lowering boost threshold with wastegate antics - Page 2 - Miata Turbo Forum - Boost cars, acquire cats.

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Old 02-11-2009, 12:18 PM   #21
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The advantage of wastegate actuator cans with larger diameters is that they require a stronger spring for a given boost rating, helping hold the flapper shut against backpressure.
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Old 02-11-2009, 12:20 PM   #22
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where does one find helper springs?
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Old 02-11-2009, 12:25 PM   #23
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Quote:
Originally Posted by hustler View Post
What does the smaller turbine housing to do EGT? Will I then have to retune on the dyno? I doubt its a bolt-and-go. That $215 housing will cost me another $100 to ceramic coat, then another $200 in dyno time. So $500 to switch to the smaller housing.

This is not a streetlight ricer fagmo car, this car sees lots of track time. So running a tiny little turbine housing is probably not a good idea.
a few datalogs across the spool region (on the street mind you) will get you more than enough data to re-tune the car. don't underestimate the efficacy of autotune!

just put on the bare housing and see if it does what you want. if it does, pull it back off and coat it.

by the way, once you get to the track, take copious datalogs and see if you even use the unspooled portion of your power band. maybe you wont and it is pointless to improve spool...?
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Old 02-11-2009, 02:13 PM   #24
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Quote:
Originally Posted by JasonC SBB View Post
The advantage of wastegate actuator cans with larger diameters is that they require a stronger spring for a given boost rating, helping hold the flapper shut against backpressure.
Isn't that a generalized assumption? I've also seen specs for higher boost opening cans state stronger springs. And I've seen rebuildable actuators state you can swap the springs out for whatever boost level you want to run. But I don't see a larger diameter can necessarily equaling a stronger spring.

I can't see any reason not to get a dual port actuator at this point, since there's usually not a cost difference over the single, if there is it's negligible. And the reference port can be left unused and the can will just operate as a single port.

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where does one find helper springs?
I got my parts at the hardware store... homedepot/lowes would have them too. The hardware store has a box of springs with all the other nuts/bolts/hardware boxes (the ones with pictures on the front).
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Old 02-11-2009, 02:21 PM   #25
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get a dual port and a MBC. If you want to run 14 PSI get a 12 PSI dual port WG and use both ports accordingly. With the MBC and it all plumbed right, you won't crack that WG open till you're MBC is really coming online. A diaphragm type MBC is better in this case too.
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Old 02-11-2009, 02:32 PM   #26
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I'm running closed loop EBC now. I want the reference port on the actuator to do what the helper spring does - only better. I'm not fully sure of the plumbing for the reference port though. Initial thoughts- run a regulator in line on the reference side so that side only see a max boost level less than my target boost on the pressure side of the actuator.
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Old 02-11-2009, 03:04 PM   #27
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One port on the WG will work with the spring to hold the WG shut. This port hooks to the intake manfold. When boost builds, it builds up an air spring, helping the stock spring keep the WG shut. In short, that WG ain't opening. Then you vary pressure on the other side to cancel out some of the other air spring as to regulate boost.

Say you have a 12 PSI wastegate. You hook the port on the spring side to the intake manifold. So when you're running 12 PSI, that port sees those 12 PSI. If you don't hook anything else up but just this port, the WG stays pinned shut and you'll boost till something breaks. The WG won't ever open.

Say you want to run 15 PSI, then the spring side port sees 15 PSI. To do this you'd need to apply 12 PSI on the second port as to cancel out all but 3 PSI of the other air spring. Now you get 12 PSI from the real spring + 15-12= 3 PSI from the "air spring". And you vary the air spring with your MBC.

In this case however, the MBC won't open till just shy of 15 PSI. And with the spring side diaphram hooked to the intake manifold, the wastegate stays pinned shut till you get to say 14 PSI when the MBC finally opens, then all of a sudden 12 PSI shows up on the other side of the diaghram and you run 12+ (15-12=3) PSI.

Better than EBC, no tuning ****, less variance with temperature, etc. And with a diaphragm type MBC (ie, not a boost leak), there is less variance of pressure to the WG from the MBC so boost is more solid when temp changes.

