How much boost can I run without sacrificing reliability?
Boost is so much more than PSI. Imagine for a moment that you have a box, its 1 cubic foot big (1 foot x 1 foot x 1 foot). One turbo can take 10lbs of air (it・s a lot of air), and compress it to 5 PSI, and stick it in that box. Another turbo can take 20lbs of air, compress it to 5 PSI, and also stick it into that box. Obviously the 20lbs of air will make more power than the 10lbs of air of the smaller turbo charger (provided you have the right fuel mixture).
If you are worried about reliability and how much downtime your car will have, then your best bet is to stay away from turbochargers and aftermarket superchargers that weren・t designed for your vehicle. The problem with people who add boost to their vehicle is that they are looking to add boost, but don・t want to spend the money to do it right. They add the boost, but forget about the fuel, hoping that their stock injectors will hold up. Depending on the turbo or supercharger, the injectors might hold up for a little while, but don・t count on it.
Long story short, there is no magic number to tell anybody. There are too many variables from type of turbo or supercharger, to the long term previous maintenance of the engine. Every motor has different breaking points. It is generally accepted that you should be able to run the following:
Assuming a T3 Style turbo
2.4 / 2.2 Ecotec
6-8 PSI Non-Intercooled with proper fuel and timing mods
8-12 PSI Intercooled with proper fuel and timing mods
2.2 / 2200 SFI
4-5 PSI Non-Intercooled with proper fuel and timing mods
6-10 PSI Intercooled with proper fuel and timing mods
Another thing people seem to forget when running boost is the transmission. If you have a 5 speed I would suggest a clutch at the very minimum. ACT or SPEC are great clutches, don・t buy cheapo E-Bay clutches. Auto transmissions hold up to boost better than manual transmissions. Especially the Isuzu, they seem to have a tendency for the differential to self destruct. Your axles and CV・s are also weak points.
