Turbofags, I need some help. Basically, I've got a boost spiking issue...

Turbofags, I need some help. Basically, I've got a boost spiking issue. If I ease into the boost it holds pretty well at 5 PSI, which is wastegate pressure. However, if I stomp it from a low gear at a high RPM (4k+) it will overshoot to as high as 8 PSI. At wastegate pressure this isn't too bad, but with an MBC and the boost set to 10 PSI I will see over 15 PSI. This is bad.

Recently I replaced my standard exhaust with a 3 inch catless straight pipe from the turbo back. I noticed that after the exhaust install my overboosting issue became worse, however it would still sometime overshoot by a couple PSI before I installed the exhaust.

My car is an R33 Skyline GTST, only relevant mods being the exhaust, an FMIC and a pod filter. Everything else is standard.

Because my overboosting issue became worse when I installed my new, high flowing exhaust, would this indicate that my standard internal wastegate isn't flowing enough to divert enough gas from the turbine, due to there being very little resistance in the exhaust? Or perhaps when I stomp the throttle some of the air gets past the diaphragm in the wastegate actuator due to it being old and shit? Before you ask, yes, the hose from the intake piping to the wastegate actuator is fresh and as short as physically possible.

So fags, what do you reckon it is?

split dump or bellmouth dump? my old r33 boost spiked a fair bit when I was running a split dump, changed it to a bellmouth for better flow and problem solved

JJR mild steel bellmouth

ahh righto, that's the exact same dump I had so idk what the cause of your problem is. Overboosting is most likely a wastegate issue though so I'd be making sure you're wastegate is working as it should be.

As I'm not getting boost creep I'd think my wastegate is opening fully, it just doesn't seem to be opening quickly enough when I stomp it

does it overboost and then drop back down to the desired boost? or does it overboost and hold that boost level to redline?

Drops back down after a second or two

Or moreso it takes a second to get back to the right pressure level, doesn't hold the spike for long at all

You'll need either a restriction plate in the exhaust or a proper external gate because the stock setup uses the restrictions of the exhaust which you have now removed.to help control the boost.

The other alternative is getting the car properly mapped which would be better.

What leads me to believe this isn't the case is that a 3 inch turbo back system is one of the most common mods for this car, and I haven't seen a single person with the same issue. That, plus I was experience overboosting before I changed out the exhaust, even though it wasn't as bad

Seems like the actuator is slow to respond, or the gate is sticking.

I just ordered a brand spankin' adjustable actuator, so when I install it I'll move the arm back and forth and see if there's any resistance. Won't be too cut if the new actuator doesn't fix the issue, I'll be wanting one in the future when I upgrade my turbo so might as well rule it out

Fair enough - I am from the JZ land and what I described is a 100% common issue that happens to everyone with a stock engine who puts a catpipe in.

It could be that RBs are different given that you cant see anyone else having this issue, if you searched for JZ removed cat boost spike you'd get about 100000 threads.

I can confirm at least that putting my test pipe in with a standard 2.5 dump/front pipe and a 2.5 catback there was no noticeable difference in boost spiking :P

Had another thought: I may be getting worse overboosting with my 3 inch exhaust simply because it now spools even faster, giving my potential lazy actuator an even harder time keeping up

Since a good number of turbofags are here, I'd like to ask a boostfag question of my own. I hope OP doesn't mid.

Does anybody have experience with a GReddy Profec Spec-A? I just got one real cheap and haven't installed it yet because I haven't found the proper manual. GReddy's website has a very basic wiring/hose diagram and the manual for programming the head unit but I still have my doubts. The solenoid has three ports, one going to the top port of the wastegate, one to the intake manifold (which I'm thinking of t-ing with the BOV line) and the third one says should go to the charge pipe but I don't know how and it shows nothing special. Should I just drill a fitting to the pipe after the intercooler and plug that hose to the solenoid?

Help massively appreciated, got a TA on Friday and I've only done the easy part of the job.

Pic related.

The one I have no idea about is #2. Also, the EBC came with two little round filters, which lines should get filters?

OP here, don't mind the hijack :)

Nice and close to the throttle body is the best for an accurate boost reading, from what I've read. However lots of cars tee straight into the turbo for the actuator reading, so I don't reckon it makes much difference where it is. If your car is a factory turbo simply tee into the standard gauge/boost sensor hose, ezpz

I haven't used the greddy profec before but have used a hks evc which runs the same hose setup that you mentioned.
One line goes to wastegate as you mentioned, one goes to the intake manifold (bov line will be fine to t into), the last line goes to the charge piping after the turbo and before the intercooler.
Your car should already have a connection somewhere so you shouldnt have to drill a fitting in. What car are you installing this on?

on a standard turbo porting the wastegate should sort it

Thanks for the help guys. IIRC, theres a hose from the turbo to the side port of the wastegate and the top port is currently free. Car is a Swift GTi (pic related) with an external wastegate and I havent seen a place to plug into the charge pipe since obviously it's all custom. Should I just drill baby drill or maybe T that #2 line from the one that goes to the boost gauge?

Lack of boost creep would suggest standard wastegate flows sufficiently, no? It's just lazy in opening when I stomp the throttle

No need to go drilling into anything, just tee into boost gauge line. Cool little car you've got there. Got any pictures of the setup?

Not neccessarily actually.
However I thought it was creeping when I read the OP - I misread.

So, to recap, #1 T to blow-off valve, #2 T to boost gauge and #3 to wastegate's top port, right?

Thanks user. Credit goes to the prev. owner desu, he sold it because he needed funding for racing touring cars and I snatched the little fucker when I gave up on my FEDOHC Mazda. Haven't got good engine pics but it's quite a basic yet brutally effective setup, a big turbo, a Haltech S500 ECU and big ass 880cc injectors, internals are stock (low comp pistons though). PB of the prev owner at over 30 psi and with slicks was 11.8.

Plug the hose for the charge pipe into the connection on the turbo. The line that is currently running from the turbo to wastegate wont be needed when you're running an ebc.

Pictures of the setup would be great as the other user has suggested. That way we can tell you exactly where to put each hose.

How so?

#1 goes to the intake manifold, which is what the bov uses so t-ing into the bov will be fine.
#2 goes into the turbo, so you'll have to remove the hose already on the turbo.
#3 is the top port of the wastegate.
Now the hose that you removed from the turbo will also go to the intake manifold, so you'll have to t it in somewhere as well. You can t it into the bov line as well. The other end of this line should still be in the side port of the wastegate.

>tfw Veeky Forums is actually being helpful

Alright, I'll take some pics when I get home in 2 hours and bump the thread. Thanks for the input!

Most Veeky Forums browsers do actually like to be helpful. The key to finding them is post a pic of a 33 in the op and this scares the burgers off