Weber v's Dellorto

[carlo rossi]

ON my never ending investigation attempting to find that lost 0.3 hp
from almost 40 years of motoring I think I have stumbled across a little known fact, well at least to me.
The old argument, not the holden versus ford  one, but the far more extensive battle,
which is better, WEBER OR DELLORTO
this little research only identifies the 40dcoe v's dhla 40
as they are both 40mm throttles at the manifold side I have found that on the inlet side the weber is 37.5mm opening (odd)
and the dellorto is virtually 40mm as one would expect.
Now this sounds minuscule however after a little surfing the cfm on the weber is around 175cfm per venturi but and i suspect due to the larger opening  the dellorto is rated at 210cfm or 35cfm more or 20 % more
This should result in more power
Incidently the weber 45 DCOE has a 50mm opening at the inlet and 45mm at the manifold ( a much more serious carby) and around 450 to 475cm or 225 to 237 cfm per venturi
which seemed a little small i thought compared to the dellorto
SO do you need 45mm webers on a street alfa ?I think NOt ,not worth the effort if you have Dellorto dhla 40s
as it would seem , but if you have weber 40 dcoe ,then yes it is worth it! or save the money and put dellortos on, much cheaper !
Happy to be corrected just an interesting anominally

[bazzbazz]

ON my never ending investigation attempting to find that lost 0.3 hp

I see the old axiom of "diminishing returns" has had no affect on you what so ever. 

[carlo rossi]

Yeh a bit of a stickler for the useless
I was tidying up as do over easter
And was reorganising and cleaning the carby section
When i noticed this
Incidently the webers came of an italian police car that was
Abandoned for over 5 years so i helped myself to the cams and carbs
I have add this was some 40 years ago and the car was still in the ditch rusted almost completely away before it was removed only 5 years ago
Its amazing what could be hand luggage back then

[105gta]

Just a few points, to be any where near accurate. We're both carbs flowed with the same size chokes installed. Also the 8mm butterfly shaft would cause far more flow restriction than the carb opening, also any protrusion of the screws hanging out of said shaft would disrupt flow along with wall texture etc.. I don't think the minor diameter change at the opening would play much part to the actual flow. Does either one have a better radius at the opening? That alone could account for a flow change. Was the dellorto measured with a trumpet fitted? Don't forget the booster Venturi design, size and shape and also at what water depression were the carbs measured? Just a few small points to take into account.

[carlo rossi]

As I dont have a flow bench I googled the cfm results where they used same inches of water the same conditions
these figures are for 36mm choked 40mm carbs STock so all equal
I also dont hold the american system of CFM as a reliable rating of carburettors
example being fort gt ho with a 750 cfm double pumper WOW HUGE
Well a  1750 alfa standard has around 700 cfm
SO a huge pinch of salt ,also for those who love their 350 holley ? they lied ! it is actually closer to 300 cfm !
they used a higher atmosphere pressure exactly 50 % more air pressure.
Now nothing changed the fact that the 40dcoe use a different aux venturi system to the big brothers
consequently an issue with a smaller inlet than outlet is quite wrong ,this has to result in a smaller flow than a dellorto, the weber needs trumpets! both carbs of mine are stock for the openings and if you work out the area of opening thats 11.08cm2 for weber and
12.57cm2 foe dellorto  IT has an advantage at the start
MIND you go to the larger 45 plus carbs and the weber walks away
Sadly all this info would have handy 40 years ago , all too late for most of us
The new battle lines are electrics. How exciting..... yawn !