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Technical Questions & Answers - Question It

Fixing what you broke.

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Got a burning question or simply need some advice with problems you've encountered while wrenching on your current/future projects? Ask our automotive guru Eric Hsu anything-literally, he's going to answer every single question, as long as it's automotive related.

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Turbo Upgrade

I own a stock '04 Subaru WRX. However, the turbo compressor wheel is wobbling, and I'm thinking of upgrading it to a TD05H-18G. Would I need anything additional to install this turbo? The plan is to upgrade the car until it can produce 300-400 hp, but I'm not in a rush to produce that. I just want a turbo that will be able to grow with the mods that will be added on later and would like some advice on this.

-Luke Sullivan, Bryn Mawr, PA

You can install the turbo as long as it is a TD05H-18G made specifically for a '04 Subaru WRX. When you hear the terminology "TD05H-18G", this is simply a turbo size for the CHRA (center housing rotating assembly). T = turbo, D = D type bearing system, 05 = turbine wheel family, H = high flow, 18 = compressor wheel's maximum flow in m^3/min, and G = compressor wheel design. There are TD05H-18Gs made for many different applications so you would not be able to bolt one onto your Subaru if the housings were configured for a Mitsubishi Eclipse.

You can bolt a TD05H-18G directly on your WRX, but you'll need other supporting parts to allow the engine to make the power: high-flow exhaust system, air filter, injectors (750cc) and fuel pump (255 lph). On top of this you'll also need a better performing intercooler and have your ECU tuned to orchestrate all of these new parts. I'd recommend the COBB AccessPort for this since you'll also be able to monitor key parameters and be able to switch maps for different situations since the AP can hold multiple maps.

The 18G compressor wheel is good for about 300-350 hp at the wheels on pump fuel depending on the parts you end up with and other factors such as build quality and engine health, but you'll be rewarded with a WRX that'll pull you back in the seat pretty good. Make sure to upgrade your brakes, suspension, and tires too. There's no point in having all that power if you can't control the car, right?

Lightened Flywheel

I need to know what I will encounter when rubber meets the road after installing an 8-pound flywheel on a 5,500-pound Isuzu Trooper. This 4x4 five-speed has a 3.2L SOHC engine that makes 170 hp and uses a 25- or 30-pound flywheel. I plan on installing an Eaton M90 supercharger, high-flow exhaust, and cams and port and polish the cylinder head as well as lower the compression ratio. How much horsepower would a stock cast V-6 crank, piston, and rod handle? Someone mentioned 350 hp but I am thinking lots more as the crank has a four-bolt main. I can't find aftermarket forged pistons, cranks, or rods for this particular engine, but if it can handle 450 to 550 hp using stock internals then I don't care.

-David, via

What you can expect are frequent clutch replacements. Since an 8-pound flywheel has a much lower inertia, you'll need to slip the clutch significantly more to get your Trooper to accelerate from a stop. If you're slipping the clutch more, you're going to replace it more often. If you're in a hilly area (e.g. San Francisco), then you're really going to be in for a treat. With an 8-pound flywheel, you probably can't even accelerate from a stop on a high-grade hill in a 5,500-pound car with an anemic V-6. I'm definite your factory flywheel is much heavier than 25 or 30 pounds. In fact, I'll bet it weighs more than 40 pounds. Isuzu designed it this way to make the Trooper easier to drive.

If you're OK with the more frequent clutch replacements, you will be rewarded with faster acceleration. The lighter flywheel takes less power to accelerate and allows the engine to get more of its power to the wheels. I am not familiar with the Isuzu V-6 engines so I couldn't say how much power you can make with the factory components. Keep in mind that even though the engine has four-bolt mains, it also only has four main bearings. Compare that with a straight-six engine that has seven main bearings and maybe you'll rethink how great a four-bolt main V-6 is. I think it is safe to say that your engine can probably handle 40 percent more power with relative ease in stock form. Anything beyond that should be approached with caution. Contact JE or CP pistons for custom forged pistons and Carrillo for custom connecting rods. All of these companies will require samples of factory components to design a custom piston. I doubt you'll find anything off the shelf for the Isuzu V-6. Try Castillo's Crankshafts; they may be able to find you something that can work.

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