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Old 11-17-2012, 10:45 PM   #1
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Default ITT: fmic size and piping diameters for optimum efficiency

Like the title says: been reading about this topic for quite a while now. I know there are generalizations out there on whats best, but I wanted to find out EXACTLY what works best for SPECIFIC power levels and needs.

Read through a ton of threads on this. So many wildly varying opinions and "calculations" it made my head spin.
Here's one of the more interesting ones:
[RESOLVED] How much will different sized intercooler piping flow? - DSM Forums

General rule is "smallest size you can get away with". Also many reputable people mentioned "no wider than 20" core". Also many reputable people mentioned there is no reason to run oversized piping, and for most setups 2" is enough, 2.25 is plenty, and 2.5" is oversized.

So with that in mind, I'm planning out my fmic for the 01. It will be running a disco potato (2860rs) and compressor outlet is 2". Goal is no more than 250whp for now, with emphasis on torque under curve and broad powerband. One thing to point out though is I DON'T want it to choke up top.

From the reading I've done, here is my proposed setup:

28x5.5x2.5 bar/plate fmic with 2" inl/out (fits the 01+ bumper perfect)
2" mandrel alum piping on cold side and hotside (makes it easier to route)

Can anyone find anything wrong with this idea?

I know bell and others run (and recommend) smaller hotside (2ish) with larger cold side (2.5ish). Is there significant gains to be had from tapering piping up towards the tb (which is 2.5ish iirc), or at least a MEASURABLE LOSS I'd experience from using 2" all the way? Again, keep in mind my goals stated above. This isn't going to be a 500+whp topend monster. Power levels expected are 250 for now and maybe 300-400 WAY later (and I'd probably re-do most of the setup by then anyays, so lets focus on 250 for now)

Thoughts? Input? Opinions?
Bring it on

Last edited by 18psi; 11-17-2012 at 11:45 PM.
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Old 11-17-2012, 11:36 PM   #2
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FWIW: I priced out same setup on siliconeintakes.com going from 2" hotside to similar ic and using 2.5" coldside and the difference is like $30-40 when compared to the ebay all 2" setup, so if anyone has a good reason why I should do this I don't mind going either way.

BTW I will be welding most of it together, and making my own brackets, and basically making the mounting TOP NOTCH as well as using 5ply silicone couplers and t-bolt clamps. In the end it should be on par with a BEGi kit for half the price. Routing will be behind the drivers side headlight like my previous setup for the cold side, and traditional like my previous setup for the hotside.

My only question is about sizing for all of it. Want to get it just right for my setup and not just do whats popular.
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Old 11-17-2012, 11:40 PM   #3
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I'm very interested in this topic as well, and reading through the thread you posted now. I'm turboing the NC this coming summer, and 2 inch piping would be sooo much easier to route than 2.5 inch through that crowded engine bay.
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Old 11-18-2012, 12:50 AM   #4
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I always like to look at OEM's for questions like this. All of them run tiny charge piping from the factory. All the euro turbo cars have 2" or smaller piping along with teeny tiny turbos. Same thing with subaru, granted the piping is ridiculously short with the TMIC, but it's very small diameter. Take that for what it's worth, but I'm planning 2" piping with my TD-04 turbo setup.
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Old 11-18-2012, 12:57 AM   #5
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You are correct. But most cars you listed drastically choke up top, and also none were designed to put out much more than they do stock (though most can, of course), so they run restrictive components (which is also because of smog of course) and undersized turbos.

Look at the MSM routing:


Notice how it starts tapering up midway through the coldside piping. I wonder if that's so its easier to mate to the tb or whether our cars need the taper there to create more.....I dunno: flow? Or accommodate for denser air?
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Old 11-18-2012, 01:00 AM   #6
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Also check out BEGi:



This is the #3, which is why the core is giant, but notice the rest of the piping - it tapers from 2" to 2.5 midway, and 2.5 all the way after the ic

What I want to know is if it would kill power if it was 2" all the way. Has anyone tested this on a miata? Or done comparisons? Or anything they could share? Or read about it somewhere?

If so post up
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Old 11-18-2012, 01:04 AM   #7
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PS I'm re-reading "maximum boost" as well as google searching about this as we speak lol

*edit:
per the posted links, and Maximum Boost, the 2" piping is more than adequate for 250whp and even 300.
2.25 is good 300-400, and 2.5 is good for 500+

It says not to use bigger piping than needed.

But nowhere does it say anything about the need to taper it up after IC. So I wonder why they do it then?

Last edited by 18psi; 11-18-2012 at 01:23 AM.
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Old 11-18-2012, 01:21 AM   #8
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The only thing I can think of off the top of my head is that larger diameter piping will yield a lower Reynolds number.
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Old 11-18-2012, 01:25 AM   #9
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What a great topic! I've always been curious how larger intercooler plumbing would affect spool, and also IAT temps.
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Old 11-18-2012, 01:28 AM   #10
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A friend of mine tested exactly that on his festiva, and going from 2" to 3" piping and small stareon ic to large ebay unit net ZERO power gains and a LOT more lag (400rpm worth iirc). Hopefully he see's this thread and chimes in.
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Old 11-18-2012, 01:30 AM   #11
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Quote:
Originally Posted by 18psi View Post
You are correct. But most cars you listed drastically choke up top, and also none were designed to put out much more than they do stock (though most can, of course), so they run restrictive components (which is also because of smog of course) and undersized turbos.

