Dumb First Question

[FlamingRectumSyndrome]

So I'm an old guy with a lot of experience with ancient technology like carburetors and points ignition. Don't know nothing about ecu tuning. So a couple of questions.

I keep hearing about the flat spot in the power curve. And when you look at a dyno chart, it's staring you right in the face:


Big ol' drop off in torque and horsepower between about 3200 and 4700 rpm (red line on this chart), compensated somewhat by tuning (blue line).

My question is where does this drop off come from in the first place? Is there some sort of intake resonance that's interfering with flow in that rev range? Sure, you can fix it to some degree with tuning, and to a greater extent, apparently, with forced induction, but it would make sense to actually fix the problem, rather than band-aid it. Is this a characteristic of the Subaru flat fours, or is it unique to this particular version?

[steve99]

If you get an OpenFlash Tablet and run their tunes (or most other tuners can do similar) the torque dip is pretty much eliminated. They used a combination of adjustments to fueling ignition timing and intake exhaust valve timing adjustment to achieve this.

To Totally eliminate it on an NA car you need headers (UEL seems to work best for torque dip) generally catless (or High flow main cat).

I would imagine it occurred originally due emissions requirements , restrictions of cats, and possibly fuel economy.

These tunes often introduce a raspy sound around 4000 rpm (unless your on UEL headers) which some people find annoying.

Probably various other theory's though

[fooddude]

I believe (I could be wrong though), it comes primarily from the header design, exhaust design and/or emissions controls.

btw..love the avatar.. love the music even more

[ZionsWrath]

Whenever I see these torque dip posts I think of that line from Tokyo Drift

"Wouldn't have that problem with a v8"

[Circuit Motorsports]

This is a combination of exhaust design and factory tune, all related to emissions.

Any decent tune, including an EcuTek custom tune, can greatly reduce the torque dip with the stock header. Add an aftermarket header with no cat or high-flow cat plus a tune, and the dip is gone. I've been able to eliminate the dip completely with Equal Length and Unequal Length headers. I've seen a bit more mid and top-end power with the Equal Length headers over the Unequal Length headers. And of course forced induction with the necessary header upgrade eliminates it as well with tune.

And no such thing as a dumb question

Cheers,
Bob

Originally Posted by FlamingRectumSyndrome

So I'm an old guy with a lot of experience with ancient technology like carburetors and points ignition. Don't know nothing about ecu tuning. So a couple of questions.

My question is where does this drop off come from in the first place? Is there some sort of intake resonance that's interfering with flow in that rev range? Sure, you can fix it to some degree with tuning, and to a greater extent, apparently, with forced induction, but it would make sense to actually fix the problem, rather than band-aid it. Is this a characteristic of the Subaru flat fours, or is it unique to this particular version?