Critique this Intake Manifold - Page 3 - Miata Turbo Forum - Boost cars, acquire cats.

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Old 11-25-2009, 11:47 PM   #41
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interesting
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Old 11-25-2009, 11:47 PM   #42
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the point of a velocity stack is to speed up the air entering it. you want the air to flow around it to pick up speed. that why they are designed to not have a constant radius entry
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Old 11-25-2009, 11:51 PM   #43
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i would think that if it was for a turbo application, flaws in design would be hid a little due to the forced air, but it would be crucial to a NA engine to have a proper plenum design to supply equal air to all cyl. that is why most NA cars tend not to use a plenum on ITB setus
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Old 11-25-2009, 11:54 PM   #44
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Okay, so as long as the plenum is large enough to supply an adequate volume of air, the velocity stack increases air speed kind of like the top of an airplane wing (ie, longer surface to flow over)?

I know I'm reaching here but this is a philosophy major trying to understand this.
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Old 11-26-2009, 12:01 AM   #45
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im not physics major but i think your on the right track. i took alot of ideas from the honda guys when i built my mani, honda-tech has an awsome fabrication form and you can learn alot from those guys. also i had the handbook from our superflow flowbench too, there is alot of good info on airflow in there, thats how i was able to calculate my runner lengths
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Old 11-26-2009, 12:09 AM   #46
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Quote:
Originally Posted by MartinezA92 View Post
Shorter and wider, or just shorter? As far as I know, and I may be wrong, longer smaller runners increase velocity for low end power at the expense of overall flow and wider, shorter runners would increase flow at the top end. Making them just shorter seems like it wouldn't do anything.
He only said shorter. I'm a bureaucrat though, not an engineer.
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Old 11-26-2009, 12:10 AM   #47
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wait wtf?

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Old 11-26-2009, 12:17 AM   #48
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tapering the runners makes the engine think that the runner are longer. some taper is good for runners. the problem is to buy them its very expensive. like $100 per runner. and so make them..... with the correct taper...... to the correct port shape.... to the correct length, is a major pain in the ***.
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Old 11-26-2009, 12:25 AM   #49
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Old 11-26-2009, 12:43 AM   #50
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pretty good find, it confirmed my length was right atleast. to merge the runner to the port shape, i used cylinder head epoxy from ramracing. so my runners have some tapper to them.
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Old 11-26-2009, 12:55 AM   #51
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I would put the stacks angled forwards and have the intake around 35-40 degrees from the front. I think this would provide the most air everywhere more efficient than having all the air rammed into the back of the plenum and then it starts to fill. imo
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Old 11-26-2009, 12:59 AM   #52
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Quote:
Originally Posted by Bassmachine View Post
I would put the stacks angled forwards and have the intake around 35-40 degrees from the front. I think this would provide the most air everywhere more efficient than having all the air rammed into the back of the plenum and then it starts to fill. imo
right that was my thinking behind using exhaust manifold style piping
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Old 11-26-2009, 01:20 AM   #53
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It is a shame I'm not at all motivated to compare mine to a stock manifold.



Plate being cut on a large table cnc... designed to do decorate wood door/panel work


I can say one thing. If the air isn't going in evenly with mine... I haven't blown up in the last two seasons due to some random lean condition. Sadly the only dyno plot I have is with a damaged turbine wheel and a borrowed ignition map... and simple fuel tune.

And thats about all the tech I have. Runner length was gathered a few years ago from a few different sources... the details of which I've forgotten. But I think 5-6" was the spot we aimed for. Short for high rpm power.... longer for low/mid.... so i sat in the middle.
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Old 11-26-2009, 02:35 AM   #54
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I'm not an expert on this stuff but I just read about it on the net for an hour. My research finds:

Yes, you will have no ram air bonus with those runners unless you rev like a sport bike. When tuning your runners you need to keep in mind that you are supposed to measure from the intake valve inlet to the (intake not engine end) runner radius. This gives you what looks like 6 inches which gives you a ram tuning effect somewhere around 14,000 RPM. The ram air effect is not negligible but as has been mentioned earlier in the thread, since you are boosted, runner tuning is not critical.

As previously stated, fixed runner length only tunes for a specific RPM (and it's harmonics). Mazda and other OEMs actually are pretty cool with their variable intake length manifolds. For super coolness though, check out this patent:

Continuously variable intake manifold - Patent 5687684

It's for a continuously variable length intake manifold.

