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Old 02-10-2009, 08:46 PM   #1
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Default lowering boost threshold with wastegate antics

I have a gt2860rs with a 14psi wastegate actuator with a vac line connected at the compressor housing. I'm hitting 11 psi at 3400rpm, and about 14psi at 4000rpm. I have some pretty grotesque 911-turbo style lag...we're talking about 1/2 a second or so. (lag = time requried to hit target boost withing boost threshold engine speeds) Adding a manual boost controller helped lower boost threshold about 400rpm.

I checked my wastegate actuator's adjustment and I was able to make one complete turn "shorter" on the little arm to snug up the flapper (it was barely cracked).

Then i started to think about pre-loading it by shortening the arm, then using my massive guns to pull it out a bit...making it harder for the wastegate to open initially. Will this work to lower boost threshold without causing overboost?

Other things I considered:
getting vac line signal from the intake plenum
putting a canister (fuel filter thingy) on the vac line to give the turbo a little more time to spin before the wastegate actuates.
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Old 02-10-2009, 08:53 PM   #2
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If you shorten the rod it will raise boost level.

The reason for the slow spool is because you have a 2860 with the larger turbine housing.
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Old 02-10-2009, 08:55 PM   #3
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Quote:
Originally Posted by Saml01 View Post
If you shorten the rod it will raise boost level.

The reason for the slow spool is because you have a 2860 with the larger turbine housing.
1)yuo didn't answer the question adabout pre-load.
2)There are many people making more boost at lower rpm than me
3)i make it rain
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Old 02-10-2009, 08:56 PM   #4
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1. Yes I did. If you shorten the rod and make it tighter against the housing it will raise ur boost level.
2. They probably have EBC, to make it lower or run a smaller turbine housing.
3. Whatever you say rain man.
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Old 02-10-2009, 09:17 PM   #5
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Is 11 psi at 3400 rpm bad?? That sounds ok..
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Old 02-10-2009, 09:49 PM   #6
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yes, preload away. mine's that way with no issue for months.
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Old 02-10-2009, 10:14 PM   #7
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Dude I make 11psi at like 3600 rpm, and my turbo should be somewhat similar... I don't see the problem.
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Old 02-10-2009, 10:15 PM   #8
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What you want is the flapper to resist the force exerted upon it at boost rise. Adjusting the actuator arm only changes when and how far the flapper opens. Two things that reduced my boost leaks (spool kill) on my internal gate were a helper spring and EBC.

The one thing I noticed on my actuator is that it doesn't open right at a given point, but rather gradually opened from movement starting at ~7psi and completing extension at nearly 10psi. Proper tension on the spring held the gate shut during that initial movement up to the point at which the actuator overcomes the pull of the spring. So there's a quicker opening and longer shut vs. w/o the spring. Ghetto, yet effective.
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Old 02-10-2009, 11:29 PM   #9
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Other things I considered:
getting vac line signal from the intake plenum

+1

But what do I know?
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Old 02-11-2009, 08:44 AM   #10
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what is this helper spring?

I wish the EBC code worked correctly, I have all the stuff for it but I don't feel like running random boost pressures.
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Old 02-11-2009, 10:20 AM   #11
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helper spring thread

another post describing my spring

The ebc can't doing anything with the leak that's going to happen below the wg actuator's open target. Another option is a dual port actuator used with an mbc. I'm considering that at the moment since my actuator is trashed.

similar thread started today
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Old 02-11-2009, 10:30 AM   #12
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Quote:
Originally Posted by m2cupcar View Post
The ebc can't doing anything with the leak that's going to happen below the wg actuator's open target.
Could you please explain that?

Unless we are thinking of different things...

Wouldn't the EBC keep the signal from the WG actuator until target boost was achieved, thereby keeping the wastegate closed longer and building boost quicker?
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Old 02-11-2009, 10:35 AM   #13
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Yes- the ebc does keep the actuator from "seeing" a pressure signal. BUT the ebc can't keep the boost in the turbine housing from physically blowing the flapper valve open. It literally overpowers the actuator (counter) spring that keeps it closed. That's the reason dual port actuators (and helper springs) came about - to assist the actuator spring in holding the valve shut as boost rises.
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Old 02-11-2009, 10:50 AM   #14
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Quote:
Originally Posted by m2cupcar View Post
Yes- the ebc does keep the actuator from "seeing" a pressure signal. BUT the ebc can't keep the boost in the turbine housing from physically blowing the flapper valve open. It literally overpowers the actuator (counter) spring that keeps it closed. That's the reason dual port actuators (and helper springs) came about - to assist the actuator spring in holding the valve shut as boost rises.
Gotcha, that makes sense then.
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Old 02-11-2009, 11:25 AM   #15
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Quote:
Originally Posted by m2cupcar View Post
Yes- the ebc does keep the actuator from "seeing" a pressure signal. BUT the ebc can't keep the boost in the turbine housing from physically blowing the flapper valve open. It literally overpowers the actuator (counter) spring that keeps it closed. That's the reason dual port actuators (and helper springs) came about - to assist the actuator spring in holding the valve shut as boost rises.
Ironically similar to a dual port external gate I might mention.
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Old 02-11-2009, 11:29 AM   #16
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Almost exactly the same in principle and application.
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Old 02-11-2009, 11:32 AM   #17
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is there any way you can connect the wastegate actuator to the .64 turbine housing? that should help.
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Old 02-11-2009, 12:10 PM   #18
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Quote:
Originally Posted by y8s View Post
is there any way you can connect the wastegate actuator to the .64 turbine housing? that should help.
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.
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Old 02-11-2009, 12:13 PM   #19
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thanks m2cupcar. I'm fine with boost threshold now, but I'd love to lower it if possible.
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Old 02-11-2009, 12:13 PM   #20
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just use the spring to pretension huslter i worked great for me.
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