do these really work or are they a gimick? and if they work which is the best to increase mpg on a 5.9/360?

 

Its a gimick ...

 

I know some guys that think they are the greatest thing and would love to sell you theirs!

 

gimick/not gimick. It serves it purpose, but not really worth it on a stock tb injected motor.

 

I've heard they help cruising power and mpg, but acceleration stays the same

 

As has been mentioned in several other threads. With the Dodge Magnum Multi-port Fuel Injected engines the throttle body spacer does nothing at all for the setup. The design of the spacer does cause the fuel to swirl as it leaves the throttle body and enters the intake. Then the air has to travel almost another foot before it reaches the point where the injectors spray the fuel. The stock barrel intake manifold is designed where the air for each cylinder enters the intake tunnel on the opposite side of the intake from the cylinder it is feeding. Looking at the front of the engine, for cylinder #1, is the drivers side front cylinder. The air for this cylinder goes throught the throttle body, into the air tunnel on the passenger side of the intake, follows the tunnel back across to cylinder #1, finally receives the fuel spray from the injector, and then enters the cylinder. All benefit from the spacer mixing of the air is long lost before the fuel is sprayed into the air.
For Throttle Body Fuel injected engines (where the engine has the injector mounted into the throttle body) the spacer possibly would provide some improvement as it does mix the air and fuel and would probably provide a more even mix of air/fuel to all cylinders.

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it really bugs me that they try and charge a hundred bucks for a block of aluminum with minor milling done to it too

 

Yep, there's a sucker born every minute. I can say this because my throttle body spacer is being used as a paper weight on my desk. It's a reminder to fully research a mod before spending my hard earned cash on it.