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A discussion on tuning Webers with wideband AFR started in this thread http://www.alfabb.com/bb/forums/carburetors-fuel-injection-air-intake/207008-wideband-o2-sensor-kit-recommendations-2.html
but we think that it is more appropriate to continue it here.
I posted this data that I got using a Zeitronix ZT-2 on my 2L Spider when I did WOT runs in 3rd and 4th gear on an uphill stretch of road.
This agreed well with the data from my dyno runs.
I then attempted to lean out the mixture below 4000 rpm by swapping the 55F21 idle jets for 50F21's. It had NO effect. My conclusion is that this confirms my idea that with emissions Webers the idle jet has no effect upon WOT operation.

So I have given up on the AFR in that range and I will next have a go at leaning the top end above 6400 rpm where the drop in AFR seems to coincide with the roll off of the power curve. The first step will be to repeat the WOT runs of a few days ago but going to 7000 rpm. Then I plan to switch the AC's from 210 to 230 and see if it makes a noticeable difference.
 

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You may not have run the 8's long enough since with NGK the higher numbers are "colder"
From another site.....
NGK:

NGK indicates the heat range in the middle of the plug number. For example, BCPR6ES-11 has a heat range of 6. (The number after the “-“ is the Gap.) NGK plugs are colder the higher the number, hotter the lower the number.

Starting with part # BKR6E-11 (Heat Range 6), a colder plug would # BKR7E-11 (Heat Range 7), a hotter plug would be # BKR5E-11 (Heat Range 5).



EXCEPTION: NGK Racing Plugs: (Any NGK plug that begins with the letter “R”)

For NGK Racing Plugs, the Heat Range is located AFTER the hyphen.

Example: R5671A-10 has a Heat Range of 10. A colder plug would be # R5671A-11 (Heat Range 11), a hotter plug would be # R5671A-9 (Heat Range 9).

Some NGK Racing Plugs are also available in half heat ranges. These are displayed as a 2 or 3 digit number after the hyphen. For example, R6120-85 has a 8.5 Heat Range and R6120-105 has a 10.5 Heat Range.
 

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Air corrector jets

I did 4 more runs today, first 2 with 210AC's (the ones that were in when we dyno'd it) and then 2 with 230's I did the runs in 3rd gear and took it a little over 7000 rpm each time. The data on run 1 was close to run2 and run3 was close to run 4 so I just plotted one of each. It is clear that the bigger AC's leaned out the AFR everywhere when I was at WOT. AC's are supposed to affect the top of the range more than the middle but I don't see that. Any comments?
 

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I think your AC's are too large or you could go up in main size. Typically when tuning a Weber carb the AC's and main jets should follow a 50 point spread. i.e. using 150 main jets then you should be using 200 AC's.

It also looks like the graph start at 3500 RPM. If this is true than the mixture has not been effected across the entire range. 3500-4000 RPM is typically the transition from idle to high circuits.

I would be curious too see what happens if you went up to a 180 main jet with the 230 AC. If you start losing power on the top end you know you have went too far.
 

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We arrived at 150 main, 210 AC on the dyno. I did not have anything bigger than 210 and this combination made the best power - 169 hp at the flywheel. My torque/AFR curves show that power falls off when the AFR goes below 12. Bigger main jets with 210 AC made less total power - area under the curve.

My experiments with idle jets showed that transition is below 3000 rpm at WOT on this motor and with these Webers. I posted that data somewhere. I started those runs at 3000 but stopped at 6500 as I was focusing on the 3000 - 4000 where I lose torque due to the mixture being too rich. Today I was focused on the high end so I started the runs at higher rpm.


I would be curious too see what happens if you went up to a 180 main jet with the 230 AC. If you start losing power on the top end you know you have went too far.
That may be something to try when I next have it on the dyno.
 

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I've been intrigued and would like to log some data for accuracy. I have the Innovate gauge and Bosch lambda sensor but the data logging doesn't get great reviews.
In researching I found this...."In general, however, optimum horsepower is achieved between 0.85 and 0.90 lambda (12.45 AFR to 13.2 AFR using regular gasoline)." I doubt any of us are running regular gas and I'm wondering what if any differences 89 or 93 would make.
 

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I doubt that octane number has any effect. There may be differences between oxygenated and oxygen free fuels. Ours with 10% ethanol has some oxygen. I think that racing gas has no oxygen. I ran racing motorcycles on 100% methanol in my youth and the AFR for them is very low as the methanol supplies much of the oxygen that it needs to burn.
 

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"In general, however, optimum horsepower is achieved between 0.85 and 0.90 lambda (12.45 AFR to 13.2 AFR using regular gasoline)." I doubt any of us are running regular gas and I'm wondering what if any differences 89 or 93 would make.
Octane will have no effect. Octane is simply a rating of a fuels ability to resist pre-ignition; nothing more.
 

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I agree. Why mention it at all? It could have something to do with temperature? I'm not a chemist but methanol is just an alcohol and behaves like any normal fuel with CO and water being the remnants. Race gas, ie nitro methane is a blend of methanol and nitro, oxygen and nitrogen, which is what supplies the oxygen. I did a cruise run this morning and was seeing a steady 13.2 @ 4, 000 in 5th, 83 mph which was about 5/8ths throttle as best I could tell.
EDIT! I spoke a little to soon, ehanol does add Oxygen to boost combustion. Nitromethane is the extreme example.
 

