Weber Carbs, what's the difference between 40 and 44 IDF carbs Options

[Type 47]

I've seen 2 cars with 2056 engines that have 44's my 75' 2.0 had 40's.

What does all this mean?

[nditiz1]

Virtually nothing, the size of the carb body is the only difference. Where you can get into trouble is with ease of tuning. An engine that wants to breath a large amount will benefit from 44s - 2.2 and above. Whereas the 2.1 and below will have an easier time with 40s. Can you run 44s on a 2.1, sure, but you're most likely going to have to choke it down unless it's a pure track car. Some run 44s on the 2.1 and swear by it, but imo the 40s are the best for it and can do so running 28 vents.

[michael7810]

The size of the throttle plates, 40mm or 44mm. I think 44 is overkill for a 2056cc.

[jdamiano]

I run 40s on my stock 2.0 type 4 in my 914 with a Pertronix coil and distributor and like it. I run 44s on my Type 1 Gene Greg 2006 that has big valve heads and a tall cam in my Baja Bug. It has to do with the entire engine build more than the CC. Unless the engine is built to flow more fuel 40s are the way to go.

[sixaddict]

Good info

[Mark Henry]

I run 40s on my stock 2.0 type 4 in my 914 with a Pertronix coil and distributor and like it. I run 44s on my Type 1 Gene Greg 2006 that has big valve heads and a tall cam in my Baja Bug. It has to do with the entire engine build more than the CC. Unless the engine is built to flow more fuel 40s are the way to go.

I have a Berg 2006 with 42 berg specials. I bought the kit in 1992.

[Mark Henry]

I won't use 44's till 2270cc and even at that size they're borderline.
I'd even state that 44's without a proper 4 to 1 or 4/2/1 (Tangerine) header is silly.

[jdamiano]

I run 40s on my stock 2.0 type 4 in my 914 with a Pertronix coil and distributor and like it. I run 44s on my Type 1 Gene Greg 2006 that has big valve heads and a tall cam in my Baja Bug. It has to do with the entire engine build more than the CC. Unless the engine is built to flow more fuel 40s are the way to go.

I have a Berg 2006 with 42 berg specials. I bought the kit in 1992.

Got mine in 1986. I just freshened it up with new pistons and cylinders last year. The way he did the heads, crank and deck hight threw me for a bit but it works.

[GregAmy]

All this.

Very generally speaking, the smaller the venturi, the better the driveability (throttle response) which means a lot on the street.

The larger the venturi, the more the airflow capability, which is more important at highest revs (which is not so common on the street.)

So where's your compromise?

I think the range of venturis available for the 44IDF is 32-38mm? On the 40IDF it's around 28-36? I'm sure someone knows the correct numbers. But there's not any real value to oversizing your carb unless you're planning to race it (drag or road).

For reference, I have a 2056cc with 86A cam in my historics race car, and it runs 36mm venturis in 40DRLA Dellortos. Revs nicely to 6500 RPM where I typically shift it, but it'll be happy to go to 7k if I let it.

[rhodyguy]

32mm Venturi for a 2056.

[rfinegan]

how to find you venturi size:
2056 / 4 = 514
Also

Venturi Size

Venturi size refers to the narrowest channel in the carburetor throat. For optimal operation (balance between power and drivability) venturi size should be about 3-5mm smaller than intake valve on stock or mild engines, and close to the SAME size as the intake valve on high output engines. You should also note that heavy vehicles must be more conservative with venturi sizing than lighter cars.

[rfinegan]

how to find you your throttle bore diameter:

[Superhawk996]

how to find you venturi size:
2056 / 4 = 514

Pretty. Sure it might be right for racing or max horsepower. I've seen it somewhere before - might be from Weber book?

However, there is more to it when it comes to driveability and throttle response.

I'm not aware of anyone running 38mm venturis on the street with good low end driveabilty at 514 cc / cylinder and 6500 rpm peak power. Maybe I'm just reading it wrong (IMG:style_emoticons/default/confused24.gif) In actuality, how many /4's make peak horsepower at 6500? Even taking that down to 5500 rpm which is more likely still yields a 34 mm venturi which I had at one point on my Weber 40 IDF's and it was still too big of a venturi for good throttle response.

Keep in mind the 2.2L (2195cc with 125HP@5800) 911T with Zennith 40 TIN's for street use ran well on 27.5mm venturis. As I read this chart I think it would say 29 mm at 5500 rpm or 31mm at 6000 rpm.

Seems about right to me for max HP but you're going to give up some driveability using the chart as gospel.

[nditiz1]

Well said.

For anyone that's wants some good information on weber tuning and actually testing different venturis, this guy on YouTube has been playing around with 44 idf Chinese clones on a 914 engine in a beetle.

Motor7710 - channel
Lots of good info on carbs.