Just been tuning my Blitz boost controller today, and turned off the unit to see what the standard wastegate springs would deliver. Im running the 3.5" downpipes and 3" exhaust (APS) with the standard APS actuator springs. Managed to get a spike of 11.2 psi on the springs alone. Anyone else noticed this? I get about 8.5psi after the spike, in the higher gears.

 

Is it just during the shift? Where are you measuring from?

 

On full load, when i nail the throttle. Its only a quick spike. Ive got 3 points of reference, my zeitronix, my defi gauge and the Blitz BC. Plenum tap for the vac hose.

 

Sounds like the actuator/gates are not opening/responding quick enough to the pressure change.

 

^^^ What he said.

Where at in the RPM band? Down low in the beginning?

 

It must be due to that big exhaust, its only if i punch it in the lower gears, its spools up that quick, it just spikes. Like I say, thats with just wastegate control.

If im at like 4k rpm, then nail it, it will spike up (2nd gear/3rd gear) very quickly then come back down again.

 

If it was with the boost controller on I would have said the wastegate duty cycle setting was incorrect but if its doing it on wastegate only then the acuators/internal gates are not responding quickly enough. I'm sure there could be a veriety of causes for this though. Are you running Forge actuators? If so are you running a true divorced gate setup to reduce turbluance in at the turbine discharge? While this may not solve the issue it certainly wouldn't hurt. It will take some fabrocation to do it of course.

 

No, im on the standard actuators (6.5psi springs).

 

Hmm may be time to upgrade to some Forge units. Although again I'm not ready to say this is the cause of the spike. Something interesting in your statement though. You have 6.5 PSI springs in the actuators and have NO boost controller hooked up right? If thats the case you should not being seeing more then 6.5 PSI of compressor outlet pressure as this is where the actuators measure for their pressure to open the internal gate. Perhaps you have surpassed the flow limit of the internal gate. You could try dumping the internal gate flow to atmosphere with nothing else changes and see if this better controls the pressure ratio you get. It may be time for external gates though. Or at the least a true divorced internal gate setup. Similar to this but with the wastegate discharge venting to atmosphere.

 

Sorry mia, you've got me wrong. I do have a boost controller, i just turned it off today to see what i would get off the standard gates. The 3.5" Dp's and twin 3" exhaust are basically giving zero backpressure. Interesting!

 

...but you are getting a consistent 8.5psi reading on a 6.5psi spring?

 

That is correct, yeah.

 

No I understand what you are saying. I guess I should have clarified. With the boost controller turned off (ie: no boost control) and 6.5 PSI springs in the actuators you should not see above 6.5 PSI of comrpessor outlet pressure. Thats assuming your actuator pressure source is on the compressor outlet (typical). But even if you are pulling the pressure source for the actuators at the intake manifold you still should not being seeing above 6.5 PSI manifold pressure. 8.5 PSI is to 2 pounds to much and 11 PSI is a entirely too much. So I guess the question is are the actuators not up to the task of controlling boost? Swapping in Forge units would tell you this for sure. Or have you reached/surpassed the limit of this systems internal gates? Dumping the internal gate discharge via divorces piping would tell you that. The cheapest route to test first would be forge acuators.

 

Thanks Mia, yeah your right.

 

You might give Sharif another call I think he stock Forge Acuators that you could try... If they don't work then its time to look at (a) attempting to divorce the internal gate discharge and vent it to atmosphere or (b) switch to external gates.

 

Plenty of people running the internal gates (in fact everyone i think) on the APS kit with no probs. Its not a massive problem, but its making tuning my BC a bit difficult.

 

The people running the internal gates are all at your power level I believe though. I don't think anyone has gone above what you have with out of box APS actuators. I know bigbri and marlucci are making big numbers 500+ but I don't know if they both have the out of box APS actuators or not. Even if they do I don't think either of them are far past what you are making WHP/airflow wise. It does say something though that APS is using external gates on their Extreme kit.

 

Very true, im sure some Forge items will do the trick.

I'll speak to my guru.

 

I can help if needed. But try the things I mentioned over the phone first, just to make sure we arent chasing a simple issue.

 

Thats a good point. I am operating under the assumption the system is correctly installed and configured (ie, actuator rod length, vacuum line routing, etc).