Weber selection and initial jet tuning

[240260280]

I did some checks and one Weber book has this:

 

The 42DCOE Throat is "over-carbed" so a 3.5 is used.  They also use the 3.5 on a 3 X45DCOE on a 3.8litre Jag so they go smaller Aux with larger Carb.

 

But Passini states:

" A small-bore nozzle is, on the whole, better from the economy aspect and, unless the pulse energy transmitted to the well at high revs is so weak as to demand a very rich setting that can spoil the lower range, it is better to try a small one first. Engines with fairly large cylinders and siamesed inlet ports normally prefer larger auxiliary venturis."

 

His comments about being lean at high end and rich at the low end with smaller Aux Venturis seems to be the problem with the 45DCOE's and 4.5Aux.

 

@Chickenman What are your thoughts on how to flatten the strange WOT A/F shape of 45DCOE's on Z's?  Is the Aux Venturi a significant player?
 

 

Edited June 6, 2018 by 240260280

[240260280]

What we learned:

1. It was hoped the rich dip at the start of the Main Circuit was due to the Accelerator Circuit's squirt but you proved it to be not the case:

 

2.  Etubes were tried  but the rich dip at the start of the Main Circuit remained:

 

3. Other Datsun engines of different sizes with 45DCOE's experienced the same rich dip at the start of the run

 

 

 

Maybe enlarging  holes near the mid-to-top of an Etube is needed to lean the start greatly?

 

The F11 tubes look like an easy candidate for drilling.  They have 4 0.1mm holes that are horizontal.

 

 

It looks like you can drill straight through the body to enlarge two of these 4 holes at a time.

If  you are keen, you can consider the following:

1. Put F11 in and appropriate main and air to get a few baseline runs.

2. Cross drill on one axis to enlarge two of the 4X100 holes

3. Conduct a few measurement runs.

4. Analyze results.

5. Drill out more or solder as needed.

 

 

 

 

 

 

 

 

 

 

 

[Chickenman]

Quote

@Chickenman What are your thoughts on how to flatten the strange WOT A/F shape of 45DCOE's on Z's?  Is the Aux Venturi a significant player?

 It can be.  But the easiest way is this: https://www.youtube.com/watch?v=aj-Z33MO2Gk

Maintaining a decent booster signal while not restricting flow is a major problem of a constant venturi carb. You can make really, really good carbs.   Buy it costs $$$$ and  lots of R&D time. Look at Nascar and Pro Stock NHRA. Warren Johnston was quoted as keeping over $150,000 worth of carbs in his hauler back in 2000. Each one setup up for varying conditions. Density, ambient temp, grains of air, track condition  etc. They have no time between rounds to mess around with changing jetting , Emulsion tubes and air bleeds.  Once they got a baseline with the new EFI, they could load a new  tune in seconds. And it was much more consistent. 

Nascar found the same thing. No overall increase in HP ... but off corner driveability and fuel mileage greatly increased. The really big deal was Fuel mileage under yellow flag conditions. And Nascar doesn't even utilize the full potential of the McLaren system.  ( No driver adjustable Maps like Indy Car, F1 and WEC ) 

 

Edited June 7, 2018 by Chickenman

[Chickenman]

Here is a scan of the AFR curve I made back in 2003. 355 cii SBC, mild camshaft. Made 346 RWHP nad 368 RW Torque. Figures later went up a lot higher with a bigger cam and different Intake Manifold. Car passed Air care and got 23 MPG on Hwy. Daily driver . Autocross, Hillclimb and Track Day car. 

Carb was very trick. Built it myself. Started with a Holley 3310-1 vacuum secondary. Added Holley HP Main body, Annular Boosters, Quick change Vac secondaries. Biggest change was Weber Power plates replacing Holley fuel blocks. This changed carbs from 2 circuit to 3 circuit using DCOE and IDA components. Emulsion Tubes, main Jets , Air bleeds etc.

Dyno operator could not believe how flat and accurate the Fuel curve was. we had about a dozen cars at this Test Day. Mine was the only Carbureted car. All the rest were Tunbo Honda's Turbo BMW's and a couple of Corvettes thrown in. Most were stand alone EFI systems.  EFI Tunes were all over the place ... just bad Tuners. 

