Weber tuning with Lambda sensor - Page 7 - Alfa Romeo Bulletin Board & Forums
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post #91 of 188 (permalink) Old 12-15-2014, 05:39 PM
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Chokes down by the valve bowl, I've been tossing around the idea that using a 75 deg cut on the intake seat also functions somewhat as a choke, the charge expands as it travels through the increasing volume of the seat helping to prepare the fuel/air for ignition. It's one sop for big valves and not having a flow bench I've been trying to visualize what's going on besides just making things bigger.
I liked the Smokey story where he had two heads in a barrel of varsol during a tech inspection and pulled up the legal head and had the race head in the bottom of the barrel while France and everyone was crowded into a makeshift shed screaming at him he had to be cheating. Early 50's, crazy.

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

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71 Berlina in 2L restored driver
the ones that got away:
1959 750 series Giulietta Spider Veloce
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1965 Giulia Sprint normale
1972 GTV
1974 GTV
1974 GTV
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post #92 of 188 (permalink) Old 12-15-2014, 05:39 PM
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AFR plots from Zeitronix

I apologize for repeating some stuff that I have already posted in the "79 Spider on the dyno" thread but this is specific to the title of this thread. I did some WOT runs these past few days to tune my Webers for the modified auxiliary venturis that I got from Richard Jemison. One picture shows the raw data in the Zeitronix data logger screen. The green trace is AFR and the blue trace is rpm. This is part of today's efforts. It shows a pull from around 3000 rpm in third, a shift at about 7000 rpm then continuing to almost 7000 in 4th - about 104 mph. The part of the curve that I am using to tune the Webers is 5000 to 7000 in 4th as that is the high power band for my motor.
I exported this data from Zeitronix into a text file then imported it into Excel. I then plotted AFR vs RPM with an X-Y line plot. I did the same for 3 other sets of data from similar runs with different Weber setups. I then used the "add trend line" function to generate best fit curves with 6 order polynomials. I tried all of the possibilities and these suit my data the best. I then made the original line plots disappear and I was left with the curves that you see in the second picture.
The blue curve is the baseline with unmodified auxiliary venturis 145MJ/150AC
The orange line is with modified AV's and no changes to the jetting. You can see that it is leaner.
The grey line is with modified AV's and 150 main jets. You can see that it is significantly fatter - too fat.
The green line is with modified AV's and 150 main jets and 160 air correctors. You can clearly see the curve has shifted lean by about 0.2 AFR.

This manipulation of the data shows the main trend of the AFR and makes it easier for me to see the effects of changing jets in the Webers and figuring out what to do next.
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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 #93 of 188 (permalink) Old 12-15-2014, 05:58 PM
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Could you put a theoretical ideal curve in there to show what your shooting for. It would help me better understand what is going on. Just a thought.

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
1974 GTV
1977 Spider
1974 Spider
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post #94 of 188 (permalink) Old 12-15-2014, 08:25 PM
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Quote:
Could you put a theoretical ideal curve in there to show what your shooting for. It would help me better understand what is going on. Just a thought.
That would probably be a straight horizontal line at the ideal AFR but that is not possible with Webers. When we did the dyno tests earlier this year we got peak HP at 13.2 AFR so I am shooting to be close to that. Another consideration is that the same Weber jetting will produce a leaner mixture when the air is denser, ie colder, so being a little on the lean side in December might be OK.

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 #95 of 188 (permalink) Old 12-16-2014, 04:09 PM
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started to put my 33 venturis in, upon taking the 32 out I noticed the backside had a slope whereas the 30 I modified to a 33 the backside had no slope so back to the lathe, I measured the slope by counting turns on the tool posts and cam up with 1.5 to 10. I was able to turn a consistent slope onto the back side of each venturi so they actually look pretty good.

Before turning the backside

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
1974 GTV
1977 Spider
1974 Spider
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post #96 of 188 (permalink) Old 12-16-2014, 04:29 PM
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The fun part is modifying the actual airfoil shape with a given throat diameter until you see either a dyno or acceleration time improvement. Then make a template of that shape and replicate it with choke throat diameters altered by .5 mm. When you find a set of four that is really nice as far as power or time, try MORE shape alterations. Eventually you will discover what shape airfoil works best with given throat sizes. Note the performance changes will be VERY slight.
Like I said earlier, "WHAT FUN!!"
I don't do this anymore!
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post #97 of 188 (permalink) Old 12-16-2014, 06:33 PM
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Trying to keep the airfoil from stalling and maintain laminer flow. I doubt I can get my hands on enough 30's to try all the combinations but if I could I'd have a really big thermite gadget from all the swarf! I suspect if I was just concerned with straight line time I could put 60lbs of air in the tires and see as much or more improvement but it wouldn't be nearly as much fun

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
1974 GTV
1977 Spider
1974 Spider
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post #98 of 188 (permalink) Old 12-17-2014, 06:00 AM
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The aluminum dust does get a bit frightening. We used to mix with just a bit of Mg dust (for assed fun) steel from the lathe, and touch it off in the parking lot. It melts into concrete! Neat!
Yeu see the possibilities with ANY size choke design? Good thing Weber did not offer too many standard variations! The cast ones were not a great shape, made for easy mould release, but provide plenty of test subjects complete with air bubble holes! The cavaties left by the air bubbles seem to do no harm as does a media blasted surface due to "boundry layer" air flow over the slightly irregular surface.


