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911st 911st is offline
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Join Date: Jan 2004
Location: Sacramento
Posts: 7,269

I would not think that with the HF head's already increased fueling capacity and being able to access more fuel with lower control pressure on boost using the adjustable WUR that you would need to bump system pressure further.

In most cases the cast iron HF head should deliver another point of richness by its self (8-10%). There should also be another point of fuel richness by lowering on boost control pressure agressively. For example, the HF FD should take you from say 14/1 to 13/1. The lower CP should then take you form 13/1 to 12/1. That is, the two should get you about 15-20% more total fuel or so at full tilt.

However, one should note that at some point when trying to increase the system pressure, the fuel pumps many or may not be able to support the increased delivery pressure. As Brian said, 7.5 is getting pretty high.

Unfortunately and as noted: the HF fuel head, bumping SP, and or lowering control pressure can increase fuel delivery places you do not want it.

When taking our CIS out of spec to deliver more fuel up top we need to also balance against this by taking our WUR out of spec to compensate.

I suspect one might start by setting on boost CP so it can deliver the fuel you need at high rpm and not more.

11.5 to 12/1 at HP peak and up to 12.5 at red line seems ok. 11.5 at HP peak would be safer but you do not want to be any leaner than about 11.8 at TQ peak is my thinking or opinion for what it is worth. This is usually not an issue if you can stay under 12.5 at red line. Yes, 12/1 at red line would be nicer.

Then, you should try to increase pre-boost control pressure and play it off against your on boost CP to bring your idle and cruse AFR's back in line. You may have to use the factory CO adjustment screw to get idle AFR where you need it. It is the cruse AFR that needs a higher pre boost CP.

Basically you are after increased pre boost control pressure and decreased on boost control pressure. All these settings are interrelated so adjusting one may effect another so it is kind of trial and error.

If you needed a lot of extra fuel up top and you are making big HP numbers, this will leave you with a fat AFR on first boost. If you are dropping solidly into the 9's, this is where many use the BL boost clamp to delay enrichment.

A better set up would be the use a Digital-WUR. In my opinion, the D-WUR is the key to unlocking the potential of high flow fuel distributors.
Old 03-28-2010, 08:26 AM
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