don't know the cfm, but they will be a restriction on a high HP build. The IR setup will make good torque, but there's no common plenum to "borrow" air from like a regular manifold, so what you get through each barrel is what that cylinder will get. I know the Hilborn 2 3/16" throttle bores flow 300 cfm or a bit less, and they are much bigger than a 48mm. But even if they flow 300 cfm per barrel (pretty sure they're less than that) most good big block heads flow well over that, hence the restriction.

Jody

 

Thanks Jody.My customer likes the look and does not plan to run the 460 over 5500 rpm.He thinks he remembers that the drla 2 barrel flowed 400 cfm total.If we desk top this combo for fun,would 200 cfm per cylinder be in the ball park???He has rectangular iron ports.With the IR setup will he have a strong booster signal?The cam is an xe284h-10.240/246 @.050.:beers:

 

I would think they'll support 400-450 hp pretty easy. You'll need "roughly" 250 cfm per barrel (500 each carb) to support 500 hp or so. The IR has great low AND mid-range torque, and great throttle response when correctly tuned. Plus they look awesome.

I was just warning about the HP limits with that setup, especially on a big block. A lot of people see 2000 cfm total for example and think it's plenty big, but fail to realize that it's only 250 cfm per cylinder, no common plenum. With some nice 350-375 cfm heads you can see what happens.

Get the real cfm and you can make a good estimate as to how much power they'll support.

Jody

 

What people have to remember when comparing carb and head flow is the pressure drops. Most carbs are flowed at 1.5"Hg where as heads are often measured with a 28" H2O pressure drop, which is about 2" Hg I believe. So heads that appear to flow better than a carb may not.
I think the 48mm webers flow about 300cfm per barrel, and the dellortos a bit less, cos they're based on a 45mm unit

 

May be, but I doubt they flow 300 cfm. The 2 3/16" Hilborn butterflies are less than 300 cfm each, and I do not believe a 45 or 48mm is 2.187" barrels.

Jody

 

The 48mm =1.89 inches.I am searching the euro crowd to find the flow but still do not no if this designation is butterfly or venturi size.If and when I find out I will post it in case others run into this.Thanks folks for the interest in helping out.

 

The carb may be "48" mm, but the venturi is smaller, you need to know the venturi size, since that is the real restriction. Weber 48 IDA carbs have an optional maximum "choke" size of 45mm, 42mm or 38mm is how they come configured from Weber.
According to David Vizard, each barrel of a 48IDA flows 330 cfm. He doesn't state the choke size that figure is based on, or the pressure drop used.

There are people that can bore them out to 51 bore size for a little gain.
David

 

The carb may be "48" mm, but the venturi is smaller, you need to know the venturi size, since that is the real restriction. Weber 48 IDA carbs have an optional maximum "choke" size of 45mm, 42mm or 38mm is how they come configured from Weber.
According to David Vizard, each barrel of a 48IDA flows 330 cfm. He doesn't state the choke size that figure is based on, or the pressure drop used.

There are people that can bore them out to 51 bore size for a little gain.
David

Thanks Dave.That is what i figured.If the drla48 flows 660 cfm I would think it is tested at 3.0 hg instead of 1.5hg.The euro boys right now are all into fuel injection but I am awaiting a reply from an old school carb guy abroad.You wouldn't just have Vizards e address in front of you would you?lol.:beers:

 

Nope, but you might search the web for his address, he used to have a web site.
The Book I found it in is Vizard's "How to Build Horsepower, vol 1", but it doesn't have any more details.

I have 48 IDA's on my Lola T-70 with 350 engine, it makes around 550 hp I'm guessing. I keep up pretty well with the other guys but I'm sure I'm giving up some top end horsepower. I heard a guy with a 600 hp engine swapped to Injection from 48 IDA's that were bored out to 51mm, and gained 60 hp!

But if you are below 550 hp and don't rev real high, the carbs will probably work out fine. I've been thinking of how I could make a plenum between the carbs and manifold that would increase the flow by allowing sharing of pulses between the carbs. I wouldn't want to decrease the torque though.
David

 

I've been thinking of how I could make a plenum between the carbs and manifold that would increase the flow by allowing sharing of pulses between the carbs. I wouldn't want to decrease the torque though.
David

David,

Save your time. I had the 2 3/16" Hilborn setup on a 406 and since they were a bit small we cnc'd small spacers for each pair of barrels to "borrow" some cfm. We lost a ton of power, like 60-70 rwhp if I remember. Did not see why it was so drastic, but figured it was relevant to what you were thinking of doing.

Jody

 

Probably b/c of no more than screwing up the natural flow each stack or whatever made....

pdq67

 

Jody,
Thanks for the input, your results are what I was afraid of seeing. It probably screwed up the ram tuning.
David

 

From across the pond.200 cfm per barrel with the drla 48.Thank gosh my customer is into show and no go.His rectangular ports will flow 320 cfm but are choked off by the restriction.The good news is that the 460 makes 532ft/lbs@3500 and holds it to 5000rpm.Peak is 547 at 4000rpm.The HP# is 468@5000 rpm.Throttle responce should be good and be a nice streetable package.These are just desktop dyno numbers but appear to mimick real world combos.fwiw-A 950hp and a single plane picks up 50hp and 20 ft/lbs.The IR look is sweet though.I vote he wins overall.Big torque and looks to go with it.

 

Investigate the largest choke sizes you can install. I assume the chokes are replaceable? You can allways bore out the present chokes if they are removeable.

 

Choke size is 40 mm factory on a 48 drla choke size on a 48 ida is 37mm factory. seems i researched this a few years ago comparing bore sizes to holly 2bbl.(2100 series) and i recall that a 40mm dellorto with 32mm chokes was approxamate size to the 500cfm holly. i own a pair of 48 dells as well as a pair of 40 dells and believe me when i say that the 48 are huge but there to small to feed a 140 cid 2275vw much past 6800rpm in a 1 bbl per cylinder application. using just one carb on the engine makes it too big a carb for motor. seems the vacuum draw from one barrel is rather low compared to say a plenum where all cylinders draw from. dont be mislead by the cfm figures of the carb until all you factors are know like how the carb was measured. most 4bbl are measured at 1.5 iinc while 2bb are measured at 3.0inch. big vw racers with 3.0 plus litre engines are running gene berg 62mm carbs which fit 48ida manifolds(hint hint) id suggest looking to the vw world guys for more info as well as weber..good company's for info are cbperformance and gene berg enterprise...the response of multi carb engines is amazing smooth power from idle to redline ,improved mid rang torque sweet stock like idle with cams up to 300 deg advertised,awsome fuel economy only rivaled by injection.weber/dellorto are way more tunable then a holly or carter/edelbrock(also note easier to mess up tuning too!) only draw back really is lack of vacuum for brakes and top end power like that of a centermount 4bbl system! just my $.02