Losing boost at 4k RPMS?

[Hruke]

So I bought the Aeroforce gauge about a month ago, and couldnt help but noticed at the higher RPM's my boost starts to drop. I have an Injen short ram intake, ported intake manifold, Catless downpipe, BNR Forge Atmospheric BOV, and the trifecta tune. My boost builds up in 2nd and 3rd to about ~18-20PSI then at 4k to 5k RPM's it starts to drop, it goes from 18 to 15 to 12 and by time it hits the lower 5k's its around 7-8PSI. I was just wondering if everyones did this, from what I was reading it could be a couple things, either a boost leak or the turbo is to small (a friend also mentioned it could be the exhaust is too restictive.)

The boost leak is going to be my first thing to look at but the weahter hasnt really been permitting me to do much outside, but now thats its warmer im going to take a look. I am going to take a bottle with some dishsoap and water in it and spray all the areas on the charge pipes that i can, to see if they bubble up. If anyone knows a better way let me know.

The second is the turbo is to small I got this from another forum that someone had the same issue as me:

"Stock turbo's arent really there for huge power. They don't push enough air for that. Similarly, when the engine is turning higher RPM's and requiring more air, the stock turbo can't possibly keep pushing enough air at full pressure to keep up with the engine without damaging itself, because the faster the engine turns, the faster the cylinders are evacuated and refilled. To keep up with that exponential increase, the turbo has to push a LOT more air to keep full boost, and the turbo simply can't push that much air. So they taper it off at the end, to save your turbo, and your engine."

And for my friend that says its the exhaust, I only saw that on a honda forum where the guy said his tuner said it was his exhaust. But non the less I will take off my Mid pipe and see if the boost loss is still there(but I highly doubt this is what the issue is)

So please comment if you have or had this similar problem, and if you did have it what was the problem and how did you fix it.

Thanks,

 

[Breezybro]

Temperature?

 

[Hruke]

Its been pretty cold around 10-20F. Some days are even colder

 

[Blue Moon Sonic]

Even at 10-20F you should be pushing a solid 18-20psi. Now if its in the single digits and below zero, expect only about 14-18psi.

 

[Hruke]

Yeah I think i have a boost leak some where, the boost builds up and peaks at 4k rpms then it starts to drop. I heard the IC pipes leak so im going to start there and maybe with my charge pipe connected to the TB and IM because those are the only 2 things ive touched.

 

[Blue Moon Sonic]

Did you ever port the intake manifold or check the valve covers PCV rupture disc that's under the ignition cover?

 

[Hruke]

Yeah I ported the intake manifold, but I haven't checked anything yet

 

[Hulty]

In those temps, I can push 22psi all day long, FYI. I would start by doing the bypass the bypass mod and go from there. That makes your boost/vacuum numbers more intelligible and takes the sensors out of the mix to begin with. Thoughts?

 

[Trevinator]

what rpm range do you hold a steady 22 psi Hulty?

 

[Hruke]

Yeah I haven't done the bypass mod yet but I'm planning on doing it. It was already done when I ported the IM but there was a problem unrelated to the bypass and I undone it. And never got around to redoing the mod.

 

[BSD]

I'm having the exact same problem. Boost builds to ~23 then I shift up to 3rd and 4th it starts to drop off in the high RPM range. around 40-50 temp wise where I'm at. Ported intake & bypass mod done.

Here's one other possiblity, taken from this thread:
http://www.sonicownersforum.com/for...cussion/9289-how-do-you-get-high-boost-2.html

Why certainly.

"Boost" is a cute racer term that means air pressure above that of barometric. It is actually a measure of a restriction in the path of airflow. Typically the only restriction you want to be in the path of airflow is your engine. However if you replace your charge pipe (the pipe after the turbo) with a drinking straw, you will have a huge restriction and make a ton of boost (but no power.)

It's been discussed on this forum before that people with Trifecta tunes (in the days before HPTuners) will get other mods like intakes and exhausts or manifold ports and see their max boost numbers drop and not understand why. The reason is because there is now less restriction in the system and so the same airflow can be obtained while measuring less boost.

Many people do not understand the difference between boost and airflow. Airflow is a function of volume. In order to make power over time you need some amount of airflow. If your engine flows 100 CFM (cubic feet per minute) of air to make 200 horsepower while measuring boost at 10 psi, and then you get a bunch of mods to make it flow better, you can flow 100 CFM to make 200 horsepower at 8 psi.

The point of this is that boost does not make power... airflow does! So since our cars are programmed for some specific output torque and you make the system more efficient it will continue to make that same output torque with less boost (but same airflow, unless your mods are making the engine internals more efficient.)

TL;DR it's a boost thang baby

So the way that I'm reading this is that the engine has more then enough air so it opens up the wastegate to ratchet back the boost. If i'm right, then would the limiting factor be not having enough fuel? Could that be solved with bigger injectors?

 

[ScarabEpic22]

Guys, the ECM is looking for a delivered TQ value from a programmed table in the ECM. If it can output that value with 10psi of boost, it's going to limit boost to that. Dont care about the actual boost #, care about the actual AIRFLOW being delivered to the engine.

If you didnt change anything and now you see a lower boost value with the same ambient air conditions, baro pressure, and temp then you should start with a boost leakdown test and diagnose appropriately.