O2 Sensors

[Alpine 1789]

That is certainly an option and the only one to my 'bung patch'. AEM makes a "no-weld" sensor mount, but they don't seem to come any smaller than 1.75" and my exhaust is 1 5/8".

I don't currently have a muffler shop I trust (I did, but my guy left) but could probably find one. Finding a 1 5/8 band clamp is also not easy; I needed one once before and never did find one.

 

[Alpine 1789]

So, now what?

I now have my 02 sensor and gauge hooked up, which brings me to the next question: how do I use it to check and ultimately maximize my carburetor jetting? I did some surfing (the instructions that came with the kit are worthless past installation) and learned that an air/fuel ratio of 14.7:1 is supposed to be ideal, but when? At warm idle (around 1000 rpms on my car), the gauge reads about 12.5, more or less. I just went out for a highway cruise and at a reasonably steady 3500 rpms it read pretty close to 14.7. It moved in response to the throttle, but rarely went to or stayed much above 15 or 16. Being rich at idle certainly agrees with my nose, but I don't know if I can change that without screwing up something else.

So, what are my next steps?

 

[sunbby]

Jim,

Which car is this on? What carb(s) are you using? For that matter what is the entire fuel system, pump, etc?

14.7:1 is the theoretical air/gas for complete combustion, but best power is usually made at a richer 13:1. Leaner mixtures, like your 15:1 or 16:1 can work but you lose power and may increase heat. Also, too rich or too lean will eventually cause noticeable driveability issues (misfires).

I couldn't really tell if this setup used a heated sensor, I'm assuming it does. If not the exhaust gas at idle may not be hot enough to get a proper reading. Did you get 12.5:1 at idle after high speed running?

I assume Jarrid will chime in with more and accurate info.

 

[Alpine 1789]

This is on my SV (unfortunately, the only one anywhere close to being on the road): 1725 engine with +60 pistons, Chevy rods, KB camshaft, Vizard head, and Weber 32/36 carb. The 12.5:1 reading at idle was after a 30 minute highway drive, although I had the same reading after letting the car warm up before the drive. As far as the higher (15 or 16) readings, it never seemed to stay there very long. I think this was more in response to short term throttle changes than anything. I could bury the needle by blipping the throttle, but it would go right back to the previous reading. I was driving alone, so it was hard to be too specific about readings at different RPMs, but the most steady readings were the highway cruising at 14.5-15 and hot idle at 12.5.

Thanks for the help.

 

[RootesRacer]

14.7 would be ideal across the board for best combustion, but if you want more power, you would need to run richer, the 13 AFR figure is accurate.


If you are looking for a compromise between power and economy, you will want the following:

Get the engine to idle at the figure nearest 14.7 which achieves the smoothest idle quality (AKA best lean idle). Do not go leaner than 14.7.
Under very light load have the AFRs near 14.7, OK to be a bit richer, also OK to be in the 15s if there are no misfires.
Under power to WOT, the AFRs should be 13 to 13.5.
Dont go richer than 13, it wont give you more power and will hurt economy.


Now getting the carb set so it does all the above is a tough task, one of the reasons that EFI came along.

Now some info from my own setup.
My hotted over 1725 wont idle smoothly leaner than 13.5 AFR. It also loves 13 AFR at wide open throttle.
The progression though is a bit messed up as it goes to 11 AFR in between idle and power. The engine doesnt seem to like to run near stoichiometric under any condition, I suspect the fuel droplet size is too large to support normal combustion due to the oversized carburettion.

Your mileage may vary.

 

[Alpine 1789]

If you are looking for a compromise between power and economy, you will want the following:

Get the engine to idle at the figure nearest 14.7 which achieves the smoothest idle quality (AKA best lean idle). Do not go leaner than 14.7.
Under very light load have the AFRs near 14.7, OK to be a bit richer, also OK to be in the 15s if there are no misfires.
Under power to WOT, the AFRs should be 13 to 13.5.
Dont go richer than 13, it wont give you more power and will hurt economy.

