A Couple Of A/f Gauge Q?'s
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A Couple Of A/f Gauge Q?'s

  1. #1
    Senior Member H20MOFO's Avatar
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    Default A Couple Of A/f Gauge Q?'s

    I seem to be finding/figuring out that there are no "marine" a/f gauges, all automotive?? I should have my new/used "dry" headers by tommorow so I can put up a pic if need be, but judging from past threads I should mount the bungs about 4-5" past the collectors? Does it matter if they are an "upswept header" It looks like most just monitor 1 side of the motor, I was thinking maybe put a bung on each side and then plugging the other, and then vis/versa to check the other side also. Lastly once I get things where I think they should be # wise, I'll be putting my tt bassetts back on, what kind of tuning difference would/should one expect going from dry ot's , to wet tt's? Also any experiance good or bad with any particular brand would be appreciated. Thanks in advance, Kreg
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    cfm
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    Do A/F ratio tuning with the exhaust that will be on the boat as the exhaust can/will greatly effect the carburetor metering and cylinder evacuation of course.

    The sensors won't take getting wet. I'd run the injected headers that are going to remain on the boat dry to tune the A/F. This should get you closer.

    Marine gauges are sealed to keep out moisture better and etc. If there is no 'marine' gauge available, then you choose your only option.

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    Senior Member H20MOFO's Avatar
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    I know my plan isn't "ideal" but I don't feel like melting another motor, and I don't know how I can run my tt's dry and not melt my exaust hose. It would be cool if someone made some type of stainless 4" exaust hose. My biggest fear is that when I put the upswepts on I won't want to take em back off.
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    cfm
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    Sorry, didn't realize the 'tt' meant thru transom. Not a jet boat guy so I'm a little slow with the terminology. Doh !

    So, now, I'm still assuming you have water injected (not water jacketed) headers ?

    Yup, that's a tough one.

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    Senior Member H20MOFO's Avatar
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    Uh oh. Brown just brought my headers, I didn't realize that the collectors weren't welded. Do you all think that will cause a false lean? BTW CFM these are dry.
    Last edited by H20MOFO; 05-06-2008 at 12:43 PM.
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    21 Daytona Outlaw's Avatar
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    yes it could. if placed after the collector
    Last edited by Outlaw; 05-06-2008 at 04:25 PM.

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    Senior Member H20MOFO's Avatar
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    Quote Originally Posted by family matters View Post
    usually 6-7 inches of the exhaust valve is normal.
    IMHO I think 6-7 inches is a little close and tends to effect the signal at the carb (thus changing AFR after removal), especialy when using them in every cylinder. We have found that 12-14 inches works best. I would definatly not put them closer than 10, even when monitoring one cylinder at a time.

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    Senior Member H20MOFO's Avatar
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    Warp, you would put an egt probe 12-14" or an 02 sensor for an a/f? or both? looks like I'm just testin a couple of holes instead of one bank or the other. Help anyone.. I'd like to talk about egt set ups also , but I guess that's another thread
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    I was refering to an o2 sensor as that is what I thought this was about. If you are talking EGT probes then the closer placement is recomended.
    I am not familiar with an EGT type air fuel meter, but be careful of this when tuning a fuel system as timing has a way bigger impact on exhaust gas temp than actual air fuel ratio. It can take up to 5 jet sizes or more to make a significant impact on EGT's, and this can relate to half an air fuel ratio or more depending on set-up. We did a study on this a few years ago (man, maybe longer than that!) and it was pretty "eye opening". It used to be standard practice to tune an engine on the dyno using EGT's and BSFC numbers. With the introduction and development of O2 sensors and systems over the years it has shown us just how inaccurate this method was for tuning AFR's. Just part of the evolution of race engines (and testing methods) and how they are tuned.

    As always, just MHO!

  13. #11
    Senior Member H20MOFO's Avatar
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    Thanks Warp. in post #5 familymatters asked if I was using a egt style meter, so I was confused. I'm doing an a/f for sure and still debating on the egt. Just checking.
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    Senior Member H20MOFO's Avatar
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    Well that was nice. Fired her up yesterday with the a/f and dry headers, it read 11.5 to 12.0 all the way out the harbor then right as I went to get on the gas, it quit working. The digital readout went to 3 lines/dashes. And the light on the outside went all the way up lean. Do you think it may need just a new 02 sensor. BTW it's a AEM EUGO gauge set up. I've been calling there tech line all morning, I'm not impressed. I guess thats what I get for buying a used gauge.
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    No Sandbar To Far sanger rat's Avatar
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    Sounds like your too lean. Guage will only read so far.
    Quote Originally Posted by One More Year View Post
    The only blab's I will even be a part of is just when it is me they are talking about. Aaaah yes I can see a few good looking shiny tall deck motors on the beach, with barely enough fuel to get back to the launch saying, "Holy crap how fast you think that Daytona was going man? That's like the 20th time he's gone by today?"

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    Senior Member H20MOFO's Avatar
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    I think either the gauge is junk, or the 02 sensor. After that it wouldn't read at idle either, nothing but lines(no #'s). I guess I'll buy another 02 and cross my fingers. BTW it's a wideband, before I ran it ,with the key on, and the motor not running it was showing like 15.6?
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