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Old 04-17-2012, 07:51 PM   #1
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You know what's funny? A few months ago I was writing a somewhat cocky response to some fellow wherein I was criticizing the Kraftweks / Rotrex supercharger system, and I said something to the effect of "you wouldn't try to regulate the boost of a turbocharger by deliberately adding restriction to the exhaust, would you?"

And then I see this: http://forum.miata.net/vb/showthread.php?t=456058
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Old 04-17-2012, 08:18 PM   #2
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This is essentially what I'll be doing until I can afford Artech's 3" exhaust. My 2.5 exhaust is going to be bolted up to his 3" dp. It looks funny.
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Old 04-17-2012, 08:24 PM   #3
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1. The Rotrex inlet restrictors are not even remotely the same thing as an exhaust restrictor in a turbo

2. The real way to fix the issue of boost creep caused by insufficient wastegate flow is to - get this - fix the wastegate flow.



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Old 04-17-2012, 08:26 PM   #4
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Yeah, and Corky has been throwing this suggestion out for quite some time, if porting the WG doesn't fix boost creep issues. I still don't like the idea of adding a deliberate restriction.
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Old 04-17-2012, 10:24 PM   #5
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i'm torn. this is clearly the cheapest solution.

and probably also the least awesome.

better would be to make some sort of boost actuated bypass that diverts gases into a 2" pipe instead of the 3". IF you dont intend to fix the actual problem.
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Old 04-17-2012, 10:25 PM   #6
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im confused why they are opposed to porting wastegate.

i hold 15psi perfectly flat to redline.
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Old 04-18-2012, 10:36 AM   #7
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Quote:
Originally Posted by Braineack View Post
im confused why they are opposed to porting wastegate.

i hold 15psi perfectly flat to redline.
It has been done enough times on this site alone that I can't imagine why it would be considered a "bad idea."
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Old 04-18-2012, 11:03 AM   #8
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They're about 2 years behind the power curve:
https://www.miataturbo.net/showpost....3&postcount=44
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Old 04-18-2012, 11:16 AM   #9
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/thread.
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Old 04-18-2012, 11:57 AM   #10
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We have a FM 2560r 94 on the dyno right now. It has whatever "new style" wastegate actuator FM offers. It overboosted like mad with a 3" exhaust, even when I pinned the gate full open mechanically. I'm not sure how much boost it would have made up top because we aborted the runs by 6k rpm, as the boost was at 15 psi and climbing hard. The owner did not want to take the turbo back off to port the housing and gate out, so he replaced the 3" exhaust with a 2.5" system. It no longer overboosts, and we can even dial in more boost with EBC.
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Old 04-18-2012, 12:32 PM   #11
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This is like chopping the tip off your ***** when your girlfriend complains about it hurting.
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Old 04-18-2012, 01:33 PM   #12
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I guess Garrett never tested if the wastegate was large enough on the GT2560, on a setup as efficient as current turbo miata setups.
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Old 04-18-2012, 01:40 PM   #13
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Quote:
Originally Posted by JasonC SBB View Post
I guess Garrett never tested if the wastegate was large enough on the GT2560, on a setup as efficient as current turbo miata setups.
I don't have any trouble with overboost on my setup, I wonder why some people have these problems and others do not. GT2560 with 3" exhaust and a decent manifold should be all the same in that regard, right?
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Old 04-18-2012, 04:31 PM   #14
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Off the top of my head, other variables will include:

- exhaust valve opening time (i.e. cam used, and cam gear setting if any)
- downpipe - if you look at a wastegate flapper cocked open a bit. The gases will come out at an angle, and not aimed into the wastegate pipe (in hte case of a divorced d/p)
- intercooler pressure drop - if this is large, the turbine will need more power (and less exhaust needs to be wastegated)
- engine displacement and VE
-etc
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Old 04-18-2012, 05:50 PM   #15
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We finished tuning the car. Boost was wild and had uncontrollable creep with the 3" exhaust. With the 2.5" exhaust, the IWG had no problem controlling boost, and we even had to dial in some EBC to make ~12psi. I think it was a 10 psi can.
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Old 04-19-2012, 12:05 AM   #16
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Ugh.
FWIW my 2560 is ported and I still struggle to keep it under 10 psi on colder days. 3" exhaust.
At a track day a couple weeks ago I don't think I ever went past 50% throttle. Overboost protection would immediately kick in.

---- all this, I'm going with EWG eventually.
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Old 04-19-2012, 12:39 AM   #17
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In that thread, Jeremy says that the reason FM doesn't port wastegate housings is because Limit Engineering told them not to. So the question is, why won't Limit do porting? Is it just liability, or do they want to sell more EWG turbos?

--Ian
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Old 04-19-2012, 12:45 AM   #18
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Quote:
Originally Posted by codrus View Post
In that thread, Jeremy says that the reason FM doesn't port wastegate housings is because Limit Engineering told them not to. So the question is, why won't Limit do porting? Is it just liability, or do they want to sell more EWG turbos?

--Ian
Paging jkav.
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Old 04-19-2012, 01:49 AM   #19
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Quote:
Originally Posted by Ben View Post
We finished tuning the car. Boost was wild and had uncontrollable creep with the 3" exhaust. With the 2.5" exhaust, the IWG had no problem controlling boost, and we even had to dial in some EBC to make ~12psi. I think it was a 10 psi can.
any logs / pics of the spool differences of 2.5" vs 3" would be interesting
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Old 04-19-2012, 11:33 AM   #20
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curious to see how loudly everyone screams "but the wg port will crack after many miles!"

but only because that happens anyway on most turbos.
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