[Cliff R]

Our springs are custom wound and not the same as the spring in the Edelbrock kit.

At any light throttle cruising the vacuum produced by the engine is really high, and any power piston spring is going to have the power piston all the down, metering rods in the leanest position.

Power piston springs raise the metering rods when engine load requires additional fuel. They all work pretty much the same way, the cut in points being slightly different due to tension/rate of the springs.

One must also consider that fuel delivery increases as throttle angle increases due to the pressure differential, air speed and flow volume across the boosters and thru the venturi area of the primary bores. This is why we are able to set up q-jets to run straight off the jets without a power piston and metering rods right to start with.

Later q-jet designs switched to metering rods with .036" tips, and a different airbleed configuration, leaving very little difference between the upper tapered portion of the metering rod in the jet with the PP down, and the tip in the jet with the PP up.

In any case, we offer 4 springs in our kit. Lightest to strongest, orange, light blue, green, dark blue.

The "cut-in" points are approximate. The orange and light blue are close, around 5-6" and 6-7" respectively, the green is closer to 8-9", and the dark blue about 10-11".

I've tested them quite a few times, which is very difficult testing, as I used a real engine and varied idle rpm and ignition timing to determine the cut in point. I placed a drinking straw on top of the PP, and reduced engine vacuum until the PP moved upward.

In any case, we've been using and selling them for years, and they give the tuner a wide range of options. We put a long green spring in the kit which can be trimmed for custom applications and those who really like to "split hairs" with these things.

Just some advice when it comes to tuning with PP springs. Determine the best jet size FIRST. Then use the APT (later carbs) or change metering rods to get the light part throttle A/F perfect. Then use PP springs for best transition. In most cases, the strongest spring used will provide the best throttle response, and contrare to popular belief, light springs aren't going to provide improved fuel economy by keeping the metering rods deeper in the jets longer, or more often. Engine vacuum is always high enough at cruise this happens anyhow, and time the engine is heavily loaded (heavy/full throttle) more fuel is required and the vacuum timing needs to fall out as well......Cliff