Author Topic: Unbolting exhaust (Read 5311 times)

renfield90 · « **on:** April 03, 2009, 11:28:57 AM »

...just how nasty (or good) does it sound? Some 4 bangers actually sound awesome unbolted (like the Celica GTS) and some sound so terrible (like my Celica GT) that it's simply too embarassing to drive under ANY circumstance.

I'm asking because there's quite a nice weight savings potential doing this, and then simply having a custom muffler shop whip up a turndown with a flange that I can bolt on and off for autocrosses/track days. The top car in the ST class is the '89 Civic Si, most of those guys are getting their cars under 2100 pounds. Any bit of weight I can shed within the legal limits would help...

318isfolife · « **Reply #1 on:** April 03, 2009, 12:21:50 PM »

i would not recommend this at all on this car or on any 4 cylinder for that matter. unless you are turbo charged and even then i would not do it. you will lose all your bottom end and the exhaust scavenging that the BMW engineers have setup from the factory. back pressure is your friend and so is having your exhaust come all the way out.

quinn11m20 · « **Reply #2 on:** April 03, 2009, 12:48:35 PM »

I just did that not to long ago. I cut just short of my o2 sensor and lost all of my bottom end power. I just recently had it welded back on. Yeah! its heavy but this engine needs the low end. If you change your cams you can get more power.

xwill112x · « **Reply #3 on:** April 03, 2009, 02:00:49 PM »

it sounds good if u cut it past the cat.

other than that, its a no go.

AcSchnitzer318is · « **Reply #4 on:** April 03, 2009, 03:18:22 PM »

I can post a video with open header... I was changing my header gasket a shot a quick video. LOL sounds like a harley to me.

renfield90 · « **Reply #5 on:** April 03, 2009, 06:26:47 PM »

My understanding is that backpressure is hogwash with a fuel injected engine.

Exhaust scavenging...I see your point to that. But considering some of the severe crush bends that are present from the factory, I can't see how there's all that much of that going on (or at the least, whatever is present is getting offset by flow restrictions).

I'm talking about unbolting the axleback portion, nothing too crazy. Cat must remain in place and the exhaust must exit behind the driver, according to the rules. Cut too close to the O2 sensor and you may cause it to read incorrectly.

And some four bangers DO sound mean and aggressive unbolted...like the Celica GTS I mentioned. Revs to 8400 (higher with aftermarket engine management), almost starts sounding like a sportbike. Not just a coincidence; Yamaha designed the head...

B318M42W · « **Reply #6 on:** April 03, 2009, 08:22:46 PM »

Quote from: AcSchnitzer318is;69391

I can post a video with open header... I was changing my header gasket a shot a quick video. LOL sounds like a harley to me.

please do:D

xwill112x · « **Reply #7 on:** April 04, 2009, 07:50:23 AM »

Quote from: abcd036;69427

URLs deleted by moderator

abcd036, when does i getz teh spending moneyzz??1?!!?

spammer bump

318isfolife · « **Reply #8 on:** April 04, 2009, 11:12:43 AM »

i had the axle back portion taken off and ran a pipe just out the back when i was in florida i did it for a while. i don't see any gains out of doing this it is just stupid loud and sounds like a honda b18 with a fart pipe.

renfield90 · « **Reply #9 on:** April 04, 2009, 07:29:43 PM »

Quote from: 318isfolife;69439

i had the axle back portion taken off and ran a pipe just out the back when i was in florida i did it for a while. i don't see any gains out of doing this it is just stupid loud and sounds like a honda b18 with a fart pipe.

I don't care if it's stupid loud or even a little annoying/obnoxious. It's a fairly decent weight savings. The only thing that would stop me is if it sounded so incredibly terrible that I'd be embarassed to be seen in the driver's seat.

I guess I'll just try it out myself...

papercutout · « **Reply #10 on:** April 06, 2009, 11:13:37 AM »

I ran my car for a whole with no cat (UK cars didn't have one, they have 2 midboxes), and only 1 midbox. I kept the first midbox and a straight pipe from there back. It was ridiculosuly loud, a day of blatting, let alone trackdays leaves your ears RINGING! Trust me. Can be heard from about a mile away if you accelerate hard, my dad has listened to me from the garden before!

Side exit with 2 mixboxes or cat/midbox in will be loud but more acceptable.

AcSchnitzer318is · « **Reply #11 on:** April 06, 2009, 11:14:09 AM »

Here you go... I wouldn't ever run like this, but hey that's just me.

Open header Youtube Vid

renfield90 · « **Reply #12 on:** April 06, 2009, 11:06:00 PM »

Quote from: AcSchnitzer318is;69563

Here you go... I wouldn't ever run like this, but hey that's just me.

Open header Youtube Vid

I like how the car alarm goes off the instant you turn it on. :p

If it's really loud I can just wear ear plugs. If it sounds similar to that with an unbolted axleback, I'd totally rock that. It'd be worth it for the weight savings.

papercutout · « **Reply #13 on:** April 07, 2009, 04:52:33 PM »

It'll sound nothing like that from axleback. The 6+ foot of pipe will make it a total rasp, no burble. Even with the open header, as soon as it revs past 2000rpm (trust me, anywhere past 2000rpm on my 1 mid box exhaust was ridiculous), it'll rasp and blow your ears out. Funny that 2000rpm is the point it starts though! But with a point that low, its hard to drive remotely quietly anywhere (which isn't your aim I know).

As said - you'll lose power and its ridiculously noisy. Painfully so! Take it from those of us who've tried mate.
My recommendation is a front box and a glasspack/cherry bomb on the rear. Or cherry bomb out the side or whatever.

AcSchnitzer318is · « **Reply #14 on:** April 07, 2009, 05:43:55 PM »

Oh I forgot to mention... I run delta cams, which is why it has that lopeyness to it, yours might sound slightly different.