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Weber 40 DCOE mods for more flow

spmdr

Donation Time
Well, one thing I found.... Cheaper prices of 45 mm carbs!

Tis the season?

I pulled the trigger on a pair of New Weber 45 DCOE knock-offs.

I figured I would never know how well my modded 40s are unless I compare them to 45s.

Even IF the knock-off 45 carbs are not as good as the current or original "Webers", I should be able to FIX

them, if needed.

An early 'Xmas for me!....??
 

Five Reviver

Silver Level Sponsor
Which Is Best? Ford Pinto Carb Edition - 32/36 DGAV Vs 40/45 DCOE Weber - YouTube

This video is on point. Test man says, in relation to the 45's 'the big carbs pull through' and 'let the engine rev on better'.

I was not happy with my engine feeling asthmatic at the top end with DCOE 40's and after watching this video bought some 45's from Weber Performance in Melbourne and fitted them in standard spec as supplied. From the WeberPerformance website:

FACTORY CALIBRATIONS FOR THE 45 DCOE 152G are;
36mm chokes, 4.5 aux venturi, F16 emulsion tubes, 145 main jets, 155 air correctors, 55F8 idle jets, 45 pump jet, 40 pump spill, 200 needle valve
The carburettor is fitted with 62mm air horns

In my 40’s I had 32 mm chokes, 4.5 aux venturi, F-16 emulsion tubes, 135 main jets, 170 air correctors, 45F9 idle jet,, 40 pump jet, 50 pump spill, 175 needle valve, 39 mm air horns

My clear seat of the pants experience is exactly as described by the man in the video. I am very satisfied indeed.
 
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jdoclogan

Platinum Level Sponsor
Well done Five Reviver. I embrace the scientific data.

I've use the 38/38 and found noticeable (seat of the pants) power increase over stock Alpine carbs. I use 38 DCOEs (because I can get NOS Italian) and find even more power. I'm not certain that, for street use, there is enough value in the 45s over the 40s. For racing any advantage should be implemented.
 

phyrman

SAOCA Secretary
Diamond Level Sponsor
A "Weber" guy here in the Los Angeles area feels a single DGAS (synced venturis) offer better drivability over DCOEs on non-race engines
Something to consider!!!!
 

jdoclogan

Platinum Level Sponsor
I've got both DGAS and DCOE. The 38/38 DGAS on a standard .020 overbore rebuild compared too the DCOEs on a mild (KB cam) .020 overbore engine rebuild. The latter will give a (seat of the pants) noticeable increase in power. Downside, there is more to the installation of DCOEs and they cost more. Once properly tuned, just like DGAS, DCOEs have reliable performance. The cars drive the same as to other aspects related to suspension, wheels/tires, etc. I will note that in the 2004 SUNI I competed in the autocross as a first time competitor. I used the 38/38 DGAS described above in a Series 3GT (I removed the hardtop). On the track the only thing I knew was "don't hit the cones and follow the course exactly". As I made my way around the track after three runs I looked at the timer's board with several other competitors. I was 3 seconds less than anyone else. There were others running 32/36 DGAS conversion. I could conclude two things. The 38/38 DGAS outperformed the others. And possibly the close ratio Series 3 transmission made a difference (even though I only ran the entire short course in second gear). Not as clear a comparison as Five Reviver's dyno results.

I will add to support the "drivability" notion that on start up the DGAS is far better than DCOEs. My DCOE setup really wants to warm up. Once that has occurred then everything is good.
 
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spmdr

Donation Time
Well, I think Five Reviver proves the bigger Carbs/more flow are needed,

...At least on the top end.


And I have proven bigger chokes (than 30s) in 40s, even for the street, are not a bad thing,

...at least on moded engines.

It will be interesting how well the 45s work on the street.

BUT, the question in this thread is, Can I get 40s to work nearly as good as 45s?

Down the road, it may be interesting to try a custom intake manifold with a V8 sized

Holley 2 or 4 V Carb?

A 38/38 DGAS is Good, as far as it goes, but most likely still a bit short on CFM for a RACE Alpine.

It may well be the Best street carb.... for a stockish Alpine??

DW
 
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spmdr

Donation Time
My first (limited) look over of the repo 45s make it clear the Moded 40s WILL

have their work cut out for them to flow as well!

The 45s have Velocity stacks that start with a 50mm ID opening

and end up with a 46mm ID transitioning to the Aux venturi.

The Aux venturi is also Very close to 46mm!

I wonder how the Repo 45s compare to REAL Webers?

DW
 

spmdr

Donation Time
It's looking like the 45s have an insurmountable

Unfair advantage over ANY 40s... Hmmmm

DW
 

alpine_64

Donation Time
It's looking like the 45s have an insurmountable

Unfair advantage over ANY 40s... Hmmmm

DW
Off to the homologation scutineers to explain how the 40 scoe used on period alpines are completely NLA and the only suitable substitution is a 45DCOE ... Like the argument for willwood 4 pistons over the completely rare Girling 16p front calipers made a few years back :p:D
 

spmdr

Donation Time
MK, You ...well, ....embellish... the story and I'll swear to it! ;-)

....I can Definitely swear to the availability of the 45s...

DW
 

alpine_64

Donation Time
MK, You ...well, ....embellish... the story and I'll swear to it! ;-)

....I can Definitely swear to the availability of the 45s...

DW
I can Photoshop the original Homologation papers that show 2 x 40-DCO2 webers for alpine series II-IV...

I mean photograph the papers showing the 2 x 45DCOE for alpines
 

spmdr

Donation Time
Not that I NEED more proof that an Alpine running

in the upper RPM range (north of 5000) Needs more

CFM (or maybe LESS restriction), but there is another

Video, like the one above, but shows going from 40s

to 45s gained 14 HP!

The point being, the more mods (cam, head work and exhaust)

the more gain from a higher flowing/less restriction

induction.

 

spmdr

Donation Time
And what I just posted brings up the REAL issue here.

Namely, RESTRICTION.

Carbs are rated by CFM but in reality it is the Restriction

to flow.

Just because you bolt on a bigger carb doesn't mean you are going

to flow the max capacity of the carb.

But, hopefully you can USE the lower Restriction.

To make more HP.

And the BIG trick with a Carb is to Properly mix air and fuel,

under a wide range of RPMs and Throttle positions.

All of that being said, there are some unexpected things found

in the Repo 45s that may play into the Mods to the 40s.


The Repo 45s have an interesting Aux Venturi, take a look:

IMG_20221204_081524221.jpg


The step on the inside of the Aux Venturi goes against CW of a PROPER

Venturi.

I assume Original Weber 45s have a Std Aux Venturi?

Hmmmm, some loose ends in the Info world....

DW
 
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