Orifice diameter for idle (stock L6)?

[74Adam]

The title pretty much says it all. I have the 60mm throttle body but it doesn't have a bypass for idle so I am just going to get a needle valve from Mcmaster and plumb it into the manifold. Is 1/4" too small, 3/8" just right? I don't want to get so large that if I barely touch the knob the idle jumps up 500 rpm. And this is a megasquirt application, BTW. Thanks.

[Tony D]

A 1/4" tubing will run you at 2,200 rpms fully opened. I took an N/A bypass valve off the side of the plenum and heated it with a propane torch, that loosened the glue holding in those big 10mm thin wall hoses. I then tapped the holes for 1/8NPT and put in barbed fittings. Put one to my "J" pipe, the other to a 1/4 barb connected by fuel injection hose (because I don't trust carb fuel hose at 20PSI). This allows me to set the idle from zero to 2,200 rpms. A simple solenoid on that line and a bypass to the needle valve with a carb jet (or another needle valve) in it will act as a nice fast-idle if you have a GPO in your input that can be configured based on CLT.

 

If you go with the needle valve you want "linear coeficient off seat, ten turn valve 0.125" orifice" that will get you aroudn 1100 turned all the way out....but it will be susceptible to plugging if you aren't running a good filter just like any bypass. Make it easy to get to so you can give it a shot of cleaner now and again.

 

When JeffP saw mine made from cheap leftover Nissan pieces he had laying around his garage... he called me names and questioned my parentage, specifically my lack of a father...and my mother being some sort of inbred cur...

 

We love each other surely! Pfft!

[74Adam]

Thanks Tony!