Thread: NO lean Issues
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Old Apr 18, 2010 | 05:32 PM
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From: From North TX..To SoCAL..Now Cnt Philly
Default Re: NO lean Issues
If at WOT, you’re a/f starts around 11.8 and at redline prior to shifting, it ends around 12.8. That is a lean condition, it definitely is not detrimental but it is a leaning issue. It’s an indication our fuel system is not able to keep up with fuel requirements. Why? The reason leaning occurs in the higher rpms is because that’s when you create max boost. The closer to 20psi you get the leaner you will go.

In 4th gear, I reach 20+ psi in cooler weather and I have experienced extreme leaning at max boost with the SL55 pump. In 3rd gear I can reach 19ish psi and my a/f mimic those in the first paragraph with the SL55 pump, which is an acceptable lean condition, I presume. In 3rd gear with the OEM fuel pump, a/f would reflect 12.3 to start and end at 13.3, same boost level but the OEM pump flows less at boost levels less than 20psi. Once you reach 20+ psi it doesn’t matter what fuel pump you are running, your leaning condition will no longer be acceptable, IMO.

Prior to LET creating the 181 and 185 pulleys, the largest pulley available was 178. IMO, the reason for this was because the 178 pulley was capable of producing the maximum amount of boost without having adverse affects on the factory fuel system and other variability’s.

SLK32Germany is correct the SL55 pump works around 19psi but not at 20+. Thanks for sharing SLK32Germany!
 
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