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Old 02-16-2016, 02:09 AM   #1
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Default Would port matching my Skunk2 to FlatTop lose power?

Is there any way port matching my flat top intake manifold to the Skunk2 tb would lose power?

I seemed to lose a significant amount of power just bolting on the Skunk2 (10whp on virtual dyno, but 25* ambient air temp difference) and I'm thinking this is because it is not port matched.

There is a step, currently, that might be causing turbulence... I have no idea.

However, I don't want to make the situation worse (and ruin an expensive flattop) by improperly portmatching.

Is there a specific method of portmatching (ie smoothing 1 inch vs .5 inch vs .25 inch into the intake manifold, or purposely creating ridges or something) that is proven to increase power? Or am I just overthinking this.

Thanks everyone.
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Old 02-16-2016, 02:22 AM   #2
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I don't run that TB, but I have port matched a stock TB before.

My approach is to smooth out any rough steps on the throttle body.

On the intake manifold, I ported the "neck" so that the air takes more of a straight shot vs an S bend. The less-sharp the bend is that the air has to turn, the better.
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Old 02-16-2016, 09:27 AM   #3
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Isn't there a write up, about why you actually want that step on an intake port?
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Old 02-16-2016, 10:25 AM   #4
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Old 02-16-2016, 10:27 AM   #5
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Wrong end of the manifold. I think he is talking about the mani to head interface.
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Old 02-16-2016, 10:28 AM   #6
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No, he's talking about TB to IM interface.
He's talking specifically about the step down right after the TB. IIRC many here have "port matched" that part without issue. Since the Junk2 is a bit larger in ID than the stock tb, the manifold directly behind the TB now has a slight step.

The car is n/a and will stay that way for a while, I don't really think it lost power from the TB as much as it did from doing the pulls in the day time vs at night, so there was like 20-30* temp difference.

I'm kinda hesitant to take a grinder/file to the manifold since it's gonna take a lot of time, be messy, and in the end likely not gain even 1 hp.

But if I'm wrong, and this is a big deal, I suppose we can do it. I'll check out that link thanks

*edit: so I wonder if anyone's ever measured before/after from something like this and seen more than 1hp swing in either direction.

Last edited by 18psi; 02-16-2016 at 10:40 AM.
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Old 02-16-2016, 10:59 AM   #7
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My bad, I didn't see the TB mentioned, when I first read.
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Old 02-16-2016, 01:23 PM   #8
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I wouldn't think you'd lose 10 hp worth of airflow from having a small step after the now-larger throttle, especially on an otherwise stock motor. I could see 30F ambient temperature difference between runs doing that though.

Smoothing it might gain you a hp or two, but my feeling is that the stock throttle is more than capable of delivering whatever the BP head can flow. IIRC, emilio only sells the skunk2 as a reliability mod, not a power mod. Which reminds me, I need to epoxy my throttle body before I put it back.

edit: look what I found after 5 seconds of googling:

http://www.mx5atlanta.com/forums/sho...017#post221017
Quote:
I used to sell overbored TB's so I have some experience here. (see www.solomiata.com). If a person had a near stock engine (ie had flowmeter and stock cams) I tried to talk them out of buying one. If someone had a built engine or a supercharger over 160 hp or a turbo over 300 hp then we would talk.

The stock TB is 55mm which is way oversize for a normally aspirated 1.6 and even the 1.8 liter engine. A 55mm hole will theoretically flow 300 cfm at 10 inches of water (A standard for NA engines, 28 inches is a boosted standard). The butterfly shaft and imperfections on the casting eat some of that so the as-manufactered Miata 55mm TB flows 246 cfm @ 10 in (I measured). Careful and laborious smoothing of the taper and thinning of the throttle shaft can get you close to 270 cfm (I did it, and measured it).

An engine is an air pump. The largest restriction in a Miata prior to the valves is not the TB, the airflow meter is the largest followed by the intake manifold. The TB is the last restriction. (a suck-through supercharger is a different story so either engine can benefit if over 160 hp, a blow through turbo threshold is about 280-300 hp)

A near stock 1.6 spinning less than 9000 rpm does not need a larger TB. A stock 1.8 only needs 220 CFM to spin 7500 rpm so the TB is not the bottleneck in a 1.8 either.

If you remove the airflow meter and port the intake manifold then a 1.8 can benefit from a slightly enlarged one if spinning to 8000 rpm. I got 3 hp by putting a 57.5mm overbore unit on my 1862cc (+,5mm) engine if I spun it over 7700 rpm (dyno measured).

You can probably put that money to better use if you have a near stock engine.
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Old 02-16-2016, 07:19 PM   #9
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Ok, I guess I'll leave it for now. I did buy the tb for reliability, and for future forced induction.

