My brother has built a BMW E30 318i Turbo, it runs on Megasquirt and Standard Cossie injectors. Now he is running a pretty large turbo(like T4 sized) but only at around 8psi boost so far.

He is duty cycling the injectors at 110% at top end but still going lean and spluttering with anything over 5000rpm and full throttle. Up until that point the wideband readings are spot on.

We have checked fuel pressure at idle is 3bar.

Now the car feels ok until 5k, full boost is not until 4200rpm though he bought too big a turbo , but it doesn't feel anything like a Stage 1 Cossie as far as I remember. So is it possible to be maxing out these injectors that quickly?

Do Stage 1 Cossies run more pressure??

Help guys.