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Old 11-15-2012, 12:22 PM   #30
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Member#: 9264
Join Date: Aug 2001
2016 BMW M235i 6MT


It's a relatively large OEM single scroll turbo; therefore, it will have a bit of lag. You'll feel a decently strong surge of power as the turbo achieves peak boost.

Many will say things like the WRX turbo "it dies off in the upper rpms", but that's really not true. The motor is still making 95% of peak power at fuel cut. What happens is their mind is expecting the constant surge of power (acceleration g's) initally felt when the turbo spools up. Once spooled, the big surge is done and then you just ride relatively wide powerband that isn't peaky. There isn't a huge change in peak power between 5000rpms and 6500rpms therefore the acceleration g's aren't going to feel like they're building up. That's the nature of a well designed turbo setup. It has a wide powerband and flat torque curve spread out over a lot of rpm. It's basically like a well tuned V8 powerband, much like GM's LS series motors. When the LS V8 came out in 97, people said it didn't feel remotely as powerful as the LT1 it replaced. However, when dynoed, the LS made a lot more power. The difference was the power was delivered early, sustained longer, and wasn't as peaky.

The sensation of speed in the WRX is somewhat deadened because there is no peakiness compared to that of most naturally aspirated (NA) motors, especially smaller displacement motors. NA motors make power through displacement and rpm.

The key to true acceleration potential is power under the curve and this is where turbos excel. Overlay a turbo dyno plot over an NA dyno plot and you'll see what I'm talking about. The turbo's torque curve arrives much sooner and is substanially higher and wider across the powerband rpm range. The turbo might not achieve as much peak HP as a high winding NA motor, but it's HP curve is much broader; therefore, more average power is being created and more acceleration available.

A peak power advantage of even 20hp from 6000-6500rpms will not make your car mearsurablly faster; however, elevating the entire powerband 20whp at all points like make the car decently quicker. Reason being you spend much more time accelerating in the mid range than you do in the last 500rpms of the powerband.
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