Factory carberator

[bradartigue]

I'm not sure the DCNF is the holy grail, it doesn't fit the car for one thing (you need a manifold made just for it), and the synchronous nature of the DCNF is better suited for dual-carburetor setups. On the Ferrari Dino they used three of them (one barrel per cylinder). I do agree that the DCNF is far superior to the IDF (more compact, more tuneable, actually works for more than a week, etc.) - but they're expensive, hard to find, and you still need to find the manifold, single or dual.

In terms of what carbs were performance on the Spider...frankly most were pretty pedestrian. The 1608 in Euro form had twin IDFs, which were nice for that engine, sporty, but I think they're lousy on anything larger (e.g. 1800, 2000). FIAT equipped two cars with larger single carburetors, the very early cars had a 34DFH and 1974 cars had a 34DMS. The DFH is a DMS with vacuum secondaries, so the initial acceleration is kind of lame but it otherwise is a nice little carb. Besides these they used a variety of vacuum operated carbs prior to 74 and a mechanical carburetor, the 32ADF, from 75-78, then an awful vacuum toilet called the ADHA in 1979 and 1980. The DHSA2 series is actually the largest carburetor ever installed on a Spider, with a 36mm secondary barrel, but it's vacuum actuated so the acceleration performance is pretty lousy. But once it's going its real nice, especially if you install the DHSA2 on the 1400, which had the much smaller DHSA1.

All of this is better summarized in my book, which is free, on http://www.artigue.com/fiat

The fact is you can find any of the carburetors new if you're willing to pay for them. A 34 ADF was never cheap - a $500 carburetor even a decade ago and around $600 now - but consider you need to buy one every 20 years or so and it's rather inexpensive. When the 32 ADF was OEM in FIAT packaging - 1977 - they wanted about $500 for it (that's like $2500 in today's dollars).

The easiest thing you can possibly do for performance is get an 1800cc intake manifold and bolt on the new DFEV carburetors. It will yank you around town nicely. If you want the balls get a 36 ADL or 38 ADL on that same manifold.

[fiat218]

I think I have the twin dcnf

[spiderrey]

Mr DJ, I went back to the twins because they are more correct for the car in my opinion.

[spiderrey]

Brad, nice write up.

[fiat218]

i dont mean to just jump in but i have a dcnf 40's and im looking for the parts inside, the kits and plus the shafts and butterflys,\
can some one direct me to get that
thanks

[toplessexpat]

If you want the balls get a 36 ADL or 38 ADL on that same manifold.

That's what I keep telling people Brad....

.... and I've got a spare 34ADF now too

A

[spiderrey]

I would have to agree, as far as singles go. You cant beat a 38.

[bradartigue]

If you want the balls get a 36 ADL or 38 ADL on that same manifold.

That's what I keep telling people Brad....

.... and I've got a spare 34ADF now too

A

The argument is not which carb but to get to spend money. Performance does cost money, it can be a little bit or a lot, depends on how much you want.

[MrJD]

Can a single IDF be used like what is done on some VW's? I have seen them run single 36 and 40 IDF's. Is the method they use to deliver fuel different in some form?

On a relatively stock 2.0, the 38adl would be quite boggy would it not? From my understanding, its a matter of air velocity.


$500 on a 34 or 32,,, or $250 on a 32/36. How much more performance does that extra $250 get you? I have to assume very little unless you have increased compression.

[toplessexpat]

On a relatively stock 2.0, the 38adl would be quite boggy would it not? From my understanding, its a matter of air velocity.

I'm going to need some help to explain this. I've got a relatively stock 1800 - stock cams, stock pistons... but a header, free flow exhaust and dizzy-less ignition... and the 38ADL doesn't bog down at all...

[bradartigue]

On a relatively stock 2.0, the 38adl would be quite boggy would it not? From my understanding, its a matter of air velocity.

