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Using a velocity stack on your intake pipe will definitely be worth some extra HP. Fluids simply don't like flowing around sharp corners, and a blunt-cut intake pipe has a sharp corner all the way around it. A large % of the airflow into any tube happens from around the periphery of the tube, not from directly over the end. That's the reason a smoothly radiused entry into the tube enhances airflow.
So by reducing the turbulence around the tube's periphery you're effectively making the tube larger without actually increasing its diameter. Using a 4" intake pipe on a 2 liter engine is unnecessary unless its spinning at 12,000+ RPM.
 

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Using a velocity stack on your intake pipe will definitely be worth some extra HP. Fluids simply don't like flowing around sharp corners, and a blunt-cut intake pipe has a sharp corner all the way around it. A large % of the airflow into any tube happens from around the periphery of the tube, not from directly over the end. That's the reason a smoothly radiused entry into the tube enhances airflow.
So by reducing the turbulence around the tube's periphery you're effectively making the tube larger without actually increasing its diameter. Using a 4" intake pipe on a 2 liter engine is unnecessary unless its spinning at 12,000+ RPM.
So what is your take on the square opening intake boxes for these ITB cars?

Seems to me since it slows the air it creates a "ram" air effect.. Could we get this effect using a plenum style intake?
 

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Square or rectangular shapes are easy to fabricate, that's the reason you see them so much on low level cars. They're never the best way to duct the air, or any fluid for that matter. Round is the best shape, and if round is out of the question then oval comes next if you're talking about an airbox entry straight on into something flat like a bumper cap or air dam. With a generous radius all around the periphery of the hole the air's flowing into
Now if you're talking about airflow through a high pressure roughly horizontal surface that's traveling into the wind, like the forward part of the hood of a car, then a NACA duct is the best method of getting the air to flow through that surface.
Having a set of velocity stacks sticking up through the hood is just pissing good HP into the gutter.
If everything's completely sealed so you've created a pressure chamber then you can get roughly 1/2 psi of boost at 100 MPH from the ram air effect. If there are any leaks you'll get nothing.
Increasing the overall air density using cooling is generally much more effective, especially if the ambient air is hot to begin with.
Using both is even better.
 

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Using a velocity stack on your intake pipe will definitely be worth some extra HP. Fluids simply don't like flowing around sharp corners, and a blunt-cut intake pipe has a sharp corner all the way around it. A large % of the airflow into any tube happens from around the periphery of the tube, not from directly over the end. That's the reason a smoothly radiused entry into the tube enhances airflow.
So by reducing the turbulence around the tube's periphery you're effectively making the tube larger without actually increasing its diameter. Using a 4" intake pipe on a 2 liter engine is unnecessary unless its spinning at 12,000+ RPM.
I wanted 3.5" my fab guy went ahead nd made it 4"....going to add a v-stack to it, hope to gain a few ponies.
 

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Square or rectangular shapes are easy to fabricate, that's the reason you see them so much on low level cars. They're never the best way to duct the air, or any fluid for that matter. Round is the best shape, and if round is out of the question then oval comes next if you're talking about an airbox entry straight on into something flat like a bumper cap or air dam. With a generous radius all around the periphery of the hole the air's flowing into
Now if you're talking about airflow through a high pressure roughly horizontal surface that's traveling into the wind, like the forward part of the hood of a car, then a NACA duct is the best method of getting the air to flow through that surface.
Having a set of velocity stacks sticking up through the hood is just pissing good HP into the gutter.
If everything's completely sealed so you've created a pressure chamber then you can get roughly 1/2 psi of boost at 100 MPH from the ram air effect. If there are any leaks you'll get nothing.
Increasing the overall air density using cooling is generally much more effective, especially if the ambient air is hot to begin with.
Using both is even better.
wish i had the skills to tig together a nice oval air duct like the DSS car but like you said the ease of fabrication I did a square box. still seemed to work quite well with the few runs i got in gauging my back half vs a lighter more powerful car(dyno). 105/131 vs 103.8/132.5 in mine.
 

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my 300hp setup gained a few hp everywhere on the dyno going to a 4 inch pipe and vstak. picked up big time at the track just a week apart. we couldnt really believe it. gained 2 tenths and 2 mph and i was consistent all day. hard to say because of weather variables but it was super hot and humid couldnt have been any worse. never ran the slower times i had with the 3 inch setup ever again.
 

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Dyno lol I was waiting to see what his results were after all the back and forth .
Thanks to member @katman K20a.org has all the information you need. This was the best back to back overall thing I ever saw, thanks to katman, how challenged all the effort collecting the IM and to dyno them and published them for us. Massive THANKS to katman 🆙!

Here you go: Skunk2 K-series Manifold Test Fit
 

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Thanks to member @katman K20a.org has all the information you need. This was the best back to back overall thing I ever saw, thanks to katman, how challenged all the effort collecting the IM and to dyno them and published them for us. Massive THANKS to katman 🆙!

Here you go: Skunk2 K-series Manifold Test Fit
In your experience Is the rrc manifold really THAT good compared with other off the shelf options?
 

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Arouse the DAMPFHAMMER!
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In your experience Is the rrc manifold really THAT good compared with other off the shelf options?
Good question Bjorn. It depends on the engine setup and displacement, the head, the port match and so on. I saw examples where the RBC cam out better, I saw examples where the RRC came out better. What I saw also was the RSP was always in between both. The long runner setup makes a great mid range torque curve and still overs enough support till redline. The tuner (Erik), who done the tune on the K-series IM shootout, maybe challenged the tune of the RRC most. Tuners are no machines: feelings, favorites, passion for something makes it challenging to be fair on all parts in an equal way. We are talking about some ponies back and forward, I wouldn't take that to hammered in stone, but as a result for that specific engine, dyno roll and tuner.
 
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