afr how

Discussion in 'PSI Superchargers Tech Questions' started by blownapex, Jun 20, 2020.

  1. blownapex

    blownapex Member

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    how is every body calculating or getting air fuel ratio
    screw blown promod hemi automatic race pack datalogger jetsize
    so once you get the plugs afr correct in high gear
    how are you getting afr with your fuel timers with no 0/2 sensors(mfi)
    my experience 02 will not work with mfi
    i helped a team this weekend and they just opened jets and didnt know till they tried it and they still didnt know early in the run if afr was to rich or lean early
    plugs seem to only read burn in high gear
    my thoughts are get fuel correct from .5 on then use timing graph to correct driveshaft gmeter et
    what are the ways to get boost to fuel correct in all the different rpms early in the run
    discuss
    thanks
     
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  2. Mike Canter

    Mike Canter Top Dragster
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    Tried 02 sensors and they are all over the place and did not produce usable data and did not last long. The 02 sensor data was worse in the first half of the run and did start to stable out in the second half but still not producing very useful data. People use Boost to Fuel or Fuel to Boost but that will only put you somewhere in the ballpark. It boils down to plug reading and watching performance indicators.
     
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  3. Templar Motorsports

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    Is there any way to get a handle on it? Or can you not because of the constant variable load until you hit high gear?
     
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  4. aj481x

    aj481x Member

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    You knew Mike would say to read the plugs. Most people have found O2 readings to be erratic at best on blown applications, although they are great on NA particularly on a dyno.
     
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  5. Templar Motorsports

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    Yes I did know. lol

    But it is really hard to get a reading on the plugs on the front half of the track
     
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  6. Mike Canter

    Mike Canter Top Dragster
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    When you say the front half are you meaning the 1/8th mile. If so we read them all the time at 1/8th mile.
     
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  7. Templar Motorsports

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    Yes. Sorry I'm in the north west. Mostly 1/4 mile stuff here.
    But if you are setup (geared) for the 1/4, do you just do a full hit in each gear and shut off? Then read the plugs?
     
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  8. TOL

    TOL Active Member

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    Thanks Mike. I'm kind of curious about the whole O2 sensor thing. Appreciate your input.

    So you had no luck with UEGO readings? You were using heated UEGO's retracted so they were not penetrating into the main exhaust primary pipe and getting wetted/impinged by globs of unburnt fuel? Were they pre-heated before the run? Sorry for so many questions.

    Have others had any luck with O2 sensors in blown meth applications? Would be really curious to hear more. The timing of this discussion is perfect as I was planning to order some.
     
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  9. Mike Canter

    Mike Canter Top Dragster
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    Templar, yes you can do that but you don’t want the 1/8 mile readings too lean so you can’t get to the 1/4.

    TOL, had heated UEGOs. Did not turn them on until the motor was running because they were not retracted. Didn’t want to hit hot sensors with liquid fuel. They still didn’t last long and cost big bucks.
     
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  10. comp altered 632

    comp altered 632 New Member

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    If you need to check o2 / plugs early on run then just shut off early.
    How do you think a team tunes for 1/8 mile.
     
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  11. Bjs344

    Bjs344 Member

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    I figure if you have a good blower ( not a crappy std helix or whatever that is just making heat up top), then you tune it to the 1/4 with no leanouts until the plugs start to scare you. Then you know you can take fuel out earlier. When do you take it out (and do you put it back in at some point) is where guys really start to earn their keep. The more you look at bearings and the more you squish the better you will be.

    That’s what I think I know. Wouldn’t be surprised to know something different in a couple years.

    Will had something on here a little while ago about don’t read the threads on the outside of the plugs, read the insides (not like a nitrous motor, other side of the inside). I’m not that smart yet because I can beat bearings out and not read nothing in the inside of the plug.
     
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  12. Mike Canter

    Mike Canter Top Dragster
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    If you are smashing your bearing you are detonating, if you are detonating you are losing power and being hard on parts so why tune that way. You do not read inside the spark plug on a blown alcohol motor you don’t care what it is showing down there because you are running the coldest plugs you can get.
    Try reading this and see if it helps you put understand
    https://www.dragstuff.com/techarticles/reading-alcohol-spark-plugs.html
     
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  13. TOL

    TOL Active Member

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    Great article Mike. A staple in the field. Some illustrative pics would be nice though to go along with it ;)......
     
