Why might I want a turbo boost gauge?

[Ryan]

Do you know whether the solinoid is an "on-off" digital type output or is it
an analog out-put opening the wastgate gradually?? I have a 97 legacy with
sequencial turbos and I can't quite get my head around how they work
together, If they are syncronized using the ECU then I assume that my next
upgrade ( a new ECU) will give me greater control over this aspect

 

[Ken Gilbert]

Yeah 4-5 psi could probably be a little over the top, however much fun it
might be on the odd occasion.
I've been thinking about why your boost tends to taper off at higher
elevations and I think I might have the answer, What probably happens is at
higher altitudes the ambiant air pressure is a lot less, this would tend to
suggest that the amount of pressure required to open the waste gate is less
because there is less atmospheric pressure on the back of the diaphragm.
Because it takes less pressure to open the waste gate it will open alot
earlier preventing you from getting to full boost. If this is indeed the
reason why you get less boost and you wish to fix it, a boost controller is
relativly inexpensive and easy to intall.

the boost controller will not fix the problem. it may increase boost
slightly but the charge will be warmer as well due to a loss of
efficiency.

in a nutshell, turbos work on pressure ratios, not absolutes. if the
ambient air pressure is lower, then the manifold pressure will be
lower as well.

the only thing you can really do is put a turbo capable of larger
pressure ratios on so that it will run at a higher manifold pressure
and still be efficient.

ken

 

[Ken Gilbert]

Do you know whether the solinoid is an "on-off" digital type output or is it
an analog out-put opening the wastgate gradually?? I have a 97 legacy with
sequencial turbos and I can't quite get my head around how they work
together, If they are syncronized using the ECU then I assume that my next
upgrade ( a new ECU) will give me greater control over this aspect

the wastegate system works by adjusting the duty cycle of the
solenoid. iirc, the wastegate solenoid cycles at 14Hz, and its "on
time" is adjusted by the ECU.

when the solenoid is closed, the air makes a direct route from
compressor to wastegate actuator and "wastegate boost" levels are
achieved. this is an output pressure equal to the spring tension of
the wastegate actuator.

the solenoid bleeds some of the fed-back air (which is routed from the
compressor housing back to the wastegate actuator) from the system.
when the solenoid is open, this air is bled off, and the end result is
a higher compressor output pressure due to the wastegate not opening
and bypassing the exhaust turbine.

hth
ken