44 IDF Venturi sizes.

Rusty · 02-21-07, 04:10 AM

Could I please get some feedback from the forum members about the suitability of Quad 44 IDF Webers on a 355 cubic inch engine.
Will they supply enough fuel and air for a 6300 rpm rev limit on an engine this size?
Also, has anyone tried or heard of someone machining (boring out) a set of 36mm venturis to around 38mm, and if so, did they still work ok?
Thanks for your time guys.
Rusty.

CliffBeer · 02-21-07, 10:42 AM

Rusty, four 44 IDFs should work fine for a 355 engine provided a few basic parameters are appropriately sized. The bore should be sized correctly and the progression hole spacing/size considered along with basic jetting. I may have some data sheets on 44s on a stroker - will take a look later in my files for you.

Ron Earp · 02-21-07, 10:54 AM

Bear in mind the 44mm IDFs do not have 44mm worth of flow area as there are chokes inside the carb. 48mm carbs fit a maximum of a 44mm choke, I'm not sure what the 44mm IDFs will allow. If they'll allow around a 42mm choke I think you'll be fine.

I did look into having some 48mm IDA enlarged to 52mm, it wasn't cheap. I'm sure it can be done and you'll find the links to that company that offers that if you read around on the forum about venturis.

This has been discussed before, use the search engine and you'll turn up a lot of posts I think. Here is one:

Venturi Discussion

Bernard · 02-21-07, 06:06 PM

According to a Weber part supplier, usual venturi sizes for a 44IDF are 32, 34 or 36mm (see page 3/5 of this link: http://www.piercemanifolds.com/calpart.pdf)
38mm should be possible but it is not usual for a 44IDF.
If we refer to the Weber chart, we can see that 44IDF (equipped with 38mm venturi) are acceptable for a 289 engine (about 600cc per cylinder) wich not exceed 6000rpm. Regarding a 355ci (above 700cc per cylinder) runnig at 6000rpm, ideal venturi sizes will be 41 or 42mm (that are only available with the 48IDF). Anyways, it is better to have a 38mm venturi with a good getting adjustment than a 48 IDA with a 42mm venturi badly tunned

CliffBeer · 02-22-07, 02:50 PM

Rusty, don't forget to consider the arrangement of progrression holes drilled into the throat - these, along with different jetting are the distinguishing characteristics of the various version of the 44IDF. The jetting can be changed, however, the progression holes once drilled are difficult to reconfigure.

Rusty · 02-22-07, 03:43 PM

Thanks for all your feedback guys. I'm sought of at a crossroads so to speak on whether to try these, buy a single plain manifold and a 750 Mighty Demon or sell the 44's and buy some 48's. Would love to see those data sheets CliffBeer as seeing this set up (quad 44's) on a similar engine would set my mind at ease.
Thanks again guys.
Rusty.

CliffBeer · 02-22-07, 04:44 PM

Rusty, can you tell what version of IDF you have? The data I have is organized by version of IDF (VW v. Porsche v. other/etc.).

Here's the book you really need to research the whole issue: Amazon.com: Weber Carburet Hp774: Books: Verlon P. Braden

If the above link doesn't work just search for Weber Carburetors by Verlon Braden on Amazon. And, talk with Pierce Manifolds, they have much hands on experience with IDFs for SBF - no doubt somebody has done a SBF with 44s in recent history.

Hope this helps.