whats the air fuel ratio at idle supposed to be? this is race only no street. im about 14-1 +/- 2 right now.
Dave
Dave
A/F ratio at idle
1 reading
sheetmetal
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whats the air fuel ratio at idle supposed to be? this is race only no street. im about 14-1 +/- 2 right now.
Dave
Dave
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Dave when I dial my idle mix screws in for the highest idle speed and high
and vacuum, I end up at around 15.0-15.5 afr in Park.
I have found you really have to dial in the idle mix screws after the engine is at full operating temp AND after the engine compartment is fully heat soaked..... Lastly I adjust the idle mixture screws with the car idling IN GEAR.... I end up around 14.0-14.5 in gear at 850rpms.
the overlap in your cam is allowing fresh air through and pulsing in the exhaust is sucking fresh air from that end too. You really can't use a AFR meter at idle on a race engine. If you richen it to where it idles best you'd find out it's in the low 13's if there were a usable way to measure. try stuffing a rag loosely in the tailpipe on the side where the sensor or both if there a crossover. Watch the meter go rich. Don't leave it there too long or you'll have a new completely different problem.
If you're using leaded race gas, you can't use an A/F meter anyway, it'll blow out the oxygen sensor(s).....you're back to tuning it to the highest idle vacuum you can achieve with a gauge.
They last a good while, even with leaded fuel. Then you go buy another 02 sensor and your back in business.
Dave, set the idle mixture to what works best for your engine. Doesn't matter what the numbers on the 02 are.
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Race only engines I like to idle at or near 13:1 because the engine is more responsive and less pump shot is needed. I like around 12.5 right off idle when you get into the transition slots a little deeper.
If you're running open headers an extension pipe bolted to the end of the header will help get more accurate AFR readings.
If you're running open headers an extension pipe bolted to the end of the header will help get more accurate AFR readings.
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551 Posts
ok more info. this is pump gas, 93 octane engin. my bullet mufflers are about 14 inches behind the collectors and are 14 inches long ending the exaust system. the 02 sensor is in the h-pipe section bewteen the collectors and muffs. yes im at 14-1 hot and this was done with air bleeds not idle screws. my thinking here was to be as close to 12.7 to 13.2 and still not be so rich as to foul plugs.
it'll read a lot leaner than it really is with the sensor back towards the end of the system. So, do you leave it sitting around idling for hours at a time? Why do you even care what the meter sez at idle? Tune it to lean best idle and forget about it.
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If this is a serious STRIP/Street application....we tune it to have 12.20's on the the dyno on WOT....and its carbed...dont we have to live with what we get at idle to a extent???
I mean...if you are old school tuning...tune for the highest vacuum at idle...what more can be done?
I mean you can lean it with the air bleeds...but like mentioned, you could mess with performance else where...
I mean...if you are old school tuning...tune for the highest vacuum at idle...what more can be done?
I mean you can lean it with the air bleeds...but like mentioned, you could mess with performance else where...
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They last alot longer then you think. And your not going to "blow out the oxygen sensor". Eventually the Zirconium and ceramic in the sensor will get coated with lead and the reading quality will be degraded.
After about 40 1/4 miles passes and a few thousand street miles i get my bosch sensor warrantied by a friend that works at an auto parts warehouse. If you look at my last data log with the old sensor and the first datalog with the new sensor they are identical.
As far as idle AFR goes, don't strive to get a perfect number because every engine is different. As stated try for the highest vacuum and happiest idle.
My chevelle with a really tight overlap sits around 13.9 to 14.2:1 at idle when it's fully warmed up. Once warm it does not load up and stall or need to be cleaned out every few minutes.
I stand corrected. But, I still wouldn't use them myself while running leaded gas, that's just a waste of money when they do "degrade" for no good reason.
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A Bosch sensor for the Innovate wide band is 52 bucks from Advance Auto Parts.
If you use the sensor for 40 passes and get your car perfectly tuned then it's worth the 52 bucks. We motorheads spend alot more on much more usless gadgets that won't get you anywhere near what a wideband O2 will get you as far as optimal performance.
There are guys on this board that would rather spend 600, 700 even 900 bucks on a "Pro Built Carb" vs spending money on a wideband system, a throw away $52 sensor, and some air bleeds and just tune either what they have, or just a regular carb ( i'm not knocking you guys, just pointing out dollars spent vs a sensor)
You see a $52 sensor as a waste, i see a $52 sensor as a tool that gives me data that you simply cannot beat. And certain autopart suppliers will warranty the sensor when the heater circuit goes bad, just save the box cause the $52 sensor carries a lifetime warranty.
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i see a $52 sensor as a tool that gives me data that you simply cannot beat.
Rick, you and i are on the same page!!! thats not to say im not above spendin $$$$$ on other junk, but to me this is all about sqeezin every last .001 out of my investment.
Dave
Rick, you and i are on the same page!!! thats not to say im not above spendin $$$$$ on other junk, but to me this is all about sqeezin every last .001 out of my investment.
Dave
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11,823 Posts
Dave..what are you using to measure your A/F ratio? Do you have a onboard laptop?
What is your main purpose with tuning the idle...keep it from fouling plugs and trying to get more power off idle?
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