hi guys,
just wondering when boost first usually starts in a stock turbo 2.............. is 4.5 to 5 normal or too high?

 

Boost gauge is a good indication! :P

But normally around 3.5879999967 x10^3 rmp

 

On the stock turbo, boost should be almost instant regardless of RPM. Well, within reason. Don't expect full boost at 1.5K to come on immediately.

 

mazda uses a twin scroll system to try and eliminate turbo lag to help with low and torque problems of the rotary engine. how it works is at 3500 rpm boost is already at max psi. then at 5500 rpm the boost is reduced to 5 psi and continues until redilne. this is to help with detonation at high rpm. without turbo mods or porting waste gate or modding the ECU stock boost is max of 8.5 psi(pretty positive but not 100%)

 

Fuel cut is 5.5 psi for the S4 but the redesigned s5 turbo with equal exhaust runners etc allowed for 8.5 psi before cut.

 

No, fuel cut is ~8.6 psi for both S4 and S5 cars.