Wierd boost spike after turbo swap

[SketchyRollin564]

So i just changed my blown t25 that smoked and had shaft play with a pretty decent one that has no shaft play and doesnt smoke. My last turbo had a 1.4 bar wastegate (20ish psi) attached to it, and i had a boost controller on it to limit it to 8psi. It would only spike to 9psi real quick, but it would always hold 8psi untill redline, no matter what RPM i would go wide open throttle at

The old turbo would only hit 3 or 4psi at 3k rpm, while this one will hit 7psi
The old turbo wouldn't hit full boost till 4.8k, while this one hits it at 3.5k (spiking)
So that being said, this one makes boost a lot faster

This replacement turbo came with a stock wastegate (7psi), so i am using it. The BC i have hooked up to it is some cheap ebay valve type boost controller. My car now spikes real weird ever since i put the new turbo in, but the boost controller is the same. The spike is interesting, it doesnt drop if in relation to RPM, but more as how long its been at boost for. It is also a slow spike, almost like a leak

For example, lets say im in 3rd gear. From 4k, i will go WOT and hit 10psi, and drop slowly to 8 or 7, and it will go back to 8 and stay there until redline

different scenario. I will be in 3rd gear. Going WOT from 3k to 4k it will do pretty much the same thing, but only hit 9psi, dropping to about 7.
-Letting off and going WOT again from 4k to 5k it will do the same, but at 10psi and drop to 7 and then back to 8.
-From 5k to 6k, i will stay at 10psi til about 5.5k and it will drop down to 8.

But now get this, from time to time, if i go WOT after 5.5k It will spike to 11psi, and hold a steady 10/9psi until i shift at about 7.2k. This is weird seeing as it doesn't really drop off at high rpm, where if i get on it at a lower rpm, it will drop off right away and wont go past 8psi.




My understanding of boost spikes, is that when the turbo hits the initial rush of "full boost" faster than the wastegate can open, it spikes until the wastegate opens, and then will stay at that boost level after the WG is opened. But it will also (mainly on a small turbo, like a t25) drop off as you get past its efficiency range in higher RPM. For example, floor it at about 4k, it will spike real quick, and then hold at lets say 9psi, and as you get closer to redline, it will drop slowly to about 8.

Mine however, will stay at 10psi if i floor it in the power band, but if i go at wide open throttle a little before, like at 3k, it will keep falling down, and even if i keep the pedal pegged until redline, it will never see higher than 8psi


I am wondering why it now acts like this?

Another thing to note is that my BOV used to just surge once, maybe twice, at low rpm/boost levels, and then it would let off. At higher boost it would just go off. With my new turbo, the BOV doesn't go off at all at low rpm/boost, and just flutters like crazy. At higher RPM boost, sometimes it surges a little and then blows off, or sometimes it just blows off.




I am wondering if these two problems are related, and how they would be caused? I have T clamps on my entire hot side, and regular hose clamps on my cold side, but they are tight, and hold fine. This turbo makes boost quicker, and goes (or at least spikes) to a higher boost level, without having touched the boost controller at all since the turbo swap. So theoretically, it should blow off easyer, not less.

I am also wondering if this wierd spiking issue i have has anything to do with my cheap boost controller. I know manual boost controllers are known for spike, and the ball or spring type manual boost controllers are better than a valve type one, like i have, but it was fine on my old turbo, and didnt have a bad spiking issue. Also if this has something to do with the boost controller, i dont see how it would effect the blow off valve. Just incase anyones wondering, i have my blow off valve hooked up to a vaccum line on my throttle body. The wastegate vacuum goes to the boost controller, and then to the hot pipe.

Has anyone here experienced similar spike like this and figured out what caused it? I know spike is normal, but the way its doing it is not normal at all.

Any input greatly appreciated

[badbob2121]

sounds like the boost controller, just remove it and see if that is the problem

note: i did not read the whole page of text....

and not hitting full boost until 4.8k with a t25 is beyond asinine.... fubar

[SketchyRollin564]

read it if you can. The spike is completeley different from a normal quick spike, this one changes how it spikes at different RPM. At lower rpm it will spike 8 and hold 7, at higher rpm, it will spike 11ish and hold 9 til redline. But no matter what rpm i go WOT at, it slowly drops off, and sometimes goes back up. Its wierd as hell

if you didnt read, another thing to note is my last wastegate was a 1.4 bar wastegate, this one is stock 7psi wastegate

[SketchyRollin564]

Anyone else got any ideas? Im thinking its either my BOV opening up, or the boost controller

I raised the boost today. It will spike at 14/15, and will hold anywhere from 10-13 depending on what it feels like doing. But if i stay in 5th gear at a cruising rpm and i go full throttle and watch the boost build, it will go up to 13/14 and stay there. In first gear it will stay at 14, probably because there isnt enough time to come back down. 2nd 3rd and 4th they come down to about 11 or 12ish. Somtimes 10, sometimes 11


Im betting it has to do with the boost contorller. I opened it up today, all it is, is a little spring held with pressure by the spinny knob and a locking nut. If i replaced the spring with a similar sized spring thats a tad bit stiffer, would that minimize my spiking a bit?

[Morph]

What happened when you removed the boost controler?

[SketchyRollin564]

No spike, but thats also only 7psi vs 8/9 and 11/12. I might have a boost leak that only opens up at higher, boost, and the natural spike of a manual boost controller amplifies it, if that makes sense

i want to try either another boost controller or another spring, but i dont wanna get a spring too stiff, and i dont want to buy another BC if its gonna do the same thing