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if i put a y pipe or a collector on my hedman headers, wont that be right in the sweet spot?
My primitive understanding is that you want the O2 sensor hot, but not TOO HOT. Thus the distance for the sensor from the port. I do not think it is a problem to mount it in the exact spot ford put them in the first place.
Most of the widebands are placed into very fast running engines 8-9k rpm redline. The inline 6 is redline maybe 4k rpm, even if you went above 4k rpm you would only lose power and torque.
I say put it there, the worst that happens is it burns out a few months earlier, I say it lasts longer because the one thing the O2 sensors hate is being cold and having big temperature shocks.
According to Matt at AEM, the problem isn't with the tip of the sensor getting too hot, but the outer part where the wires attach. And that usually happens in new vehicles with one or two turbos and extreme heat in the engine compartment, so people fashion shields that protect the sensor from the radiated heat. But, that typically isn't a problem in our trucks with the huge engine compartments, no turbo, etc.
HOWEVER, the distance from the exhaust port does make a difference in the reading the sensor gives. Too close and it will read slightly rich and too far and it'll read slightly lean. But, slightly rich/lean, and probably not a problem in a carb'd vehicle as the AFR isn't controlled that closely.
Patrick - Little enough to be of no consequence in carb work if the distances are kept reasonable.
All - Here's today's installment. I used Edelbrock's excellent manual on the Performer series carbs, which tells you how the carbs work as well as how to tune them. Since my carb is a 1406 I turned to Page 22 where the chart is for that carb. Here it is and here's what I've circled:
The red circle shows the stock jetting that I tested yesterday.
The yellow circle shows going 1 notch lean on the power (power goes horizontally and cruise goes vertically)
Green shows 1 notch lean on both power and cruise, which is what I wanted.
Now, what jetting do we need? Here's the next page, and I've circled the stock jetting in red, the 1-notch lean power in yellow, and the 1-notch lean in both power and cruise in green. And that means I took out the .098" primary jets and replaced them with .095's. Then I replaced the stock metering rods that have a .075" cruise diameter and a .047" power diameter with the .073" x .047" rods recommended.
So, how did it work? Here's the results:
It cruises in the mid-14's AFR and the WOT runs from 11.0ish to 11.8ish in first, but stayed around 11.8 for most of 2nd & 3rd gears. I'm thinking it is time to change the secondary jets to lean WOT up a bit. But, what do you think?
I can't really see on my phone, but its an obvoius improvement.
If you're in the 11s you can go leaner without danger.
Just remember things will lean out come winter and colder, denser, drier air.
These need to be corrected to the temp of your air cleaner.
Yep, it is better. But I'd like to get into the high 11's in first and low 12's for 2nd and 3rd. That way there is still enough room for things to be good in the winter, as you pointed out, Jim. So, I'll check to see if I have the right jets for leaning the secondaries out. That would be a .092".
I need to talk to Bill about jets and rods. I have 3 kits and still don't have a good selection.
Yep, it is better. But I'd like to get into the high 11's in first and low 12's for 2nd and 3rd. That way there is still enough room for things to be good in the winter, as you pointed out, Jim. So, I'll check to see if I have the right jets for leaning the secondaries out. That would be a .092".
I need to talk to Bill about jets and rods. I have 3 kits and still don't have a good selection.
I dont like being at AFR 13 in the summer while crusing down the highway , way way too lean for summer. I would prefer 12 or so going that fast..
The WOT can get slightly leaner though. 11 is a bit rich on the fuel and isn't as powerful compared to like 12.5 or so. Then again, better to be a bit rich than have to buy a new engine with overlean condition, especially at WOT.
Patrick - You have different goals and deeper pockets than I do. My goal for cruising, which is supported by many books and lots of experienced folks on here, is to cruise at 14.7 or maybe closer to 15.0. That provides much better economy and still isn't lean enough to burn pistons if only seen during cruise. In fact, if I remember correctly Bill said he used to see ratios as lean as 16 when he ran the carb and ignition shop - which he did for several decades, by the way.
As for WOT, hopefully I can lean that a bit more via the secondary jets. I would like to see that into the 12's consistently. But, as Jim pointed out, that can be problematic in the winter since cold air leans the mix. So I will be running a temp-controlled air cleaner on Dad's for sure, and hopefully on Rusty. That way the inlet air temp won't change all that much from summer to winter and the AFR will remain stable. And that's necessary for both WOT as well as cruise.
Good point on the air temp affecting the AFR. This is the reason behind the tube coming up from the exhaust manifold to the snout of the air cleaner. Doing this allowed the factory to lean the carb a bit more, in the name of emmissions, but had a side effect of slightly better MPG. Emissions are far more important to the manufacturer than MPG, so it's rare to see something that lowers emissions and improves MPG, at the same time.
Side note about intake air temp. I can't help but laugh when I see guys claiming to have a "cold air intake" on a tuner car, and see the air filter sitting behind the radiator........... The factory setup is usually an actual cold air intake, since EFI vehicles tend to have a heated throttle body. On a carbed engine, there is usually some sort of heat riser passage in the intake, though many non-OEM intake manifolds do away with that runner.
Those last couple of posts beg the question: how does high temps affect AFR? I'm talking 110-120. Those are the summer temps I see. Winter temps range from about 30-60 where I prefer to live. I know up in OK you're seeing lower average temps. I've always been told cold air is better. Denser charge, so more oxygen to burn. That leads me to believe there is also an ideal temp range for gasoline engines.
Yes, I get a good laugh when I see folks with a carb and an open air cleaner under the hood. Talk about lack of understanding! That gives the worst of all worlds - HOT air from behind the radiator and off the engine in the summer, and very cold air in the winter. And since a carb can't tell +200 from -20 it can't adjust for the change in air density so the AFR varies widely. At least an EFI system measures inlet air temp and adjusts for it. So, I am constantly amazed at the folks who ditch the temp-controlled air cleaners that came on every one of these trucks for an open one. Perhaps the open cleaners look "cooler", but they sure aren't functional.
On a side note, I just had a realization that when we get David's (1986F150six) truck here for the GTG we can record the AFR but without additional YFA jets and rods we can't make any changes. So, if anyone has one of those carbs laying around perhaps we could consider them as donors for rods and jets? I don't know if there was much variation on those items, but suspect there was some and that might give us some options.
Gary, most of the time when I see an open air cleaner it's strictly for looks. Most of the cars equipped with them see limited driving. They are popular on race set ups and show vehicles. I am constrained by budget and trying to find one that works. Mine is shot internally. And the ducting sucks. Maybe I could build a new one.
