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Old 12-10-2006, 10:33 PM   #1
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Default Oil Inlet Restictors... research and opinions

It must have been doing this from the start, only the cat was burning it all up. Now that the cat is gone, it's smoking ever so slightly and I've got oil residue at the exhaust tips. I didn't check the IC pipes... a little afraid to. However, based on my research, I've bought into the oil inlet restrictor thing and am getting one.

First, my research. Here's a few posts that got me started:
https://www.miataturbo.net/forums/sh...ght=restrictor
https://www.miataturbo.net/forums/sh...ght=restrictor
https://www.miataturbo.net/forums/sh...ght=restrictor
Then I just google'd the **** out of everything I could think of... mostly looked at posts in other import forums.

These next statements are generalized.
Your average Ball Bearing turbo doesn't need as much oil as a Journal Bearing (non-BB) turbo. Most guys with BB turbos (do or should) run a .035 restrictor and -3an line. Most guys with JB turbos (do or should) run a .060 restrictor and a -4an line. Of course this all depends on how much oil pressure your particular car makes. Jap cars don't seem to vary that much in the amount of oil pressure they can provide... say about 20psi at idle all the way up to 100psi maybe at WOT. I took a drive today and at WOT I saw as much as 80psi. At that pressure, an unrestricted -4an line should ensure that my entire intake and exhaust system has a good coat of Mobil 1. Not to mention severely limiting the life of the seals in the turbo.

It seems to be a given on other forums that a restrictor be an automatically included piece in any turbo system. No kidding, DSM, Honda, Subie, SR20, etc... all the posts I read just take it as a matter of course that you run one. They say even if you're not leaking now, you will be. Some guys get away with it of course, but it looks like I'm not one of them. So... I'm in!

QUESTION: Should this be something we as a forum start to mention to NEWBs that they invest in (like motor mounts that nobody ever thought of until a few weeks ago). Brain points it out in his FAQ, but I never hear anyone talk about it unless someone brings up that they're smokin'.

Anyways, I'm pretty sure that the ATP restrictor for the GT series turbos are also 1/4 inverted flare, but it comes with a .035 restrictor... just need to drill it out to .060 (where the hell do I get that bit?.. a 1/16" is .065... guess that will work). Here's the restrictor: http://www.atpturbo.com/Merchant2/me...gory_Code=GTBB

Anybody know where I can get a .060 1/4"IF to 4an for a T25???
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Old 12-10-2006, 10:39 PM   #2
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I dunno much about restrictors. However, just so it is written to not spread misinformation I know for a fact that ALL GT series BALL BEARING turbos have an oil restrictor built into them. The restrictor that ATP sells is most likely for the GT series with a standard journal.

On another note, you might want to just go ahead and shoot an email to ATP tonight so you can get a reply sometime tomorrow. They should be able to answer you incase no one here can.
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Old 12-10-2006, 11:01 PM   #3
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wouldnt a restrictor also help with oil pressure?
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Old 12-10-2006, 11:22 PM   #4
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That restrictor is for GT Ball Bearing Turbos. R=Ball Bearing.
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Old 12-11-2006, 12:27 AM   #5
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www.jgsturbo.com has the restrictor you need.
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Old 12-11-2006, 03:36 AM   #6
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I use one in my JB turbo, and blew the seals immediately in my first turbo because of the lack of an oil restrictor. I'm not real saavy on the BB stuff, but for a JB I wouldn't even attempt it without one.
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Old 12-11-2006, 09:14 AM   #7
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I think it really depends on the turbo; I'd take it on a case-by-case basis. I, too, have heard that many of the GT BB turbos are self-restricted, but I wouldn't trust that every one will be this way.

