Weber 40 DCOE mods for more flow

[spmdr]

This thread could be in a different place, I assume this is the best place.

I'm late to this world of Alpines with Side drafts, but I'm trying to catch up.

I'm fast coming to the conclusion 40s are too small for a serious Racing Alpine,

But a LOT of Alpiners have them, as do I.

This thread is an effort to drag the lowly 40 DCOE up a notch or 2.

If I fail, this thread would just be better in Mod Alpine....


The goal here is to increase the MAX air flow.

The flow chart generated by the Z world points out the diminished flow increases

with bigger choke sizes.





Clearly, the Auxiliary Venturi is the main focus of modification.

Starting with the transition from the Velocity stack to the Aux venturi.

The Velocity stack has a 40 mm ID and the Aux venturi necks down to 37 mm.






And continuing with the transition to the choke.



Also on the table is opening up the Aux Venturi as much as possible.

The secondary focus is the transition from the choke to the throttle butterfly.





DW

 

[alpine_64]

Dan,

Your mods are really interesting, Mark VR in sth africa did some similar mods to open up his chokes.

When i first started palying with DCOEs back in 2003 i read lots on jetting, chokes, progression holes and the velocity stack radius etc...
Surprising how people never really talked about the "porting" improvements that could be done inside the carbs

 

[spmdr]

The more I think of this project, the more I think the answer

is the same that Holley came up with the 650 cfm 2 barrel.

Chuck the Aux venturi all together and go with the least restriction of

an Annular ring discharge Venturi/choke.

With all the changeable bits, the Weber may be as good as it gets for testing the concept.

 

[spmdr]

Getting back to the first stage mods:




Rumor has it, back cutting the choke can yield as much as a 12 % flow increase.

DW

 

[spmdr]

I started hacking on the Weber bits.

The Aux Venturis need some more work to remove the casting seems,

and transitions.

And I did conclude there is JUST enough meat to open up the Aux from the current

37mm all the way out to 40mm, all the way through. It will be quite thin walled in spots.

You mite say I have finished the First Cuts...

We'll see if I get Brave enough to cut some more.

DW

 

[alpine_64]

Nice work Dan,
How are you doing the cutting?

Would be great if you could do before and after flow comparisons of the chokes and venturis.

 

[spmdr]

Every now and then I have to change hats, from spmdr to mtldr (metal Dr).

I have an OLD American Lathe that has a LOT of experience making Chips.

But at this point I think I will put the Carbs back together and make sure they still work.

Later I may haul out the Rotary Table on the Mill and attempt to make the half round cuts

between the spokes/webs of the Aux venturis.

I do have a lead on some early Weber 34mm chokes that have the better transition from the Aux to the choke.

And then there are the different Stacks to play with...

DW

 

[alpine_64]

Every now and then I have to change hats, from spmdr to mtldr (metal Dr).

I have an OLD American Lathe that has a LOT of experience making Chips.

But at this point I think I will put the Carbs back together and make sure they still work.

Later I may haul out the Rotary Table on the Mill and attempt to make the half round cuts

between the spokes/webs of the Aux venturis.

I do have a lead on some early Weber 34mm chokes that have the better transition from the Aux to the choke.

And then there are the different Stacks to play with...

DW

There is a good article on thr various air flows pf the velocity stacks .. The ones with the completely rounded tube edge were best.. But there was a specific radius.. Ill try and dig the info up.. Then there is the question...will you be making a cold air box?

 

[spmdr]

Yes, I DO plan a Cold air box AND some way to keep/reduce the exhaust heat out of the intake manifold.

Along with the older chokes, are a mix of stacks to play with, hopefully coming soon.

Also hopefully, is a comparison of the stock and modded parts.

DW

 

[spmdr]

Also, just for the record, the chokes are back cut at 6 degrees.

And the reason there is a small step at the inside machining of the Aux venturi

is because I ran out of Tool length,

And decided to machine all the parts the same before changing the setup.

...plus, I was running out of time in the day...

DW

 

[Thor 1211]

Getting back to the first stage mods:

View attachment 25577


Rumor has it, back cutting the choke can yield as much as a 12 % flow increase.

