A simple and cost-effective way to increase valve seat pressures by 10%


These sit between the valve spring and the collet, increasing the spring preload on the seated valve from 35lb/in to 42lb/in inlet and 38lb/in exhaust, as a way to achieve good seat pressure with the standard springs.


Gene Berg of 50's VW racing fame first maintained that a stock engine used for racing should have the valves shimmed a further .060" intake and .030" exhaust. Much like Gene and his contemporaries, I build these engines - based on cost-effective standard components - to run faster and stay more reliable than others in a competition setting.


Increasing the valve seat pressure helps to mitigate compression losses and counters the inertia of the valve, keeping it under control at high speeds and preventing valve float/bounce. I've adapted the sizing and placement of these shims to suit the 1KR-FE; the result produces a more robust valvetrain.


These shims should not be stacked

The shim configuration suits the specification of the original camshaft. If a non-standard cam profile is used then you should go with that cam manufacturer's own recommendations - typically you would install a stiffer spring if the cam profile calls for an increased spring rate.