aterminatorz

I noticed the other day when driving normal I will get boost to a certain rpm and then the boost will drop off to zero or slight vacuum. I'm wondering if this it normal behavior because I never noticed it before. Perhaps at low throttle, boost cuts off by 3k rpms to save fuel and or extend the life of the turbo? When I went 50% throttle the boost seemed to hold as long as I was on the gas. But at low throttle when I hold the gas steady, the boost will cut off between 2,500 to 3,000 rpms.

CudaJoe

iTrader: (1)

as the rpm's rise, your engines spinning faster than your turbo. assuming your at a normal throttle. where the butterfly is just slightly open.

aterminatorz

Ok that makes sense. Normal throttle 3psi boost till 2.5k+rpms when the engine is pulling more air on it's own without the need for boost. But lay on the throttle and a ton of fuel will flow in and the turbo will spool pushing a lot of air 5psi+. In a specific gear at a certain rpm the boost psi can have two different behaviors related to the throttle input.

CudaJoe

iTrader: (1)

yeah, when your throttling enough to accelerate, your boost guage will be at 0, on a level surface that is. Of course going down hill is another thing. When your boost guage is at 0, your turbo maybe spinning but its not spooling fast enough to do work, engine is doing all the work. And yeah, once your engine getting up into the higher rpms, its doing most of the work pulling air in at low throttle levels than the turbo spooling. The exhaust pressure at low throttle isnt significant enough for the turbo to utilize fully.

Terminator2

That is normal because the stock Desired Airloads that regulate the throttle opening and wastegate (boost level) actually drop off as RPMs increase as long as the load stays constant. Generally at constant throttle load decreases to as the RPMs increase so that is the other reason.