Weber tuning with Lambda sensor - Page 9 - Alfa Romeo Bulletin Board & Forums
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post #121 of 188 (permalink) Old 08-21-2015, 07:37 PM
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I plan to try moving the intake cam from 101 to 98 as suggested by Jim Steck but I am running out of things to mess with. October might be a nice time to drive up to Virginia and I have a set of V6 headers to deliver to Al.

Ed Prytherch
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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 #122 of 188 (permalink) Old 12-01-2015, 06:23 AM
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AFR with 45DCOE's

I have returned to my old RJ575/785 combination with 45DCOE152's. Here is the Zeitronix chart for a 3rd & 4th gear WOT run. The AFR is much better controlled now. The crazy stuff at the end is wen the flywheel bolts sheared.
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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 #123 of 188 (permalink) Old 06-04-2016, 02:22 PM
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tach input protection circuit for Zeitronix

RJ's Zeitronix ZT-2 was damaged at Sebring by a high voltage pulse on the tach input wire. This is easy to do if you are using CD ignition and you connect to the wrong terminal. I recently lent my ZT-2 to a couple of friends to help them tune their Webers and I built a little protection circuit to shunt high voltages to ground instead of going into the Zeitronix. I tested it on the bench and it worked fine on a car with a Pertronix pickup. It then worked fine on the car with points after the value of the resistors was increased to 20K.

Here is a module that I made for RJ. Yellow wire to ignition, green wire to Zeitronix tach input and black wire to ground. I will post the circuit if anyone is interested.
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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

Last edited by alfaparticle; 06-05-2016 at 08:41 AM.
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post #124 of 188 (permalink) Old 06-05-2016, 08:30 AM
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I have been following this thread for a few years and have been intrigued with "tuning by numbers" using a wide-band AFR meter as discussed above. I have owned my stock '65 Sprint GT for 22 years but have never been able to measure mixture strength and therefore "know" if the Webers are jetted correctly. Earlier this year, I changed the original 9.1mm cams to a 10.5mm IAP cam on the intake side and to a 10mm reground cam on the exhaust side. Richard Jemison profiled the 10mm reground cam and provided setup guidance. The new cams provided a noticeable performance improvement at the top end and the engine ran fine at the bottom but was pretty flat from 3200 to 4500 rpm. This issue was improved by changing to smaller main jets yet this change was partially a guess that happened to be in the right direction. To dial in the jetting, Ed (alfaparticle) generously offered to loan Ken Vaughn (generalwade) and me his Zeitronix ZT-2 while he completes the engine rebuild on his Spider. He also provided the above protection circuit which worked fine using a Pertronix Ignitor and a Bosch blue coil.

Below is a graph from Excel showing AFR curves collected during three wot, third gear runs with different main jet / air corrector combinations. I like the 115/170 combination the best. The dip in the AFR curve that begins around 3500 does not go below 11 (rich) and the maximum AFR around 5700 is 13.7. I was a little concerned about this number until Ed pointed out that AFRs a little above 13.5 are not likely a problem in engines with a 9:1 compression ratio.

The result is that the engine runs better than it ever has and I would not have guessed that 115 main jets would be part of an optimal jet combination. There is simply no substitute for objective data.
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post #125 of 188 (permalink) Old 06-20-2016, 05:53 PM
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Protection circuit

Here is the protection circuit diagram.
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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 #126 of 188 (permalink) Old 08-13-2016, 09:32 AM
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Great thread and great work guys!

I have installed an AFR meter in my Lancia.
Just a quick question:
going through the RPM range in neutral shows totally different AFR-readings than when Im doing WOT runs on the road. Why Is this? Does the engine produce a very different vacuum when under load?

Torstein
www.flattjern.com

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post #127 of 188 (permalink) Old 08-13-2016, 12:12 PM
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Pretty slick! I would also be concerned with the 13.7 afr @ 5700. I suppose with 9.0 compression that makes it not as much of a concern though. Have you measured at 6500? Just to be sure I'd check the plugs after a couple of WOT runs just to increase the "sleep at night" factor. Just having all this information blows my mind as to how far we've come, flat amazing!

