Drivefast, what vent's are you running? I've got an IDA laying around the shop and I have 36,40,42mm vent's to go with it. I can crank up the flowbench and give you some numbers.

Yeah Brad, you're right on with the manifold. I could have sworn mine's a RB manifold, but it's definitely not. I've just started running lean lately using the stock return restrictor for the Hitachi (no real regulator). What regulator and pressure are you running?

I own 38mm and 40mm venturi's. Been using the 38mm's more often, the low end throttle response is much better.

I use a holley regulator with a return line, and 2.75psi measured after the regulator and fuel filter, using a respeed gauge.

it would be really cool to see some numbers with all the venturi's!

I've read some really impressive numbers. The carb was designed to origionally work with 36mm venturis and supposedly flows 450cfm with them in it. The larger you go the more it flows. I run 43mm venturies in my car. Now i read 450cfm on a few VW sites. I'm sure if you were to call someplace like Gene Berg or JayCee they would already have the answers for you.

Got a question, where are you all getting your air filter elements and the top and bottom for the weber? Are you getting the Racing Beat ones or something else? I see them cheaper other places but wasn't sure they'd fit.

I got the bottom filter plate from a local VW shop for five bucks.

Cut and adapted a 1st gen stocker air cannister to fit said lower plate. And use a K&N stocker size air filter drop shipped from K&N in Riverside, CA (cheapest price).

*Everything* Weber IDA related is cheaper at VW shops than at Racing Beat.

OK, as I was leaving the shop I remembered this thread and I clamped my IDA to my flowbench using the fixture I made for testing exhaust ports.

The carb has 42mm vents in it for the first quick test. I have to dig up the other vents over the holiday and I'm going to double check these numbers and make sure I don't have any leaks or other issues with the bench(Superflow 110/120).

With the 42's I get a corrected CFM on one barrel with velocity stack of 311cfm@28". So that would end up at 622cfm@28" depression. So, the 48IDA w42mm vents should be capable of feeding 372hp on gasoline.

This was a quick and dirty test, when I get the other vents I'll sit down and do a whole run cover all the variables like velocity stacks etc.

Other info so you guys can compare apples to apples. Carb test depressions don't really have a standard but in general 20" is used in automotive applications. To get the numbers at 20" from numbers at 28" you multiply by .845

That would give our 48IDA a cfm number of 526@20".

I would say that number would be better for a HP estimate at 314. I never really use that formula so it goes to show you that unless you know the test pressure the cfm number doesn't mean much.

I actually had to test at 7" depression on the carb and its easy to double what you get for 28" values.

Wow impressive, please keep sharing with us all that info :)

awesom thanks for the test results! So wtf is the point of going to a 51 IDA and %% gene berg if the 48 IDA can flow enough to make more HP than most PP's are making.

Just premix, you big bunch of pussies.:lol::lol::lol:

I've found a few different formulas to figure out theoretical maximum HP from CFM numbers through the carb alone. They all end up being optimistic but it gives you an idea of what is possible. The rest of the intake tract really comes into play to cut the final number.

Carbs are rated at different levels of vacuum. Four barrels are rated at 1.5"Hg,(20.33" H2O) and two barrels are rated at 3"Hg(40.67" H20). The biggest reason for the difference in rating pressures was because the most flow benches couldn't pull a 3" depression through a 4 barrel when they first came on the scene.

Given that a race engine is usally carbed to pull less than 1" of H20 at full throttle, top rpm, is that 800cfm carb really flowing 800cfm? Nope. What you end up trying to balance is fuel atomization(need that vacuum to pull fuel) and choking the engine too much. Over carb and you'll make good top end power with shitty midrange and no bottom end. Under carb and it will be very responsive down low and midrange but it will run out of breath on the top side.

And that is why I hate carbs! If I have the choice I give them the floatation test. I take them to the nearest large body of water and throw them as far as I can. If it floats, its a good carb.

OK, OK.... Webers are kind of fun...