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  Topic Review (Newest First)
08-09-2019 07:44 AM
PS70 Funny expression!

This afternoon I received photos of the laying of the cover Tonneau.

Attachment 1581712

Attachment 1581714
08-09-2019 05:40 AM
IRONBLOCK
Quote:
Originally Posted by PS70 View Post
Hello !

The saddler had moved on something else and nothing was moving on my car.
Two days ago, I raised my voice.
Things are moving forward again.
The 'squeaky wheel gets the grease'. Very nice work too!

Mark
08-09-2019 03:56 AM
PS70 Hello !

The saddler had moved on something else and nothing was moving on my car.
Two days ago, I raised my voice.
Things are moving forward again.

The soft top cover is finished.

Attachment 1581690

Attachment 1581692

Attachment 1581694

The tonneau cover is in progress.

Attachment 1581696

Attachment 1581698

For my part, I take care of the door panels and soft top compartments.
07-14-2019 04:37 AM
PS70 First seat nearly finalized, second ongoing :

Attachment 1576724

Attachment 1576726

Attachment 1576728

Attachment 1576730

Attachment 1576732

Quality is still at the level I expect.
Confort seams to be very good :
The springs of the seat have been reinforced.
On the back, lateral reinforcements stop at the deltoids and seem to block the back well in roll.
We'll see when driving ...
07-07-2019 02:40 AM
DPeterson3
Quote:
Originally Posted by PS70 View Post
It is exactly what I plan to do.

How was Bogota ?
A gentleman should not comment upon such matters.....
07-07-2019 12:19 AM
PS70
Quote:
Originally Posted by DPeterson3 View Post
From here, I'll stick an Innovate AFR sensor up the exhaust and start swapping VF tubes until my mid range mixture flattens out. Once I've gotten the driving AFR looking good I'll go back to the dyno.
It is exactly what I plan to do.

How was Bogota ?
07-06-2019 04:07 PM
DPeterson3 Sorry for long notes. I'm
Sitting on the floor of the Bogota airport with nothing better to do until the check-in desk opens in two hours.
07-06-2019 03:44 PM
DPeterson3 As for Sprint falling over.....

At this point, I suspect that Alfa used their odd, dislocated FBV tubes to cause the mixture to lean when the throttle was fairly open, but the revs were in the transition zone. This was probably needed because Weber never really perfected either their carbs or emulsion tubes. The DCOMs that I previously had installed did a much better job than my current early 45DCOE9s.

So, Weber continued to chase a flatter transition curve until carbs were no longer a profitable product. All of the Alfa installations I've seen used DCOE carbs, not DCOM.

So, I don't believe the remote FBVs were because of localized pressure perturbations, I think they were seeking a higher pressure source to compensate for emulsion tube/progression hole inadequacies.

My Sprint fell over because my simple change to ram tubes from plenum took away the "fix" Alfa used to partially weaken the mixture during transition.
07-06-2019 03:25 PM
DPeterson3 The FBV does flow air, not just compensate for pressure. The upper end of the emulsion tube carries an "air corrector" jet that accepts the air that is used to emulsify the fuel. Not a lot of air compared to the main flow into the engine, but some.

Keith Franck and a few others are spending a lot of dyno time, and using AFR meters while driving around to perfect their concepts. As I understand them (and I may not) there are two main goals: remove all dips and peaks in the mixture as the RPM/throttle changes trigger transitions from one circuit to the next, AND to eliminate the need for a small primary Venturi to amplify the signal to the secondary Venturi.

It might jar everyone loose from "that's the way Alfa always did it" to tell you that Keith has abandoned the concept of emulsifying the fuel. This is a fundamental change from Weber's core concept.

In spite of it being such a major change, installing his VF tube using my existing main and air correction jets improved the mid range immediately, with no other change to the jetting. Keith has told me he sent his VF5 tube, which he was sure would be too rich. From here, I'll stick an Innovate AFR sensor up the exhaust and start swapping VF tubes until my mid range mixture flattens out. Once I've gotten the driving AFR looking good I'll go back to the dyno.

Keith's extensive sampling of Weber equipped cars is that the transition from the idle circuit to main goes tragically rich, causing the common big slump in that range. Note that he has quite sophisticated and adjustable idle jets to participate in seeking perfection.

