Weber tuning with Lambda sensor - Page 3 - Alfa Romeo Bulletin Board & Forums
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post #31 of 188 (permalink) Old 08-13-2014, 09:51 AM
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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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76 Suzuki GT500
2011 Jaguar XKR

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post #32 of 188 (permalink) Old 08-13-2014, 10:08 AM
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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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post #33 of 188 (permalink) Old 08-13-2014, 10:15 AM
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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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post #34 of 188 (permalink) Old 08-13-2014, 01:35 PM
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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.

The passenger seat is 15 miles an hour faster than the drivers seat.

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post #35 of 188 (permalink) Old 08-13-2014, 02:08 PM
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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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76 Suzuki GT500
2011 Jaguar XKR

A little government and a little luck are necessary in life, but only a fool trusts either of them. - P.J. O'Rourke
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post #36 of 188 (permalink) Old 08-15-2014, 11:52 AM
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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/spid...ider-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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Ed Prytherch
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76 Suzuki GT500
2011 Jaguar XKR

A little government and a little luck are necessary in life, but only a fool trusts either of them. - P.J. O'Rourke
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post #37 of 188 (permalink) Old 08-15-2014, 04:34 PM
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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.

Tom

1963 Giulia Spider (1750 engine)
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post #38 of 188 (permalink) Old 08-15-2014, 04:38 PM
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I drove myself fast with it!

Ed Prytherch
79 Spider
76 Suzuki GT500
2011 Jaguar XKR

A little government and a little luck are necessary in life, but only a fool trusts either of them. - P.J. O'Rourke
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post #39 of 188 (permalink) Old 08-15-2014, 05:16 PM
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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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post #40 of 188 (permalink) Old 08-15-2014, 05:44 PM
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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?

Ed Prytherch
79 Spider
76 Suzuki GT500
2011 Jaguar XKR

A little government and a little luck are necessary in life, but only a fool trusts either of them. - P.J. O'Rourke
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post #41 of 188 (permalink) Old 08-15-2014, 06:18 PM
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Yes Ed. That was helpful, but I kept wondering why I was playing on various dynos whe I could have been either driving or racing? Those same pulls work on the track (or street) just as well. Years ago Ron Neal at Prototype Engineering, spent quite a bit of dyno time with a GTA engine I built with 80 mm 2 ring GTA forged pistons and 12:1 compression. We were sorting through the "best" cams and after hours of running noted a slight drop in high rpm oil pressure. We shimmed the relief valve spring (bad practice, I've since learned) and I went racing. It was quite an engine, but at my first bearing check, I found the rod journals on the GTA nitrate hardened crank were begining to hourglass. It took a few years before the mains followed, but the long and short was I needed a new GTA crank. I still have the engine, and now with a 79 mm bore and 10.7 compression with three ring pistons, use it on the street. GTA crank #2 has now been replaced by #3 built by Marine Crankshaft through John Norman.
I've learned over the years to spend much less time in diagnostic tuning, and more time driving as I get older. Most professional dyno shops don't really like to wear out vintage engines in testing, preferring to get close and a tad rich, and let the driver wear out the engine. Seems a reasonable plan using Webers. With FI (tuneable) I revise the above as once set, the electrons make adjustments impossible with my favorite Webers!


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Last edited by Gordon Raymond; 08-15-2014 at 06:22 PM. Reason: I edited this. Didn't like my word useage,
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post #42 of 188 (permalink) Old 08-15-2014, 08:28 PM
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My AFR cost about the same as a couple of hours on a dyno and I get the thrill of going fast on bumpy country lanes while I collect data. As I keep on saying to friends, it beats working for a living.

Ed Prytherch
79 Spider
76 Suzuki GT500
2011 Jaguar XKR

A little government and a little luck are necessary in life, but only a fool trusts either of them. - P.J. O'Rourke
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post #43 of 188 (permalink) Old 08-18-2014, 10:36 AM
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Idle jets

The Zeitronix has helped me now with idle jets. I was running 55F17 when I took the car to the dyno. I swapped in leaner 55F21 to try to lean out the low end. I then bought some size 50 idle jets - 50F17, 50F21 and 50F18. I then learned that they have no effect on the AFR in the power band so I went back to 55F17 - the fattest of the collection. It was clear from the AFR that the engine was not picking up as well as it could in the progression range due to lean mixtures. It was around 15 when cruising at around 4000 rpm. So I converted the 50F17's to 60F17 by drilling out the fuel orifice with a 0.60 mm drill. It was so small that I had to work under a magnifier.

It worked. My AFR is now around 13 at 80 mph in 5th and the pickup is much better. I have a small hesitation when I feather the gas pedal and the AFR is 17 or so on the over run but it picks up cleanly if I floor it. I have increased the idle speed a little from about 600 to 800 rpm and maybe that will help.

Ed Prytherch
79 Spider
76 Suzuki GT500
2011 Jaguar XKR

A little government and a little luck are necessary in life, but only a fool trusts either of them. - P.J. O'Rourke
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post #44 of 188 (permalink) Old 08-18-2014, 10:46 AM
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Yeah, 600 is way low. I was always told with Webers to set the idle at 900-1000 and that's been working well for me.

Tom

1963 Giulia Spider (1750 engine)
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Former: 1987 Milano Gold
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post #45 of 188 (permalink) Old 08-18-2014, 02:18 PM
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It will idle at 500 - pretty impressive for a motor with racing cams.

Ed Prytherch
79 Spider
76 Suzuki GT500
2011 Jaguar XKR

A little government and a little luck are necessary in life, but only a fool trusts either of them. - P.J. O'Rourke
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