Thanks everyone
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Old 02-16-2016, 08:07 PM   #10
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NOT porting the manifold with a Skunk2 TB is a bad idea:

Skunk2 TB mated to OEM Miata manifold
Air tends to flow along walls so it's going to generate a LOT of turbulence when it smashes into the lip of the manifold (ie. restricting air flow).

Get some carbide bits for your Dremel, trace the inside edge of the TB onto the manifold with a marker pen and port it - doesn't take long at all (just don't be too aggressive, the carbide bits chew through aluminium very easily).

My efforts: http://mx5cartalk.com/forum/viewtopi...bide&start=488
and http://mx5cartalk.com/forum/viewtopi...bide&start=498
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Would port matching my Skunk2 to FlatTop lose power?-80-73723d1366153558_does_64mm_throttle_body_needs_intake_manifold_inlet_bored_same_size_eo2k_152.jpg  

Last edited by Lokiel; 02-16-2016 at 08:23 PM.
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Old 02-16-2016, 11:08 PM   #11
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Yes, blend the (any Miata) intake manifold flange to the Skunk2 if you can. We do. It's worth some power.
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Old 02-16-2016, 11:27 PM   #12
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^Just out of curiosity, did you A B test the portmatching before and after?
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Old 02-16-2016, 11:45 PM   #13
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druken armchair..... I'd just port the cheap2 TB to w/e intake manifold and go from there. Turbulators for air going in can't beeee too good so the smoooooothest transaction would be bestz. Polishing the insides is up to you after TB.
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Old 02-17-2016, 01:01 AM   #14
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The skunk2 tb is 64mm. The square top is 59mm. I just opened up my square top to 64pm last weekend. Still waiting on the Skunk 2 tb, they are backordered. I don't see any benefits NOT portmatching. It takes maybe 1 hour to get it done.
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Old 02-17-2016, 02:34 AM   #15
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The theoretical flow rate through a pipe isn't the issue. The step causes turbulence and extra flow restriction similar to how a square entry into a runner reduces the diameter (can by by up to 1/3rd of the diameter)... With that step present and even with the larger throttle body, the intake manifold could be flowing less air than it did with the smaller throttle body and no step.

I drew a simple image of the effect when talking about bell mount design for ITB's. (top left picture shows how turbulence will reduce the internal dimensions of an air intake tube). Adding a bell mouth stops this effect, or in this case merging it to the throttle body.



Even a simple taper on the leading edge would be an improvement to it's current state, though boring the IM out to the throttle body would be preferred. Unfortunately you'll have to remove the IM to do that.
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Would port matching my Skunk2 to FlatTop lose power?-80-bell_mouth_zpsufepurjt_e962ad307ae65731f1933cc4b39745569fe7c506.jpg  

Last edited by Madjak; 02-17-2016 at 02:35 AM. Reason: spelling
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Old 02-17-2016, 02:39 AM   #16
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Quote:
Originally Posted by Madjak View Post
The theoretical flow rate through a pipe isn't the issue. The step causes turbulence and extra flow restriction similar to how a square entry into a runner reduces the diameter (can by by up to 1/3rd of the diameter)... With that step present and even with the larger throttle body, the intake manifold could be flowing less air than it did with the smaller throttle body and no step.

I drew a simple image of the effect when talking about bell mount design for ITB's. (top left picture shows how turbulence will reduce the internal dimensions of an air intake tube). Adding a bell mouth stops this effect, or in this case merging it to the throttle body.



Even a simple taper on the leading edge would be an improvement to it's current state, though boring the IM out to the throttle body would be preferred. Unfortunately you'll have to remove the IM to do that.
100% this. I've tested this stuff too, he's spot on.
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Old 02-17-2016, 02:51 AM   #17
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OP, look up Mobius and his build thread. He has many pictures of him port-matching his squaretop to his Skunk2 TB.
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Old 02-17-2016, 12:27 PM   #18
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^thanks!

ok so that makes sense about the step reducing the effective diameter... The car is much slower with the skunk2 on...

Port matching it is!
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Old 02-17-2016, 12:42 PM   #19
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If the car is slower with the Skunk2, something else is wrong. You did not lose power by swapping the TB.
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Old 02-17-2016, 12:47 PM   #20
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Dyno'd car on a cool night with at least 30* cooler AIT's (I'll actually double check tonight and post the exact numbers).

Installed S2

Dyno'd car on a warm day with at least 30* hotter AIT's (again, just guessing, I'll post up numbers).

Car made 129 at night and 123 in day. Nothing else was touched. Actually we even upped timing a couple degrees after baseline to see if it would gain power, it didn't, as posted above.

He's trippin. It's not slower.
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