Last edited by patsmx5; 02-11-2009 at 03:14 PM.
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Old 02-11-2009, 03:28 PM   #28
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Helper spring +5
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Old 02-11-2009, 11:38 PM   #29
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this **** is gay...I need properly functioning EBC code.
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Old 02-12-2009, 12:02 AM   #30
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Quote:
Originally Posted by m2cupcar View Post
Isn't that a generalized assumption?
The force that a can exerts on the flapper is =

cracking pressure in psi * pi * can_diameter^2 / 4

It's physics.
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Old 02-12-2009, 12:08 AM   #31
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Quote:
Originally Posted by patsmx5 View Post
One port on the WG will work with the spring to hold the WG shut. This port hooks to the intake manfold. When boost builds, it builds up an air spring, helping the stock spring keep the WG shut. In short, that WG ain't opening.
Do you have a dual port wastegate?
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Old 04-01-2009, 03:38 PM   #32
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Dragging this back up because I just installed a dual port actuator.

One thing pat's comment doesn't address is the force of the spring - so I assume that spring rate is equal to whatever boost signal (on the "open" side) starts the actuator arm moving. These means that the pressure needed on the "close" side of the actuator = boost - spring - a few psi. Here's how I plan to set this up and start tuning. Comments welcome.
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Old 04-01-2009, 04:05 PM   #33
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who sells such an actuator and how much?
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Old 04-01-2009, 04:08 PM   #34
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atp sells them for a nominal cost.


about $40 on ebay:

http://cgi.ebay.com/ebaymotors/T3-T3...Q5fAccessories
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Old 04-01-2009, 04:23 PM   #35
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how bout the adjustable regulator?
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Old 04-01-2009, 05:33 PM   #36
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I picked mine up from a forum member barely used. It's definitely a cheap piece like the last actuator I had (from a chinacharger), but I think being able to put pressure on the back side to assist the spring is the ticket to making it perform. Straight signal off the compressor to the "open" port I saw 5-6psi. I logged the run, so I'll do the above setup and another log to compare it too.

harborfreight Brass Air Inline Regulator ITEM 32905-0VGA $2.99


I just picked one up (they've got an aluminum version on line fwiw). Have not put air pressure to it yet to find out how well it works, but I've used one with airbrushes when working with low pressure. That said, I was even able to dial in my regulator off my old sears compressor to 5psi yesterday.

Just took it out of the package and rolled the adjuster while blowing through it- no doubt in my mind it will do the job.

edit: if you have a spare actuator, it's possible to put a port on the backside (according to this guy):

Last edited by m2cupcar; 04-01-2009 at 05:56 PM.
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Old 04-01-2009, 10:40 PM   #37
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Quote:
Originally Posted by m2cupcar View Post
One thing pat's comment doesn't address is the force of the spring - so I assume that spring rate is equal to whatever boost signal (on the "open" side) starts the actuator arm moving.
Exactly.

The way to get boost to hold the 'gate shut, is to have 2 solenoids set up so that when you want more boost than you have, get the boost in the side that closes the wastegate, and when you want the wastegate to open you let boost in the side that opens it and out the side that closes it.
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Old 04-02-2009, 12:40 AM   #38
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thanks, I'll stop in there tomorrow and grab one.
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Old 04-02-2009, 10:36 AM   #39
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Quote:
Originally Posted by m2cupcar View Post
Dragging this back up because I just installed a dual port actuator.

One thing pat's comment doesn't address is the force of the spring - so I assume that spring rate is equal to whatever boost signal (on the "open" side) starts the actuator arm moving. These means that the pressure needed on the "close" side of the actuator = boost - spring - a few psi. Here's how I plan to set this up and start tuning. Comments welcome.
Where do you plan to hook up your two boost signals and how much boost are you wanting?
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Old 04-02-2009, 10:38 AM   #40
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Don't you just T/Y the boost line and connect one directly to the upper port and the other through the regulator to the lower port? If it's more complicated than that I might just bail.
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