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Discussion Starter #1
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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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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Discussion Starter #3
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.:)grn
 

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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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Discussion Starter #5 (Edited)
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.
 

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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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Discussion Starter #9
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:)grn
 

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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!:)sphss) 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! :)hand
 

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Discussion Starter #11
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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Discussion Starter #12
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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Sounds like your too lean. Guage will only read so far.
 

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Discussion Starter #14
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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Don't condemn the AEM gauge just yet.

O2 sensors do go bad and that is more likely the problem.
Get the number off the sensor and put the brand name and the part no.s in a search engine and see what a new one costs.

With O2 gauge setups there seems to be a situation where some of those guys want to resell a $70. O2 sensor for $ 300.
You need to find out where to buy it direct.
 

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Discussion Starter #16
I guess it must be the sensor ,the guy at aem told me to disconnect the 02 and it should default to 14.8 or .7 and it did.
 

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I know my plan isn't "ideal" but I don't feel like melting another motor, My biggest fear is that when I put the upswepts on I won't want to take em back off.:)grn
:|err i think your plan is a good one , just leave the dry set with the a/f meter on though :p seriously it should only go a little fat after changing back to the wet headers so at least you will be safe . curious as to why you chose the AEM gauge , i've been thinking of getting a innovate LM-1+ rpm handheld will be interesting to jet it by a gauge not just by seat of pants, tach and reading plugs :)sphss
 

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A couple things to remember for anyone wanting to run an O2 sensor.
Make sure that there are no leaks in the header flanges or the meter will not read right.
If you put the sensor in the collector of a set of Bassett headers be sure to plug the weep holes in the bottom of the 1st bends too.
This is a little less of a problem with a turbo setup because the headers have back pressure so no air is going to leak in, only out.
 

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Another thing to keep in mind is that (most all) O2 sensors don't like leaded fuel (or running in the header with system power off). That has been the single biggest killer of sensors for us, and since we have switched to unleaded fuel it has about trippled there time limit.
 
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