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Thread: A/F ratio

  1. #11
    Hallz
    if you can I like to fatten it up at peak tq (or high load) to about 12.5 at WOT and peak hp lean it back down a little to 12.8-13.1. This is with 91 octane or better on a NA motor of course.
    Using a little off the shelf octane booster on fresh plugs and doing some WOT pulls and immediately pulling the plugs and reading them can usually give you an indication as to if the motor likes the AFR your running. The octane boosters usually discolor the plugs slightly making them easier to read.

  2. #12
    Nubbs
    Jet boats are under load at 3300 rpm ....... My guess is that it probably does need to be 13:1/ 13.5:1 for better power
    Ok, I'm going to stir the pot some here. If the motor is already spinning 3300 rpm with a "lean" fuel mixture, why would you want to richen the mixture for better power? The extra fuel will just be a waste. The motor may be capable of more power at 3300 rpm, but the load on the motor will remain the same unless you go to a bigger impeller.
    Nubbs (just stirrin the pot some)

  3. #13
    cook1
    The problem with runing an engine at a lean mixture is excessive heat. This type of heat burns valves and can actually create light deto. At high vacum the amount of air/fuel in the chamber is lower so the amount of btu's released is less so then engine can tolerate a leaner mixture at lighter loads. The old chrysler lean burn systems would go higher than 14.7:1 but they had to increase timing to compensate for the slower burn rate of the lean mixture. They could reach as high as 60 deg at light throttle.

  4. #14
    SoggyJet
    I am using a lm-1 wide band a/f meter. .......
    Cook 1,
    What do you think of the LM-1 A/F meter? Good quality? Easy to use? Any pros and cons? How do you have it rigged in your headers?
    I was thinking of trying to use one to help tune my project, when (not if) I finally get it into the boat. That unit is a little pricey, so I would like to hear some feed back on system before I part with the bucks, if ya know what I mean.
    Thanks
    Doug McCoy

  5. #15
    cook1
    Its pretty easy to use and seems to work well. I had to weld a bung in my lightning heads through the water jacket to keep it away from the water. They have a new one that is a 2 5/8 guage that you can mount.

  6. #16
    cruser
    Unchained,
    Nothing wrong with the cycle you are running. I just did a little math for the heck of it. You said you were batch firing the injectors once per rev so: (60 seconds/7000rpm)=8.57mS pre revolution. You said you were using 6.9mS pulse width. 6.6/8.57*100=80.5%.
    If you feel the need to turn much more rpm, I think you would need to go to sequential or jack your fuel pressure back up.. Sequential would give you 4 cycles(2 revolutions) to get the fuel squirted into the intake at each cyclinder.
    At least that is my guess.

  7. #17
    Taylorman
    Can you use a a/f monitor with Bassett Headers?

  8. #18
    cook1
    Yes, if they are water injected then you would have turn the water off while using it. The water will not only make the reading wrong but it will screw up the sensor to.

  9. #19
    Taylorman
    Ive been wanting one. Who makes a reasonably priced one that is decent quality? Where would you put the sensor on Bassetts?

  10. #20
    cook1
    Inovate motor sports makes them. They have dealer all over. I would put the sensor in the collector about 2-3 inches from were the pipes come together. You need to install it on top or down to about 90 deg so that any moisture wont make its way into the sensor.

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