I had the Hayward & Scott decat downpipe fitted to my Sti2 last week and had previously fitted a 3" bore, pretty well straight through, exhaust system. Now I find that in 1st and 2nd gears the overboost cut out seems to come in so quickly its hard to control. Even trying to 'short change', especially in 1st, doesn't work anymore. Is it a case of learning to time the throttle with the revs very carefully so that the boost doesn't rise too rapidly or are there any other mods I can do to stop the engine cutting out when the boost rises so rapidly? I know the overboost cut-out is there to protect the engine but the car was way more driveable before the downpipe - in the low gears I mean.

Any help appreciated !

Colin

 

You really need to establish if you are overboosting because the wastegate is not working efficiently enough, or becuase your boost control is not working well enough.

Easiest way is to connect the actuator on your turbo straight to the bleed nipple on the turbo housing. This will remove ECU boost control. If you STILL overboost, you have a wastegate problem: Check exhaust is not fouling wastegate, perhaps change for a different downpipe.

If you DON'T overboost, you will either need:

1) A remap (see www.scoobyecu.co.uk..it's cheap and good)
2) A dawes device to limit the boost.

 

i went for the dawes device!

 

Thanks for the tips guys.

Is the idea to use the Dawes device to allow higher boost without the overboost cutout coming in?

Also - my cars an Sti2, so I need to use octane booster to get up near to the 100 RON to prevent pinking/knocking. If I increase the boost further there will be an even greater chance of knock - is there a way round this?

Cheers

Colin

 

colin,

I had overboost with my decat so i tried a few different size resrictors in the solenoid pipe,put a slightly larger one in and its fine now.

 

the dawes is fully ajdustable so just turn it down slightly!

 

Ok, I just want to make it completely clear that before you can proceed you need to work out what the problem is. To do this, you will need to connect your actuator directly to the turbo (i.e. remove the hose from the solenoid to your actuator, and connect it to the hose coming from the compressor output on the turbo). This will mean the wastgate opens at 0.8(ish)Bar. The ECU has no say in it.

If you still get an overboost problem, then your exhaust is fouling your wastegate, or at least ruining it's flow efficiency. This means that you are going to have to change the downpipe (if it is an open neck design, you may wish to have a baffle welded into the neck) or choose another model.

If the problem goes away, then your boost control mechanism is not accurate enough for your new exhaust. Your options are now:
Get ECU remapped (perhaps a visit to www.scoobyecu.co.uk...might be able to help), or simply stop the ECU controlling the boost.
This is where a Dawes comes in. You set the dawes to the exact boost you want (i.e. the factory setting...or lower if it makes you feel safe on our horrid petrol) and it will keep the boost under tight control.



Another word of advice on a seperate note: If you are running an imported scoob (STi) then you should have a knocklink fitted....if nothing else so you know if a bad batch of petrol is hurting your car. Do a search on Knocklinks. If you don't belive me....ask John Banks.