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what is "ideal" a/f ratio

This is a discussion on what is "ideal" a/f ratio within the Nitrous forums, part of the LSx Technical Help Section category; I just bought a zex kit. I currently have jets for a 75hp shot. I have a wideband so I ...

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    what is "ideal" a/f ratio

    I just bought a zex kit. I currently have jets for a 75hp shot. I have a wideband so I plan on tuning the a/f ratio. I'm wondering what is an ideal a/f ratio to shoot for. I could just run the jets supplied but what would the fun in that be? Also, I've leaned the car out for N/A from the stock 11.6:1 a/f ratio to 13.0:1 so that will throw off the a/f ratio on spray and I don't want to pop the engine. Does anyone know what a/f ratio zex aims for with their jetting?

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    11.9-12.0 would be fine with a 75 shot. Drop your timing to 26* to play safe. I currently spray a 200 out of the hole and am running 22* with 10.9 AFR on a stock bottom end. So far it's staying together.

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    Senior Member Danger731's Avatar
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    I have a stock tune , 100 shot, I'm 11-12 w or w/o spray at wot. At 75 I wouldn't worry, the A/F gauge is nice - it is like a Tetnus shot , good to have but figure the odds of REALLY needing it.
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    thanks guys, I think I'm pretty much running 23-25 degrees as it is. I'm wondering if I should just run one size larger on the fuel jet because I leaned the car out.

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    TunedbyFrost.com Tuner Frost's Avatar
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    Quote Originally Posted by Danger731 View Post
    I have a stock tune , 100 shot, I'm 11-12 w or w/o spray at wot. At 75 I wouldn't worry, the A/F gauge is nice - it is like a Tetnus shot , good to have but figure the odds of REALLY needing it.

    Maybe I misunderstood... are you seriously telling someone that they *Don'T* need a wideband?

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    Quote Originally Posted by Frost View Post
    Maybe I misunderstood... are you seriously telling someone that they *Don'T* need a wideband?
    Maybe he's good at reading plugs?

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    sorry but I'd be reeeeeeeeally hesitant to run my kit without the wideband hooked up but this is my first time foolin with nitrous so I'm a little nervous. I think I'll just get the wideband hooked up before I hit the spray, its gonna be really hard to resist the urge to hit the button though.

    I bought this kit off my buddy and it has .021"/.040" jets in it now, the jetting was tuned for a trailer blazer SS with a stock tune. I have a feeling I'm gonna need to richen up the fuel jet since I'm already running leaner N/A and zex recommends a .024" fuel jet with that nitrous jet for a 75 shot, I'm assuming I'll need about a .026" or .028" fuel jet.
    Last edited by JDMC5; 07-15-2008 at 06:43 PM.

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    TunedbyFrost.com Tuner Frost's Avatar
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    Quote Originally Posted by JDMC5 View Post
    sorry but I'd be reeeeeeeeally hesitant to run my kit without the wideband hooked up but this is my first time foolin with nitrous so I'm a little nervous. I think I'll just get the wideband hooked up before I hit the spray, its gonna be really hard to resist the urge to hit the button though.

    I bought this kit off my buddy and it has .021"/.040" jets in it now, the jetting was tuned for a trailer blazer SS with a stock tune. I have a feeling I'm gonna need to richen up the fuel jet since I'm already running leaner N/A and zex recommends a .024" fuel jet with that nitrous jet for a 75 shot, I'm assuming I'll need about a .026" or .028" fuel jet.

    Don't worry, it won't be drastic at that level. If you have the wideband and are tuning, why not just set it at a safe(r) 12.5-12.6:1 off the bottle for the first spray tests.

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    does the engine like the same basic a/f ratio on spray as it does off spray? I know people usually run it rich to be safe but what is usually a good target for peak hp? I know 12.8-13.1 is target N/A so how about nitrous?

    I would be really nice to know what a/f zex is targeting, or what a/f ratio a stock tune would pull on spray using the recommended jets.

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    TunedbyFrost.com Tuner Frost's Avatar
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    Quote Originally Posted by JDMC5 View Post
    does the engine like the same basic a/f ratio on spray as it does off spray? I know people usually run it rich to be safe but what is usually a good target for peak hp? I know 12.8-13.1 is target N/A so how about nitrous?

    I would be really nice to know what a/f zex is targeting, or what a/f ratio a stock tune would pull on spray using the recommended jets.
    11.5:1 on the gas
    12.6-13.2 (NOT neccessarily a straight line, contrary to internet belief) N/A

    You could put that zex kit on 3 different cars and get 3 different results. Your results are your own and are all that matters. FWIW, most of the wet kits I tune need [relatively] drastic fuel jet changing.

    Then again, I have never met anyone who actually used a 75 hit unless it was a first stage

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    oh wow thats a good one. I'm just trying to get this thing working and I'm going to probably step the jets up once I'm comfortable.

    So, in regards to your response, 11.5 is what I should be aiming for on the juice? I have my N/A curve set to 12.8 at 4K tapering to 13.1 at 6K.

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