Chip or MBC?

Posted by Lucky on 7/30/2012 to ARD Blog Articles
Chip or MBC?
MBC's are great devices and by and large can provide decent performance upgrades, however there are some issue to be aware of before simply installing one. Since the ECU is no longer in control of boost and the MBC will allow boost to develop as fast as the turbo can provide it (up to the adjusted target) you're flowing quite a bit more air and consequently have more load against the engine than the ECU is tuned for. This means you may have too much timing and not enough fuel in the early part of the RPM band where you really need it. This is the primary source of how and why MBC's can damage these engines, specifically with respect to bending rods or spinning rod bearings.

Both Chip and MBC?
As for a tuned ECU. ARD does offer our White tune for cars with MBC's and it does have adjustments in both timing and fuel to help the engine work with an MBC more safely. However everyone should be aware of the potential risks this brings before deciding on going this route.

Chips Make Safe Levels of Boost
With all other ARD Tune offerings the ECU is left in control of boost development so that not only is boost kept at safe levels throughout the RPM range but the ECU can reduce boost pressure if necessary if it deems there to be faults in the engine configuration that might make it unsafe for full boost level to be developed. This safety feature is something that an MBC overrides and prevents the ECU from limiting boost when it detects a fault in the system. This is the second area where engine damage can occur that might otherwise be prevented.

Electronic Boost Controllers Can Limit Boost
Electronic boost controllers with gain control are starting to show up more and more in the market and can be very useful since you can specify a max boost level per any given RPM. This helps to prevent too much boost too early and is a further step in the right direction when using aftermarket boost control systems.

850 T5 w/ MBC Produces 10psi in 1st, 15psi in 2nd/3rd/4th... Why?
With respect to your findings as it relates to boost development in each gear.... 1st gear is a pretty short gear in Volvo transmissions both auto and manual and thus does not provide enough engine load to allow the turbo to reach a 10+ psi boost target. Once 2nd gear is reached then the transmission loading to the engine has a better mechanical advantage and can load the engine enough to allow the turbo to spool to the higher boost targets as you have found in your testing.

Robert Lucky Arnold
ARD Tuning
 

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