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Air volume for dual 40s


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I have a fresh motor, total new build.  292 cam, 9:5 pistons.  I have dual 40s...new and properly jetted. Here is my question....how many CFM of air do they need under load at say 5000 RPM.  Reason?  I have a nice Alpina A3 air box with a cold air intake.  Car runs great when it is off.  When it is on I get air restriction (rpms jump up some) and rich running.  Take the air system off and stick the ITG ion and it runs great.

I think I may have too small of a filter on this A#3 setup.  

 

I have Jenvey Heritage DCOE style EFI going on next month and would like to use the A3 air system ...so I need to buy a bigger element and see how it does.

Knowing what size I need would help.  I can extend the filter down into the front so I have more space if needed.  Any info would really help

 

Pic 1 is the A3 setup...you can see the filter element  Pic 2 is with the ITG setup and it has no air starve issue with the ITG

dual 2.jpg

IMG_2213.jpg

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Thanks....that is kind of what I suspected.  I plan to run the ITG for regular use and slap on the Alpina A3 for stuff like MidAmerica show etx.   I have a lot of room up from   But no need to go too large.   That’s why I was curious as to the CFMs I need for this setup 

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What Andrej said.

 

With an intake, and throttle bodies, you want the largest filter possible for the least resistance, and a large volume of still-air to pull from. 

 

The Alpina box should breathe just fine, and should have a large filter element inside of it. You just need to run the hose to fresh air. Don't bother with cone filters, that one ya got looks like it's off the rice shelf at VatoZone. 

 

 

 

 

Edited by 2002Scoob
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Assuming a 2.0 Liter at 6500 RPM, with a Volumetric Efficiency of .85  for a street motor.

 

2.0 Liter = 122 cu in

 

Formula:

{[Displacement (cu in) * Peak RPM] / 3456} * Volumetric Efficiency = Needed CFM

 

~200 CFM

Edited by visionaut
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9 minutes ago, 2002Scoob said:

What Andrej said.

 

With an intake, and throttle bodies, you want the largest filter possible for the least resistance, and a large volume of still-air to pull from. 

 

The Alpina box should breathe just fine, and should have a large filter element inside of it. You just need to run the hose to fresh air. Don't bother with cone filters, that one ya got looks like it's off the rice shelf at VatoZone. 

 

 

 

 

The A3 uses external filter.  The A4 used a filter inside the box   Post below says around 200 CFM which is my issue.  This tiny filter moves like 125cfm lol. 

Time to get a bigger one!

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4 minutes ago, visionaut said:

Assuming a 2.0 Liter at 6500 RPM, with a Volumetric Efficiency of .85  for a street motor.

 

2.0 Liter = 122 cu in

 

Formula:

{[Displacement (cu in) * Peak RPM] / 3456} * Volumetric Efficiency = Needed CFM

 

~200 CFM

Tom,

You are being too academic.  Car linguists won't understand.  They only speak in terms of some volume of flow at some magical pressure drop (that nobody seems to know what it is) thru an element of interest

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1 hour ago, nbristow01 said:

The A3 uses external filter.  The A4 used a filter inside the box   Post below says around 200 CFM which is my issue.  This tiny filter moves like 125cfm lol. 

Time to get a bigger one!

 

You're right indeed :) I stand corrected! 

Edited by 2002Scoob
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45 minutes ago, uai said:

in comparison tio the standard ti Airbox with dual "alpina" filters on a 165 hp engine

We plan to dyno tune the car so we will be able to see what it does.   Lots of Changes in filter technology since the 70s.   If it is too restrictive ima hang it in the man cave lol 

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