I put a plastic (phenolic) one on my V8 Ford to insulate the carb and prevent the fuel from boiling right after shutdown. It's a lot easier to restart in the summer now when I dive into the post office or whatever for a minute or two.
As far as the turbulence effect, I have a buddy who put one on his old Harley and it got rid of the popping and flat spot he had. The Harley has a short intake with a straight shot to the valve, so I can see that helping. I'm not sold on the idea of using one (for the turbulence effect)on a V8 or straight six, since the fuel and air have to make numerous sharp turns before it gets to the valve. So, in my opinion, any turbulence will be lost when the mixture slams into the intake floor or side wall. I would definitely not waste any money on the ones they sell to put in the intake tube behind the air fliter on fuel injected motors. There isn't even any fuel in that area to have to keep in suspension.
