Help! Injen exhaust install question

M

mikek

Well-Known Member
73
53
VA
Vehicle Model
370z
Hi,

Today I installed the Injen Axle Back Exhaust for my 2012 civic si. Before the install I had a K&N intake and a ECU reflash and at about 7200 rpm (redline) on 2nd gear, I could hit 55 mph. Now with the injen axle back exhaust, I can only hit 50 mph at 7200 rpm (redline). I'm thinking that this reduction in speed (mph) is uniform throughout the gears and rpm range (although I don't have specific numbers).

The axle back exhaust noise is different than stock but the thing that worry's me is that the tone changes. Sometimes between 2000-4000 rpm (normal driving) it sounds pretty quiet but sometimes it sounds awfully loud. The sound is not consistent.

Are the 2 changes I mentioned above (lower speed at a given rpm) and sound of the exhaust constantly changing normal or do you guys think I installed it incorrectly?...meaning the fit between the new axle back and the existing cat back exhaust pipe wasn't tight?? If the exhaust connection isn't fit tightly can these problems occur? Or are the changes I mentioned normal?

Any suggestions you can give me would be helpful for I'm completely new to cars and adding parts is a first for me.

Thanks,

Mike
 
The engine rpm will equal the same speed, unless the tire size changed, or the clutch is slipping. There is no possible way that the same RPM would yield slower speed other than those two conditions. The exhaust behavior you noted is normal. At certain frequencies ( RPM related ) you can have resonances which make the exhaust noise quite loud compared to other engine speed.
 
sounds software related = ecu and reflash, not hardware (new Injen).
 
Thanks guys for the response. I'm gonna jack up the car again later to see if the connection point between the new injen axle back and the existing exhaust pipe has a tight fit. If there was a small leak of air, would that effect the performance in a bad way?

Also I find the injen axle back exhaust to be louder than I expected inside the cabin at around 3,000 rpm (normal driving)....is this normal? At full throttle, it has a nice sound but during normal driving it has an annoying sound that makes me feel dizzy. Did anyone have that experience with this exhaust? I also have a ECU reflash and a K&N SRI intake.

And hotdogjohnny, I'm gonna try to get my car tuned rather than running a base ecu reflash. Hopefully I can get more power out of the car this way??
 
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You'll get more power out of a dedicated tune. Talk to VitViper about hondata/tune packages. As for noise, the car is going to be louder with your aftermarket parts. You're essentially removing some restrictions to gain power...and you're seeing increased sound levels as a result. People with the tsudo exhaust on here were triggering car alarms driving in parking garages it's so loud. Check your connection, as you don't want an exhaust leak.... it'll not help matters.
 
Thanks Webby! I purchased an etune from Vit today and I'm really looking forward to getting my car tuned by him. I haven't had a chance to jack up my car to check for leaks at the exhaust connection point yet (I work long hours Mon-Fri :() but I will check for that soon (latest by this weekend).

But after driving the car again tonight I've pinpointed the annoying sound from the injen axle back. It's between roughly 3000 to 4500 rpm. There's this seriously annoying resonance/deep humming sound that literally shakes my cabin at times to the point where my ear hurts. I'm not sure if an air leak is causing this resonance or if the Injen axle back naturally sounds like this between 3000 to 4500 rpm. But once it hits vtec at 5000 rpm, I really like the new exhaust sound :D. If this specific resonance is normal then I think I can live with that....I'll just avoid keeping my car at those rpms during normal cruising speeds.

But just curious if anyone else has had this ear hurting resonance between 3000 and 4500 rpm with the injen axle back on your 2012 civic si?

Thanks,

Mike
 
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Sup guys, yes I had the injen axle back. Personally I loved it, however after breaking in after a few hundred miles you will have cabin noise like a deep rumbling sound. However it was never to the point that my ears where hurting, my car just sounded aggressive.
 
That resonating does sound like a possible leak, it's easy just to double check the connections.
A method I used when I was installing mine was I filled a squirt bottle with a soap/water mix, spray it on the connections with the car running, and see if the water bubbles or not
 
Thanks guys for all the responses. It's really helpful hearing all the different thoughts. And 323, I'm gonna definitely try your idea with the soap/water mix to check for leaks. I'm praying that I can get off work early enough to be able to work on my car again tonight. I'm dying to get this resonance problem resolved.

But today I was thinking that something else besides an air leak might be causing this ear hurting resonance at certain rpms?? I took a pic of the connection point between the new injen and existing exhaust pipe (it was hard to take without lifting the car but I finally took a good enough pic through the tires haha). There's a spring between the bolt (see attached pic). I know I tightened the bolt really tight and it occurred to me this morning that the spring probably can't act as an absorber because it's wound too tight. Do you guys think that's the function of the spring (to act as an absorber or am I completely off here)?...so I should try loosening it up a little or am I suppose to screw the bolt as tight as possible to collapse the spring (which is what I did)? I tightened the bolt as tight as I could because I didn't want it to unscrew.

What do you guys think about the screw and spring? Do you think the tightness of the spring is related to the resonance problem?
 

