Tired of minor compressor surge?
 

I have a T04B H-trim with a .84 divided turbine on a custom divided tubular manifold attached to a S4 block with stock ports and a S5 LIM & FD UIM all connected with 2.5" intercooler pipes....And, I was getting a lot of compressor surge under light acceleration when I was anywhere in the vacinity between 0-1 psi and 3-5" of vac. This was with a tial 50mm bov, first with a 9psi spring and later with a 7psi spring (which only made it a hair better). Basically, the tial was staying shut and the volume of air coming out of the turbo had no where to go since the throttle was open so little. This got anoying fast as this is a street driven car, shit... it's a wagon.
So I decided to add a stock style Bosch bov to work together with the Tial unit. You may be saying wtf, but hear me out, becouse it eliminated all the surging.
I tested the tial with a vacuum pump and discovered that it opened at about 13-14" of vac.... no wonder it would surge at a lower vac.
The Bosch unit opens much earlier, almost intantly...like 3" vac.. The thing about the Bosch unit is that the valve diameter is only 1" and it only pulls open like 3/8" of an inch...not a lot of flow to say the least. This is why we all buy larger bov's that can flow way more.
Using them together has like a stage effect. When accelerating lightly it's possible to let off the bosch valve first and then the tial. If you let off hard, they both blow and it sounds like theres only one. There are no signs of the bosch leaking under boost or that it messes with spool time. If they do "stage" the tial still lets off a lot of air when it gets it's turn, which is to be expected since the bosch is so small...my point is that the tial is still needed. Consider the bosch unit more of a surge relief valve.
I Mounted it near the turbo, heres a pic.

holy cow is it crammed in that engine bay, but it looks good. :bigthumb: for a good idea

What about just using a softer spring in the Tial BOV so that it opens at a lower vacuum?

as far as I know the 7psi spring is the softest

i had this problem on my old turbo FB. i was using the Turbo XS RFL. all i did was cut the spring back some and it solved the issue. but, your setup works and that's what matters :)

I got a second Tial BOV in a trade , it had a "hard" spring for a piston motor in it , I just opened it up and cut a few turns (about 2) off the spring and it got just as "soft" as my other Tial with the rotary friendly spring in it .

Tial sells the softer springs for low boost applications.
they work good.

YAY tial bovs. but has any one tried the hsk ssqv valve on higher hp stuff.
i am running one right now (ssqv) and have seen NO surge what so ever. im only running 10lbs right now on a t67 with stock ports so i cant say how it will vent larger ammount of air but from what i can tell its doing a great job. you can hear it working at very low boost levels and it gets very loud at 10-ish psi.

i also took out those stupid fins in the middle of it because they serve no practical purpose other then blocking the flow of air. and it sounds like the tial. but i never ran it with the fins so i have no idea what it is supposed to sound like.

I can't believe you removed the flabadaba diverter valve fins! :)

HUH ????

oh but i can and its amazing! and im even thinking about just chopping off the whole front part that the fins used to sit in. just because it will put the valve about 2 mm away from atmosphere then.

So after driving around for a few days I have some stuff to report. The "Surge relief valve", as I like to call it, definetly works...however there are some issues. There is a noticible drop in responsiveness when it opens. I like the fact that the valve opens early (where it used to surge so much) but it is simply venting too much and killing responsiveness and that crisp throttle response I worked so hard to get. The other problem is that while cruising at 5" vac. or higher theres a constant air/boost leak sound since the valve is open, which is a bit annoying. I'm glad now that my tial bov isn't opening that early since it is so large.
My plan is to put some sort of restriction, like maybe a piece of aluminum round stock with a hole in the center on the output of the bosch valve to limit the amount that it will vent, hopefully just enough to keep the surging at bay.


Edit: the cool thing is that I am realizing how well my turbo & manifold combo is working, as the turbo surging is a direct result of the turbo producing more air than the engine wants at the given time (when the surge occurs).

More good news for the few that may be interested....
The aluminum stock with a hole drilled in the center worked like a charm! All the surging is gone, there is no noticeble drop in responsiveness like before, and even the noise went away.
I had to keep drilling the hole larger until all the surging disapeared, it was cool... the larger the hole the less it surged until it just went away.
Here is a pic of the plug on the silicone hose