Thanks Jarrid. This is exactly the information I was looking for. I will try to take this one step at a time, although I am sure it will be an iterative process. I think getting the idle right is the first step, but please correct me if I am wrong on that. Now that I have the gauge, I will see if I can play a bit with the idle mixture, although I suspect I will also have to try a different jet.

So, more to follow. As always, thanks for the education!

 

[RootesRacer]

Setting idle mixture will probably both the first and last thing you do as changing the idle jet to modify the progression will also require a change in mixture position.

I wouldnt mess with the secondary idle jet unless you have a hole in the beginning stages of secondary, and if so good luck proving it.

So jets that are on the table are the primary idle, primary main and secondary main.

I would try to tune the primary portion so that it runs 13.5 to 14.5 AFR, then the secondary (WOT) for the 13 figure.


This would yield a good compromise in power and economy, you must understand though that you cant expect it to pull hard at mid throttle since it will be leaner there.

 

[Tom H]

Jim, So how did you end up doing the installation?

Tom

 

[Alpine 1789]

Setting idle mixture will probably both the first and last thing you do as changing the idle jet to modify the progression will also require a change in mixture position.

I wouldnt mess with the secondary idle jet unless you have a hole in the beginning stages of secondary, and if so good luck proving it.

So jets that are on the table are the primary idle, primary main and secondary main.

I would try to tune the primary portion so that it runs 13.5 to 14.5 AFR, then the secondary (WOT) for the 13 figure.


This would yield a good compromise in power and economy, you must understand though that you cant expect it to pull hard at mid throttle since it will be leaner there.

Thanks Jarrid. I am going to try to get started on this over the weekend, but it may have to wait a bit as I also developed a speedometer problem yesterday that I will post questions on shortly. None-the-less, I will keep this post going as I progress for the benefit of those interested...and of course, for my own benefit too.

 

[sunbby]

Jim, just for completeness, are you using the stock mechanical fuel pump? A dodgy pump or mis-speced electric pump/regulator could give too much or too little pressure and cause bad jetting like symptoms.

 

[Alpine 1789]

Jim, So how did you end up doing the installation?

Tom

I did end up with installing the sensor in a connector; not so much to make it removable, but because drilling the bung hole in the end of header would have created two challenges. First, it would have been really difficult to do without removing the header to gain access for both drilling and welding. I know Jarrid has done them attached, but I don't think I have the skills or tools for doing it in such close quarters. I really don't want to go to the trouble of taking it off until I am ready to take it off in the winter for recoating (I have other tweaks I want to do then).

But other problem was that installing the sensor at the end of the header without removing it would have meant drilling through the junction point where the exhaust pipe enters the header. It would have then been near impossible to disconnect the two pipes later, as the bung would have partially penetrated the exhaust pipe. So, I bought an exhaust connector with a 1 3/4 ID on one side and a 1 3/8 ID on the other and drilled the bung hole in the 1 3/8 section. I then had to shorten the stainless exhaust pipe by about 3 inches to be able to reassemble. I planned everything out so that I would eventually be able to cut off the 1 3/4 end of the pipe and weld the remainder, including the bung, onto the header. I'll do this prior to having it re-coated. I then have a permanantly installed bung and a one piece header. (Bill Atalla: If you are reading this and ever decide to make a new batch of headers, you might consider having the outlet end made a few inches longer, which would make this step easier for anyone who want to go this route. I don't know about others, but I had to shorten the exhaust pipe a bit when I first fit the header anyway, so it woudn't have been a big deal at all to shorten it another inch or so.)

I'll try to post a couple of photos this weekend, in case the above description isn't clear.

 

[Alpine 1789]

Jim, just for completeness, are you using the stock mechanical fuel pump? A dodgy pump or mis-speced electric pump/regulator could give too much or too little pressure and cause bad jetting like symptoms.

I am running the stock pump. I have a very good electrical one and a regulator that I bought a bunch of years ago when I was playing with the DCOEs, but never ended up using it and have just put it away for the V6. As far as I know, my stock pump works just fine.

 

[Alpine 1789]

Here are two photos of the bung installation. The first shows the connector that not fits in between the header and the exhaust pipe. The second is a close up of the bung. The pictures make it look like I have the sensor at a 90 degree angle, but it isn't. It might not quite be at the 30 degrees that Jarrid recommended, but it is pretty close.

