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Discussion Starter #1
Dynoed a 555 yesterday. Here's the shakedown on the motor, started out with 1250qf 96 jets square and the a/f ratio from 7000-7500 was in the 16.8 range, put 100 jets in came down a little, then 104 jets still was in the high 16.2 range. Motor combo as follows - Merlin aluminum block with callies magnum crank 24* edelbrock heads with super vic intake, [email protected] cam with 870 net lift . I used some c-15 gas with an ngk-9 plug. I wanted to turn it higher but with the a/f so high we just stopped at 7500. It made 948 at 7300 and peak torque was @740 at 6500. Do you think playing with air bleeds will fatten this thing up so it will live! lol thanks for the help in advance.
 

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Did you read the plugs? That is your gold standard... that way if there is a contradiction in the plug reading(fuel ring) versus the a/f you know what's right or wrong.

The plugs don't lie.
 

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Absolutely read the plugs!!!! Your AFR is great for looking at the curve, however a lot of things can affect the actual reading. I would be real suspect of the O2 system, did you have another carb to try? And look at the ground strap, you might be able to go up a heat range as 9's are a bit cold.
 

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If you need help understanding how to read a plug, Patrick at Pro Systems use to offer a video on reading plugs... i think it came with the scope he sells.... very helpfull for those who want to learn.
 

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Something amiss for sure. Motor lean as that wouldn't have made the power it did. Big jet change and no significant afr change - i bet i could see that much change by leaning the fattening the idle adjusters. How did they get O2 readings, with an O2 sensor or with fuel flow/air flow with a magnehelic? Maybe they had a contaminated O2 sensor. Did they give you cfm too to see if carb maxed out? How about the egt stuff, temps pretty normal there?
 

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Discussion Starter #9
16.anything is way lean. Do you have any other numbers to match-up like BSFC, EGT or water temp rise?

Can you post the dyno sheet?
I'm kinda computer illiterate, as far as posting pics, but the bsfc numbers are .442 @4800 [email protected] [email protected] all these numbers were really close all the way up. The scfm numbers( if this means anything were [email protected],[email protected],[email protected] [email protected] and vol. eff was in the 122-123% range. Now you must take in consideration this dyno didn't have all the new gadgets everyone else may have! lol And the water temp shows it started out at 188 and at 7500 it was 192. And yes I will have my plug readers at the track- I'm not plug savy yet lol
 

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Sounds like the o2 and bsfc don't correspond. Not unusual. a wideband goes bad quickly on race gas and I really don't trust turbine generated a/f calculations
 

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Discussion Starter #12
If you need help understanding how to read a plug, Patrick at Pro Systems use to offer a video on reading plugs... i think it came with the scope he sells.... very helpfull for those who want to learn.
Thanks Chris i'll check it out, sometimes it's the easiest things that you overlook!
 

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did the dyno calculate the a/f from o2 sensors or the fuel flow and airflow meter??......the land n sea dyno i use does'nt have o2's (yet) and it seems that if u dyno say a 500hp street engine the a/f ratio is right where you would expect/want.......but if you dyno a 500" 1000hp engine it reads way lean with a bsfc in the 390 range.again you have to read the plugs.also patricks video dynos a 555 and the a/f ratio is lean like yours....i called and talked to him on this and he said it was o2 sensors but that particular dyno(can't remember the brand)always reads like that and you have to know how to interpret that data...............very confusing at times
 

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Discussion Starter #15
It's from the fuel flow and airflow meter. Apparently it must be ok, it's like you said it must be ok cause the dyno operator seemed to think that everything was fine. I was just concerned with a/f ratios showing low 16's lol. thanks for all the help!
 

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Make sure there are no air leaks in your exhaust, hi temp silicon is your friend.
Simple thing to check but it makes a difference!
 

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Make sure there are no air leaks in your exhaust, hi temp silicon is your friend.
That's what I'm thinking.

G
 
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