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Old 03-11-2002, 09:43 PM   #1
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What is a safe boost on a stock engine?

I have a 2.0 dohc 4cly 127hp all stock. I was wondering if I turboed my engine what a safe amount of boost would be?
99 Pontiac Bonneville SE

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Old 03-11-2002, 09:49 PM   #2
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0 Boost is safe boost!

Nothing is really "safe".

What kind of motor? How many miles? This all comes into play.

On any stock motor 6 pounds of boost is usually the "safest" number that I'd ever recommend. From there bad things happen to different motors. Some blow headgaskets asap, some throw rods.

Get a car that was meant to be fast if you wanna be fast.

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Old 03-12-2002, 10:44 AM   #3
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I would agree with seabass about 6psi boost being the safest amount to go with.
Turbo's are not the 'bolt-on' part that people have come to think of them as. For reliable forced induction it is a good idea to fully understand what the turbo does and how it needs to be regulated.
The obvious parts for regulation are the Blow-off valve (BOV) and the wastegate (usually in the turbo houseing), but the MOST important part to safeguard against detonation is a knock sensor. This sensor listens to the engine for the early warning signs of detonation (hence the name). This sensor (when utilized correctly with a turbo computer) is your detonation guard.
In Saab Turbos (I am a saab guy and they know turbos ) the turbo system is controlled by a computer they call the APC. It uses data from the knock sensor on the block, the mass air sensor on the throttle body, engine speed, throttle position, boost level, exhaust heat, and many other sensors. This data is analyzed constantly and used to regulate boost pressure and fuel delivery. It is an amazing peice of equipment; if you put premium fuel in the car the APC raises the boost higher (up to around 10-12psi instead of 6psi). But the greatest part about this level of monitoring is that the boost can be raised up to 18psi (max) without fear of detonation. As soon as the APC senses knock it lowers the boost until the knock is at a low enough level.
Not knowing what kind of engine you have (model) it is hard to say whether this level of monitoring is capable. If you can't find a computer controll unit that works well on your engine but still want to turbo charge the car the following are a MUST:
  • Air/Fuel ratio gauge attached to O2 sensor to keep an eye on mixture density (you don't want to be too lean or too rich with boost)
  • A fully adjustable boost regulator so you can fine tune your boost to the highest amount while stull being safe
  • A "turbo kill switch" (electronically controlled BOV that can be opened if things get hairy)
  • A beefier fuel delivery system (if you plan on going above 10psi)
  • A Rising Rate Fuel Pressure Regulator (adds more fuel as manifold pressure's increase) (I don't know where to find one for your car or if they exist outside of Saab land )
  • Make sure your car is all in good working order (use page as a guide)

Hope some of this is usefull. I would definetly find as much literature as possible. The following links might help a bit too; they are saab based sites but much of the info will help you decide whether a turbo is feasible.

BTW, if there is a model of your engine that comes from the factory with a turbo, get one of those systems it should bolt on just fine.

Good Luck

This site has some good general info eventhough it is saab oriented.
This page is all about saab tuning but it contains some general info about regulation

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