How much air do you think IDAs rob from the cooling fan..... ?

[Jim Ratto]

Do you think a street motor, same CR, same cc, same cam, same cooling setup, same exhaust, same car, same R&P and gears.... BUT one setup runs 44IDFs and one setup runs 48IDAs.... which will run cooler? Is it the IDF motor, thinking they will gulp less air than IDAs, allowing fan to pull more? Or does the cool crown go to IDA motor for better VE?

I really don't know....  your thoughts?

[Sam K]

That's an excellent question. If I remember correctly, IDA's with big venturi's pull around 12 to 1300 cfm's and I would assume that IDF's pull a lot less. I suppose it depend on how much air was avaiable i.e. if you had a vented decklid or standoffs and things like that. I'd be interested in doign some testing if we could find out how to do it.

[Jim Ratto]

That's an excellent question. If I remember correctly, IDA's with big venturi's pull around 12 to 1300 cfm's and I would assume that IDF's pull a lot less. I suppose it depend on how much air was avaiable i.e. if you had a vented decklid or standoffs and things like that. I'd be interested in doign some testing if we could find out how to do it.

what about a controlled environment... i.e. dyno room. 

[Fastbrit]

IDAs every time! Everyone knows IDAs are cooler than IDFs!

[Jim Ratto]

That's an excellent question. If I remember correctly, IDA's with big venturi's pull around 12 to 1300 cfm's and I would assume that IDF's pull a lot less. I suppose it depend on how much air was avaiable i.e. if you had a vented decklid or standoffs and things like that. I'd be interested in doign some testing if we could find out how to do it.

thinking about it, those CFM #'s /\   that would be peak torque and full throttle to pull those #'s....and really, how many guys, John Rayburn excluded,  , drive around under those conditions anyway? I bet 90% of the time the carbs are pulling 15-20% of their CFM potential.... think about how often you're driving full throttle sustained.... again John, never mind you.  

[John Rayburn]

 

[Tony M]

I dont think that you could pull that much air from the cooling system with any carb. Maybe with a blower ? Cooling fan drafts so much air as it is. Allway pulling it in.

[Jim Ratto]

I dont think that you could pull that much air from the cooling system with any carb. Maybe with a blower ? Cooling fan drafts so much air as it is. Allway pulling it in.

OK how much air do you think the FAN is robbing from the CARBS?  There is only so much air volume in that goddam little compartment for everybody to get... somebody's gonna get F*'d  at some point (Jerry impersonation)

[Tony M]

YOUR NOT GOING TO LIKE WHAT I HAVE TO SAY - ( in Jerrys voice) What would tell us that - chassie dyno with decl lid on and off doing the same pull ? As said befor Great question - Maybe time for someone to try this out ? Is it possible to pull all the air from the engine compartment via the fan and large carbs ?

[Jim Ratto]

I wonder what effects of power pulley and/or 36hp fan would be (less blades).

[Hotrodvw]

I figure the cooling system was designed a peticular way, as was the intake vents below the rear window.  You're only going to get "X" amout of CFM through those vents.  Adding to the demand of consumption would lead me to belive that either the cooling system, or the carbs will suffer air flow.  It boils down to which draws harder.  My answer is YES........more air flow would be required at WOT. 

[ian c]

but as the revs rise the fanbelt slips , helping the idas get more of the air

it seems the german designers wanted idas to be fitted , and wot to be used wherever possible

[Jon]

Four air horns and a crude squirrel fan can create vacuum in a compartment vented by 18 huge louvers... I don't buy it.

[Jim Ratto]

One of us should fit an home brewed manometer into the engine comp and see what happens at different rpms....  I think we have some 4mm plastic tubing around here....

[Speed-Randy]

in case you have forgotten, there are 30 someodd vents directly above the decklid, so since it is NOT a sealed system there is an infinit amount of air for both carbs and fan. so the answer to your question is absolutly 0%

[EL PINGO 66]

IDAS RULES........

[j-f]

Why would IDA's gulp more air than IDF's on the same engine?
Engine will need the same amount of air and gas to run the same way, no?

[Peter]

thats what i say as well J-F

[Jon]

Why would IDA's gulp more air than IDF's on the same engine?
Engine will need the same amount of air and gas to run the same way, no?

That's true unless the IDF are strangling the engine...

[Jim Ratto]

Why would IDA's gulp more air than IDF's on the same engine?
Engine will need the same amount of air and gas to run the same way, no?

That's true unless the IDF are strangling the engine...

[Jim Ratto]

in case you have forgotten, there are 30 someodd vents directly above the decklid, so since it is NOT a sealed system there is an infinit amount of air for both carbs and fan. so the answer to your question is absolutly 0%

I wonder why, then, in 1971 when VW went to the wider fan, they added two rows of air vents to the decklid, in addition to the vent below the rear window. Also, I look at the Porsche 356, a 1600cc dual carburetor (either 32mm or 40mm 4 bbl) with same fan as 1500cc VW engine (yet driven at a slower speed = less fan rpm at any crank rpm than Beetle with stock pulley).... why did Porsche cut such a big hole in decklid then?

[John Rayburn]

When I added my convertable decklid, my oil temp dropped almost ten degrees.

[Speed-Randy]

they only thing that changes is the velocity of the air as it travels through the vents, you add more vents the slower the air moves, less friction, equals cooler air. its basic heating and ac duct theory. add the sq. in of the 4 barrels and the fan intake and it is still way less than the sq. in. of the vents above the decklid, add a vert lid and you increse the intake even more. if the carbs were pulling as much air as you guys are thinking they do it would strip the paint on the vents and whistle like an nba ref in the last 2 minutes of the game. just put your hand by the pushrod tubes and rev the motor and you will see that its not a huge gust of wind and that is what is being pulled through the vents. the put your hand by exhaust tip and feel that. if you want an exact number you can call an a/c air balance guy and  put a cfm hood over each and showexactly how much air is moving.

[Speed-Randy]

and you're right, 48 ida's kick ass