I think there had to be other things in play here to get better mileage......Possibly better weather conditions, more air pressure in the tires, better tank of gas, and the cold air intake (the cold air adds mileage btw)......I have to say I would need more real world proof with the VR stack to make me get it. Anything you put in your TB to is going to restrict air, who do people hone/port them out? To make the bigger, right? Then why would you stuff a piece of plastic in it to make it smaller? Any other opinions on this?

 

I felt the same way when I heard about this. Bigger is usually better when it comes to moving air so I didn't think adding a restriction to the intake track was going to help (actually figured it would hurt performance). I took my HD for a ride after installing the stack. At one point I wasn't paying attention while sitting at a light. I looked up to find that it had been green for awhile and the people behind me were probably starting to get pissed so I layed into it a little when I took off. I felt that the truck was pulling a little harder as I crossed the intersection and then I thought - "damn, it actually does work!" It's not a performance increase like you would see from a set of long tubes but it helps a little down low. I've been through quite a few tanks of gas and found that I get just under a 1 MPG increase. I even took it out for a little while to see the mileage go down. This little piece of plastic seems to be doing something

Tom

 

Well, I guss I am just not a believer yet I feel that it if it really worked we would hear more about it every day! I just done understand why people spend hundreds to make their TB's bigger and 50 bucks to make it smaller. If ported TBs are getting more HP and better throttle response, then why clog it up with a VR?

 

I can tell you theoretically how it probably works. I'm still a little skeptical that it would be a lot of help, but I might get one and try it myself.

I'm an aircraft electronics engineer and a former Detroit Diesel Mechanic. Also, I have a commercial pilot's license and was a flight instructor for a number of years and have studied aerodynamics a fair amount.

Anyway, the key to improved air flow (both mass and velocity) through any opening is to have a smooth/streamlined path for the air to pass through. The ridge around much of the circumference of the throttle body interior near the throttle plate/butterfly and the openings for the PCV discharge and the idle air control (IAC) inlet all cause the air to burble or swirl with eddy currents of air molecules. These turbulent eddy currents become obstacles to the air trying to get through the throttle body at high velocity. Envision what happens to the water in the vicinity of the oars or paddle as you row a boat or paddle a canoe.

Now, in properly porting a throttle body one of the most important things is filling and smoothing the area around the IAC outlet and PVC outlet. Also, the throttle body necks down and then makes an abrupt angular transition to the throttle plate diameter. Proper porting of this area should not only remove the ridge, but it should approximate a curved airfoil shape rather than the abrupt angular transition.

The basic principals involved for porting a throttle body are the same as porting the intake and exhaust valve bowls, ports and combustion chambers in a cylinder head. You want smooth transitions and not just hogged-out orifices. The VR plastic insert could achieve these goals as well as a good porting job even if the cross sectional area of the opening is slightly decreased. I just don't know if it would make much of a difference, but I may give it a try myself one day. Also, I may try my hand at porting my throttle body. I've done the other "free mods" so I might do this too.

 

I agree with
you Steve Bryant......A TB porting job would yeild the same effects for less/nothing.