Overboosting?!?
 

Hi guys

I'm running a stock 13BT engine in an s5 TII, with the stock turbo (and a ported wastegate, although not quite sure HOW big the port was).

I kept the exhaust silencer insert in for the last 6 months, and under WOT i would hit 0.4bars of boost (5.8psi). The silencer came out today, and keeping my boost controller turned off, I went WOT and my factory boost gauge went past the 45 mark, while my own boost gauge probably went well over 0.8bars (11.6psi). I would go as far as to guess that it actually hit about 0.9 or 1.0 bars. Then I noticed the Check Engine light come on for a second, then go off when I decelerated.

As for my Engine Management System, I'm running a Techtom Rom chip, which prevents fuel cut and has a fuel map good for 13psi on the stock turbo.

Why am I overboosting by so much? How do I stop it?

Additional mods to take into consideration: 94mm downpipe, GReddy/Trust Evolution II catless exhaust w/ about a 3.5" tip, stock TMIC, 550cc primaries and secondaries.

hmmm...sounds like ur wastegate wasnt ported much....time to start looking into aftermarket wastegates....or take it apart and port it bigger!

nothing wrong with overboosting. its a good thing. instead of down grading you should upgrade, your fuel system so it wont run lean. get bigger injectors, and 255lph fuel pump. I blew my motor overboosting 12psi on stock fuel setup..

overboosting sucks. You are better off having a properly sized wastegate and proper supporting mods and then using an electronic boost controller to have a better boost curve. Think about it--when you overboost you are building boost, but the wastegate is wide open. 12psi overboost is not going to spool as well as a properly tuned boost controller getting 12psi and having it be stable.

BUT we are talking about a stock turbo which can't hold 12psi to redline anyway. So on a stock turbo it doesn't matter as much.

definitely get some bigger injectors in there, you dont want to blow your motor, lol. even though your ROM chip may have a good fuel map up to 13 psi, the stock injectors won't give you enough fuel for that amount of boost. get some secondaries, and a boost controller and call it a day.

I believe the fuel map was tuned under the conditions of: stock turbo, stock engine, stock injectors, stock fuel pump, and stock tmic.

Anyhow, I DO have a boost controller, a PRofec A (I know, I know...). I think the problem was just a vacuum line to the PRofec control box that came apart.

I have yet to actually test my wastegate actuator, but it seems to me that if I can be at 2000 rpms in 5th gear, and at 3/4 throttle build over 12psi of boost (I immediately let off at this stage) in a split second... it's not my wastegate that's too small, it's that it never opened.

It's funny how the exhaust silencer actually kept me under stock boost... I couldn't run more than 6 psi with it in.

its overboosting because you took your silencer out and turned your boost controller off.. the silencer most likely blocks alot of air going through the exhaust if its the kind im thinking about, and gives it backpressure making it hard for lots off air to get through / flow , how big is your exhaust? and like the others reccomend.. upgrade the fuel system!

so lets picture this....... your in 5th gear, 2000 rmps, then you give it more than half the distance between no throttle to and the "floor". im sure that from 2000 rpm to 3000 rpms on - 5th gear - takes a while....yes your definately over boosting and your engine is at a low rpm. with out any kinda fuel upgrade your shits gonna blow.

all i had on my car when my swap was done, was a walboro fuel pump,3" down pipe and exhaust. i ported my wastegate when i got my engine and still over boosted. i figured that tial 38mm is bigger, so i got that. threw the actuator to the garbage, made the whole for the wastegate bigger, welded metal in between the wastegate whole and the turbine wheel, cut a whole on my down pipe flange,
then put the 38mm there with a .5 bar spring thinking itll stop over boosting. Wrong!


turns out that a 3" down pipe with a 3 inch exhaust is alot of flow for the stock turbo, and with out some back pressure youll get the overboost problem.
so what i did was cut my down pipe on three diffrent spots and weld some flat stock into the downpipe for some back pressure. at first it used to boost 14psi no matter what, now i get spikes to 12psi on 3rd. your gonna need some fuel upgrade so i think that a walboro 255, an AFC Neo, and some injectors will fix your FUEL problem for the overboost. i bout a neo at first, but it still not enough fuel with out maxing out my stock injectors. im rocking 720cc injectors now and the car is safe to over boost. now, im still over boosting but i have the proper fuel for it. a boost controller controls boost up and your running 1 bar as it is. i think before you find out how to stop over boosting your gonna blow up. i mean think about it. how many times are you gonna over boost your car, before you find out "if i do this to itll stop over boosting" seriously man, theres no fuel for your stock boost.

If I turn my boost controller off... it will revert to stock boost. In any case, I also tried the same 5th gear pull with the boost controller on slightly higher than stock boost, and it was no different.

I'm scared to mess with my fuel system because the chip has a fuel map based on stock TII 550cc injectors and the stock fuel pump. I'd rather have an overboosting car that I can throw a silencer on to restrict the boost rather than one that I won't even be able to drive around in the city.

Unless someone has tuned the Techtom to handle the extra boost and unless the fuel system is able to put out enough fuel, this is a good way to pop a motor. If you get knocking, and maybe even if you don't, I'd stop driving until the problem is fixed. It only takes a single strong knock to pop the motor. One day it's hot out or your octane is a little low or there's a little more restriction in the fuel system or etc. and bamn, no more motor. This is the most common way for a turbo motor to die.

Though maybe someone will chime in and say, "With your mods your car can easily handle that much boost," I dunno.

I found out from the company that made and tuned my chip, that boost cut has been removed and the fuel map is good until 13psi. That is the ONLY reason I have ever even turned my boost controller past stock levels.

And the problem is fixed. It was a vacuum line, with an inline drier that cracked and broke in half, thus the PRofec box wasn't seeing any pressure and thus no pressure hit the wastegate actuator.