Overboosting Due To 4inch Exhaust

[benson]

I have installed a 4inch exhaust for the stock dump, high flow cat to match & 4inch sytem through now the car is overboosting, engine & management is stock, the car cannot rev over 4000-4500 rpm the boost climbs as you accelerate, I have read near 11psi on the guage, first gear not so bad, can some time rev to 6000rpm. The engine management must read to much flow & breaks up sound the same as when you hit your rev limiter. Does anyone know how to rectify this without a tune/flashing (would a flash tune even fix the problem). The amount of extra pull & punch is awesome just wish it would rev out as you can feel it want to go than shuts down about 4000rpm.

[Ralph Wiggum]

get it tuned before it goes

[jordak]

To elaborate on the grim reapers comments above.

Put your old exhaust back on, spend some time reading the associated threads on this forum, find yourself a tuner and get a custom tune.

Your engine will be running lean because it is flowing better it is creating more boost without the delivery of additional fuel which a custom tune will sort out.

[Buf-Phoon]

what they said. PM sent just in case

[Headsex]

The problem comes down to the Turbos exhaust housing.

Quite simply, the wastegate port is not big enough, and the exhaust gases are not encouraged to exit via the wastegate due to the lack of back presure, but rather spin the turbo up.

3 ways this can be fixed..

1) remove turbo, enlarge wastegate port, get bigger exhaust wastegate flapper..

2) get custom tune, and possibly injectors because your boost will not be lower than like 12psi. (mine wouldnt go below 17psi on a cold night...)

3) put standard exhaust back on.

danny.

[rboksic]

  Headsex said:

The problem comes down to the Turbos exhaust housing.

Quite simply, the wastegate port is not big enough, and the exhaust gases are not encouraged to exit via the wastegate due to the lack of back presure, but rather spin the turbo up.

3 ways this can be fixed..

1) remove turbo, enlarge wastegate port, get bigger exhaust wastegate flapper..

2) get custom tune, and possibly injectors because your boost will not be lower than like 12psi. (mine wouldnt go below 17psi on a cold night...)

3) put standard exhaust back on.

danny.

Danny that will not help him

He has not Edited the car!

[Headsex]

  rboksic said:

Danny that will not help him

He has not Edited the car!

Option 1 and 3 will fix his problem.

The problem is the wastegate is not big enough with standard exhaust the back presure was hiding the problem.

You DO NOT require a tune to make the wastegate flapper/port bigger. Only if you change the actuator,

Danny

[ZAP]

I think option 1 will still cause the ECU to limp. It will detect the boost spike and shut down like it is now. Just because the turbo will handle the boost better will not help the ECU.

It is either Edit or remove the exhaust

[Headsex]

  ZAP_F6 said:

I think option 1 will still cause the ECU to limp. It will detect the boost spike and shut down like it is now. Just because the turbo will handle the boost better will not help the ECU.

It is either Edit or remove the exhaust

Option 1 WILL fix the problem. One car I worked on, I had to redo the wastegate port a second time as it wasn't done enough the first time.. The car ran perfect with the std tune after that. No overboost

[RAP1D]

Just baby it along without ever going over 6psi until you can get a Capa Edit box and get it and the car to a tuner that will dyno tune it so you can run it safely.

Like its been said above, its just overboosting due to the new found lack of airpressure on the turbos exhaust wheel, thus the turbo can now spool heaps faster and wont be held back by the restrictions of the stock exhaust.

It wont blow up if you just keep the foot out of it and keep a close eye on your boost guage, dont let it go over 6psi... so no flooring it or half throttle until it tuned for the higher boost.

Unfotunatley our cars in stock form have such hugely restrictive intake and exhaust systems that any mod like this will cuase you tuning and overboost issues... this is why we all have Edit tunes.