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Weber selection and initial jet tuning

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If the tube is too rich ~ 3000-4000 then reducing main will lean across whole band.  Reducing air should  enrich across the whole band but less at 5000- 7000.  Just trying to figure out how to deal with your findings.

 

Lets wait to see a plot.

 

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WOW THAT LOOKS SWEET 11.5 to 13.5... RIGHT where it should be.  13.0 +/- 0.5 for most of the run then dropping to 12.5 at the high end.... WOW WOW WOW.

I am painting inside right now.  I'll try to plot tomorrow.  Hold there. it looks great!

 

Edited by 240260280

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You know this thread started Oct 2016... two years of work, down time for the head problems, so many runs and Etube changes and we finally seem to have nailed the 45DCOE on larger L engines. 

Perseverance and finally a gift to the Z folks out there! F19 eTubes are the cat's meow! 🐒😺

Cheers and a big thanks for your hard work! :beer: YIPEEE YAAAAHOOOO

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Two coats on the dining room and Janet is happy!

 

The only thing left to play with is to mess with the acceleration circuit as you see fit.

You can try to quench that common lean gasp at the start. You know the parts and what they do so I'll leave it to you now that you are a Weber Experten! 🙂

Edited by 240260280

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F19  165/175

 

Range of 1.7 points.

image.png

 

Note: this is close (but better) than the elusive June 28, 2017 plot that suddenly went too rich on subsequent runs. It was never repeated. The configuration then was (F16 165/215).... so the F19 runs leaner than the F16 and needs a smaller air corrector.

image.png

Edited by 240260280

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Very happy with the results. The F19 was a great call!  As I said before, the car pulls great!  I think the lean spike at the beginning may be due to the 35mm chokes and losing velocity.  I could try the 34's and see if that helps it, but that will hurt the top end a bit. 

 Also it has a nice lean cruise at these setting as well.  I want to try to get the car on the dyno before the snow flies here.  I'll have to call and see when I can get on their schedule.  Thanks for all the help! I want to get a few more weeks of monitoring under my belt and then I'll get the other E Tubes out to you. 

 

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More thoughts.  The rich dip at  3500rpm could be a few non-carb things:

 

1. Valve, cylinder, and cam geometry with valve opening overlap allowing unburned fuel to escape into the exhaust causing a richer a/f ratio

2.  A too short manifold with too large an opening preventing the air and fuel to mix well resulting in unburned  fuel in the chamber.

3. Non-ideal air horn length. (longer may help with air velocity and low rpm resonance to help mix the air and fuel).

 

For @Chickenman 's great flat curve, I wonder if a manifold/header bung was used as the sensor mount or if the Dyno-shop used a sensor in the tail pipe.  Some A/F transient smoothing does occur in the passage to the tail pipe.

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17 hours ago, 240260280 said:

More thoughts.  The rich dip at  3500rpm could be a few non-carb things:

 

1. Valve, cylinder, and cam geometry with valve opening overlap allowing unburned fuel to escape into the exhaust causing a richer a/f ratio

2.  A too short manifold with too large an opening preventing the air and fuel to mix well resulting in unburned  fuel in the chamber.

3. Non-ideal air horn length. (longer may help with air velocity and low rpm resonance to help mix the air and fuel).

 

For @Chickenman 's great flat curve, I wonder if a manifold/header bung was used as the sensor mount or if the Dyno-shop used a sensor in the tail pipe.  Some A/F transient smoothing does occur in the passage to the tail pipe.

It was a T/Pipe bung, as are most Dyno setups.  I don't think that was a big factor, as we also ran a test day on the same dyno with about 10 other cars. Most were EFI, and my curve was far flatter than any other cars. Some of the aftermarket EFI AFR curves  were all over the place ... 

The tunable Vacuum secondary also helped smooth things out.  The Vacuum secondary carb was really good in Autocross.  Very smooth power delivery.

I later built a double pumper with the same specs and parts. That was much more difficult to drive in Autocross, but proved to be slightly faster on Road Course and Hill climbs. In autocross you would just haze the tires if you got into the Secondaries too quick.  