I'm going to need some help to explain this. I've got a relatively stock 1800 - stock cams, stock pistons... but a header, free flow exhaust and dizzy-less ignition... and the 38ADL doesn't bog down at all...

I bet it's like a kick in the pants. That's a big carb!

On the question of the single IDF, it's been done, and someone made manifolds for a while to do it. I think you'd do better with a progressive type carburetor but if you just like the look then the IDF or DCNF would be cool.

[toplessexpat]

I bet it's like a kick in the pants. That's a big carb!

Just got back from Cars and Coffee in Houston.... I'm simply smiling more than usual.... The second barrel is just beautiful!

[MrJD]

This is going to be a big post... and again, keep in mind my ignorance in terms of carb work. I'm just trying to learn from you guys

So you can run two 44 idf's... but a 38 single is considered at the top of the range. Is this a matter of air velocity and vacuum?

When I worked with ITB's on Toyota 4age's, the aim was to make the velocity stack, through the TB, and down the runners to the head into one big funnel.. this was to be constantly increasing the air velocity and prevent turbulent air flow.

4 44mm carb bodies (dual 44 idf's) would, in essence, perform this same function (increasing air velocity on the way to the head). one SINGLE 38mm would not be the same in terms of fluid dynamics... but that does not explain why a 34 or 36 is typically considered "better" by most. This has to boil down to people not understanding how to jet the carb efficiently. From my perspective, IDF's (on an individual basis) are pretty cheap compared to a 34 or 36. I am pretty sure I have seen really cheap 36 IDF's somewhere (having trouble now) so the thought on my end was: "get a cheap 36 idf, build an adapted manifold (this is not hard) and call it a day. BUT, I want dual 44 IDF's in a few years... so if I could buy a single 44IDF and use it for now...

But a 44 idf is MUCH larger than a 38. In the end, more air in should equal more air out. Bogging at low rpm and other random "big carb" issues should be more about the jetting than anything else... or the nature of the vacuum physically sucking the fuel into the engine. A "Big" carb has less vacuum and thus, more issues with pulling in fuel. A small carb = more vacuum, but less air in when at WOT. This is why i asked if IDF's deliver fuel in a different manner to ADF's and others... that wold explain why people are running BIG dual IDF's with success on these engines while many still have trouble running single 38/38's.

Somewhere in this is a healthy medium. I am simply searching for that.

[bradartigue]

38mm twin barrel progressive at WOT is delivering more A/F mix than a 44IDF at WOT. Potentially that is. Simply more opening for more air to get through, and more little holes drilled between the two barrels to let in more fuel. Either carb can deliver way more fuel than our little motors are going to want, which means that regardless of how you look at volume we seem to agree that volume really isn't the point.

Unfortunately with our engines getting to the point - or the valve in the case of fuel - is really the problem to begin with. You can't optimally position a carburetor to get there in the first place because the brake booster is the way of everything. Sidedrafts are actually pretty awesome on a TC if you ever get a chance to drive a Spider with them; the next best thing is take a run in a Euro-spec Alfa Spider (despite what the books say I never liked SPICA FI over DCOE Webers). Something about that instant blast a sidedraft gives...on a FIAT the next best thing is all you can have, twin IDFs or a downdraft progressive.

Which I'll then say you're just down to feel. With a highly tuned motor it would be hard to argue against the tunability and high speed delivery of the IDF. While (I think them to be) sluggish off the line, they've got tug for weeks and are dead-on precise with high speed throttle changes. Progressives just aren't that way, they deliver much nicer off the line but give up somewhere up there at the top and the throttle changes are just a little vague. Of course that's the point of a progressive carburetor, they're for driving around in traffic and for fuel economy, not for pedal down performance.

Three paragraphs in which I've said really nothing. You like IDFs or you don't is what it boils down to, and while I personally love them, I don't recommend them to anyone who doesn't like to fiddle. Because you're going to fiddle.

[toplessexpat]

It was verbose brad... but we've learned you're a fiddler!