articfriends

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Heres a question for those in the "know", what is the real world, safe maximum lean afr # a bbc motor can live with at sustained high speed? Yes, I KNOW what tailpipe target readings to use. I normally target mid to low 12's at wot depending on rpm, etc. I target sub 12 #s on blown applications, thats NOT the question here.
I recently finished upgrading the software on.my dyno and inputing my daytona 8 pack o2 system into it, i am now reliably and consistently able to see, read, review the individual cyl afr's. I was able to before but constantly had connectivity problems with the aem interfsce boxes and laptop.
so, dynoing a zz502, vic jr intake, customer chose to put 502 mpi cam.in (HE assembled and planned this motor, NOT me). Typical "hot" cylinders are hot, 1, 7 and 8. And when i say hot, i mean BLOW up hot.

articfriends

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So, begin dynoing this, 17-1 on #7/# 8, 12.5 ish on coldest, drops down to mid to high 15's by end of pull, coldest cylinders in sub 12 range. NOT a carb problem, stagger jetted , high speed bleeds, etc, etc, spacers tried. Numbers look like a disaster. Once you fatten back up enough to finally get 7/8 into mid 14's to high 13's at wot, youve got #6 so fat (sub 11's) that you almost get below point o2 sensors can even read (10.5)

articfriends

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I previous saw a 3 to 3.5 spread in afrs on.my 548 when dynoing carbed with various open plenum intakes, was able to get wot numbers in high 12'w enough stagger jetting, adjusting on carb etc and close gap up on afrs to around 1.8 #s from.lean to rich. Not the case on this 502 though

articfriends

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So, guy who owns/built this motor created a mis matched combination with this vic jr intake, totally in appropraite cam etc, yes, these intakes suck unless you are rpming the **** out of something or have some cubic inches, but just like dominator carbs, everyone THINKS they need one!
So we know a firing swap cam or even a a cam with corrected lobes in lean corners/rich corners would help but what about the "typical"guy whos trying to run without getting that fancy?

articfriends

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So i wanted to see where numbers goe w intake swap to dual plane. We swapped on a old school performer 2.0, sum things up, just shifted lean afrs to differemt cylinders, made 20 to 30 more ft lbs tq (545 ish) and just shy of 500 hp (490 ish) about 6 to 10 less than the vic jr (from 5000 up).
all the kings horses and all the kings men cant get cylinder 3 to something that DOESNT put visions of exhaust valve out ex port and molten aluminum! Put enough fuel into this to get #3 to high 13's at wot, its "paired" cylinder on intake, number 2 , is below limits of 02 sensor, sub 10.5.

articfriends

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So, ive been on alot of dynos in my life before owning one, most had egts, none had individual 02 sensors ,wasnt uncommon to see same lean cylinders in the high 1300's, even low 1400's and rich/cold cylinders in the low 1200'even high 1100s. We always tried to get those 1400's into the 1300's . I have a feelung those high "1300's" when translated to a 02# prob end up in the high 13's to 14's.

articfriends

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Average tail pipe readings, these are numbers were used to seeing, tune for 12.5 lets say, motors usually "safe" , ive known for long time that AVERAGE number can get a guy in trouble in a endurance application. Lets say for sake of discussion, number 1 is 13.5, 3 is 11.5, 5 is 10.5 and 7 is 14.5, guess what, tailpipe average will show you 12.5, number 7 is in burn down territory. So, point of this thread, what IS that maximum cyl afr on a typical bbc, forged pistons, decent parts where it melts down vs chugs along a happy life?

articfriends

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MILD THUNDER

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Ill say this smitty. Todays technology, should be changing the way we all think. That information you have gathered, is pretty darn critical in the engine build/tuning process.

i really have never understood the infatuation with a single carb single plane intake setup. Especially on a higher end build. If i was targeting over 700hp with an NA deal, I likely would be looking at a tunnel ram setup with twin carbs.

the bbc is such an imbalanced engine. Head runners are uneven, most intake manifolds have uneven runners, it be dam near impossible to get a 800hp bbc to make 100hp per cylinder.

back in the day, used to hear guys say "number 5 is the lean cyl on a bbc" or whatever number they felt applied to all bbc engine builds. Its just not the case. Every build is different.

I wish i had an answer to your question. Seems to me, that typically 12.5 afr makes best power on pure gasoline, and 12.2 with a 10% ethanol blend. Id prob shoot for that, and adjust timing from there?

articfriends

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The problem with that Joe is to get those hot cylinders into the mid 12s you've got other cylinders below 10 5