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Old 08-04-2007, 01:14 PM   #1
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Default boost creep - external wastegate placement questions

Recap- SSAC tubular type stainless manifold with external wastegate on the #4 runner. The WG came with an unknown very stiff spring, I replaced it with one that was sold as 3.6psi. The WG has an open dump pipe and it is very obvious when it is open or opening.

WG signal reference is the tap on the compressor housing. ECU and gauge reference is the intake manifold.

I'm trying to get wastegate control to be sub 6-7psi and I'll control it with the boost control solenoid after that.

Results-
With the 3.6psi spring, boost would easily go over 7-8psi in 2nd gear at high rpm. Cutting the spring down seemed to make the WG open earlier but the boost levels haven't really come down. The WG is now opening before any boost is present in the intake manifold.

At low rpm, sub 4k, the boost is regulated to 2psi but it climbs linearly to 8psi by 7k. As a sidenote, it's kind of fun to have power build linearly with rpms.

The big question and fear is that the WG placement in the #4 primary is not allowing enough bleed off to control boost below this 8-9psi level. I'm pretty sure there is no way exhaust from 1-3 can backflow up the #4 primary to the WG. I just don't want to go through the hassle of reconfiguring the entire WG setup.

Anyone with experience or suggestions? Hopefully suggestions don't ask me to make the exhaust more restrictive or tear everything apart and do a bunch of fab work.
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Old 08-04-2007, 09:39 PM   #2
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ok, how is the vacuum/boost hooked up to the wastegate? side port or top?

Is the solenoid in the equation? if so, try only running one line to the wastegate's side port, with nothing in between...
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Old 08-04-2007, 10:19 PM   #3
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Solenoid is currently not being used. Silicone hose going directly from a fitting on the compressor housing to the 'side' (the side of the diaphragm that makes the valve open when it sees pressure) fitting on the wastegate. The 'top' side is open.

I'm almost positive that this configuration (WG on one runner way upstream, very far away from the collector) is not capable of controlling boost to very low levels.
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Old 08-04-2007, 11:15 PM   #4
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I can control mine from 6psi (6 psi spring) to whatever using a solinoid. I have a manifold that's exactly the same as the ssac 4 into 1 with WG on #4. I'm using a Tial 38mm WG and the solinoid is the old Miata purge solinoid wired to my EMS.
Your WG might be sticking if it can't control what the spring pressure is set to. What WG are you using? New, used, name brand, generic?
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Old 08-04-2007, 11:53 PM   #5
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lazzer408 - Glad to hear that it works, gives me hope.

The WG is a new generic eBay one. I disassembled it, checked it out, cleaned up a couple things - all seemed fine. I tested operation with a regulator, boost gauge and air compressor prior to install.

I'll do some tests, I admit that I haven't tied it open (mechanically or applied vacuum to the top side of the diaphragm) yet. It's just that at low rpms the boost control is steady then it creeps.

Do you know have a source of WG springs? I'm going to have to get more.
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Old 08-05-2007, 12:29 AM   #6
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FWIW, I run a tial 35mm on my JGS manifold, directly where all the flow hits the turbo, right underneath the flange. I have never had an issue with boost creep.

I have heard horror stories about malfunctioning ebay wastegates..... be careful!
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Old 08-05-2007, 01:09 AM   #7
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Quote:
Originally Posted by dvcn View Post
lazzer408 - Glad to hear that it works, gives me hope.

The WG is a new generic eBay one. I disassembled it, checked it out, cleaned up a couple things - all seemed fine. I tested operation with a regulator, boost gauge and air compressor prior to install.

I'll do some tests, I admit that I haven't tied it open (mechanically or applied vacuum to the top side of the diaphragm) yet. It's just that at low rpms the boost control is steady then it creeps.

Do you know have a source of WG springs? I'm going to have to get more.
You mentioned it's steady at low rpm? Maybe the turbo just isn't building enough boost yet to know for sure? If you have boost creep either the WG isn't opening fully or the opening thru it is restricted. Remove the spring completely, reassemble it, opperate it manually to be sure it's opening all the way, then install it without the spring and see if you still have boost creep, or any boost at all. Is it a 38mm or smaller?
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Old 08-05-2007, 04:59 AM   #8
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Quote:
Originally Posted by dvcn View Post
Results-
With the 3.6psi spring, boost would easily go over 7-8psi in 2nd gear at high rpm. Cutting the spring down seemed to make the WG open earlier but the boost levels haven't really come down.
FWIW, cutting the spring reduced it's free length, but it increased the spring rate. I would guess that a quality spring of the right rate will have you back on track. Either that or your WG is a timebomb.
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Old 08-05-2007, 08:39 AM   #9
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Quote:
Originally Posted by lazzer408 View Post
You mentioned it's steady at low rpm? Maybe the turbo just isn't building enough boost yet to know for sure? If you have boost creep either the WG isn't opening fully or the opening thru it is restricted. Remove the spring completely, reassemble it, opperate it manually to be sure it's opening all the way, then install it without the spring and see if you still have boost creep, or any boost at all. Is it a 38mm or smaller?
With the full length spring, 4th gear, boost onset was around 2500rpms and at 4-5psi by 3k. With the cut spring it will stay at 2psi until around 4k. I think it is in the 35mm range. I will test it with no spring, that's probably the easiest thing to do.

Quote:
Originally Posted by mschlang View Post
FWIW, cutting the spring reduced it's free length, but it increased the spring rate. I would guess that a quality spring of the right rate will have you back on track. Either that or your WG is a timebomb.
I did think of the spring rate rising. The spring seemed to be so long that it was heavily preloaded and I thought that it might be near full compression as the valve opened. I don't think it's a timebomb, it opens fine, just possibly not enough. I'm also lucky enough to have an ecu with an overboost limiter.
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Old 08-05-2007, 03:33 PM   #10
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Eliminate all suspects then work backwards. No spring, no solinoid, no mbc, ect. Problem still exhist? If so what's left? The wastegate could be to restrictive or the manifold design isn't working.
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Old 08-06-2007, 06:24 PM   #11
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Completely removed the spring, same result. The valve actuates fine. I'm guessing that it is just too small for the placement.

Some parts of it are 38mm but the stainless (removable) valve seat goes down to 31-32mm.

Any suggestions on a wastegate size/brand? At this point I'd like to run something with a LOT of extra capacity.
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Old 08-06-2007, 06:37 PM   #12
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yeah i think that 1 trying to controll it via a signal preturbo source, doesn't seem ideal to me at all. perhaps try to join it with another runner so you can move more air out.
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