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Discussion Starter #1
I have webers with a (double) Pipercross air filter. It looks like I have about 1 1/2" (40mm) clearance inside the filter
to install air horns. I have been reading about air horns and how they effect the performance of the engine.
Some say that they help in the higher RPM's and others say they help in the lower RPM's.
So my question is who is correct and is it worth the effort and cost to add them to a street car?
They look cool but in my case nobody will see them.
Anyone have experience?
 

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They can make the torque curve lumpy. Many Alfa motors benefit from a longer induction tract and horns help you with that but they also accentuate the rich dip in the AFR curve during reversion which results in a dip in the torque curve. I like to have a nice flat torque curve and the factory plenum and airbox is a good solution.
I have seen a dyno curve from Jim Steck of a 2L race motor that made 230 HP with no horns. It had the manifold/adapters lengthened by 2" and it had a modified AR plenum
 

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Discussion Starter #3
In this second case, manifold/adapters (lengthening the air track) were located after the Webers (as the wind blows) so I could see a different effect
on the air charge as it progressed through the intake area. i.e. the longer run takes place after the fuel is mixed with the air.
Neat approach but this would take, as you said, a custom plenum. Not going to happen in this case.
In the first case, I'm surprised that they have this kind of effect.
Anyone else with experience in this area?
 

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Take a look here...
1618470
 

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Discussion Starter #6
101/105guy: As noted in the OP this is a street car.

Gordon: looking at the info sheet, I think I am going to put my money into "Hog Futures" instead
of air horns.
 

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Things have changed with thinking about stacks with both flow bench and dyno testing as well as better cam designs. In days-of-old, longer stacks offered better low end torque because of cam design with older factory cams. With modern designs, the short, full radius stack offers the best overall performance.
 

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Discussion Starter #10 (Edited)
Those Pipercross ram pipes (at least the shape) agree with the info sheet Gordon showed above. Interestingly the the length has little effect on power gain. The the shape of the top of the horn does. So most of the really long pipes on those drag racers has to do with the level of testosterone in the car owners system not there to go faster. :sneaky:

If my Hog Futures work out, on the up side, I will look in to getting a set. ;)
 

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With whatever your application my be, TRUTH is delivered with both dyno and street or track testing, which is why I did not comment with the photo of the chart.
 

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The reason for longer intake runners is to increase the momentum of the air/fuel charge at the intake valve. This enables more of it to get into the combustion chamber as pressures start to become adverse.
The reason that long horns are a problem is that during reversion fuel/air is pushed back out of the carbs and is then sucked back into the carbs where it picks up more fuel and becomes over-rich. The horn allows more of this mixture to linger in the intake and thereby amplify the rich dip.
 
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