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post #99 of 188 (permalink) Old 12-17-2014, 08:34 AM
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What does one do with the left over dry ice from seats and guides.... put some in a 2L soda bottle and get away! It takes about 20 minutes, it will take your hand off, humm combine with al dust and the black helos will be over the house or a drone strike.
The others had even more air holes. The 32's I took out are machined and have a different profile so I could open them up to 33 and compare to the profile I made on the cast ones. That actually would be interesting to know.

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
1974 GTV
1977 Spider
1974 Spider
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post #100 of 188 (permalink) Old 12-17-2014, 10:41 AM
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NOW you are getting into the true spirit of choke manufacture!


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post #101 of 188 (permalink) Old 12-18-2014, 03:06 PM
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With my "special sauce" 33mm venturi profiles and bumping up to 135 mains from 32 venturis and 130 main jets I went from 8.5 secs to 8.16 secs. It also and I don't say this lightly has beginning at 6300 rpm significantly more "kick" and revs to 7200 fast. I wasn't used to it hitting that so fast and shifted out of fear and surprise more than anything else.
I began with:
130 mains
F11 emulsion tubes
32 venturis
200 AC
50 f8 idle jets

Now:
135 mains
F15 emulsion tubes
33 venturis turned from cast 32's
200 AC
50 f8 idle jets
My afr's went way lean with the 33's and 130 mains so I didn't do any timed redneck dyno runs until I put the 135's in.
Now the AFR's are at WOT through the gears in the mid 12's but go to 13's at 7000. I need to get the rev limiter in the msd repaired so the 6.5k or 7k plug works. I really don't see much advantage in taking it past 7000 but if it made the difference between victory or defeat in a drag with Ed you can bet I would

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
1974 GTV
1977 Spider
1974 Spider

Last edited by gigem75; 12-18-2014 at 03:14 PM.
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post #102 of 188 (permalink) Old 12-18-2014, 03:39 PM
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Weird aint it?


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post #103 of 188 (permalink) Old 01-18-2015, 04:33 PM
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I have added some information in post #9 of http://www.alfabb.com/bb/forums/engi...ml#post6004281

It relates to the effect of jet changes on AFR at part throttle and high cruising speeds. The main jet had a large effect and the Air corrector had very little effect. Another piece in the Weber jigsaw puzzle .

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 #104 of 188 (permalink) Old 01-18-2015, 04:38 PM
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I really don't see much advantage in taking it past 7000 but if it made the difference between victory or defeat in a drag with Ed you can bet I would
It might make sense to go close to 7000 if your peak power is around 6200 as mine is. Shifting at peak power rpm will almost always result in slower acceleration because you have dropped too far out of the power band in the next gear. You want to maximize the combined area under the power curves. Based upon my dyno curves my optimum shift point from 4th to 5th is 6800 rpm. It is higher in the lower gears that are wider spaced. As my tach over-reads by 10% I have marked it with a red line at 7500. It impresses folks who see it and don't know the whole story.

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; 01-18-2015 at 04:42 PM.
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post #105 of 188 (permalink) Old 01-20-2015, 09:28 AM
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I reported in the EGT thread that the Weber settings that I thought were ideal for torque and power from my motor produced very high exhaust gas temperatures when running at a steady 5200 rpm in 4th gear - 80 mph. They were more reasonable in 5th. Installing bigger main jets,150 to 155, dropped the EGT at 5200 by 100 degrees but it made the AFR too fat in the high power zone so today I ran with 200 air correctors instead of 170's. It did the trick. The EGT's were pretty much the same as with 170 AC's and the AFR's in the high speed/part throttle were also about the same but the AFR in the high power zone was returned to where it needs to be.
So the message is that air correctors affect the whole of the WOT range but have little effect at part throttle, even at high rpm. Main jets influence part throttle even when the throttle plates are barely open if the rpm's are high.

And now to brag about the car. I did a rolling start 7 to 100 mph pull in 21.5 seconds up a gradient of about 2%. That was with 3 gear shifts. I think that says almost as much about RJ's gearbox/clutch/flywheel as it does about his influence on the motor.

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; 01-20-2015 at 09:30 AM.
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