Turbo without wastegate [Archive] - SaabCentral Forums

: Turbo without wastegate

9th March 2004, 05:01 PM
Does anybody has ever tried to blocked the wastegate to see what happen ?
I mean for example if i have a blocked wastegate and that i run the car like that, what will hapen to the boost, what will the boost the limit ?
Supposing that i have no knock, how will run the engine at such huge boost?

900 spg
9th March 2004, 05:26 PM
Hi Niko,
I believe you would fry the engine very quickly. do not asko for figures or data as I do not have it but it seems pretty logical to me according to the limited mechanical knowledge I might have.

please correct me if I am wrong, anyone.

best regards


p.s. I are an audi a6 the other day as well in a small street race ooops (hope noone is listening :) )although my spg is not top notch lately. I feel like it is lacking power or is it me who is I ready for a major mod. I wonder? ;)

Johann F
9th March 2004, 05:49 PM
Why not try it and tell us what happens - I'm sure it's perfectly safe.

10th March 2004, 03:56 AM
Why not try it and tell us what happens - I'm sure it's perfectly safe.
Missing a couple of emoticons I think :nono; :nono;

10th March 2004, 05:03 AM
Thomas, you'll have no means of boost regulation other than your right-foot. Even your 16G compressor wheel will very quickly get out of its efficiency range, resulting in high inlet temperatures and detonation (and with your MBC, you get no protection from an APC).

The car would be undrivable, with IMO shattered gearbox and damaged engine happening very quickly.

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10th March 2004, 06:25 AM
Why not try it and tell us what happens - I'm sure it's perfectly safe.

Thank you Johann for your help. That's really the kind of answer that make me wonder if you are so indispensable ?

Thanks matthew for the answer.

Johann F
10th March 2004, 12:48 PM

11th March 2004, 08:48 AM
Well, to make this a truly internation affair...

This is only safe to do in the U.S. Other countries, including Europe and Asia suffer from a condition called noboostatall. :D

Just kidding, actually all of the above are spot on...you will damage your engine in short order because of the inability to control boost, boost spikes, EGT's, etc.

ANd a big 'Ow do you do to the boys across the pond!


11th March 2004, 12:17 PM
The only time that it is worth trying to run with the wastegate wired shut is if the car is suffering from lack of top end boost. Either the wastegate is blowing open under exhuast manifold gas pressure (requires a stronger actuator), in which case the boost will increase with a locked actuator or the turbo cannot make the boost desired (new turbo).

Doing so is very dodgy, requires careful throttle control in the midrange, and close watch of the boost gauge at the top end which isn't always easy if the car is accelerating hard.

11th March 2004, 01:42 PM
Thanks Alex
As you told me, i suffer boost creep, i'm pretty sure of it. Since i changed the bypass valve for a Forge, the bypass is no more leaking, the boost rise too fast, and the wastegate arm is too short to be able to counteract the rising of the pressure...
I shorten too much the wastegate arm because i was unable to sustain high boost at high rpm... now, i reach 1.7bar !!!
At this pressure, i don't have knock, but the car doesn't run well because the pressure fluctuate too much and it seems that there is a leak somewhere...

Anyway, many thanks to ALL guys for inputs.

11th March 2004, 02:03 PM
Niko what type of actuator are you using :-??

EDIT: re- read your thread and looks like you're getting the total opposite of what I originally said :lol: i.e. your boost was tapering down. I associate "creep" with boost going up & "taper" being boost going down - sorry bit of a mix up :oops:

11th March 2004, 05:06 PM
With regard to stronger actuators - apologies if this seems glaringly obvious - would fitting a stronger one mean that the maximum boost would then be higher? Or is there no change of maximum level, purely a case of how it would maintain the existing level.

11th March 2004, 05:20 PM
An uprated actuator won't increase your maximum boost if your fitting the right one (for a 900 0.5 bar is generally accepted - roughly half your maximum boost).

An uprated actuator will have a stronger spring and is more able to control higher boost pressures. If your actuator is too weak (or knackered) the wastegate can blow open under boost. Also the wastgate can start oscillating effectively meaning it's out of control :o

11th March 2004, 05:39 PM
Hmm... perhaps I may have a bum actuator. It was set to "stock" settings after a trip to the rob-me-blind Swedish Specialist (aka The SS). When I was driving back from the place my vta blow off valve wasn't going a damn thing. But then that probably means that the previous owners of my vehicle just maxed out the shortness of the rod to get boost.

Side question:
Everyone says that external wastegates work much better since they can maintain higher boost levels and are more responsive. Is all of that true? And isn't there a special 3" downpipe floating around which can house an external wastegate without having to bore into the manifold?