Sorry this is a little long:

So last week, I decided to trade out my current 3" downpipe (Megan) with a Helix version. In retrospect, that was probably not the best choice, but hindsight is 20/20. My Megan fit alright anway...didn't rub at all, but was a little close to the TCase for my liking. So I was told the Helix version 2 downpipe would fit better. And it does...slightly more clearance to the tcase which was nice...the only downside is that I had to space out the lower bracing that goes under the downpipe - not a big deal.

So after getting the part on and tightened down, I start up the car. It idles fine of course, but I notice excessive noise coming from the downpipe area. It sounded like an exhaust leak, but I couldn't detect anything around either downpipe flange. I figured the pipe must be a little thinner and more noise was resonating since the new Helix didn't have a flex section (the Megan did).

So I got to drive the thing. At low engine speed (part throttle or WOT) the car just sucks. I mean...its like I'm driving on 3 cylinders. Now I'm running a UTEC system, and right around 3k, where the UTEC begins to take control of fuel and timing, the car just lights up like normal. I would even get hesitations and stuff below 3-3.5K. After driving like that for a day or so, I finally admitted that something was wrong. First - I thought boost leak...why?....I dont know, but that wasn't it. So I get out some logging software and notice that timing is somewhat erratic at low engine speeds. And just as I notice the car come alive on a part throttle or WOT pull just as the UTEC starts to take control of the computer.

Now I havn't totally solved this yet, but it seems to me like the ECU thinks the car is knocking. Maybe the excess noise I heard has something to do with it? It does sound similar to knock ping....but theres now way its knocking at idle with the ignition timing I'm seeing. I'm going to put the old pipe back on tomorrow and hopefully that corrects the problem. What do you guys think? Anyone else experience this? Did I install the darn pipe wrong?

 

Going from what you say in the description, the Helix Pipe has no flex pipe section?

If thats correct my guess is that while driving the exhaust is swinging around on the underbody of the car and transferring vibration, banging, etc... into the cylinder head and the knock sensor is sensing this. Thus timing is being pulled/added. I would put on the old downpipe (Megan) and see if the problem goes away. My guess is it would. A downpipe with no flex section is not really a good idea. By the way make sure that your knock sensor is still plugged in or the wires are not pulled.

 

OK, so I pulled the Helix pipe off and replaced it with the old one and that seems to have solved the problem. The Helix pipe has no flex section, but I was using the OEM spring bolts to allow movement...similar setup to the OEM downpipe.

Well I don't really know what to say about this Helix part. I havn't heard of anyone else having this problem. I'm just going to assume its my combination of parts mixed with perhaps a slightly noisier or more sensitive engine. I thought of maybe wrapping the pipe for a second, but decided against it because 1. I've never heard positive things about exhaust wrap on a downpipe and 2. IMO if a part doesn't work the way it was intended, than it doesn't work at all.

So thats that.