 

 

 

 

 

Edited June 7, 2018 by Chickenman
Not all of scan showing

[Chickenman]

Blip at 11.5 seconds was just interference. Black vertical pen marks are beginning and end of Dyno Pull. 

Edited June 7, 2018 by Chickenman

[blodi]

^Thats impressive chickenman! 

I got a response from Leon on hybridz:

 

“Hi Ryan, the problem lies in the emulsion tube. I did what I could with that setup, I believe the air jets were down to 110 on that graph in an effort to try to limit the amount of airflow through the e-tube which is part of the issue. I'm now running Keith Franck's VF tubes but haven't been back to the dyno. It should cure the fat dip that Weber tubes tend to produce. I used Keith's old jetting on my last Z and AFR was flat all the way across the powerband. I plan to dyno again "soon"...”

 

Debating my next step. What fuel level should I be targeting? 27mm? 

New manifold gasket arrived today but it was bent in shipping. ☹️ The wait continues.....

[240260280]

I don't think fuel level or stock ETubes will make a difference as F2, F9, F16 were all tried and no big change in the dip.It is always there.  Likewise Leon runs 25mm fuel depth and you run ~29mm and the dip is there.  The only parameters not changed yet are the Aux Venturi and eTube modifications.

[240260280]

Try drilling out the F11's and give it a go. Your fuel ~ 29mm should be ok.

Edited June 8, 2018 by 240260280

[240260280]

On 6/7/2018 at 2:48 AM, Chickenman said:

 It can be.  But the easiest way is this: https://www.youtube.com/watch?v=aj-Z33MO2Gk

I am analyzing their data now.

 

It is interesting the first run with just the Webers and stock distributor have the same wonky A/F Run that seems to be on nearly all 45DCOE's on L engines....with the big dip at start and a wide range (from 11 to 14 A/F in this case)

 

 

 

Below: No big change at all to the A/F or power (surprised that no low-end gain) with the 45DCOE plus the highly customized electronic ignition system.

 

 

Below: The final results are interesting comparing the EFI to Webers on the same graph. A/F below 115km/h  (where DCOE has a big rich dip) seem to make little difference in power between carb and EFI w timing.

In comparing the power to A/F, it seems that by smoothing the higher RPM A/F  be between 12.5 and 13.0 made the biggest improvement in power.

 

Edited June 11, 2018 by 240260280

[240260280]

Attached below is a pdf of all the tests conducted to date. They are plotted with the  12.5 to 13A/F sweet spot of  the dyno tests,

Plots #4, #11, and #14 are good fits to the A/F curve of the EFI system in the dyno video.

 

#  4 35mm F16 155/170  50% in sweet spot 50% rich by 0.5 point max

#11 35mm F16 155/225  65% in sweet spot 35%lean by 0.5 point max

#14 35mm F16 160/230  35% in sweet spot 30% lean by 0.5 point  max & 21% rich by 0.5 point

 

#4

 

#11

 

#14

 

 

FYI: F2 tube had tightest and smoothest shape but it was very rich. Further exploration with 140 to 145main and 180ish air corrector may be worth testing.

#16 35mm F2 160/230 

 

 

 

blodi af Summary.pdf

Edited June 11, 2018 by 240260280

[blodi]

Great data analyzing!  Still waiting for the replacement manifold gasket...everything is apart right now. I got your message as well..sorry, it was a busy weekend. 

I will get it all back together and do 29mm fuel level again....F2 140/180 or so...I have to see what I have for air jets, I forgot. 

What accel/exhaust jets should I use? 

[240260280]

Great. No need to rush.  I think the work is providing a lot of new and interesting observations that will help all.

I think your fuel is close enough to 29mm to be fine for now. After seeing the shape of Leon's A/F is similar to yours (and I am pretty sure he runs 25mm),  fuel level does not seem to affect WOT run shape significantly.... but I bet he has a very rich cruise ? .

Also from your work it seems the accel circuit does not seem to affect the WOT run shape significantly so you can keep whatever you have in there for now.  It may become more prevalent if the man jet goes smaller. The only recommendation I can give is never to use the 00 exhaust as it will burn too much fuel every time you press the accelerator pedal.

You may wish to apply copper anti-seize to both sides of your manifold gasket.  It helps seal and makes future maintenance and replacement easy.

 

Edited June 13, 2018 by 240260280