When I built my turbo kit, I checked the Volvo 940 that it came off of, and saw basically a 1/4" feed line with no restrictors, so that's how I feed it on my car. I've been running it over a year, and it's never even hinted at producing smoke.
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Old 12-11-2006, 09:41 AM   #8
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while my T3 JB would smoke at idle without a restrictor.
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Old 12-11-2006, 11:07 AM   #9
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Would seem that a restrictor that we could add between the 4AN line and whatever 4AN fitting we have in the turbo (or better, at the block) would be the simplest solution, instead of dealing with all the fittings to adapters to restrictor to adapter to line issue.

Anybody find a source for something like that? I haven't been able to.
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Old 12-11-2006, 11:12 AM   #10
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Quote:
Originally Posted by Efini~FC3S View Post
www.jgsturbo.com has the restrictor you need.
Yup, about halfway down this page: http://www.jgsturbo.com/index2.html
It says that a T25 is 7/16", but I know the 2G DSM CHRA I'm using is 1/4"... WTF with these things... WHY CAN'T THEY ALL BE THE SAME??? Wouldn't it be easier to just make the threads on all turbos universal. ****!

I thought that GT turbo's were all BB's... that's what makes them "G".

You'll still get that same pressure of oil at the restrictor, but it will let less oil through. I think the idea is not to let the CHRA fill up with oil and become pressurized... A bigger drain is not an option, so less oil in is the key.
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Old 12-11-2006, 11:12 AM   #11
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mine is a Male/Female that screws right into the turbo, my regular 90* fitting then screws into it.

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Old 12-11-2006, 11:18 AM   #12
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Sam I'd suggest using the one you linked to in your first post and drilling it out a bit. Nothing wrong with that. Some people go crazy lengths do make them: http://www.dsmtuners.com/forums/showthread.php?t=171317 The one you found would take 3secs to drill out.
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Old 12-11-2006, 11:20 AM   #13
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What makes them GT's are the new compressor and turbine wheels that an improvement over the standard T stuff. What makes a GT a "GTxxR" is the ball bearing center section.
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Old 12-11-2006, 11:36 AM   #14
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I'd be all over that if my 1g dsm turbo with it's stupied 12 x 1.5mm oil feed port!
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Old 12-11-2006, 11:46 AM   #15
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It's still a -4an fitting though? You could do a -4AN M to FM fitting for like $3 and try the NOS nozzle trick.
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Old 12-11-2006, 12:06 PM   #16
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Sam, something you could do for now is run a 1/8" aluminum poprivet inbetween your two AN fittings at the turbo for now. The inner diameter of the rivet is .075" here's a post on my oil pressure measurements on my 99 1.8 with -4 AN line.
https://www.miataturbo.net/forums/sh...5&postcount=14

Last edited by cjernigan; 12-12-2006 at 03:12 AM.
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Old 12-11-2006, 12:13 PM   #17
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I think there was a thread on M.net the other day where folks were/are using pop rivets. They apparently fit right into the -AN fitting, and there's a couple sizes that work.

Here it is: http://forum.miata.net/vb/showthread.php?t=209249

Edit: Whoops, there I go again waiting too long to compose my post
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Old 12-11-2006, 12:21 PM   #18
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h**p://forum.miata.net/vb/showthread.php?p=2178338#post2178338

The thread I had posted in about using pop rivets, looks like he had great results. Can't hurt they're $1.25 for a box of 20.
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Old 12-11-2006, 04:19 PM   #19
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That aluminum rivet thing is the deal. I'll stop by Home Depot on the way home and see what they have. As a side note, it started smoking pretty good today. I hope I haven't done any serious damage. Looks like I'll have to check the charge pipes after all when I get home today.

I'll let y'all know what I find out.
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Old 12-11-2006, 04:29 PM   #20
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Speaking from experience, contaminants can also enter the turbo via the oil feed and block some of the oil passages. In my case, some permatex rubber somehow got in there from the previous owner thus starving my turbo of oil. Even if you were careful in the rebuild, something could have gotten in there. If the restrictor doesn't help and you're positive the drain is flowing the way it should then you might want to check the shaft play on the turbo again to see if you're having oil starvation problems which could be evident in journal bearing wear.
This has happened to me twice.
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