If you are new to turbocharged cars or just have a stock 3000GT VR-4 or Stealth Twin Turbo and don’t know where to start, the following basics will get you immediate returns for not much money. Turbo cars respond very well to some modifications, while others should be avoided or left for later. This will serve as a detailed FAQ and primer for those who want to get involved and find some power — the first fifty to one hundred horsepower may only cost a few hundred bucks!

1. The Very Basics: make sure your car is healthy. Not everyone is fortunate enough to start with a low-milage car, but basic engine health can not be ignored if you intend to add power. If your car burns oil, hesitates, or hasn’t had basic maintainence done (timing belt, spark plugs) take care of that first and foremost. Consider using thicker oil if the engine has higher milage and it’s warm where you are.
2. Intake: The cheapest, easiest place to start. A high-flow air filter like a K&N costs penuts. Though it won’t make much power by itself, it sounds very cool and will allow your turbos to do their job more effectively later.
3. Exhaust: Helps now, helps later — factory exhaust parts suck as a rule. Dramatic reduction in lag can be expected from simple exhaust parts, and it will make you more power. If your state isn’t likely to notice, removing the pre-catalysts and main cat are worth your while.
4. Boost Control: The previous steps prepared your car for the most gains most safely. This mod is worth a ton of power, but engine monitoring becomes critical. A boost gauge should be considered essential, and a method of detecting knock is very important (though not always possible).

The above is typically worth 350-400hp total on a 3000GT/Stealth turbo when carefully executed on a healthy car. But what parts should you buy?

Exhaust comes in two common aftermarket segments: the “downpipe” and the “cat-back”. When upgrading your exhaust, it’s worth getting both at once because of the effort involved with removing rusty exhaust parts. Decent full exhausts may run you $700-1000, but those parts are typically top-quality 304 Stainless Steel and flow very well. IPS, 3SX, and Dynamic Racing, have a good selection of 3/S exhausts (though the classic ATR products no longer exist). eBay parts are inexpensive and sometimes have decent quality but might have poor design or fitment. I would recommend a single-pipe exhaust system for the best performance and lightest weight — dual exit exhaust systems are unneccessarily complex.

Boost control is a subject best approached carefully. Irresponsible use of a boost controller will blow up your engine in a hurry, and what is safe for one car may be hazardous for another. It is best to install a basic boost gauge and watch what the factory boost setting looks like first. Typically a 3/S will run 7-10psi initially which will fall to 6psi as engine speed increases. An aftermarket boost controller will usually permit you to hold onto boost longer, so even without more peak boost, the car will be significantly faster.

Safety here is important. The safest way to increase the boost is to monitor engine knock, and the typical best way to do this is with a datalogger. Because the ability to read knock is not universal for all cars and all years (generally impossible 1996+), the best thing to do is install the boost controller at a low setting and increase boost very gradually. Any hesitation should be taken as a sign that the engine is unhappy and boost should be lowered. In some cases hesitation may simply be spark plug blowout, for which you can install new plugs at a lower plug gap, but it’s safer to assume the worst. Don’t expect more than 11-12psi on 93-Octane gasoline.

Electronic vs. Mechanical Boost Control:
An “EBC” (like the Greddy Profec B Spec-II) is typically $300-400 and often reports boost pressure on the face of the unit. This is not as easy to read as a boost gauge, but “warning” features can help you keep track of it. If you like tinkering, aren’t afraid of electrical wiring, and have the money to spend, an EBC may be for you. An “MBC” can cost $20-40, and is perfectly adequate if less adjustable. They are simple to install, simple to adjust, and cost almost nothing. The MBC will be more inclined to let boost fall as engine speed increases, but it’s still much better than factory boost control.

Do I need two boost settings?
In short, no. There is virtually no need to have two boost control settings. If one boost setting is safe, why have a lower boost setting? Your right foot controls the boost otherwise, so leave your boost on the highest safe setting and be done with it.

High-flow Catalyst necessary?
“High flow” is relative, and no catalyst flows well in comparison to a straight pipe. If you can manage it, you’re better off having a “test-pipe” and reinstalling the factory catalyst only for inspections if your state has them. While this is federally illegal, if you live in CA you are at much higher risk for someone noticing. Usually it is legal to replace the portion of the exhaust after the main catalyst, but various states have stupid laws that make it possible to get a ticket for just about anything.

Exhaust Gas Temperature (EGT) gauge — good idea?
Nope. It will tell you almost nothing useful, and does not respond quickly enough. If you get to this point, you should be considering a wideband O2 sensor/controller/gauge. These days they cost about the same, and a wideband gives you more pertinent information. A wideband O2 makes sense when you are considering more comprehensive upgrades which require tuning, and is beyond the scope of this article. Check back here for a future article on further upgrades.

Do I need a blow-off valve (BOV)?
Save your money on this until after you decide to upgrade the turbos. Open-atmosphere “blow-off” valves should not be used on factory mass-airflow fueling systems. It is reasonable to eliminate the minor leaking of the stock compressor bypass valve for a couple bucks, buy a non-leaking DSM bypass valve, or just plain skip it until later.

Cams, headers, headwork… Worth It?
Nope. Not worth discussing here, but these are all a waste of money unless you’re trying to find every last horsepower, and that means buying just about every other part first.

Technorati : 3000GT, Stealth, VR-4, boost, exhaust, modification, power, twin turbo, upgrade