Boost Spiking

Basic tech questions such as future setups, different turbo kits, car diagnosis, etc
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Freise
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Boost Spiking

Post by Freise » Sun Jan 06, 2013 7:55 pm

I've got an Isis RS3871, it came with an adjustable wastegate. I've lengthened the rod to turn down the boost. If I build boost slowly, like in 5th gear low rpm, it will build fine to its limit, but in faster-boost-building-scenarios like WOT in 2nd i am getting huge 15+psi spikes (so thankful for overboosted tuning)

I've even adjusted the rod to its full length, so no pre-load on the wastegate spring at all, and still getting huge 15+ spikes, and it has me baffled. My only conclusion is that the wastegate must be faulty, but is there another possible cause?
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Post by cleantune » Mon Jan 14, 2013 4:32 pm

I know you probably already know this, but just so I, myself, can keep everything straight: The wastegate is normally held shut with the preload spring you had mentioned, but then it also has a manifold pressure actuator. Once the preload spring's limits are exceeded (i.e. the set psi), the manifold pressure overwhelms the wastegate's preload spring and the wastegate opens, keeping the turbo at the set psi.

Considering this, since the spring's force is fairly constant, I would suspect that the vacuum line may be to blame. I would check to see if the vacuum line is unobstructed. Then, if the other end of the vacuum line isn't routed to a "true boost source" (pressurized source within the intake after turbo compression) I would try to find one to hook the vacuum source up to. If it is hooked into a good vacuum source I would check to see if the wastegate moves/opens freely.

Let us know what you find out :wink:
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Post by supakat » Mon Jan 14, 2013 5:48 pm

Other issue is colder denser air is harder to bleed effectively.
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Freise
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Post by Freise » Mon Jan 14, 2013 7:07 pm

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The line to the wastegate is basically as short as possible, with little to no chance of of a leak. But then again, I did a leak test before ever starting the car, maybe a hole has appeared once everything was warmed up or something...
The wastegate flap opens and shuts freely with no issues.

I'll see if a boost leak test reveals anything new,
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Post by eazye2000 » Tue Jan 15, 2013 6:19 pm

This is also because it sounds like it's an internally gated turbo. They don't operate like a normal external gate. They are a little slower to react, in my experience.

I had a 3076R in a T2 configuration. I ran it externally gated, and it was like night and day. Not to mention great spool from the T2, but then the wastegate bypassed the small flange making it more efficient. It was a great combo.

Just my $.02
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Post by boker240 » Sun Jan 27, 2013 3:43 pm

86 the internal and get an external tial.be done w it. my .02
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Post by Freise » Sun Mar 10, 2013 4:00 pm

I'm back at this due to nice weather:
I did a thorough boost leak test, no major issues and fixed some small ones.

The line between the boost source and wastegate is not leaking.

I can run some compressed air through the line to open the wastegate, it begins to open as I increase pressure, but it takes about 20psi to open the flapper completely.

The adjustable rod has been lengthened to where the arm is about parallel with the flapper. In other words, if I make it any longer the flapper will no longer fully close. So the only ideas I have left is either I have a profound misunderstanding to how this "adjustable" wastegate works (For example, wouldn't increasing the length of the rod further cause the turbo to spool significantly slower if the flapper is never fully closed? Or is that what I must do in order to lower it??), the wastegate is somehow "bad," or there has to be something else I haven't thought of.

Any ideas before I try buying another wastegate?
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Post by boker240 » Sun Mar 10, 2013 5:03 pm

Freise wrote:I'm back at this due to nice weather:
I did a thorough boost leak test, no major issues and fixed some small ones.

The line between the boost source and wastegate is not leaking.

I can run some compressed air through the line to open the wastegate, it begins to open as I increase pressure, but it takes about 20psi to open the flapper completely.

The adjustable rod has been lengthened to where the arm is about parallel with the flapper. In other words, if I make it any longer the flapper will no longer fully close. So the only ideas I have left is either I have a profound misunderstanding to how this "adjustable" wastegate works (For example, wouldn't increasing the length of the rod further cause the turbo to spool significantly slower if the flapper is never fully closed? Or is that what I must do in order to lower it??), the wastegate is somehow "bad," or there has to be something else I haven't thought of.

Any ideas before I try buying another wastegate?
This is also because it sounds like it's an internally gated turbo. They don't operate like a normal external gate. They are a little slower to react, in my experience.
86 the internal and get an external tial.be done w it. my .02


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He'll probably blow the motor, and then join the army of retards who hate on KA's for no good reason.

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Post by ViperGT » Wed Mar 13, 2013 12:42 am

Waste gate may be too small for your application you could try running A softer spring in the waste gate ( idk if its changeable) and then get an electronic boost controller, but to me it sound like you should go external, try and pick up a used tial if funds are tight and replace the diaphragm ($30) or just get a new one mvs would be a good size
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Post by shift_down » Wed Mar 13, 2013 9:21 am

You can buy a cheap tial knock off, and replace the diaphragm with a real tial diaphragm.
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Post by boker240 » Wed Mar 13, 2013 2:37 pm

^^^^^^^^^^^^^^
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Post by Kruked » Sat Mar 16, 2013 6:05 pm

shift_down wrote:You can buy a cheap tial knock off, and replace the diaphragm with a real tial diaphragm.
I did this. The diaphragm was $100 through a local speed shop.
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Post by p00t » Mon Mar 18, 2013 7:08 am

Those adjustable wastegates only adjust a few PSI, I'm not sure how much you're trying to get out of it...

I had 7psi adjustable and with it tightened all the way I got 9 psi.... poopoo

If it keeps overboosting like that the wastegate probably has slow response and the WG port is too small. If you have time take the turbo off and see if you can port that crap hole.
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