Holley / Demon Tuning Advanced
Before trying anything below, make sure your transfer slots and timing are setup properly (as outlined in the basic tuning thread). To do advanced tuning, you need a wideband O2 sensor, if you don't have one your journey ends at the basic tuning thread.
Tune the idle mixture screws. Get a reading of the AFR at idle, turn them in slowly and evenly to lean, or out to richen. Wait a minute and rev the engine after making an adjustment. I tuned my engine to 14.7:1 at idle for good gas mileage, big duration engines may want more fuel to be happy.
Take it out and cruise at a steady rpm, the AFR will level off after about 10 seconds of cruising. It should be about 14.7:1 for best mileage, or you can run it a little fatter if you wish. 13:1-14:1 range is acceptable for high performance engines. If the cruise is too lean after adjusting the idle mixture screws, move onto the idle feed restrictors (IFRs) or the idle air bleeds (IABs). To lean, increase the size of the IABs and decrease the size of the IFRs. 3 sizes is a minor adjustment, but if your AFR is way off don't be afraid to make a larger leap. You can also insert a wire with a J hook into the IFRs to lean your cruise.
IABs are very expensive, about $18 a pack. So if you want, you can drill them. My stock IABs were .070, I drilled them out to .073, then .076, then .078 (5/64th). 8 sizes only made a difference of about 1 AFR point on my eninge. Hold the jets in a vise and squirt them and the bit with some WD-40 to keep the drill sharp.
After increasing the size of the IABs or decreasing the size of the IFRs you will need to richen the idle mixture screws to bring the idle back to 14.7:1, or whatever your preference.
Once your cruise and idle AFR is set, you can move onto the main jets. Or you can start with the main jets first, then tune your cruise. Doesn't really matter.
Make a WOT pass but keep the rpms down to be safe at first. Jet up (2 sizes at a time) to richen, or down to lean obviously. If your WOT is way off, you may want to make more of a drastic jump. Keep an 8-10 jet size split between primary and secondary blocks. If you get to a point where the WOT AFR will not richen enough, you need to decrease the size of the high speed air bleeds, 3 sizes at a time. Unless you AFR is way off, then consider a larger jump. My engine had a 15:1 WOT with the stock HSABs (.039), it took .028s to get it down to 12.5:1. With a large enough jump, you'll notice that jet size might actually need to be decreased.
Stock engines may want an AFR of around 13-14:1 at WOT, while boosted stock apps may want 12-13:1 and aftermarket boosted apps may want 11.5-12.5:1.
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I <3 forced induction.
Last edited by enkeivette : 08-21-2009 at 05:42 PM.
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