DW

When I look at the sketch it seems to me that the tightest restriction is in the area indicated by the red arrows (see my sketch).
Don't you think that to increase flow you should remove the material shaded in red or are you worried that you will lose the venturi vaccuum?

 

[spmdr]

Yup, I want to keep a starting point with the venturi.

I could go bigger and may, eventually. This is stage one...?

DW

 

[spmdr]

After Stage one Mods, the first report is SUCCESS!

Success being NO problems with the carbs function!

Having only driven the car 2 times with this engine,

I'm AMAZED how civilized it is!

This engine has a cam with 250 degrees of duration @.050 lift!

That is a FULL 31 degrees more that a stock SV cam!

Unfortunately, on the first drive, I did not have the O2 meter installed.

With the O2 meter, it's mostly Good Stuff!

Rarely does it go lean and when it goes lean, it's not a big swing.

All indications, so far, are the mods are SAFE!

IF the mods are worth doing is still unknown...

DW

 

[spmdr]

BTW, my goal here is to get to the point of

being able to use the 36mm chokes more effectively.

Based on the Z World chart/info, with a 40 DCOE:

-3omm chokes yield about 157cfm

-34mm chokes yield about 173cfm

-36mm chokes yield about 174cfm


With mods, I hope to approach the numbers of a 45 DCOE

of 207cfm with a 36mm choke, BUT with a 40 DCOE.


I'm thinking stage 2 may be to remove the support rib/spoke

in the Aux venturi, to gain the most flow with 34mm chokes.


Stage 3 would be to open up the Aux venturi to 40mm and use

backcut 36mm chokes.


Stage 4 would maybe be a custom annular ring discharge choke?

Mtldr is getting VERY excited about the prospects of making THOSE

Parts!

Also, at some point/stage, I may put the Throttle plate shafts on a Diet...

DW

 

[spmdr]

I have always wanted a CNC Mill.

Back in my computer days, I worked at General Automation, on the System Test floor.

I worked on Gen 2 CNC controllers, among other stuff.

So I was out Yard saleing and Guess what I found?

YUP!! a CNC engraver/Mill.....literally ON the sidewalk!

For Damn near Free!!


I got it home, connected it all together and it WORKS!

It's a CNC3020-800w, with a 24K RPM water cooled 800 Watt Spindle motor!

Of course, it is only the basic machine, without the Computer part...

But I Have Computers!

The Software is another matter.

Now I start the learning curve of the World of CNC!

It should be JUST the ticket to mod Weber Parts!

DW

 

[alpine_64]

It should be JUST the ticket to mod Weber Parts!

DW

Mod Weber parts.. Dan lets start designing parts... How about some billet aluminium rocker pedestals and caps

 

[spmdr]

Well, I was trying to keep it tied to the thread....

But the mind runs WILD!

Near the top of the list is CNC ported Alpine HEADS!!!

...including CNC shaped Combustion chambers!!

I may have to mod the table for some more height to clear a head...

....Piece of CAKE!

OH BOY!!

Also, they currently sell this SAME table for 3D PRINTING as well!

...just change the spindle motor for a Print Head!

DW

 

[spmdr]

I took temporary possession of a Large collection of original Weber Stuff.

It was reported to include some 34mm chokes, as well as some 35mm chokes.

The bad news is the "34"mm chokes are really Poorly modified 30mm chokes.

The good news is they are candidates for modification into 36mm chokes.


The 35mm chokes are not as I expected. They are like the 34s that I just picked up,

in that the lead-in shape does not match the Aux venturi well. Hmmmmm??


Because the Weber Stuff includes the same Aux Venturis (4.5) that I currently have,

I'm feeling a bit braver to modify the Aux venturis out to 40mm.


...My CNC learning curve is Not as Steep as I had hoped....

DW

 

[jdoclogan]

Vision + Perseverance = Yureka!!

Keep the vision rolling Dan.

 

[alpine_64]

Vision + Perseverance = Yureka!!

Keep the vision rolling Dan.

Isnt it Eureka... And the irony of me pointing out a typo