[pooster.online]

A question that just crossed my mind... does the Dual AVCS on both the intake and exhaust increase hp gains over the sing AVCS in older STi's?

I've heard that Dual AVCS is beneficial with spool... but power?

[FlashEngineer]

not exactly sure myself but from what I read in the power posts, the exhaust AVCS is actually helpful in making more power.. is why the 08's are so easily hitting 300WHP with just downpipe... I have to see for myself when I go to stage2 and try to hit 300..

[boondocksaint]

Post Engine-related discussions in the Engine Forum from now on. Thread moved.

[solovus]

I'd say almost anything that allows greater control over the engine would result in greater power gains.

[subi4justin]

^agreed. Subscribed for interest

[Clark_Kent]

From what I gather on Dual AVCS is that both camshafts are utilized to increase boost response and low end torque as well as superior power at high revolutions. AVCS on models 04-07 could only be used to efficiently manipulate one, but not both aspects. Overall, volumetric efficiency is greatly improved in turn creating the ability to produce more power with less. An example is the implementation of Dual AVCS is on the MY08 Tribeca. The new 3.6L motor is 20% larger than its predecessor, recoomends regular unleaded fuel instead of the prior premium unleaded fuel and still retains very similar fuel economy.

I'm sure some of the tuners can chime in and discuss their observations.

[gabedude]

You have more control over overlap. That simple. When you have more control, you can tweak the VE of the engine to match whatever turbo and exhaust / IC setup you have. The exhaust AVCS is probably good for 10 more WHP (maybe less). The low end TQ is what really is great about AVCS as you end up killing AVCS up high in the RPMS anyway. Expect gains of 40 ft/lb over a similarly equipped 07 STI.

[yakkosmurf]

The key to any valve control system (AVCS, VTEC, VVT-i) is the ability to get multiple characteristics out of an engine. Typically, cam lobe shapes can be done to either maximize low end torque, high end horsepower, or a compromise in the middle. Basic setups like Honda's original VTEC system, had two cam profiles. One for low rpm situations designed for better torque at those speeds, and another for high rpm horsepower. There was a crossover point built in where the system would swap from one cam lobe to the other. AVCS, VVT-i, and i-VTEC use computer controlled actuators to vary the cam timing (and possibly lift) to continuously optimize the cam profiles. This continuous optimization provides for a broader range of power than possible from two settings.

As for the creation of more power when implementing these systems, there is always an increase, but it may not be at the peak, depending on how the engine was designed without the system. If the original design was for maximum high rpm horsepower, then adding this system would give better low rpm response, but would keep the peak value the same. On the other hand, if the original design was for low rpm torque, then you could get significant increases in the top end HP.

This is one reason I feel the '08 WRX is doomed to have an early HP peak without a cam changeout or adjustable cam sprokets. Engine management doesn't do much to control where the peak occurs if there isn't an adjustable valve timing system. Obviously for the '08, Subaru chose to shift the engine characteristics more toward low rpm power, and I don't think you can get back to a high rpm HP focus without a different cam setup.

Hope that answered it.

[Iguana]

Good read.

[yakkosmurf]

Thanks.