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408 LS with blower Idle Questions

Practical Standalone Tuning

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I’m running a Fueltech and I’m trying to iron out my idle speed, but I find myself always changing the RPM target to have it move around less. Fueltech adjusts ignition timing to maintain an idle. However, my supercharger has a bypass valve, which will slowly open and close at idle should I tune my idle speed with the bypass valve blocked off first, or should I put in enough idle speed to prevent that bypass from moving at all


Great question and something many folks with blowers have likely run into. Stabilizing bypass valve position really helps this situation so you're onto something there. I don't know what style valve you have, but when I had a Procharged LS I used a Tial BOV and picked a spring that stayed open a bit at idle, opened more at cruise speed, and that worked out great for me. Idle was rock solid.

The supercharger is a Magnuson TVS 2300 jack shaft style blower. It has a small bypass valve that opens a throttle plate in the blower to bypass the rotors. My only resolve at this point is either target a higher idle speed which generates more vacuum and holds it open or let it hunt around in a range where it seems to be most happy I just didn’t know if there was a proper way to do this and how OEM manufactures do it on similar style superchargers.

Gotcha, generally the bypass would be tuned to typical engine behavior, specifically intake manifold vacuum.

The following are some paths forward in general for blower setups.

Either you can alter engine speed/behavior to get back to that idle vacuum


If the spring in the valve can be swapped, or whole actuator can be swapped, then you can swap out to an actuator that better matches your new intake manifold vacuum


Some bypass valves are electronically controlled so you can adjust their behavior in the tune

Which option is most pertinent to your vehicle will depend on your mechanical setup, and with that blower which generally has mechanical actuators, you can buy alternate actuators which bolt right on. First you might as well see if you can get the behavior you want with a little idle increase. If you have to increase idle too much, or the behavior isn't what you're wanting while driving, then you may need to swap actuators to get more ideal response.

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