Anti-stumble in the Normally (Naturally) Aspirated Engine World

Engler Stumble Valve
A recent provision from Tim Engler is his stumble valve.  It is a normally open bypass valve that closes with pressure. 

Note: Most conventional fuel injection bypass valves are normally closed and open with pressure, such as for a high speed lean-out function.

This alternative is used as an added bypass valve commonly in circle racing with fuel injection.  That is additional to the main bypass and high speed bypass that are common tuning tools.  When a yellow flag is out, Sprint cars must chug around the track at a low speed until the race track is cleared for restart.  With secondary bypass circuits typically at 40 psi or higher for a surge of fuel out of the corners, these circuits flood the engine at lower throttle position, lower speed operating modes such as under a yellow flag.  A properly set up stumble valve will open under the low speed conditions, keeping the engine from cooling down.  When the flag is removed, engine heat remains for good response on the first hit.  More information is provided in our latest manual High Horsepower Tuning for Mechanical Fuel Injection For Normally Aspirated Racing Engines, p. 151.  We thank Tim Engler for details of this provision.

Caution: The stumble valve circuit is set up for a specific fuel system.  It is unlikely to work properly in another FI system without proper adjustment.