-Heavy piston

-Large piston volute (takes time to evacuate)

-Small vacuum line (Forge offers cap with larger fitting)

There are number of things you can do about it. I will start with heavy piston. As supplied by Forge, it’s weight is 118g or 4.2oz. Compare this to say Bosch valve fitted to AUDI/VW, membrane weight is barely 1/100th of that, making it much faster in operation.

By doing some stress analysis, I came up with reduced wall thicknesses that provide balance between mechanical stifles of the piston and its weight. I have CNC machined the sample for trials to evaluate its operation and wear/tear. Reduced weigh will reduce movement delay (AKA reaction delay time) and cycle time during piston oscillation. But may increase piston wear due to more dynamic piston operation (more movements as it reacts to smaller signal inputs) as well as reduce the piston seat wear at the same time, due to piston reduced weight.

Above image is part delivered from machine shop versus origional. The piston with thick wall section is as supplied by Forge, the one on the right is the one we machined out to achieve weight reduction of over 60%. 4.2oz for Forge part and 1.5oz for sample machined by CNC. That is 118gram vs 43gram for those who read metric.

This was tested in the application of a modified turbo engine running above 450HP. Immediate feedback is that it is more sensitive with accelerator input while on boost. You are more in control and it is easier to alternate boost level. The power fluctuation during sudden throttle drop by some 20-50% during high RPM is somewhat reduced. When combined with weaker spring supplied by Forge, it’s a very nice linear feel of accelerator VS power, much like on OEM turbo motors made by VW/AUDI.

Externally almost identical, newly machined piston is 60% lighter!

Next step is to reduce amount of air that that needs to be evacuated from the volute under the piston. Smaller the volume of air to be removed from the under the piston, the quicker the pressure in intake manifold and valve will balance. Thus reducing delay between vacuum signal and the piston movement. For a trial purpose we have machined a blanking plate and glued it with the Loctite. This modification reduced the working volume of air under the piston by 50%.

Next step was to updrade the vacuum feed line. A new cap was machined with enlarged vacuum feed nipple and more agressive hand grip for ease of use. Worth to note, that you can actually buy replacements caps with larger feed nipple from Forge direct as spare part.

The result of all the above changes is the improvement of the pedal linearity to the power output of the engine. The modification has dramatically improved power surge issue that was evident during throttle drop from 100% to 50% during boost operation near engine maximum RPM. There is no more delay in the pressure drop after throttle angle been reduced, it's instant like with good old BOSCH membrane valve. But with an added benefit of high flow FORGE Blow Off Valve.