To tune your runners you or your IM manufacturer could experiment with lengthening/shortening the runners on the dyno. I guess they could rig up a manifold with bolt-on runners.

Blah blah blah though. When boosted, plenum size is apparently much more important. I can't find any formulas on plenum sizing other than 1.5 * total runner volume. If your runner radius is 1" and length is 6" then according to that formula you need 108 cubic inches of plenum. That's 1.78 liters.

Throttle body also is important. Edelbrock says large plenums should have small throttle bodies and small plenums should have large throttle bodies. This kind of makes sense to me. I can't find much data about this on the net though. A real book will have to be read.

And also what those guys said ^^^ about transition between plenum and runner is important as well.

-----


If I were your situation, and I hope to be soon (if I can find a good intake mani to buy ), I'd do this. Save your current map. Put new mani on, retune your maps ASAPPPP (hopefully just injector scaling will get you to your AFR targets), dyno, save map. Take new mani off and put factory mani on, load original map, dyno and see how they compare. Not many people do back to backs like this and this is the only way to know if your part swaps are really making a difference.

Last edited by Faeflora; 11-26-2009 at 11:42 AM.
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Old 11-26-2009, 02:43 AM   #55
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It's also been mentioned before in other threads that air velocity and pressure will affect the performance of the manifold. Splittime or you might see very different results at different psi levels. I think that at high boost the plenum size becomes much more important. Apparently these plenums are a big deal in megapower Supra land.


Onnnneee other thing to mention-- if you look at rally engine bays like this:



You'll see bigass manis to compensate for the tiny pee hole sized restrictor plate.

Hustler seems to have lots of pics of hot engine bays-- maybe him or someone else can post some pics of "pro" turboed engine bays so we can take a look at the manifolds.
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Old 11-26-2009, 03:07 AM   #56
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Quote:
Originally Posted by Splitime View Post
It is a shame I'm not at all motivated to compare mine to a stock manifold.



I can say one thing. If the air isn't going in evenly with mine... I haven't blown up in the last two seasons due to some random lean condition. Sadly the only dyno plot I have is with a damaged turbine wheel and a borrowed ignition map... and simple fuel tune.

And thats about all the tech I have. Runner length was gathered a few years ago from a few different sources... the details of which I've forgotten. But I think 5-6" was the spot we aimed for. Short for high rpm power.... longer for low/mid.... so i sat in the middle.
That looks GREAT to me. #1 starvation issue seems to be fixed or helped with that tb positioning
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Old 11-26-2009, 04:32 AM   #57
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Quote:
Originally Posted by faeflora View Post
Blah blah blah though. When boosted, plenum size is apparently much more important. I can't find any formulas on plenum sizing other than 1.5 * total runner volume. If your runner radius is 1" and length is 6" then according to that formula you need 108 cubic inches of plenum. That's 1.78 liters.
its not as much as it sounds like.
also i got 113ci not 108

pi x R^2

3.14159 * 1 * 1

3.14159 * 6

18.84955 * 4

75.39822 * 1.5

113.09734 needed

113.09734 + area taken up by the runners = 3.14159 x r^2 x L

for the example lets make the runners flush.

36 = L x r ^ 2

L and R can be anything that adds up to 36

for example 10" long and 1.897366 radius.

1.897366 * 1.897366 * 3.14159 * 10 = 113...
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Old 11-26-2009, 09:19 AM   #58
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from what i read the plenum volume should be 1.5 - 2 times the displacment of the engine, not the runners.
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Old 11-26-2009, 09:47 AM   #59
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Quote:
Originally Posted by hustler View Post
An Evo tuner who said "******" ever 3-words told me that a huge chamber with long runners and 360* horns that portrude deep into the plenum will make the most torque...and to shorten them to add horsepower.
Marco?
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Old 11-26-2009, 11:42 AM   #60
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Quote:
Originally Posted by ctdrftna View Post
from what i read the plenum volume should be 1.5 - 2 times the displacment of the engine, not the runners.
I read the following also:

70% of the displacement
1.5 * total runner volume

This guessing sucks. I want to know how OEMs and pro race teams size their turbo plenums. It probably takes a lot more math than we are using.

I suppose that a lot of aftermarket people leave power on the table or are peak torquing where they don't want to be. Probably their airflow to all runners may not be best as well. But, I think boost may conquer all.
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