newschool72

iTrader: (12)

Ive pretty much come to the conclusion that everything checks out with my setup and that my base boost pressure (" boost in first gear " thread ) is caused by back pressure in the system and losses through my innercooler and piping .
I have a 10 lbs spring (verified with a waste gate test at about 9 lbs) , but I only get 6.7 psi (verified with 2 gauges, both reading at the intake manifold ). The mid 6 psi pressure is lower in RPM range, then tapers off into the low 5s as RPMs increase.
Is it unusual to loose a little over 2 psi from spring pressure setting to actual boost in the intake track after going through a 25x12x4" A to A core and all the piping ?
I would appreciate some input and actual differences others on the site have seen in their setups. I guess Im going to start tuning in some waste gate duty % and shoot for my goal of 12 psi.
So what have you all been seeing after system losses, actual base psi vrs rated spring pressure ?

Nathaninwa

Is the Wastegate line coming pre or post intercooler? If your feeding the gate with pre intercooler pressure and measure boost pressure in the intake, your seeing the pressure drop across the core. If after the intercooler, might be just enough back pressure in the system to open the gate a wee bit early

newschool72

iTrader: (12)

Its coming straight off the compressor housing, so Im reading pressure for the waste gate pre-cooler. The gauges are reading post inner cooler below the throttle blades . Im running an LS3 short block (376 cid ) and my turbine is 89mm/77mm . I have 2 1/2" pipes running from the headers, to a 3" single pipe to the T4 flange. 4" downpipe run back to two 3" pipes through race flow mufflers and out the back of the car. The waste gate is directly in line with the exhaust flow, just after the merge for better boost sensitivity. Im running a 1 3/4" pipe from the waste gate dump to the down pipe about 4' behind the turbine. The turbine AR is 1.15

yenkomike

iTrader: (2)

mine will read about 1 psi different from turbo outlet to t/b. 24 by 3" by 12 a2a I/c

my 10# spring gets me 9 psi if I hook wastegate to turbo outlet and 10 psi if I hook the wastegate to a port just before the throtlebody.

newschool72

iTrader: (12)

so, Im loosing about 1.3 psi more than you, if my gauge was right when I checked my gate.

lets get a good sample of inputs from different setups , so we will have good answers for the next guy that has boost issues.

Nathaninwa

It's more about your cores pressure drop. I had a cxracing that was 10psi drop at 30lbs and switched to an ets core and drop went to just under 2psi at 30lbs

ddnspider

iTrader: (26)

I always reference my WG to the manifold cause thats the boost the motor actually sees. Referencing it to the compressor doesn't take into account pressure drops from the turbo to the motor.

rotary1307cc

iTrader: (5)

It's all about drive pressure

That bias skews "rated" spring pressure all over.

"Rated" is based at a 1:1 drive to boost

newschool72

iTrader: (12)

Does it screw with the waste gate to see vacuum ?

ddnspider

iTrader: (26)

some people say don't do it, but I've never had 1 fail. At the least put it on a cold side pipe right before the TB.

Nathaninwa

I reference all mine on the cold side piping