A common cause of retrofitted Weber applications falling over is due to using large venturis. This is apparently caused by creating an insufficient boost in the signal to the secondary Venturi. I'm trying to imagine what my 2300 is going to produce if I can switch from my 35mm venturis to 40s with no loss of low RPM torque.
07-06-2019 10:35 AM
PS70
Quote:
Originally Posted by tubut View Post
So, go and try the tubes you have in mind and see if the results are acceptable.
I'll do so. One month may be.
The saddler is doing a very good job, that help me to wait.
07-06-2019 09:01 AM
tubut
Quote:
Originally Posted by PS70 View Post
the diameters of the tubes are quite big (that is not a good news because the solution I image is bases on a pair of 8 or 9 mm diameter tube.
Since there is virtually no air flow to the float bowl (except for compensating for the variation in fuel volume in the float chamber) we're talking mostly about pressure variation, not air flow. I would guess the diameter of the tubes probably has to do with acoustic resonance frequency -- similar to a pipe organ -- but the length of the tube probably affects resonance frequency more than its diameter. Matters get more complicated when taking into consideration that we have to constrained volumes (the float bowl and the air intake plenum) connected by a pipe, and we could go on waxing about Venturi and Bernoulli effects.

One way or the other, I think theory and conjecture will not solve this problem -- only observation of experiments will (the diagonally cut pipe is probably no accident, either). So, go and try the tubes you have in mind and see if the results are acceptable.
07-06-2019 07:11 AM
PS70
Quote:
Originally Posted by IRONBLOCK View Post
Serge, my Duetto FCV is vented directly into the incoming air flow too.
So, we have here 3 examples of the technical solution chosen by Alfa from 1952 to 1969 to vented the weber float chamber (FCV) : In the middle and in the axis of the air flow coming from the air filter.
What is also commun to these 3 exemples : the diameters of the tubes are quite big (that is not a good news because the solution I image is bases on a pair of 8 or 9 mm diameter tube.
07-06-2019 05:47 AM
IRONBLOCK
Quote:
Originally Posted by DPeterson3 View Post

I recall many decades ago I had a 65 Sprint GT with exactly the plenum you show above. Thinking I could have fun at an autocross, I removed the original plenum and installed some horns we had in stock in our store.

It fell flat on its face. Of course, I assumed there was some sort of airflow issue beyond my pay grade, and put it all back together as original, and it worked again.


Maybe the Alfa displaced FBVs were simply a way to avoid a fire in the event of a backfire?
Why did the Sprint "fall flat on its face?"

I've been on a crusade, off and on, to get this car running better. All along, I've been thinking that the carbs were jetted too rich but a local engine builder and Alfa racer suggested that my issue (stalling after several high speed runs and refusing to restart until the plugs have been changed) may be caused by a lean condition...

Serge, my Duetto FCV is vented directly into the incoming air flow too. I am sorry you let yours go...

Mark
07-05-2019 09:27 AM
PS70 Hello Mark, hello Don, hello everybody,

Mark,
Thank you for the picture from the "Duetto". I had one (snif, snif).
For me the black 'shroud' over the FCV is directed up but in the axis of the air flow. Just imagine the air trajectory into the system. Exactly like the on the 6C or and 2000 sportiva.

Attachment 1574870

I received the part from Keith Franck but I can't play with it ... Car is still at the saddler

Attachment 1574872

The rear seats are on progress

Attachment 1574874

Attachment 1574876
07-05-2019 07:12 AM
DPeterson3 I know it may seem that I’m on something of a crusade. That really isn’t the case.

I recall many decades ago I had a 65 Sprint GT with exactly the plenum you show above. Thinking I could have fun at an autocross, I removed the original plenum and installed some horns we had in stock in our store.

It fell flat on its face. Of course, I assumed there was some sort of airflow issue beyond my pay grade, and put it all back together as original, and it worked again.

Keith Franck and his followers are working on making 40mm venturis work from idle up in 45DCOE carbs. I was taught that combination was pretty much race only for small displacement engines. Keith is focusing on the crude concepts that Weber used, and he has designed replacements for both the emulsion tubes and idle jets that work on different principles. This is achieving ever-better mixtures across the full throttle-position/RPM spectrum.

My very strong suspicion at this moment is that all of the displaced float bowl vents were an effort to fix shortcomings in the emulsion and idle jets. What all of us have been doing is try and read the minds of some now-dead Italians from the 50s and 60s.

I also suspect that Keith’s approach may not be quite so universally flexible for every combination of displacement, cam profile, combustion ratio, Weber progression hole variations, etc. Still, if his solutions are addressing the real source of the problems, then fiddling with FBVs is a red herring.

I have the 2000 and 2300 making excellent, and improving power with the FBV opening right next to the carb inlet. As our sage mentor has occasionally observed (in his lawyerly Latin), “that which has been done, can be done”.

Maybe the Alfa displaced FBVs were simply a way to avoid a fire in the event of a backfire?
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