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

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post #128 of 188 (permalink) Old 08-14-2016, 01:11 PM
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In addition to the AFR data if we had some acceleration numbers to compare it might give us an idea if the changes made actually make a difference? I'm not posting numbers to be faster than anybody, heck, I learned a long time ago there is always somebody faster than me. I'd just like to have something to compare against since I'm the only Alfa around. I did several runs in both directions and threw out the fastest and slowest and took an average. 3rd gear, 3000 to 5000 rpm with a stopwatch, a phone would also work. 5.72 seconds
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The passenger seat is 15 miles an hour faster than the drivers seat.

currently
2017 Giulia Q4
74 GTV restored daily driver
71 Berlina in 2L restored driver
the ones that got away:
1959 750 series Giulietta Spider Veloce
1962 Giulietta Spider normale
1965 Giulia Sprint normale
1972 GTV
1974 GTV
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post #129 of 188 (permalink) Old 08-14-2016, 01:46 PM
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Quote:
going through the RPM range in neutral shows totally different AFR-readings than when Im doing WOT runs on the road.
The AFR when you are revving the motor in neutral is of no consequence and has no time to stabilize if you are blipping the throttle. WOT AFR will help you select the correct main jet and air corrector. AFR when cruising at 3000 rpm will help you select the correct idle jet. The response when you stab the throttle will help you select the pump jet and bleed back orifice. This is where data logging reigns supreme.

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 #130 of 188 (permalink) Old 08-14-2016, 01:48 PM
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The AFR when you are revving the motor in neutral is of no consequence and has no time to stabilize if you are blipping the throttle. WOT AFR will help you select the correct main jet and air corrector. AFR when cruising at 3000 rpm will help you select the correct idle jet. The response when you stab the throttle will help you select the pump jet and bleed back orifice. This is where data logging reigns supreme.
Thanks Ed!

One more question: if I keep a steady RPM, lets say 4000, in neutral, why does my AFR readings differ from readings when I cruise at 4000RPM?

Torstein
www.flattjern.com
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post #131 of 188 (permalink) Old 08-14-2016, 02:37 PM
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An engine under load is using energy to move the vehicle. In "N" it's only energy expendature is turning the engine. Two different things entirely.


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post #132 of 188 (permalink) Old 08-14-2016, 04:45 PM
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Hi Mike, I was shifting at 6k and the AFR was slightly lower there than 5700, showing 13.5. About the same for a few runs to 6500. I am sure my Sprint is significantly slower than most 2L's although I don't have any acceleration data. Currently distracted by some rust repair on a Spider but plan to do some more work with the Zeitronix in the future.

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post #133 of 188 (permalink) Old 08-15-2016, 12:18 PM
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The 115/170 combination (red line) does sit nicely in the 12 to 13 AFR range. It does go a little bit lean at the very top, but not dangerously so. It's been a while since I ran a gasoline engine on a testbed, but do recall that we used to set them to about 5% CO at full load during development testing, which is about 12.5:1 AFR.

All the lines go pretty rich lower down, but 11:1 is still OK. I wonder if there is a combination of parts which keeps the AFR characteristic flatter?

Data is key. It would be interesting to see some steady state (or slow transient) speed sweeps at different throttle positions to check the air fuel ratios throughout the range.

Attached is a generic AFR table and a graph of AFR vs power/CO/HC/fuel consumption

Clearly, with carburettors, such fine control of AFR to the ideal values isn't possible.
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post #134 of 188 (permalink) Old 08-16-2016, 07:31 AM
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I have had my Weber equipped Spider (about 170 flywheel HP) on a dyno twice with multiple runs. It made best power at AFR=13.2. The owner of the dyno races Alfa's and my results were in line with his experience with other motors.

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 #135 of 188 (permalink) Old 10-25-2016, 07:26 PM
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Exclamation AFR can be misleading

AFR can be misleading if the engine is misfiring. I recently spent time getting my 45DCOE152 Webers to run properly at lower rpm. I have posted in other threads about modifications to progression holes and a burned air filter. The wideband frequently went off scale during the testing due to misfiring. When a cylinder misfires air and fuel are pumped into the exhaust. The wideband sensor is measuring oxygen content and it goes high due to the air in the exhaust and it reads high AFR even though there is unburned fuel in the mix. So if you have a misfire the AFR will always read high and you should be cautious about attributing it to a lean mixture.

I saw the same effect with my Megasquirt GTV6 motor when I had a misfire due to weak sparks.

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

Last edited by alfaparticle; 10-25-2016 at 07:29 PM.
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