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Strange High Boost Problem

gt-ahhh!

By gt-ahhh!,
in Engines & Forced Induction

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gt-ahhh! Proficient

gt-ahhh!

Posted
Posted

after an hour of searching and reading i figured id just ask the question.

R33 GTS25t, KKR430, injectors, exhaust, pod, ff plenum, fmic, z32 afm, remapped ecu, greddy profec b ebc, walbro fuel pump, splitfires

my car is going pretty well with the remap i finished today, however i am losing boost in the top end for some bizarre reason.

the boost gets up to about 18-19psi before 4000rpm, and holds that to about 5500rpm, then it gradually falls to 14-15psi. i dont think that constitutes spiking does it? it holds 18 for some time before falling.

ideally i want 17-18psi right through, but i have been fiddling with the profec b incessantly to no avail. i realise you would normally increase gain in this case, but ive already got it up to about 25%, and its not really any different to when its on 10%.

i read that if the standard solenoid is still attached it can bleed 2-3psi? anyone heard of this? the standard solenoid is near the back of the plenum right?

i thought maybe the wastegate actuator was loose, but its spooling up pretty hard and seems to hold 18psi until the revs get quite high. i guess i can try another half turn of tension.

also, im not sure about this, but from research, my set being at 70% seems ridiculous. and sounds very high to get only 18psi.

help greatly appreciated! thanks guys!

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skylinecouple Experienced

skylinecouple

Posted
Posted

That is not spiking but it is definately a weak actuator. The wastegate is being forced open by what is a lot of boost. What I mean by that is at 14lbs boost is moderate but as with all laws of physics the boost rises 2lbs but the actual pressure through the wastegate is astounding. So, at 18-19lbs the pressure is very high, not dangerous but too much for the actuator to hold. If you already have a 14lb actuator then get a 17 or 18lb one. Your profec will love you for it. But the 14lb actuator will do it as thats what I have and there is no problem. Start from the beginning. Turn off your boost controller. Then go for a full power run in third and see if you get the boost your actuator is designed for. If not then wind some turns into it till it starts to climb over the actuators boost level preset from factory. Wind back half turn. That is all you can do. if you only have the 7lb actuator your stuffed. The profec controls the wastegate but can't do miracles. Get a 14lb actuator. About 50% on boost should give you 18lbs. Set gain should be 3-4lbs below the boost your running, ie: 15lbs or as the profec reads, 150. Make sure you set your warning at 20lbs or the profec will cut the fun for you. Be warned, now that your boost will hold till redline you will make more power so get a tune.

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