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Old 01-16-2013, 03:14 PM   #1
E85head
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Intake, plenum/runner design

As more and more options become available, designs change. Anyone care to explain some theory regarding why plenum and runner design/shape/size vary to the almost unrecognizeable? Here are some of the designs.

At first look i would believe FSR, HPF or Saad to be a simple and good design...





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Old 01-16-2013, 03:22 PM   #2
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You could write a book answering those questions, lol. Just intake trumpet shape by itself is worth a couple page article.
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Old 01-16-2013, 03:42 PM   #3
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You could write a book answering those questions, lol. Just intake trumpet shape by itself is worth a couple page article.
I have no doubt but general theory, not at a detailed level would be much appreciated. Why would one for example use trumpet design for runners, while others just make a radiused entry from the plenum?
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Old 01-16-2013, 04:49 PM   #4
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I have no doubt but general theory, not at a detailed level would be much appreciated. Why would one for example use trumpet design for runners, while others just make a radiused entry from the plenum?
Well, when it comes to intake and exhaust manifolds, it's all details, and it's a lot of them.

Why would someone use trumpets versus a radiused entry? My guess why they do that is because air comes from not just in front of an opening to an intake runner, but also from the sides and behind the opening. Having a trumpet protruding beyond a wall of the plenum would also avoid possible unexpected or turbulent flow problems from air running into and along the wall. For a welded aluminum intake, it also usually means less welding.

Here is a good article on intake trumpets, but it covers the shape more so than the protruding or flush: http://www.profblairandassociates.co...mouth_Sept.pdf
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Old 01-16-2013, 05:25 PM   #5
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whoa.. more details on the DOC mani. anyone know the length on those stacks?
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Old 01-16-2013, 05:33 PM   #6
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whoa.. more details on the DOC mani. anyone know the length on those stacks?
How would that dimension affect anybody?
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Old 01-16-2013, 08:36 PM   #7
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torque. i got a phone book u can borrow.
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Old 01-16-2013, 08:50 PM   #8
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torque. i got a phone book u can borrow.
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Old 01-17-2013, 12:40 AM   #9
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torque. i got a phone book u can borrow.


Again, since you're avoiding the actual question, how would that dimension affect anybody, even yourself? Do you even know the stock intake runner length on an S54 for comparison?
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Old 01-17-2013, 03:33 AM   #10
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Well, when it comes to intake and exhaust manifolds, it's all details, and it's a lot of them.

Why would someone use trumpets versus a radiused entry? My guess why they do that is because air comes from not just in front of an opening to an intake runner, but also from the sides and behind the opening. Having a trumpet protruding beyond a wall of the plenum would also avoid possible unexpected or turbulent flow problems from air running into and along the wall. For a welded aluminum intake, it also usually means less welding.

Here is a good article on intake trumpets, but it covers the shape more so than the protruding or flush: http://www.profblairandassociates.co...mouth_Sept.pdf
Thanks! Do you see any drawbacks using trumpets vs radiused entry for boosted applications? Or do you believe that it will provide better performance?
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Old 01-17-2013, 04:21 AM   #11
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Thanks! Do you see any drawbacks using trumpets vs radiused entry for boosted applications? Or do you believe that it will provide better performance?
I think there are no drawbacks other than cost, space, and complexity. Performance wise I see a benefit, but it will be very small.
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Old 01-17-2013, 06:43 AM   #12
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I think there are no drawbacks other than cost, space, and complexity. Performance wise I see a benefit, but it will be very small.
Until testing and data. We can only assume this will be the results...
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Old 01-17-2013, 06:57 AM   #13
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For whatever reason, people seem to stop thinking of an engine as an air pump when using FI. In reality, gains in efficiency are multiplied when using FI.

When I look at the manifold designs of say the the new "world motorsport engine" that the FIA wants to use in everything from WTCC to WRC....I see highly evolved runner and plenum designs that one could easily assume were for a N/A engine...but in reality they are a fairly decent pressure ratio FI engine.

Regarding the use of trumpets versus radius'd runners, I think it really comes down to packaging more than anything else. The narrower, or smaller the engine package, the more center'd it can be positioned within the chassis. This can have a more substantial performance gain than having an extra 1% power available. On our I6 BMW engines...we see total runner lengths designed on the 3rd harmonic...which is roughly 14-20" runner length CLA from the valve. You could run a 2nd order manifold...but you'd lose torque under 5000 RPM...not really great for a street car. Adding a trumpet inside the plenum allows the air box to be pushed inwards towards the head (as you see in the S54) If you measure the distance from the cylinder head to the shock tower...you'll see we are kind of stuck within a certain set of parameters.....
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