Fc s5 t2. Running stock turbo and have a hybrid sitting on my shelf which I don't feel like installing before my next event.

If 12 psi is the max psi to run on the stock turbo, should this 12 psi be before or after inter cooler? Just to account for psi drop of a fmic.

Probably sounds like a silly question since most people will run 12 psi after stock tmic

 

Usually measured at the intake manifold.
But would be interesting to get readings fore and aft of the IC to see what boost drop is like just for ***** and giggles.

 

psi at the manifold after the TB.

 

i dont get it, why is the limit 12psi? for turbo longevity or for not outflowing stock injectors? both cases, it depends more on airflow. 12psi through a 1" hole is completely different than through a 3" hole, from the turbo's point of view. when i had stock turbo with 3" exhaust, i could unplug the wastegate and it wouldnt make more than 10psi at peak power. surely that required faster spinning turbo than 12psi on stock setup. if you mean max boost for stock injectors, again it depends on intake, porting, and exhaust setup. you probably want to keep it under 200whp on the 550's

 

the stock turbo can handle higher pressures up to 14-15 at lesser flows, but when when you have an intake exhaust mods 12 is the new safe. because of the location of the efficeny islands on the compress or map.

 

all i meant is when in the system is the turbo past efficiency. which have read for while is 12 psi on stock turbo until it just starts blowing hot air.

lastphase has sufficiently answered this question.

just wanted to see if intercooler pressure drop should be added into the equation.

 

Besides the issues with trying to exceed the limits of the compressors, you also need to consider the flow on the hot side. What goes in must come out, and more exhaust trying to fit through the stock manifold and turbine housings will drive up the EGTs. There are physical limits to the stock twins, which is why so many people have singles.

 

A. no one here is talking about STOCK TWIN S
B. on FC stock turbo has a huge hotside and doesnt suffer even when bigger compressors are hybrided on to it.

 

My bad! Obviously I didn't read the original post.
I will endeavor to be more thorough.

 

yes.

if you look at a compressor map, it is actually showing you 4 things, air flow, the pressure ratio; which is not boost pressure, turbo efficiency AND turbo shaft rpm.

airflow we know about, more air flow = more power. the efficiency is also quite straightforward, the less the turbo heats up the air as it compresses it the more efficient it is. turbo shaft RPM is simple, but we usually don't pay much attention to it.

the tricky one is pressure ratio, as we usually just think of this as boost pressure, but it is really the difference between boost at the intake manifold vs the pressure or vacuum at the inlet of the turbo. so you want 12psi at the intake, there is a 2psi pressure drop for the IC and its plumbing, and -1psi at the turbo inlet, so instead of being at the 12psi pressure ratio (12+14.7/14.7 = 1.816), it is instead at the 2 bar pressure ratio (12+2--1+14.7/14.7), which may or may not matter.

in the case of a stock turbo, it per some of the training info is already running over 100,000 rpm at 8psi, if you look at a few turbo maps this is quite high already, so 12psi has it spinning even faster, which is why the turbo life gets short at high boost. this is why the hybrid turbos work so well, as they move more air for the same shaft speed, or at some point you're turning a little less rpm than stock at the same boost, either way

so this is why we say keep it to 10psi, its a simpler