what should i get to improve HP and fuel economy in a 2005 GMC Envoy SLE 4.2L?

[Mark]

Cold air intake? Turbocharger? Supercharger?...

 

[Robert M]

Cold air intake is helpful, but the right thing to do is to use ONLY synthetic oil (Mobil One "0" series oil is the most practical). This will reduct friction and increase power. Make sure that your throttle body and idle air control valve are SHOWROOM clean. Most driving is done with the throttle only open a small amount. WHen these items get dirty, it affects power and fuel mixture. Then, remove the factory junk plugs and install either Bosch FUsion or Desno Iridium plugs. This will make the engine "FEEL" like it is turbo-charged, since the fuel will react chemically with the special metals in the plugs. Expect a 15% increase in MPG's!

 

[Richard R]

It's a soccer mom SUV . . .

The only cost efficient way to improve mpg is by changing your driving style, lighten up your right foot and you'll see a world of difference.