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Old 11-18-2012, 12:54 PM   #15
Back Road Runner
Scooby Guru
Member#: 60082
Join Date: Apr 2004
Chapter/Region: MWSOC
Location: Minnesota
2004 Forester STI


These cars, even 300whp ones, will not break tire traction before the engine runs out of power. I'm at 21psi, on winter tires, and I can not spin my tires short of a rain soaked road with a redline launch in my very low 6sp first gear. The 5sp has a much taller 1st, so they are even harder to break traction at the same engine power. Yes, you can spin tires if you shock load the drivetrain. A 2.5L NA will do that too, will also chirp in 2nd gear if you want to. I'm only duscussing actual, smooth delivery of power.

It takes a LOT of torque and gearing to break 4 tires free without shocking the drivetrain.

Because we are engine limited in this equation, we need to slip the clutch to allow the engine to keep up in revs. This also means a strong launch is a high rpm launch. The car makes the most power at or very near redline, so you launch at or near redline. You will not spin tires unless traction is pretty low or you are not smooth with your power delivery. The higher the revs you go, the more power the engine can produce for accelerating the car. Because the engine is limiting, it also means you can use full throttle. The variable will then become only the clutch. You simply slip that as much as needed to keep the revs high and the engine making power. The car will accelerate quite briskly.

Maybe you guys will start a flame war on the wrongs of redline launching and that it's magically bad for the car. Yes, it will wear the clutch more. A clutch is no different than brakes. The flywheels is the same as a brake rotor, and the clutch disk is your brake pad. They aren't really different at all in compound either, often an organic type just like many oem pads. It's also why you can glaze a clutch just like an organic brake pad if you overheat them. The ability to overheat a clutch takes a little bit of effort, more specifically many launches in a short time frame. Longevity depends on how much you do, just like brake pads. It's a wear item.

So how long is longevity with launching? Not bad really. I own a 02 Forester NA that I auto-x and rally-x. It's seen 5 years of use and every run starts with me launching the car at redline. I figured it has somewhere near 250 redline launches on the stock clutch, and this is car with 120k+ daily miles to boot. My bro's FXT had a couple years of auto-x and rally-x use before an engine rebuild. The car was again launched are redline religiously at events. A new clutch went in at 75k miles when the engine was rebuilt after a #4 piston failure. The clutch still had half its life left. The car now runs an Exedgy clutch again, just one step up, and again has years of use added up plus all daily use. Mind you this is with a "fragile" 5sp running 21psi with an 18G. It's been at 21psi most of its ownership. I have a FXT now too, this time with a 6sp, and again I launch at redline at events.

So what's wrong with launching your car? Most often it's only a problem when people shock load their drivetrain or attempt to launch repeatedly with very short intervals of time in between. I personally haven't seem a problem with launches as short as 1.5 minute intervals and repeated a half dozen or more times in a row.

Higher power cars will cause more heat. It's always good to feel for any changes in engagement behavior that may indicate an excess in heat build up. If so, let the car sit a little. Organic material isn't exactly great with heat, although the clutch and flywheel are pretty well sized and can hold and move a good deal of heat around quickly. Still, it's just like your brakes. They can overheat, they will wear, and you can abuse them.
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