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Old 12-24-2009, 10:27 AM   #11 (permalink)
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Old 12-24-2009, 11:59 AM   #12 (permalink)
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Originally Posted by tasdrouille View Post

How do you tune individual cylinders? How do you get your feedback for individual cylinders? I guess you do this on your del sol.

On TDI engines, each power stroke is sensed by the crank sensor and fuel trims for individual injectors are adjusted to compensate for variations between cylinders and injector bodies and make the engine run smoother.

On a gas engine with perfectly matched injectors and cylinders I can see how you could compute individual cylinders AF ratio from the power they generate given an equal quantity of fuel injected in each cylinder. But as soon as there are mechanical variations between cylinders, say uneven compression for example, or something that throws an injector's flow off, that all goes out the window.

I think it would be easiest for manufacturers to ensure their intake manifolds evenly distribute air between cylinders, or just go with an o2 sensor per cylinder.
Yes I'm running it through my engine management. What I found is when it goes into lean burn mode the cylinders change a lot between each other.
I'm still not to sure why but I have some theory's. So what I do is run the car on a chassis dyno and run four individual W/B O2 sensors.
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Old 12-24-2009, 01:55 PM   #13 (permalink)
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The SAE (society of automotive engineers) already answered alot of these questions it seems, I checked that paper out at my libarey a few years back, so not all the info is fresh in my mind, but from what I remember serfice gap plugs like Botsh +2 and +4 platum plugs have a cooler spark due to the spark travling accrose the ceramic insulater, they also worked better with some styles of engine combustion chamber over other styles, I think larger might have been better, it sticks in my minds that big amarican V8's worked best with this style of plug, I could be wrong on this however.
With standard style of spark plugs that most people are used to the smaller the gap the hotter the spark, the draw back to this smaller gap was that less fuel/air was in the gap so the flame spred was slightly slower if the gap was to small, with to large of a gap the spark was cooler and did not ignite the fuel/air as well, higher voltage helps to a point but to high and it caused other problems in other parts of the igition system.
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Old 12-25-2009, 12:24 AM   #14 (permalink)
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A larger gap should help with FE as you should get a better burn. The problem with large gaps is it takes more voltage to fire the plug. This starts to become more of a problem as rpm and load increase. Also as a plug gets dirty, its easier for the path to find a short to ground as the larger gap must be overcome.
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Old 12-28-2009, 07:40 AM   #15 (permalink)
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The energy for the spark is stored in the ignition coil.

As I understand it, the spark lasts longer if the gap is smaller. And if the gap is enlarged the voltage between the gap gets higher before the spark jumps and the spark duration is shorter.
I think the spark energy is the same in both cases.

Once I verified this with a scopemeter. I had different gaps in different cylinders and I could see that the gap affected to spark burn time.

I'd also like to know what affect it has to FE
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Old 01-04-2010, 04:43 PM   #16 (permalink)
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So, I tried it out, and it seems like I gained 2 or 3 miles per gallon on the highway in my Accord. I haven't A-B-A tested it yet, but running at between 65 and 68 MPH on the highway left me with 33 MPG (I-95 from Georgia to Maryland). No other mods except an upper grill block and Scangauge. Generally, I make the drive with rear wheel skirts and a lower grill block and get 34 MPG (driving at 60-63 MPH). Acceleration also seems smoother, but I want to pull the plugs and do some kind of official testing first.
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Old 01-04-2010, 06:09 PM   #17 (permalink)
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A couple of years ago, my SE-R's mileage started going down on long Summer highway trips. Mileage dropped from 38 mpg to 36, same drive, same Summer. Since I hadn't changed anything else, I replaced the plugs. Their gaps were all in the .055 range. After I got the new plugs in, my mileage went back up to 38 mpg on long highway drives.

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Old 01-04-2010, 09:48 PM   #18 (permalink)
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...look up SAE paper #700081:

Spark Plug Design Factors and Their Effect on Engine Performance,
by: Robert J. Craver, Richard S. Podiak and Reginald D. Miller,
of: Champion Spark Plug Co.
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Old 06-03-2010, 03:01 PM   #19 (permalink)
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I was wondering if anyone had done tests on this, then decided to do my own. I have a 4 banger, so changing gaps across the board is not time intensive at all.

I changed the gaps, and then checked the vacuum. Then I changed the gaps, and checked the vacuum again. Here's the data:

          Gap (inches)       Vacuum reading (In. Hg)
Test 1:    .025                       16
Test 2:    .040                       16.5
Test 3:    .045                       16.7
Test 4:    .050                       16.7
Test 5:    .060                       16.9
Test 6:    .080                       16.7
No, my gauge doesn't have decimals, but the needle moved so little between tests that I figured I should use decimals.

My question is how this relates to FE. Does higher vacuum mean higher efficiency?
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Old 06-03-2010, 03:07 PM   #20 (permalink)
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holy smokes, 0.060! What ignition coil are you using? I've never went further than 0.040. Currently on 0.028 (spec). I've got a msd blaster2. Maybe I'll try 0.060 next time.


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