Look at the MSM routing:


Notice how it starts tapering up midway through the coldside piping. I wonder if that's so its easier to mate to the tb or whether our cars need the taper there to create more.....I dunno: flow? Or accommodate for denser air?


i don't think the thought of more or less dense air ever went into the design of that -
i think that was just made to fit and w/ that little george foreman grill core and the turbo you prob never need more then 2"

i like the comment that was made about looking at oem setups for sure - just as a point of ref - the mazdaspeed3 uses a k04 - from stock boosts 15psi and with just a few mods can maintain 18-19 till 5500 or so - the tmic on it uses a factory 2.5" in/out
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Old 11-18-2012, 04:58 AM   #12
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One idea may include some gas laws. I'm curious if the larger pipe change cools the charge at all as it loses pressure going from 2in to 2.5in pipes. Is there something to do with air velocity? Far to tired to do math right now.

My guess is the change is mostly for throttle body size.
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Old 11-18-2012, 02:04 PM   #13
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AFAIK the restrictions are mostly in the bends. The more bends you have, the larger diameter you need. My TDR i/c has such few bends (2), that the 2.25" piping AFAIK shows no restriction at 270 whp. All the restriction is in the core.

It's tube and fin, btw. Its big advantage is much better cooling airflow for the radiator. (I have a thread on this with some testing):
https://www.miataturbo.net/diy-turbo...adiator-11679/
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Old 11-18-2012, 03:55 PM   #14
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Well my routing is going to be extremely straightforward - very smooth bends, and only 4 of them total.

Hot side: 1 not even a bend really, like a couple degrees, the other is a very wide 90,
Cold side: 1 smooth 180 and 1 90.

The cold side obviously having way more bends to it, you think I should step it up to like 2.25 or something?
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Old 11-18-2012, 03:59 PM   #15
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Quote:
Originally Posted by 18psi View Post
FWIW: Routing will be behind the drivers side headlight like my previous setup for the cold side, and traditional like my previous setup for the hotside.
Just curious is there a reason you will run traditional coldside routing? I went 2" under the headlight on the coldside as it cut out a foot of piping and a 90 deg bend. (And for my crooked eyes this routing had a pleasing symmetry.)
My thoughts when I did my piping were that the air is more dense after the intercooler and therefore should be less turbulent. So if 2" works on the hot side it should ok on the cold side. Also the effective stock throttle opening is around 2" when the plate is open.
I Imagine most of the air pressure drop occurs across the intercooler. I am not sure if a 2" and a 2.5" intercooler use the same intercooler body.
(In my poverty setup I used a 2.5"intercooler and stepped it to 2" piping with reducer silicone 90's because I imagined the pressure drop would be less.)
[IMG][/IMG]
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Old 11-18-2012, 04:08 PM   #16
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My hotside routing on previous car was exactly like yours. And will be that way on this car too.

Cold side though, I'm reluctant to cut into the shelf. But that is good routing IMO, thanks for posting up.

You're running a 2560 right? Does boost taper up top? Do AIT's shoot up in the upper rpm range? Do you get anything at all indicating the car might be choking up on the ic side?

.
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Old 11-18-2012, 04:30 PM   #17
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if you're getting so concerned with bends - why not just go over the rad?
it doesn't get any more simple
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Old 11-18-2012, 04:38 PM   #18
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I have gone over the rad. On my 1st setup.



Too much crap to re-arrange and modify to the car itself to actually do it right.
Don't like it. I'd rather cut 2 holes like sturovo if I'm going to be modifying the rest of the car to fit the fmic.

But ideally I want to do the same setup I had on my 00, I loved it and had no problems with it:

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ITT: fmic size and piping diameters for optimum efficiency-0811091633-00.jpg   ITT: fmic size and piping diameters for optimum efficiency-5605285022_96d8fc8a63_b.jpg  
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Old 11-18-2012, 04:50 PM   #19
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Quote:
Originally Posted by 18psi View Post
Cold side though, I'm reluctant to cut into the shelf. But that is good routing IMO, thanks for posting up.

You're running a 2560 right? Does boost taper up top? Do AIT's shoot up in the upper rpm range? Do you get anything at all indicating the car might be choking up on the ic side?
I didn't have to cut into any structural parts to make the penetration. The steel plate I cut was 0.8 mm thick like the one on the hot side. (If I understand correctly there is even more space there on later year cars there as the lights are not as deep?)
[IMG][/IMG]

Pressure drop? hard to say. I ran a 2560 for at lower boost when I first turbo'd but I thought it was a little bit laggy for dd so I swapped it to a TD04-13t. The most I pushed the TD04 was to around 220 whp at 14psi. There is some slow down above 6000 rpm but this is probably due more to the turbo than the piping. Hard to say. (I have a TD05 16g (S) ready to go in over the winter so this might test the 2" flow/restriction more.)
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Old 11-18-2012, 04:57 PM   #20
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Another thing I wanted to discuss in this thread is the whole BAR/PLATE vs DELTA/FIN argument. Read Jasons thread where both Jason and Brain switched to that style and reported better coolant temps as well as faster response?

Reading up on teh subject now, so many discussions online about it this will take some time lol.
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