LS7 lean cylinder condition?
Thread Starter
Staging Lane
Joined: Jan 2006
Posts: 69
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From: New York
LS7 lean cylinder condition? I gather there area many reports of lean mixture in cylinder #7 and sometimes cylinder #8 in many of the LS motors. Does this also apply to the LS7 with stock intake? Car is going to the dyno on a different ECU, and I'm wondering if there is need for/possibility of richening mixture in cylinder #7 to stave off detonation.
TIA.
Tom
TIA.
Tom
TECH Regular
Joined: Dec 2004
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From: Alpharetta, Ga
#7 is often regarded as the leanest cylinder. Reading my plugs verified this on my old LS3 as well. Matter of fact, #7 was the leanest, followed by #5, followed by #6. I always put my w/b 02 in the drivers side header for tuning as that is the leanest bank. Tuning for a 12.71:1 A/F ratio at WOT kept things knock free and made great power w/ 25deg of peak timing. Again, this was for the LS3...so I am unsure of what settings people with LS7's shoot for.
Thread Starter
Staging Lane
Joined: Jan 2006
Posts: 69
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From: New York
Tuning OK, maybe this belongs in the tuning section but -
my ECU allows for individual injector trims. That being the case, when does enriching the #7 cylinder apply in terms of RPM and throttle position? ie. do you enrich at part throttle at 3000 RPM, or is the enrichment really only for WOT above 4000 RPM?
Secondly, what percentage might one start with in running richer? I assume advice would be to read plugs, but I'd like to get in the ball park before pulling plugs (a major pain on my car).
Thanks,
Tom
my ECU allows for individual injector trims. That being the case, when does enriching the #7 cylinder apply in terms of RPM and throttle position? ie. do you enrich at part throttle at 3000 RPM, or is the enrichment really only for WOT above 4000 RPM?
Secondly, what percentage might one start with in running richer? I assume advice would be to read plugs, but I'd like to get in the ball park before pulling plugs (a major pain on my car).
Thanks,
Tom
TECH Regular
Joined: Dec 2004
Posts: 440
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From: Alpharetta, Ga
What ECU are you running? I don't know of GM PCM that will allow individual control of the injectors. In the past people have had the injectors flowed and used the ones that flowed the most in the leaner cylinders. Typically just tuning the leaner bank and watching the knock sensors will keep you well out of trouble. I wouldn't bother with individual trims even if I had the ability.
TECH Resident
Joined: Aug 2008
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From: Dubai
What ECU are you running? I don't know of GM PCM that will allow individual control of the injectors. In the past people have had the injectors flowed and used the ones that flowed the most in the leaner cylinders. Typically just tuning the leaner bank and watching the knock sensors will keep you well out of trouble. I wouldn't bother with individual trims even if I had the ability.
TECH Resident
Joined: Aug 2008
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From: Dubai
OK, maybe this belongs in the tuning section but -
my ECU allows for individual injector trims. That being the case, when does enriching the #7 cylinder apply in terms of RPM and throttle position? ie. do you enrich at part throttle at 3000 RPM, or is the enrichment really only for WOT above 4000 RPM?
Secondly, what percentage might one start with in running richer? I assume advice would be to read plugs, but I'd like to get in the ball park before pulling plugs (a major pain on my car).
Thanks,
Tom
my ECU allows for individual injector trims. That being the case, when does enriching the #7 cylinder apply in terms of RPM and throttle position? ie. do you enrich at part throttle at 3000 RPM, or is the enrichment really only for WOT above 4000 RPM?
Secondly, what percentage might one start with in running richer? I assume advice would be to read plugs, but I'd like to get in the ball park before pulling plugs (a major pain on my car).
Thanks,
Tom
TECH Apprentice
Joined: Dec 2008
Posts: 333
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From: Westbank of N.O.
#7 runs hotter on any lsx not using a coolant cross-over in the rear. Often mistaken for a lean cyl., richening it up helps, I also run 1 size richer jet for that cyl on direct-port set-ups. I say it's not a lean condition because u can swap the intake around (backwards) on the engine dyno and still see #7 hotter. Coolant cavitation around #7 is going to be the culprit. This is my opinion and I would love to hear ANY other good explanation.
