For those of you that are running a holley 390, what size jets are you running in the primary's? Mine are 54's but I think it might be a little too big. The holley book I have states it would of came with 51's.

 

Hey Ranger,
I currently have a Holley 390 on mine. Offenhauser DP intake. EFI manifolds. 2.5" exhaust. (For comparison to your system).

Right now I have an 02 sensor hooked up to it, and it's running really rich. I have the stock 51s in it. I tried 47s a few days ago and it was too lean. Have some 48,49, and 50s on order (since the local performance shop doesn't carry them that small, and give me weird looks when I order them), so I'll be tuning it in a little better in the next day or two.

Either way, I tried 54s before I put the O2 sensor in (real eye opener) and after hooking the O2 sensor up, they were so rich that they were almost out of the sensor's readable range.

From what I've gathered, I'm thinking the 49s will be about right on.

 

Mine has a 390 holley with a offenhauser dual port intake and full length headers and 1 1/2" pipe . I have read about putting a O2 sensor in the exhaust to check how well the engine is running.

Where did you put yours in the exhaust? What do you use to read the output with. Since I'm running duals I'd have to use 2 of them wouldn't I?

Let me know how the new jets work out.

 

On mine, I used EFI manifolds, so I was able to get the Walker collector/downpipe designed for them. Since they were for EFI, the pipe came with an O2 port and a cap. I lucked out in this since I was able to just toss an O2 sensor in.

To add one, you probably only need to put it in one of the pipes (suppose you could do both) since it's testing the exhaust, which is determined by the carb, and therefore should be the same output in both header pipes.

Get an O2 bung (usually about $3 on ebay) and have it welded in. Then you can get either a narrowband (ave. $20) or a wideband (ave. $70) O2 sensor. The narrowband will work, and it's what I have, but I'd love to get a wide band.

Then, just run the signal wire from the O2 sensor up into the cab and hook it up to a voltmeter, run the ground of the voltmeter to the frame, and you're good to go.

If you have a narrowband, the voltage will range from about 0 to 1 volts. A reading of 0.4 - 0.5 volts during cruise shows perfect mixture. Anything above is rich, and anything below is lean.

If you have a wideband, it'll tell you your EXACT mixture and will range from 0 to 5 volts. 2.35 volts is perfect mixture. You just take the voltage, multiply by 2, and add 10.
2.35 * 2 + 10 = 14.7 A/F ratio.

It takes ALL the guesswork out of tuning, and you can watch exactly how your carb is acting under any given condition. It's invaluable.

 

Then your not using a heated O2 sensor? Do you know off hand what type of vehicles would use a wide band O2 sensor. I can pick one up cheap at the salvage yard.

That's what I would love about it, it gives you realtime results.

 

I don't know any off hand. Your best bet may be to go on to ebay and type in "Wideband O2 sensor". They'll usually say something like "For 2002 - 2005 Honda Accord, '04 - '08 BMW xxx" etc.

A salvage yard isn't a bad idea to find one. Hrm.... Nice thinking.




The heated O2 sensors, if I recall correctly, are so they can place them in places like AFTER the cat, where the exhaust temps have already cooled down a little bit. A plain old one wire will work for these applications, especially if placed right outside the manifold. Right now, I'm using a 4 wire, but three of them are just taped off.

 

Let me know how the jets turn out. I'm ordering a rebuild kit for mine before I put the 51 jets in.

I may go to the salvage yard and see if I can find a sensor and bung.

I have long tube headers and don't really want to drill holes in them if I don't have to. Do you think if I put the O2 sensor right after the flange were the header stops and exhaust pipes starts it would still be hot enough to give a good reading?

 

I guess one way to look at it would be, "it's better than nothing" If not, I wonder how difficult it would be to hook up one of the heater wires. How far away from the engine do the headers end? I can understand not wanting to cut into them.

Hrm.... Was just doing some reading on the wideband sensors. Looks like they need a special EFIE controller (not sure what it stands for) to translate a series of different currents from the O2 sensor into one, stable, readable current (the 2.35 volts for optimum, etc.) They look like they're another $70 - $150 depending. Might just stick with my narrowband for now. =P

As for grabbing one from a junkyard, a narrowband wouldn't be worth it since if they don't work, you really screw up your readings, and they're pretty cheap. I wouldn't even mess with a used bung, since you'd have to do cutting to get it. They're super cheap.

My jets should be here today so I'll keep you posted.

 

The headers are probably between 2.5 and 3 feet long if you figure in the bends.

I guess I could always use a heated on to help it get better readings.

 

It shouldn't be an issue. This is the aftermarket exhaust pipe I used. If you look to the left of the red tape on it, you should be able to see the O2 bung. It's probably a good 2 - 3 feet from the engine.

https://www.ford-trucks.com/user_gal...id=43767&.jpg=

 

Your right mine might be okay then. My son works at a place that that builds oem exhaust pipes fot the big three. He is going to try and get me a bung for my exhaust.

I posted a question on the electrical forum here and have had a pretty good repsonce. I may try and use a wide band if it's not to expensive.

 

Well, I now have a bung to try and put in my exhaust (my son found one at work). I just have to find a good O2 sensor and get the bung installed and I should be ready to try and tune the carb.

Hey AbandonedBronco, I was looking into the holley jets. The 48's and 49 jets have the same size hole in them. So you may not want to waste your time swaping between the two sizes.

As soon as I can get my O2 sensor up and going I want to check what I have with the 54's. Then I'm going to put all new gaskets in the carb and change to the 51's.

 

I actually wrote Holley with this very question. They said that even though the hole was the same size diameter, they have different flow characteristics. So even though the hole was the same size, the 49 still flowed 2% more than the 48. They said to always just go with the jet #, not diameter. Made sense.

Well, put some 49s in yesterday and took it down and had it emission tested, it passed both the idle and the high speed tests, so I'm good to go! Also tells me that 49s are probably a lot more around where I want to be as far as size goes. What's your altitude there? 51 is what they came with stock, but for sea level. Then decrease a jet size for every 1000 feet. I'm at 2500, so a 49 would seem just about right. O2 sensor seemed a lot happier with it too.

 

Jetting for elevation is the general recommendation but it was not good on my application and ended up a bit too much lean so I went back up two sizes to stock...much better. Rate of flow is what is indicated by the Holley jet numbers.

 

It shows that we are 650 feet above sea level. So I may need to go with a # 50 size jet. I'm going to try the 51's since I already have a set. What did you have to pay for the pair of jets? I've seen them for about 5 - 6 dallors on ebay. Are they any cheaper in the auto stores?

That still seems strange that if it has the same size hole it should flow the same amount of gas. There must be a small difference in them some way.

Great to hear that your truck passed emissions.