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Old 05-06-2010, 01:04 PM   #1
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Default Mazdaspeed turbo on a 1,6 '93: I need more boost

Hello

I own a old pre FM Ihi turbo kit. The turbo is cracking inside near the wastevalve, so I got a new mazdaspeed turbo from ebay. It's on the car and runs fine. But I can't get 12 psi boost with this kit. So I got a manual boost controller. Now I can get more boost, but the boost is not stable. It's 10 - 11 12 - 11,5 - 11 - 11,5 - 12 ... in seconds or less. Really boring and you can hear it too.
I was thinking about replacing the actuator. I want it to be adjustable, +- 12 psi is my goal.
The old actuator could do the trick but the mounts are cracking too and I guess it won't hurt to replace it. It is 10 years old.
What actuator (type, brand) should I buy for my project? It would be nice if it would just bolt on but I guess that's not gonna happen. The FM parts are max 9 psi and I blame the manual boost controller for the unstable boost, so I won't to lose it.

Thx
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Old 05-06-2010, 03:34 PM   #2
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It sounds like you need more pre-load on that actuator. If it does not have enough then you can get situations with an internal wastegate/wastevalve where it is opening a bit before the desired boost. So you will rocket up to 5, then slowly creep to 12. A adjustable actuator rod might be the ticket.

The real solution is an external wastegate, which can be run on a setup with an internal gate turbo by integrating it into the downpipe. But thats a big of an investment you might not have to make.
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Old 05-06-2010, 03:39 PM   #3
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Is the MBC a ball-and-spring or needle valve type? That might be the issue right there. Other than that, you could pull the wastegate actuator off and verify that it holds vacuum with a vac pump, incase it might have a pinhole leak/tear in it.
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Old 05-06-2010, 03:47 PM   #4
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My turbo has a wastegate that goes to the downpipe. The old turbo was almost the same type (just one character is different on this turbo n) , it just had a stronger actuator.
I guess mazda wanted to have max 8 psi for the mazdaspeed turbo.
Anyway, I can shorten the actuator rod, then I can make 9 psi. If I connect the actuator to the inlet (after the IC, instead of the turbo) I get +- 10,5 psi for a moment that goes to 10 psi, stable. Still not 12 psi
I'm a bit scared to shorten the rod: the spring is always compressed and maybe it keeps my wastegate from opening enough.

The MBC is this one:
http://imgs.inkfrog.com/pix/gtschris/mbc2a.jpg

It is a ball spring, but it has got a vent, once is opens. I was thinking of blocking the vent to see what it does. Superglue

You want pics, don't you?

Old setup:

http://www.flickr.com/photos/[email protected]/4584871296/

New turbo:

http://www.flickr.com/photos/[email protected]/4584242797/
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Old 05-06-2010, 04:08 PM   #5
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Looks like Mitsu hardware, which is good. You can make a DP setup that uses an external wastegate very easaly. Many DSMers do just that as shown in the picture. This unit works with pretty much any of the common Mitsubishi turbine housings. Like I said though, it might be overkill.
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Mazdaspeed turbo on a 1,6 '93: I need more boost-o2_sensor_housing__4__small.jpg  
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Old 05-06-2010, 04:24 PM   #6
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I've never seen an exhaust valve like this (on a miata). I also doubt that there is room in my engine bay for this
But I just read something about it in corky's book. Next line is 'don't laugh, seriously'
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