[/IMG]

 

[weaselkeeper]

Bill Blue.

I like your idea about the 400 cfm Carter. The hard part is finding one. I personally think the Carter is easier to rebuild and make driveable, more so than a holley, but I'll admit to limited, but frustrated experience with holley and success with a Carter afb that I had for 18 years.

dont have a spare one on the shelf do you?

 

[Bill Blue]

Bill Blue.

I like your idea about the 400 cfm Carter. The hard part is finding one. I personally think the Carter is easier to rebuild and make driveable, more so than a holley, but I'll admit to limited, but frustrated experience with holley and success with a Carter afb that I had for 18 years.

dont have a spare one on the shelf do you?

No I don't, but I wish I did. My experience with the little carb was limited to one example and it left when mom sold the Jeep to a cousin. I told him that if he ever ditched the Carter to let me know. He didn't.

Bill

 

[MikeH]

This is probably one of the most reliable and easiest carbs to work on, the Autolite 4100. With the 1.08 venturi its 480 cfm. Pony Carbs (not connected with them) also mods the 1.12 venturi (600 cfm) by sleeving the primaries to reduce their size 1.00, to create a spreadbore 4V.

http://cgi.ebay.com/ebaymotors/ws/e...r_id=120392855286&ua=WVI8&itemid=250296928982

http://cgi.ebay.com/ebaymotors/Auto...ptZMotorsQ5fCarQ5fTruckQ5fPartsQ5fAccessories

 

[Alpine 1789]

14.7 would be ideal across the board for best combustion, but if you want more power, you would need to run richer, the 13 AFR figure is accurate.


If you are looking for a compromise between power and economy, you will want the following:

Get the engine to idle at the figure nearest 14.7 which achieves the smoothest idle quality (AKA best lean idle). Do not go leaner than 14.7.
Under very light load have the AFRs near 14.7, OK to be a bit richer, also OK to be in the 15s if there are no misfires.
Under power to WOT, the AFRs should be 13 to 13.5.
Dont go richer than 13, it wont give you more power and will hurt economy.


Now getting the carb set so it does all the above is a tough task, one of the reasons that EFI came along.

Now some info from my own setup.
My hotted over 1725 wont idle smoothly leaner than 13.5 AFR. It also loves 13 AFR at wide open throttle.
The progression though is a bit messed up as it goes to 11 AFR in between idle and power. The engine doesnt seem to like to run near stoichiometric under any condition, I suspect the fuel droplet size is too large to support normal combustion due to the oversized carburettion.

Your mileage may vary.

I've finally had some time to drive over the past two days. Here is what my car is showing:

• Hot idle: 13.5
• Highway cruising, very light throttle: 14.5
• Hard acceleration: 12.5
• And, in case this is worth reporting, deceleration after hard acceleration: 15.5

It sounds like I could use, but don't need, a slightly smaller idle jet (I have the idle mixture screw in pretty far). It also sounds like I need to take the secondary jet down a notch. Am I interpreting all of this correctly?

 

[RootesRacer]

Jim,

I'd say you are fine across the board (secondary main is debatable).

If the real light throttle is showing in the 14s, I would worry about the mixture screw position as changing the idle jet will change your AFR in this area.

As for the AFR on decel, dont concern yourself at all about this, it is what it is.

 

[sunbby]

Jim,

Cool, that sounds pretty good. Is that out of the box (who's box?), or have you been changing jets? Can you list what you have in there now, maybe starting point and what you ended up with? I'm sure others would like to know and compare. How does it feel "seat of the pants" now, any different?

 

[Alpine 1789]

Thanks Jarrid. If nothing else, it is good to know that I am in the right ballpark. I have plenty of other things to worry about on the car.

And Todd: I would be happy to post the jets if I had any recollection of what they were. It has been so long since I jetted it that I don't really remember any more. I know it isn't stock (I got the carb from SS), but don't remember what I finally ended up with. I'll pull everything apart one of these days and post the results.