Tech Article: GOT BOOST??
by Michael Lee,
How many of us out there can use an additional 50+ horsepower at the wheels? Good! Now that I got your attention I want to talk about "real" gains. Not a set of headers that give only 10 HP on a good day or an exhaust system that yields 5-8 HP. This is not what I am convinced with. Yes they do work, but I want a substantial gain - and in my books, there are only 4 ways.
First there is the bigger motor... say a VG50F (5.0 aluminum V8) that supposedly fits where a VG30 motor fits. Or a Chevy 350 for older years. Then there is a supercharger, which doesnít really apply to imports very much, unless you already have a Chevy V8 (hint, hint Kirk?). Next you can use laughing gas (NOS) to make those gains... a cheap alternative, but the fun runs out. Finally, what I consider the best, is a turbo. Itís reliable and fairly simple to understand its working.
The "real" power gains I have mentioned above all have one element in common... the potential to burn more fuel, which in turn, makes more horsepower. A turbo, supercharger, bigger motor, or nitrous oxide all force or inhale more air in the combustion chambers, thus more fuel can be burned in the correct ratios. Generally speaking a turbo is like a supercharger, a compressor (much like a pinwheel) forcing more air into the intake, thus the term "forced induction." Unlike a supercharger, it uses "free" exhaust energy instead of being belt driven. When compared at its peak, 10 PSI of boost from a turbo will make more power at the wheels than 10 PSI from a supercharger since the supercharger uses 10-15+ horsepower to operate while the turbo doesnít.
As we know, when air is compressed, heat is generated. The air compressed by a turbo can easily reach 250F or more. At that extreme, the air density is down, so there is a diminishing return on forced induction. This is where an inter-cooler makes its presence on a turbo system. An inter-cooler, much like a radiator, takes the heated pressurized air down to the ideal temperature of 160F or lower. This air then goes to the intake. This is how a turbo can put as much as 31 PSI of boost on a race-prepped motor and a supercharger is usually limited to about 14 PSI.
What really makes a turbo shine? In its basic form, you can usually tune it with a new EPROM and add more boost for as much as 35-60 HP. Add components like an Electronic Valve Controller (EVC), aluminum flywheel, larger inter-coolers (or a cool night), and your bolt-ons (exhaust, air filter) and you can make as much as 80 HP on older Zs and over 150 HP on the Z32s. But what I love the most is its versatility in making the "ultimate street car." With an EVC, one can change the amount of boost from stock to your maximum limit from a touch of a button. That translates to gains of over 80-150 HP on call. A supercharger will require you to go under the hood and change a pulley to sustain a new boost level. Daily driver and weekend drag/SCCA racing without a tool! This also means you can change your car from mild to wild at stop light confrontations. What does this sum up to? You get good fuel economy and extended life on your engine since you only use the power when needed.
Any added care for all this? Well, it is recommended to let your car idle for a few minutes after some spirited driving. A turbo relies on a generous supply of cool, clean engine oil. All pressure is lost when the engine is shut off. With temperatures of 250F and a turbine shaft of between 540-630F, a hard destructive varnish or "coke" can form on the bearings or seals, this compromising the reliability of a turbo-charged car. Use a turbo timer (device which allows the car to be locked and idling for a set amount of time) and you never need to "baby-sit" your prized machine and be late to work or a movie. Also, it is recommended to change your oil early - say 2000-3000 miles under weekend performance and daily driving. Well, there you have it - next time I will focus on power upgrades of a turbo in specifics. Have fun and GOT BOOST?!!