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Those spring bolts came with the exhaust? I've never seen them used on an exhaust before, usually just a bolts and nuts with a gasket in between the pipes. Maybe Arm0 could chime in
 
Man I don't remember whether it came with those spring bolts, but I do remember I used a gasket in between. Eddie Blanco can chime in, as he just replaced his Injen Exhaust not too long ago
 
Arm0ged0n said:
Man I don't remember whether it came with those spring bolts, but I do remember I used a gasket in between. Eddie Blanco can chime in, as he just replaced his Injen Exhaust not too long ago
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The factory exhaust has a grommet that meets the two together. There is no gasket, the bolts with the spring that bolt on the factory muffler are the ones that you use to install the injen. Did you torque them to the right spec? I don't see how there could be a leak at that junction, unless the bolts were loose. Do you hear any hissing or ticking? Those are typical exhaust leak signs. Maybe your banging against a heat shield or the rubber mount is not all the way on. I know we all love those rubber exhaust hangers...lol! After looking at the pic again it appears to be on correctly, you would see some sort of carbon or black residue. Soap and water won't help, the exhaust system gets hot. You'll just make steam. Check to see if the muffler is rubbing anything.
 
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Eddie Blanco said:
The factory exhaust has a grommet that meets the two together. There is no gasket, the bolts with the spring that bolt on the factory muffler are the ones that you use to install the injen. Did you torque them to the right spec? I don't see how there could be a leak at that junction, unless the bolts were loose. Do you hear any hissing or ticking? Those are typical exhaust leak signs. Maybe your banging against a heat shield or the rubber mount is not all the way on. I know we all love those rubber exhaust hangers...lol! After looking at the pic again it appears to be on correctly, you would see some sort of carbon or black residue. Soap and water won't help, the exhaust system gets hot. You'll just make steam. Check to see if the muffler is rubbing anything.
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and this is why I referred you to Eddie Blanco, this guy knows his sh*t, I'm just lucky he's my brotha from another mother
 
Eddie Blanco said:
The factory exhaust has a grommet that meets the two together. There is no gasket, the bolts with the spring that bolt on the factory muffler are the ones that you use to install the injen. Did you torque them to the right spec? I don't see how there could be a leak at that junction, unless the bolts were loose. Do you hear any hissing or ticking? Those are typical exhaust leak signs. Maybe your banging against a heat shield or the rubber mount is not all the way on. I know we all love those rubber exhaust hangers...lol! After looking at the pic again it appears to be on correctly, you would see some sort of carbon or black residue. Soap and water won't help, the exhaust system gets hot. You'll just make steam. Check to see if the muffler is rubbing anything.
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Thanks Eddie Blanco! I don't think I torqued the bolt and spring to the right spec. I may have to get a torque wrench and look up what the exact spec is for that exhaust connection. I have a feeling that I tightened the screw and thus pushed the spring in way too much and over torqued it so to speak (if you see the pic in post #10, you can see that the top and bottom part of the spring is touching - really compressed..I'm not sure if it's suppose to be that tight). Do you think that might be causing the near ear popping resonance betwen 3000 and 4500 rpm?

And your suggestion about the exhaust not touching anything makes perfect sense. That could definitely cause unnatural cabin noise.

I really appreciate everyone's input. I should have time to work on my car this weekend so hopefully I'll get this problem resolved after trying a few things. I'll keep you guys updated. Thanks again for everyone's input.

Mike
 
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Ok here's cell phone pics. The grommet or whatever the correct name of the material that is pressed onto the factory exhaust is some sort of weird dense material like a brake pad...maybe unobtanium. Lol, I doubt the problem is a leakimage.jpg image.jpg
 
Hey guys,

Here's the update I promised. I got to work on my car this weekend and I couldn't find any air leaks (you were right Eddie Blanco, there wasn't any leaks). Because I couldn't pinpoint the problem, I just decided to take the exhaust out and re-installed it, making sure the exhaust wasn't touching anything to cause vibrations or resonance inside the cabin. After re-installing it, I'm not sure what changed but it seems to have gotten a little better.

I'm not sure if it's this way for everyone but in my car, the injen axle back is definitely the loudest between 3000 and 4500 rpm (it has a very low/deep/loud sound) but I think I'm getting used to it now. Above that, the engine noise seems to dominate so I don't hear the exhaust at all. And I noticed that the Injen exhaust gets louder after driving the car for about 10 to 15 minutes. I've read that this is normal (because of the hot exhaust).

Anyways, now I'm ready for a tune. I already sent Vit my first datalog with normal driving. Hoping to get his next calibration to upload to my car soon and eventually get more power out of my engine :D.

Thanks again everyone for the help.

Cheers,

Mike
 
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Most people say aftermarket exhaust tones change somewhat after putting some miles on it. Maybe it's starting to mellow out a bit
 
webby said:
Most people say aftermarket exhaust tones change somewhat after putting some miles on it. Maybe it's starting to mellow out a bit
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I think that might be true...or at least it feels like it.
 
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