AndrewSTI-V

Got my front de cat pipe fitted tonight. Before on a cold night the car was holding 16psi in 5th gear which i thought was about right. Now tonight its hitting well over 20psi in 5th gear.

In 3rd after 5500 rpm it jumps from about 14psi to 18psi then drops back to 17 psi.

In 4th after 5500 rpm it jumps from about 15psi to 19psi then drops back to 17psi.

In 5th gear its holding about 15psi until i get above 5000 rpm then its overboosting to about 21 - 22psi and holding it.

The mods i have are blitz nur spec R, magnex downpipe and K&N 57i kit.

Anyone any views??

john banks

The rate of boost rise is too quick for the ECU's wastegate solenoid duty cycle control, which would benefit from being modified. Alternatively you can use a flow control valve to regulate the boost rise (more accurate and more easily adjusted than drilling out restrictors which is a nightmare to get perfect). Email me if you want any more info.

john banks

Also might be worth checking that the wastegate has a free 90 degree range of movement and is not fouling the new pipe.

AndrewSTI-V

yhm

john banks

YHM back. Contents here for anyone elses benefit.

Assuming nothing else was changed except the downpipe:

You can stop it going boom for as long as you want by just not using full throttle. If you are not mechanically minded get someone to check the wastegate is not binding on the new pipe. Get them to clean the boost control restrictor and solenoid with brake cleaner.

Failing that you need to get them to change the size of the boost control restrictor (increase by 0.1mm from a probable 0.8mm to 0.9mm on an STi). They need a precision drill kit for this. With the amount of overboost you are getting you may need it at 1.0mm, but go in small (0.05mm) stages if possible as a little extra bore on this restrictor goes a long way.

In these sorts of weather conditions you should be getting a peak of up to 17-17.5 PSI max in 5th gear, although your gauge may be inaccurate. The ECU on your car is aiming to hold 15.7 PSI, hitting about 16 PSI in 4th would be about right.

A knocklink would be a good idea anyway if you are running a decat STi.