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re: Re: 5000 Turbo mods.....


Does the Intended Acceleration (IA) Mod on your car cause the OEM boost 
gauge to read lower than it should?

I have been doing some tinkering inside the Engine control module, brain 
box, computer or whatever you want to call it for my 86 5000CS Turbo. I 
changed the wastegate spring and installed a bolt to adjust the spring 
pressure. As expected this caused the system to shut off the fuel pump at 
around 1.5 - 1.6 Bar. I noticed that the pressure at which the fuel pump 
is cut off is lower at lower RPM. It was around 1.3 Bar at engine idle 
when I manually increased the pressure going to the pressure sensor with a 
hand pump. This would indicate that the boost limit is dynamic and changes 
under different engine conditions. 

I installed an op amp inside the computer to separate (buffer) the signal 
that goes to the boost gauge and also to the engine control portion in the 
computer. This allowed me to get the correct boost reading on the gauge 
and allowing the signal that goes to the engine control portion to be 
reduced. I have not yet perfected my hardware hack at this point but I 
have increased the boost limit to around 13 lbs (1.9 bar). The stock 
pressure sensor only outputs a signal up to this pressure. I have adjusted 
the spring pressure to allow around 11 lbs boost. 

On my car the dynamic boost control done by the computer is currently 
being faked out by the higher pressure signal so I need to do a better 
hardware hack to get this to work as it should. My understanding of the 
dynamic boost control is to start with a lower wastegate spring pressure 
and then make up the difference by adding boost pressure on top of the 
spring pressure. This allows the computer to keep the same level of boost 
as the spring tension changes or the engine components wear etc. It also 
allows the computer to lower boost when an overheat (excessive temp)  
condition occurs. It sounds like the early IA mod (optional) that allowed 
you to adjust the boost with a knob while driving used this concept. The 
idea of using a one-way air valve to bleed off pressure going to the 
computer pressure sensor might actually work rather well as long as the 
signal below 1.0 bar (engine vacuum) is not affected. The boost gauge 
reading on the dash would be hosed of course.

Running at 11lbs is an adrenalin rush!. Especially with a front wheel 
drive model. 1st and 2nd gear require some throttle modulation to avoid 
smoking the right front tire. 
Scott M.
glen.powell@smc.COM Wrote:
|   How did you increase the boost to >12 PSI without 
| screwing-up the stock
|   boost display? Most of the mods I have heard of hose the 
| OEM boost
|   display, that's why I have not tried to increase the 
| allowable boost
|   limit.
|   Thanks,
|   -glen