Shape of Acceleration Curve

[SVX10]

Howdy fellas. Now that I have my MT installed, I've noticed something that kind of disappoints me. As much as I want to have nothing but good things to say about the car, I gotta bring this up

How does everybody's acceleration feel above the power peak @5800 RPM? What I mean is, does your engine keep pulling strong to redline, or does it feel like it is struggling up over 6k RPM?

I've always noticed some struggling at high RPM, but with the 5MT it seems more pronounced. I get a nice strong accel up to about 6kRPM, then it seems to level off. This all makes sense, of course, looking at the SVX TQ/powerband. But, on your SVXen, is it very noticeable?

Can this be overcome with the MAF mods (either MAF bypass or Stage 1), or can it only be addressed via cams? Ideally I'd like to be able to spin up to Stage 1's 7400RPM redline without feeling like the engine is straining so much.

This is more of a discussion thread, I hope, rather than a "fix my problem" thread. So, let the information flow!

Mat

[SVXelerator]

Get LAN's stage II chip and z32 MAF....your engine is having problems breathing.

[GreenMarine]

Mat, I have noticed the same thing that you have noticed. I hardly ever (maybe a total of 4 or 5 times) take the engine above 5,500rpms, but I have noticed that the few times I have, the power just drops off into nothing... It pulls very strong below 5,500rpms though... Perfectly fine for me... Except in AutoXing when I might want alittle more speed before I shift... ... Guess I'll have to think about the STi Ra Gearset if I want to do that...

I am curious about the LAN Stage 1... interested in exactly what that could do for me on the AutoX course... Unfortunantly I am broke as a bad joke... So there will be no buying of new things for my SVX anytime soon

[SVX10]

Originally Posted by GreenMarineSVX

...Guess I'll have to think about the STi Ra Gearset if I want to do that...

I have the STi non RA gearset in my MT and the rev range is good for around town driving. Especially good is the 5-3 downshift for passing at highway speeds. I'm not sure if 3rd is different from regular WRX trans or not...I think it is.

I'm planning to do the MAF bypass mod to see if that helps out at all. I'll let you know my results. I was also perusing through the thread about using dual runner intake with a single MAF and some sort of signal multiplier coming off the MAF. Sounds interesting. I'm curious as to how the ECU would handle voltages higher than the max MAF voltage. Can it handle that at all without Stage 2 programming?

I'd like to buy stage 2, but it's just so expensive. We'll see. I can get a Z32 MAF for a good price, so I may have to do it.

By the way, Earthworm, I'm jealous that yours pulls strong to 6500 One day...yes...one day mine will also pull strong to redline.

Anybody else...how's the 6000 RPM + range feel?

[SVX10]

Just thought of something else...

In my sound clip I just made, you can hear where the power starts to drop off. From launch to ~6k RPM, there is a strong sound to the engine/exhaust, but above that it actually becomes almost silent. Not like the sound goes away, but instead of a rasp or growl like what is heard through the rest of the clip, it's just like a loud white noise. Not sure if thats indicitive of anything. Give it a listen if you need clarification. Is that a symptom of some sort of breathing difficulty or timing "issue"?

http://www.subaru-svx.net/photos/user.php?SVX10

It's the file with the long, descriptive name

[oab_au]

Mat I think you have answered your own question, that you said here:

While I had my car apart for the 5MT install, I fiddled with the exhaust a little bit. In some of the exhaust related discussions we've had here, there was some discussion as to whether or not there would be any benifit to gutting the pre-cats and using them as an expansion chamber. I never saw any truly conclusive results from those forums, so I did a little experiment

I think the expansion chambers that you replaced the front cats with, have killed the sonic action of the header pipes. The wave is being terminated at these chambers, which have shortened the effective tuned length of the header pipes. This would raise the resonate peak up out of your rev range, so the torque that it provides would disappear.

Harvey.

[Earthworm]

Mine seems to accelerate linearly up to about 6500 after which anywhere from 6750 to 7200 I believe I'm maxing out the MAF with Stage I only and it feels like I'm hitting the rev limiter.