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  14. Bjs344

    Bjs344 Member

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    According to Will and whatever top tuner he interviewed a while back, that’s the old way of reading plugs. I can’t figure out the “new way”. I think they even showed some examples and I couldn’t see anything. Like I said before, they’re not talking about reading the inside like a nitrous plug, they’re reading the other side of the inside.

    Also, If you don’t smash a bearing now and then, how do you find the limit? The more you smash, the more you know. I never said that was the tuneup you were looking for, that’s just how you learn. And by the way, I didn’t make that up, that was the guidance I got from a guy who was qualified top 4 at the US Nats while he was telling me that a couple years back. I think he actually said, lean it down until you squish some bearings and if the rods come out, fatten it back up a little. It may sound like he was being a smartass but he was really being very genuine after a mutual friend asked him to help me out a little.
     
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  15. Mike Canter

    Mike Canter Top Dragster
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    You can tell exactly where you are in the tuneup by reading the spark plugs. I don’t know of anyone that tunes by bearing smash anymore especially in the Promods. We do still check the bearings but not after every run. If you are burning the threads on the plugs then you are way too lean and if more than one thread then watch out.
     
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  16. Will Hanna

    Will Hanna We put the 'inside' in Top Alcohol
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    The way I was taught by Steve Harker to read plugs is very similar to what Mike describes in his article, but we look for how much cad is left in the inner beveled area of the plug (referring to a NGK 6061 -10 or -11). Like his article said, close/safe is when you only have a small 'eyebrow' of shine/cad left down inside. Some combinations can get rid of all the cad, but you really have to have a good handle on what jetting your engine wants because at this point you are flirting with burning a piston or detonation. If you are a put a jet in it back at the pit and not 2 pairs back, then stick with some eyebrow of cad or more.

    Reading the bearings is very important, but you have to know how to read a V bearing that we all run nowadays. Years ago with the softer M bearings, you could read the 'squish' at the bottom and tell something. I haven't found much info there besides going from safe to detonation - not much in between.

    I think it's important to point out that the rolled babbit material that happens every pass SHOULD NOT be part of any measurement. Take a sharp edge or deburring tool and debur the side of the bearings. This should be done if you are reusing the bearing regardless if you are measuring it. Just use a normal pressure and scrape till it's smooth and no more babbit is rolled over the edge. If you are going to try to measure the bottom width of the bearing, you are looking for movement of the hard material on bottom, not the soft material on the top.

    Tom Conway taught me the 'across the top' measurement which I describe as measuring across the top of the "U" or what would be the diameter of the bearing half circle. You simply put the calipers on the outsides of the bearing and roll it until it just touches. The diameter of the big end of a hemi rod is 2.500". A new bearing will be about .020 to .035 wider than that so the bearing is tight in the rod or cap. If you are detonating/beating the bearing up, it will hit the bearing at the bottom of the "U" and close the tops of the U in. I have found keeping the bearings around 2.500-2.505 is safe. Closing them up much more than that, you are getting over center. 2.495-2.500 you might be right on the edge. Anything less than 2.490, you are close to disaster. I have seen a bearing 2.470 to 2.469 that kicked the rods the next run (bearings were measured after the fact due to a breakdown in communication). The only instance a bearing will close in without detonation is just too many runs on it. I have been actively tuning cars since 2003, and this measurement has not failed me and has proven to be the most accurate way to find the limit on timing.

    Your timing limit is going to be directly connected to how lean the fuel system is and a number of other factors including compression and head temp.
     
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  17. TOL

    TOL Active Member

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    Will, do you find that coated bearings tend to alter or influence your read of them in any way?....
     
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  18. Will Hanna

    Will Hanna We put the 'inside' in Top Alcohol
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    I haven't ran coated rod bearings. I doubt it would change the way I read them as it shouldn't have much effect on the bearing closing in if it's beat on.

    Now I'm sure they're harder to throw away....
     
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  19. Mike Canter

    Mike Canter Top Dragster
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    Yes you can still smash coated bearings just like uncharted ones.
     
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