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Old 04-15-2009, 09:59 AM   #1
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Default Fluctuating WG pressure

Attached are two logs. The first is an older log, one of my first, with the stock injectors and a rough tune. It is a fifth gear pull.

The second is from the other day, new 600's, pretty new tune, autotune only. I have since retuned for 12.0>11.5 at redline.

The question that I have is around 5500, the WG pressures really start to oscillate more and more. Is this just a function of the internal WG? Excessive backpressure? I have a 2 1/2" exhaust but a crappy Flowmaster muffler that was on the midpipe when I bought it.
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Fluctuating WG pressure-fifth-gear.png   Fluctuating WG pressure-third-gear.png  

Last edited by Stein; 04-15-2009 at 10:16 AM.
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Old 04-15-2009, 10:25 AM   #2
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i tried switching to a tiny vac hose and it got worse than with the old hose and a filter. We're fucked.
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Old 04-15-2009, 10:27 AM   #3
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where's your MAP line being sourced?
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Old 04-15-2009, 10:35 AM   #4
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Quote:
Originally Posted by Braineack View Post
where's your MAP line being sourced?
Tee'd off of brake booster line.
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Old 04-15-2009, 04:55 PM   #5
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Thoughts anyone?
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Old 04-15-2009, 05:12 PM   #6
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Mine is T'ed off the FPR, try that.
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Old 04-15-2009, 05:30 PM   #7
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Mine off near/from the IM. The wastegate actuator is sourced from the compressor housing, I run no MBC or EBC:
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Old 04-19-2009, 12:41 AM   #8
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I tee'd off the small IM nipple below the brake booster line. Mine does something similar but not to the same extent. Will a line restrictor help? I've also got the 18.4 afr spike that I haven't been able to tune out.
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Old 04-19-2009, 12:55 AM   #9
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Its most likely back pressure man but its not bad enough to where you should need to worry about it.
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Old 04-19-2009, 01:39 AM   #10
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Go get urself one of those "universal" T fittings... don't cut it for the part going to your ecu so itll be a real tiny hole. That acts as a good enough restrictor to get you down to +- 3 kpa bounces if that.
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Old 04-19-2009, 03:48 PM   #11
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I just glued a pop rivet into the 1/4" reducer. Going to try it now. Might even help that lean spike???
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Old 04-19-2009, 07:43 PM   #12
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Well, no joy on the pop rivet restrictor. It's possible the .060" hole was still too big. I can try smaller. Doesn't cost anything. Didn't notice any difference in how fast kPa's change either when you are on and off the throttle.

Magna mentioned backpressure. That is distinctly possible. I'm running 2 1/2" but it has a Flowmaster on it which I understand restricts flow. It came on the midpipe, so I thought I would try it. I'm planning on a Magnaflow soon.
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Old 04-22-2009, 01:18 PM   #13
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To put things into perspective:

1) Stock CAT and **** exhaust, 7psi WG, EBC, load dyno
2) 3" Enthuza w/CAT, 14psi WG, no MBC/EBC, street

Conclusion: better spool (some 700rpm), flatter curve, less dropoff.
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Fluctuating WG pressure-spookyfish-last-year-dyno-run.png   Fluctuating WG pressure-spookyfish-street-run.png  
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Old 04-22-2009, 01:30 PM   #14
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Damn, check the MAT increase on the dyno run. Back pressure is bad!
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Old 04-22-2009, 02:57 PM   #15
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Yeah, can't wait to get the big honkin' Magnaflow. It's on order. The rest of the exhaust is 2 1/2" with FM stainlss Midpipe and FM high flow cat so should meet my needs.
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