Hopefully someone can help clear this up. When it comes to optimizing my main jetting, I was planning to do a steady state 55 mph cruise, take a/f readings, and adjust accordingly. Question is, do I JUST change the primary jets? Or do I try to keep the factory jet split "ratio" the same and change both whenever an adjustment is needed?
For instance, I have a Quick Fuel SS750AN which has factory 72/80 jetting. If I wanted to slightly lean out the cruise, would one go equally down on both to 70/78? And then if WOT was lean after that, tune it strictly with the PVCR? Or should I tune cruise solely with the primary, and tweak my WOT with secondary jetting, and not worry about the jet split? And if the latter is true, then what is the purpose of even changing PVCRs?
Holley main jetting
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Re: Holley main jetting
Just the primaries ... after that, a test done at Wide Open Throttle will tell you about the total fuel needed, then change the secondaries.eric8 wrote: ↑Tue Apr 06, 2021 9:34 am Hopefully someone can help clear this up. When it comes to optimizing my main jetting, I was planning to do a steady state 55 mph cruise, take a/f readings, and adjust accordingly. Question is, do I JUST change the primary jets? Or do I try to keep the factory jet split "ratio" the same and change both whenever an adjustment is needed?
For instance, I have a Quick Fuel SS750AN which has factory 72/80 jetting. If I wanted to slightly lean out the cruise, would one go equally down on both to 70/78? And then if WOT was lean after that, tune it strictly with the PVCR? Or should I tune cruise solely with the primary, and tweak my WOT with secondary jetting, and not worry about the jet split? And if the latter is true, then what is the purpose of even changing PVCRs?
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Re: Holley main jetting
In addition to the primary jetting, there may be a reason to investigate the high and low speed air bleeds for optimum cruise AFRs.
As for the PVCR, I've used it to great effect for part throttle acceleration. I found that with the restriction opened to the typical maximum, tailoring the vacuum setpoint provides plenty of enrichment without having to pin it. And this PVCR also enhances the WOT AFRs to the rich side. If the restriction size is opened up, the secondary jetting may have to be dialed down.
As for the PVCR, I've used it to great effect for part throttle acceleration. I found that with the restriction opened to the typical maximum, tailoring the vacuum setpoint provides plenty of enrichment without having to pin it. And this PVCR also enhances the WOT AFRs to the rich side. If the restriction size is opened up, the secondary jetting may have to be dialed down.
Kevin