Can i safely up the boost on my s4 (s5tii engine and gearbox) , im pretty much stock at the moment eg 3inch all the way through with 3" tip and a motec comp. i was wondering what stock boost actually is on a s5tii engine, ive heard all sorts of stuff and want to hear it straight from some guys who know their **** basically. cheers guys

 

FAQ and FSM. Know them. Love them. They 'know their **** basically'.

 

^^what he/she said


the majority for TII owners would tell you stock boost is 8-10psi for S5 motor and 6-8psi for S4

 

don't raise your boost with the stock fuel pump

 

Dont raise boost on stock fuel injectors nor pump.

Things your might want to consider:
Fuel pump
Larger 2ndarys injectors
Some sort fuel management

 

You have a Motec, so basically you can raise the the point to which the injectors are running near 100% duty cycle (don't go over 90%). At that point you have run out of fuel and you need to upgrade the injectors and pump.

Keep in mind that all this tuning should be done in controlled conditions with some way of measuring the A/F ratio and by someone with experience.

Max boost for the stock turbo is about 14 PSI before it starts blowing heat/oil.

 

Also, I've heard that the stock TMIC isn't very effective past about 12psi, though the S5 TMIC may be a little bit better. So, since boost spiking is easy to do with modified TII's, keeping it at 10psi or lower is wise when using the stock TMIC, turbo, ECU, some other things I'm sure... but Aaron Cake is totally right about tuning above stock boost levels, especially if you haven't upgraded your fuel delivery with at least a pump and injectors.

 

cheers guys much appreciated

 

cheers to you 2

 

I found that out the hard way... 18-20 psi on stock turbo... bye-bye oil seal. I could tell that the turbo wasnt making anymore power past about 15-16 psi. Then I smelled the seal frying. Turbo was glowing orange... fun little experiment.

Aaron hit the nail on the head with the inj and pump. I think it would be wise to plug in some 720 secondaries.

Since you have a Motec, you should have lambda tuning. You can set that up to run the AF mixture automatically in closed loop... but if you are swapping out turbos, you may need a re-tune anyway. The pressure coming outta the exhaust is gonna change if you swap turbos.