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  1. #1
    River Rat Jay's Avatar
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    Running Rich????

    Had a question about AFR's. I have been reading a lot on here that everyone is running there AFR's in the 11.9 to 12.1 range at WOT. OK, I am very educated in the maintenance and repair of Gasoline and Diesel engines... The thing I am trying to figure out is why everyone seems to be running there skis so rich. 14.7 is Stoich, so why run 11.9 - 12.1? Is there something different about these that require them to run richer, or are guys just doing that to be on the safe side? I know the engine will run a little cooler, but EGT's may also be higher because your passing unburned fuel through the exhaust and it continues to burn after it leaves the cylinder. Not to mention that your gas mileage gets worse. So, if someone has a theory or knows a good answer to this, I would be glad to be schooled!


  2. #2
    home of the dislexic fingers breon's Avatar
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    at 14. anything you will go boom and it will miss and run bad even at idle..

    gas is different than diesel..diesels need to detonate to run...

    the more boost you run the richer the mixture needs to be..to a point

    at idle i shoot for 13 13.2 ish ok even at 13.5 above that it will brake up and start missing...
    then slowly work the af to say 12.5 12.7 at vac to 0 psi cruzinng thisis your milage..if a ski can ever have that..

    then it needs to be to say 12.2 buy 6 psi

    then it needs t fall to 11.8 over the next 4 psi

    some will say 11.6 aboove 15 psi..

    basically it drops .1 for every pound of boost

    if you can get your map to do that ....you will be spot on.... but to get you tune that spot on is difficult..and takes time...

    i had the riva ecu..on there stage 3 set up as 13.2 idle then 12 at wide open but that was only set for 11 12 psi

  3. #3
    Vern's Avatar
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    What Breon said ... boosted (supercharged, turbocharged) motors must have a lower/richer AFR than naturally aspirated motors. It is NOT unique to our skis ... it is unique to boosted motors. Look at any dyno test with a supercharged motor ... all good engine builders tend to go for 11.5 - 12.5 max AFR on supercharged motors. Stoich is basically theoretical only, and in order to survive, most engines run much richer at WOT in particular, and boosted engines MUST be run even richer yet at WOT. Nobody is flushing gas out the exhaust needlessly, the AFR we try to run at are proven numbers that are run on virtually any boosted engine that needs to survive long term.

  4. #4
    River Rat Jay's Avatar
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    Quote Originally Posted by breon View Post
    at 14. anything you will go boom and it will miss and run bad even at idle..

    gas is different than diesel..diesels need to detonate to run...

    the more boost you run the richer the mixture needs to be..to a point

    at idle i shoot for 13 13.2 ish ok even at 13.5 above that it will brake up and start missing...
    then slowly work the af to say 12.5 12.7 at vac to 0 psi cruzinng thisis your milage..if a ski can ever have that..

    then it needs to be to say 12.2 buy 6 psi

    then it needs t fall to 11.8 over the next 4 psi

    some will say 11.6 aboove 15 psi..

    basically it drops .1 for every pound of boost

    if you can get your map to do that ....you will be spot on.... but to get you tune that spot on is difficult..and takes time...

    i had the riva ecu..on there stage 3 set up as 13.2 idle then 12 at wide open but that was only set for 11 12 psi
    Yeah.... Well I figured it out... Because of the RRFPR and not being able to adjust it like you can an injector map, this is the result... That is of course if everything is linear. And yes, I know it is not a diesel.....
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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  5. #5
    Vern's Avatar
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    AF (AIR FUEL) RATIO Your kit is factory tuned and calibrated at Kenne Bell at 11-11.5 AFR, the ideal ratio for street use. No expensive custom tuning is necessary. If you still choose to have your car “retuned” NEVER USE A DYNO THAT DOES NOT TUNE WITH AN OEM GRADE AFM1000, HORIBA or ETAS AFR SYSTEM. And there’s only 10HP between 11.5 and 12.5 (max power but requires higher octane fuel).

    This from Kenne Bell's website about their supercharged systems. Link: http://www.kennebell.net/supercharge...aro/Camaro.htm

    Even if you think we are all morons and love to waste gas, we are not the only ones. ANY good shop will tell you max power is at 12.5 AFR, and for boosted engines, 11.5 - 12.0.

    If you still think everybody is crazy for running that, setup your ski to run stoich at WOT ... you will need a new engine very soon.


  6. #6
    Eric Ocman's Avatar
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    Re: Running Rich????

    duke has my ski as of today at 11.9 wot and its pretty warm here. I understand the reasoning now.

  7. #7
    Doel Tiburon1264's Avatar
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    I'm running:

    2006RXT

    Idle 13.5 Mid 12.3 and WOT 11.7 [email protected] and Less Cooke 8800rpm and 60lbs injectors
    It runs great! I'm very happy! Oh! Last GPS Run 82.8mph and like Eric stated its warm here in Florida

  8. #8
    Duke's Avatar
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    Like everyone else said, boosted motors generally require more fuel as boost rises. Stock chargers or X chargers do not require to be as rich as the higher boost aftermarket chargers. RXPX comes factory running in the 13s for emissions reasons and will live fine like that with the factory ecu with its mild timing curves. Once refashed ecus with more timing and bigger chargers come into the picture more fuel is needed to keep everything cool and preventing as much detonation as possible.

  9. #9
    Duke's Avatar
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    Quote Originally Posted by Tiburon1264 View Post
    I'm running:

    2006RXT

    Idel 13.5 Mid 12.3 and WOT 11.7 [email protected] and Less Cooke 8800rpm and 60lbs injectors
    It runs great! I'm very happy! Oh! Last GPS Run 82.8mph and like Eric stated its warm here in Florida
    Glad your happy Doel!! Thats a fast 3 seater.

    Just wait til you get that issue resolved. Thinking more like 84.

  10. #10
    home of the dislexic fingers breon's Avatar
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    Quote Originally Posted by River Rat Jay View Post
    Yeah.... Well I figured it out... Because of the RRFPR and not being able to adjust it like you can an injector map, this is the result... That is of course if everything is linear. And yes, I know it is not a diesel.....
    then i guess you da man

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