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To return to the main subject: I decided that my main jets and air corrector jets were all too big. So today I did a run with 140 main and 160 air and then one with 145 main and 160 air. The 140/160 is still a bit rich at the top but I can see that I have leaned the low/middle range relative to the top - exactly as the text books say. I think a 140/170 will be a good combination based on the changes that I have observed when I swapped air correctors with the 150 main jets. I will post the plots when I think that I have nailed it.
It occurs to me that 135 main/160 AC might be even better but I am hesitant to use a relatively small main jet with these cams and 34mm venturis.
 

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Race gas, ie nitro methane is a blend of methanol and nitro, oxygen and nitrogen,
When I wrote race gas I was referring to the gas that they sell at race tracks - 100 or 110 octane. It is pure hydrocarbons. You are referring to the blend that is used in fuel dragsters. I had a little experience with that too, a long time ago. You never forget the smell of burning nitro.
 

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It occurs to me that 135 main/160 AC might be even better but I am hesitant to use a relatively small main jet with these cams and 34mm venturis.
Do you have access to an exhaust gas temperature (EGT) sensor? Monitoring the EGT would tell you if you are approaching an unsafe lean condition.
 

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Do you have access to an exhaust gas temperature (EGT) sensor? Monitoring the EGT would tell you if you are approaching an unsafe lean condition.
Al Mitchell made the same point in a private communication this morning. I do not have an EGT (yet). He shoots for a max of 1300 degrees.
 

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The innovate line has inputs for egt and cyl head temp using k type thermo couples. As well as inertia and timing for 0-60 etc, basically a rolling dyno. I can't speak to the accuracy but it sounds good in theory. Surely they aren't the only ones.
 

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Mike,
pm me your email address if you want an excel spreadsheet with these AFR plots. They show the different results of swapping main jets and air correctors.

My Zeitronix has an input for a type K thermocouple EGT sensor. It will log and display the numbers. It looks like I can but one for about $50.
 

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Summary of data runs

This data may be helpful to those of you who are tuning Webers, with or without a wideband AFR. it was collected from a series of full bore (WOT) runs in my 79 Spider. Most of the runs were in 3rd gear but a couple, identifed by 6500 rpm limit were in 4th gear. A complete description of the motor and its dyno curves are at http://www.alfabb.com/bb/forums/spider-1966-up/304825-79-spider-dyno.html.

We jetted the Webers for maximum power and torque during dyno testing and we ended up with 150 main jets and 210 air correctors. For any motor with webers there will be a number of combinations of main jet and air corrector that will produce the same maximum power. The best combination will usually be the one that gives the broadest power and torque bands. It is clear from my dyno sheet that my torque dropped off at lower rpm as the AFR went low so my objective was to investigate other jet combinations that produced the same AFR at maximum power rpm but gave a higher AFR below 5000 rpm. During this testing I learned, or was reminded of three things:
1 - idle jets have no effect on the power curve with emissions Webers
2 - Changing the air correctors will lift or lower the complete curve with less effect at lower rpm.
3 - Changing the main jets will raise or lower the low and mid range and have little effect at high rpm unless the jet is too small for the motor. In other words if it has fallen outside of the range of allowable combinations. When that happens the whole curve goes lean in a big way.
I have posted a couple of screen shots of data plots in Excel.
The first shot shows the effect of 145, 140 and 135 main jets with 160 air correctors. You can see that the upper range is about the same with 140 and 145 and that 140's give higher AFR's in the lower range. You can also see the effect of a main jet that is too small.
the second shows the the effect of changing from 210 to 230 air correctors with 150 main jets.
So for my motor 140 main jet with 160 air corrector gives a similar AFR at peak power to the 150 main jet/210 air corrector that we arrived at on the dyno. The 140/160 is preferable because while staying in the safe, sub 13.5 range at all times, it is within the optimum power AFR of 12.5 to 13 for a broader rev range and it lifts the AFR in the low range where it is clearly too rich. This is shown on screen shot #3.
I tried to attach the Excel file with all the raw data and graphs but it is too big. Pm me with your email address if you want a copy.

My next step will be to try some richer idle jets to try to eliminate a little hesitation from closed throttle. Then some exhaust work is planned.
 

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But Mad North-Northwest
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Reading this thread I'm torn between wanting a wideband AFR kit and worrying that if I had one I'd drive myself nuts with it.
 

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I drove myself fast with it!
 

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I fooled with this method for a while, and sold same just in time to save what's left of my sanity.
I like chassis dynos because every reading is different and just before you run out of money you find a compromise.
Engine dynos are most fun because at a specific moment in time you can achieve a hp / power curve that is really wonderful. Stop there because from then on you will never see the same one again.
Finally, always remember that with Webers, maximum power is always found just at the point where the engine goes too lean and suffers expensive damage. From the above, in racing, you can develop a state of tune that may NOT yield most power, but WILL allow you to finish the race, almost every time.
From my experience.
 

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Gordon,
Did you see rpm/AFR curves that were the same general shape as mine? Did you have an AFR hooked up while you were doing the dyno pulls?
 
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