IDA v. IDF

[Cliff Beer]

Was just wondering if anyone can share their thoughts on the pros/cons of the IDAs v. the IDFs for a SBF. Is it a BFD?

OK, jokes aside, any real advantages or disadvantages to the IDAs over the IDFs?

The IDF look like they're a little shorter (assuming same manifold height), is that the case? I have a feeling it's going to be close with regard to the rear window relative to carb height including some low level trumpets. I have a CAV with a 302 and an 016.

Also, for a mild (Ford Racing crate) 302 is there any reason to go for the 48s instead of the 44s?

I have tuned DCOEs on Alfas and MGs and such and have a pretty good working knowledge of the internals so I'm assuming the move to IDAs/IDFs won't be too dramatic. I know what an emulsion tube does, how the idle circuit works and what's the significance of the progression holes in the throat relative to the butterfly for example.

Any/all thoughts are appreciated.

 

[Randy V]

I have the 48 IDA carbs on my 331 and think they are a bit too large actually even though they have great throttle response...

The 44 IDF would have probably been a better choice to make more power at a lower RPM.
Since I've not run both on the same engine - I have no scientific evidence to support my theory.

 

[chuck smith]

MY IDAs fit in my CAV fine with normal size trumpets, plenty of room. IDFs may be easier to tune but there are problems with fit of valve covers as I understand it, you may need to modify the covers. I would go with IDAs with a 3rd progression hole drilled.

 

[Rob]

Hi Cliffbeer,
All the research I have done indicates that the IDFs are more "streetable". If you want all out performance, seems the IDAs are the way to go. IDF tuning seems to maybe be a little easier from what I have learned. Changing out the jets, imulsion tubes etc is a snap. Takes longer to set up than change em out.

Regarding size, IMHO the venturi size is most relevant to WOT. If you're running a big valve, big cam high revver, then I'd stick with the 48s. I never want to run out of fuel (i.e. go lean) at teh top end. The low end can be jetted appropriately for proper tune.

Those are my thoughts.......

 

[Dean Lampe]

It is really the choke size that matters. For example the 37 mm chokes come stock on the IDA and according to the weber charts, that is a little small for a 331! When you run out of carb on the top end you will not go lean because it is a function of reduced air flow. It isn't a lack of fuel. I would go with the 48's. I have Idf's on a buggy and IDA's on the 40. they are about the same to tune IMO.

 

[Peter Jankovskis]

I can verify from personal experience that IDFs are more streetable than IDAs. I had 48 IDAs installed on the 302 GT40 crate engine in my Daytona Coupe replica when it was first built. Could not find a setup that worked well at both the top end and driving around town. Replaced the 48 IDAs with 44 IDFs and the car is much more driveable around town and still works well on the track.

 

[chuck smith]

IDFs do have the advantage of being far less expensive

 

[David Briggs]

I have IDA's on a 331 Tiger and they work well and 48 IDF's on my 347 GT40.
The IDF's are an improved design and have a simpler idle circuit, the idle mixture screws on the IDF's stick out the side towards the valve covers and you can't get a screwdriver on them, it gets very toasty for your fingers when you are adjusting the idle mixture!
On the other hand once they are set up they seem to stay in tune.
Both of them are very sensitive to fuel pressure (3-3.5 lbs) and volume(lots).
I use Carter rotary pumps that are factory set to approx 3 lb's pressure.
They are very sensitive to heat soak and you need to shut the fuel pump off and let the engine idle for a minute to depressirize the fuel system and a heat shield/ turkey tray is essential(for a V8 install).
Set up correctly they are just like fuel injection, only sexier! and they have the right sound.
Dave

 

[chuck smith]

can you use the same throttle set up if you go from IDA to IDF?

 

[Mike Trusty]

Here are some observations and comments that some might not have realized about Weber carbs applied to relatively large displacement v8's. Applies to both IDF and IDA.

1. A V8 setup with IDA and stock 37mm chokes actually flows less air and fuel than a plenum manifold and proper four barrel carb.

2. Consider that the motor has two cylinders on the intake stroke at a given time which means that the effective flow through the 4 barrel is providing one half of its total throttle area to each cylinder at full throttle, i.e. two throttle plates per cylinder. I understand it is much more complicated than just that but to keep it simply lets leave it at that.

3. Now consider that those same cylinders when on the intake stroke is pulling through a much less throttle and choke area with the single throat of IDA and you can see why many people don't understand why their car ran better on the top end with the four barrel.

4. With proper tuning most of this can be rectified. The big advantage right out of the box with a "stock" weber that is properly tuned is the throttle response and of course the look. It takes a little work to make them work on the top end.

5. For an IDA system to work as well as a proper four barrel on a 350ish motor on the top end will require 44 mm chokes and something different than factory jets and emulsion tubes. As with all carbs you are compromizing the low end mixture to make the top end perform.

6. The above mentioned limits apply as well to multi throttle injection systems. Their advantage being that they don't have the restriction of the choke and are programmable to allow a proper mixture through the entire range with fewer compromizes.

7. That said, the look is worth the price whether webers or injection.

I know that my comments are off topic to what you asked but I'm just sharing my thoughts along with a little experience.

On topic would be to agree with some of the comments already made and say that if you are worried about the IDA being too big, they are not.

 

[Tim Kay]

As David said, IDF's are an improved design. I have used IDF's in offroad cars where IDA's wouldn't stand a chance. Yes, the sound created by IDA's is unequaled but given the intended purpose of IDA's - basically for racing and WOT - stands to reason that they're not ideal for street use.

I personally was struggling with the IDA 'look' vs IDF tunabiltiy on my 302. Tuff decision! Stayed with the IDF's but always wanted the IDA's. Problem solved, now have TWM stack injection. BTW, I have for sale a set of 4 IDF's in great shape if anyone is interested along with full assortment of jets, chokes, tubes ect.

 

[Julian]

Tim,

You have a PM

 

[Cliff Beer]

Wow, thank you gents - very helpful information. While there's a healthy range of experiences there seems to be some general consensus on a few points, including:

1. The IDF are likely a little more "friendly" for the street - ie. less oriented towards WOT optimization and more towards a mixture compromise between idle, part throttle and WOT.
2. IDFs are less expensive.
3. The 44 IDFs can benefit from larger chokes (larger than 37), the degree which is probably dependent upon valve sizing, cam profile, displacement (302 v. 331/347), etc.
4. The IDFs may be a little more easily tunable (idle mixture screw aside...).
5. The IDFs may bind on certain valve covers - undoubtedly, mine will happen to be the covers which interfere....
6. IDAs look and sound more like the classic weber setup.
7. Shouldn't be too much of a clearance problem with either IDAs or IDF if the trumpets aren't too tall.

This is great - thank you. Based on all this, and my orientation towards tractable street performance, I'm leaning towards the 44IDFs with larger chokes and some time on the butt dyno to mess with jetting. I'll install an active air/fuel mixture sensor downstream somewhere to provide some additional mixture data in addition to spark plug and gut instinct.

Thank you again, that's a BIG help.