Hill Climbs with weight transfer to rear tires and Road Races with higher cornering speeds, reduced the tendency to spin the tires on corner exit. So you could jump on the power quicker and harder. 

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@Chickenman Wow, you know your stuff!!!  Any thoughts on the rich dip at the start of the main that seems ubiquitous on most 45DCOE applications?  It is very difficult to address. Etube, jets, fuel level,  acceleration circuit, etc barely make a dent in it.  In the thread in the post #376 (two posts) above, the chap also tried different aux venturi and chokes with no luck.  The carbs did not seem to be able to address it. The thread digressed and was never resolved but the racers threw out timing, exhaust reversion/exhaust geometry, resonance, and cam overlap as possible causes.

Edited by 240260280

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Could be a reversion issue. Could be a lot of things. 

I recently tuned a ITB setup with MS3 and it had a huge reversion issue  ( Cam related ) at exactly 2,200 RPM. Had to lock Auto Tune out at those VE Values as it was going mental.  The pulsations in the exhaust were throwing the O2 sensor out of whack. 

Reversion affects both Intake and Exhaust sides.  One of the theories behind anti-reversion headers is to reduce Intake reversion pulses wit Independant Runner manifolds. It is also not uncommon to purposely leave a slight mis-match or step at the intake manifold side. IE: Make the Intake runner port just slightly smaller than the actual Port on the cylinder head. 

Since reversion pulses mainly travel along the outer walls of the runners, like a " Smoke Ring ", a small step at the runner circumference can reduce the strength of the pulse.  But it all varies from engine to engine. Really complicated stuff and above my Pay grade... 

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Got an appt for the dyno for this Saturday. But, right now it looks like rain, so I might have to reschedule.  Number predictions, anyone? 

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6 hours ago, 240260280 said:

These problems do not seem to exist on 40DCOE but I have not looked in such detail as this thread has done on the 45DCOE.

 I knew little about DCOE's until I followed this thread. Thanks. Now for my observation and question. Do you think the problem with the 45's is they're a bit to big for the cubic inches and that's why the 40's work better? The reason I ask is this problem seems related to the late 60's when people would install a higher cfm Holley (usually) on a small block Chevy. The results weren't good. I've always assumed the reduced performance was caused by reduced air speed through the venturis.

 

 

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It is hard to tell.  I have yet to see graphs of a/f for 40DCOE on an L28 so it may be the same case.

 

From the graph below, a 40DCOE is adequate for 2.8 litre street use (with a 33mm choke).

A 45DCOE is more suited for higher rpm racing with 36mm choke.  Blodi currently has a 35mm.

 

image.png

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2019 Wish:

 

Hi @Sean Dezart, would you be interested in taking your header to the next level?  If so, read the details below.  I think it could be thoroughly validated by @blodiafter he completes his initial dyno testing.

If all works out, you will have one of the best performing headers and we will have conquered the mid-range rich-dip. The solution is to add a simple piece in the hottest spot of each runner and transition to slightly larger pipe.

 

image.png   image.png

 

 

Improving Header Design (content from Speed Talk):

anti-reversion-jpg.57854

1. So, what does an anti-reversion valve do?
It is simply a one way resistor to delay the reversion effect and give time for the exhaust valve to close.

2. How does it work?
Since hot exhaust wants to expand, we give it the opportunity to, but only in the reverse direction.

3. Where to put it?
At the tail end of the largest pulse of exhaust, where the exhaust slows down. If your header is port matched, it is approximately 7-8 inches from the header flange. To be more accurate, you can map out the temperatures of the header pipe and there will be a temperature spike where the exhaust slows down. This spot will have the greatest affect. This spot is relative to engine displacement and not rpm. So, moving it higher or lower just makes it less effective.

 

image.png

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Hi and thanks to the introduction to this thread.

Interesting but nothing proven yet.

Also, those reversion 'valves' would fit in just where the headers' primary pipes are closest to the carbs ie a much wider diameter to interfere with the lower edge of some carb versions.

I might suppy a header for local back to back tersting but like should be compared with like - no ?

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Collecteur.jpg

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