although to get the best performance and gas mileage, premium 91 or 93 is recommended). So it wouldn't be engine knocking that the OP is hearing. The supercharger shouldn't be making rattling noises either. Something could be loose in the engine bay. Get it checked out under warranty.

newmoon

That's only part of the story. The ECU doesn't magically know you put in 87 octane and retard the timing. The knocking has to occur first, and you may or may not hear it. But the knock sensor detects the shock and vibrations and the ECU will REACT by retarding the ignition. Then the knocking will stop. So there could be a second or so of knocking, particularly when the engine is under heavy load when accelerating aggressively. That's why I suggested it, but yes, it could be anything such as a loose item.

in2dwww

I'm not an engineer or mechanic, but...

It could be ethanol blend in the gasoline, which actually would hamper ignition timing efforts by the ecu. Ethanol is higher octane but has less energy density than gasoline. Cars that can run E85 would normally have larger injectors. For instance, the A4 2.0 is E85 capable, and I've tried it out. The A4 actually has 5 injectors for a 4 cylinder engine (1 injector is in the intake manifold). E85 MPG's suffer greatly because more fuel is needed to burn. So I'd say it is possible that there's a starvation of fuel in the cylinder during ignition, even though the injectors metered in the correct amount of gasoline.

There are meters for determining ethanol content in fuels, which is mainly used for those E85 converts. Determining octane by the ecu, as far as I know, is determined by fuel/air mixture.
http://wiki.ross-tech.com/wiki/index.php/Fuel_Trim_Info

If the rattle is not coming from the engine, it could be a heat shield, but that's amazingly hard to hear over a wailing engine.

My E85 post:
http://www.audizine.com/forum/showth...Loaner-and-E85

wylee

maybe you're referring to your exhaust???