Lean rear cylinders with boost?
07-13-2006, 08:51 AM
#1
Staging Lane
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Lean rear cylinders with boost? I keep breaking the rear piston as I increase boost (12+ psi). I got all forged pistons/rods (see sig). Wideband never was +12.5 a/f. Front pistons were burning right. It's just the ones in the rear that were "too" clean. My assumption is that under big boost the air gets crammed to the rear of the intake which causes the back cylinders to have a different a/f. The wideband reads an averaged a/f across the engine right? Does that make sense? 
Detonation!
I ordered the edelbrock vic intake. It loads the air from the top and looks to give a more even spread accross the intake. Think this will solve the prob? Seems to me that by spreading the "crammed" air evenly across the motor, you would get a better a/f from the WB02 without having one on every cylinder.
Comments please!
Detonation!
I ordered the edelbrock vic intake. It loads the air from the top and looks to give a more even spread accross the intake. Think this will solve the prob? Seems to me that by spreading the "crammed" air evenly across the motor, you would get a better a/f from the WB02 without having one on every cylinder.
Comments please!
Last edited by stssilverado; 07-13-2006 at 08:53 AM. Reason: add pic
07-13-2006, 09:34 AM
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Originally Posted by stssilverado
I keep breaking the rear piston as I increase boost (12+ psi). I got all forged pistons/rods (see sig). Wideband never was +12.5 a/f. Front pistons were burning right. It's just the ones in the rear that were "too" clean. My assumption is that under big boost the air gets crammed to the rear of the intake which causes the back cylinders to have a different a/f. The wideband reads an averaged a/f across the engine right? Does that make sense?
Detonation!
I ordered the edelbrock vic intake. It loads the air from the top and looks to give a more even spread accross the intake. Think this will solve the prob? Seems to me that by spreading the "crammed" air evenly across the motor, you would get a better a/f from the WB02 without having one on every cylinder.
Comments please!
Detonation!
I ordered the edelbrock vic intake. It loads the air from the top and looks to give a more even spread accross the intake. Think this will solve the prob? Seems to me that by spreading the "crammed" air evenly across the motor, you would get a better a/f from the WB02 without having one on every cylinder.
Comments please!
Want to hear something strange? I just ate up a set of head gaskets, 7 out of 8! The only one that didn't blow was 8 !!!???
Anyways I am of the same opinion as you on the wideband issue. Measuring a bank of 4 cylinders out of 8 isn't giving you much of anything other than a vague opinion. I'm going to put my egts back in, measuring ALL cylinders.
You now know you are getting detonation. So the question is octane, too lean, plugs, timing? Also, are the edges on your pistons sharp? If so smooth all of them out.
Good luck!
Last edited by LASTLS1; 07-13-2006 at 10:27 AM.
07-13-2006, 10:05 AM
#6
If i'm reading what you posted correctly, you a/f is 12.5:1? If so that is the problem, it's way too lean to run on turbo'd LS1 and have it live.
Have the truck retuned for 11.0:1 a/f and make sure it doesn't detonate. Running it rich keeps it safe and has very little effect on the HP made.
Have the truck retuned for 11.0:1 a/f and make sure it doesn't detonate. Running it rich keeps it safe and has very little effect on the HP made.
07-13-2006, 10:26 AM
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Originally Posted by Zombie
If i'm reading what you posted correctly, you a/f is 12.5:1? If so that is the problem, it's way too lean to run on turbo'd LS1 and have it live.
Have the truck retuned for 11.0:1 a/f and make sure it doesn't detonate. Running it rich keeps it safe and has very little effect on the HP made.
Have the truck retuned for 11.0:1 a/f and make sure it doesn't detonate. Running it rich keeps it safe and has very little effect on the HP made.
Agree! 12.5-13.0 is for n/a!
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07-13-2006, 10:37 AM
#9
Staging Lane
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tune it's an SD tune so off boost wide band = 14-14.5. Once it hits 1-2 #'s boost it drops to 10:1 at full boost WOT it saw 12.5 for a very short time. averaged 11.5 though at wot.
07-13-2006, 10:42 AM
#10
What Jose does on the stock manifold LS1's is run an EGT on the rear cylinder. When it stays cool all the other cylinders end up looking great. Might want to talk to him about it.
07-13-2006, 10:45 AM
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Originally Posted by stssilverado
it's an SD tune so off boost wide band = 14-14.5. Once it hits 1-2 #'s boost it drops to 10:1 at full boost WOT it saw 12.5 for a very short time. averaged 11.5 though at wot.
Depending on fuel and timing you may have to bring it down to 11.0 across the board at wot.
07-13-2006, 10:59 AM
#13
I will not run my car leaner than 11.3:1 at ANY boost over 5psi.
I just saw in your sig that you are running a tune from Nelson, was this done in person or through the mail?
It just sounds like the tune is off to me. Are you running any kind of scanner? Might want to look into a aeroforcetech scan gage, really helps to see when the motor is knocking.
I just saw in your sig that you are running a tune from Nelson, was this done in person or through the mail?
It just sounds like the tune is off to me. Are you running any kind of scanner? Might want to look into a aeroforcetech scan gage, really helps to see when the motor is knocking.
07-13-2006, 12:49 PM
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Originally Posted by bboyferal
Strange... This is an LS6 intake correct? While it obviously has limits, there have been so many members having excellent luck way over 12 psi with it...
