OEM Exhaust Mod, What Happens to Flow/Power!

[mPlasticDesign]

Yes people like the louder sound with the OEM exhaust mod, but what happens when you remove the absorption material and eliminate the perforated pipes?

Do you increase OR decrease flow and horsepower? The engineering and physics behind it...

Start watching at 20:20 until ~23:40.... or watch the whole thing if you're interested.

Good luck in finding the right exhaust for your needs and happy motoring!

https://www.youtube.com/watch?v=RWTARjxiqlo

[Rat3d ///M]

Moral of the story is, stay away from the OEM exhaust mod and do full exhaust? Most people don't do the OEM exhaust mod because it increases hp. They do it because it's cheap as dirt and sounds just as good, if not better than a $3k Akrapovic or Eisenmann system, myself included. for pure sound and nothing more you can't beat it. besides is the power loss if any really anything to be concerned about? I'd suspect it's negligible at best.

Very informative video though. thanks for posting it.

[mPlasticDesign]

Originally Posted by ||||||||||

Moral of the story is, stay away from the OEM exhaust mod and do full exhaust? Most people don't do the OEM exhaust mod because it increases hp. They do it because it's cheap as dirt and sounds just as good, if not better than a $3k Akrapovic or Eisenmann system, myself included. for pure sound and nothing more you can't beat it. besides is the power loss if any really anything to be concerned about? I'd suspect it's negligible at best.

Very informative video though. thanks for posting it.

The video continues with "sound" design which is probably the most important factor for most people when choosing an exhaust, right after the explanation of 'perforated' vs. 'straight thru' air flow.

I don't know how much of a loss it would be, probably negligible like you said, but even if it's only 10-15hp loss, vs. a 15-20hp gain with an actual engineered and dyno tested exhaust, that is a potential 30-35hp swing. Nothing to sneeze at.

Has anyone actually taken the time to dyno the OEM exhaust mod?

[CognitiveDistortion]

Love the way this video starts out..."sometimes in all the talk about sucking and squeezing and banging we forget about the blowing part, blowing is important too'. Shit yea, its important!

[M3ANMACHINE]

On an N/A car the difference will be severely negligible. Couple HP at most

[duvinclunk]

Interesting video, good watch. Sure does make me think twice before doing the OEM exhaust mod even though as mentioned it probably is such a small difference in loss. Would love to see someone dyno before and after through.

Originally Posted by CognitiveDistortion

Love the way this video starts out..."sometimes in all the talk about sucking and squeezing and banging we forget about the blowing part, blowing is important too'. Shit yea, its important!

Wow, simple minds.

[mPlasticDesign]

Originally Posted by M3ANMACHINE

On an N/A car the difference will be severely negligible. Couple HP at most

Maybe, but I think it is a lot easier to lose power, on the existing design that BMW spent many hours in engineering and testing, then one would think. It's probably pretty difficult to improve and yet there are a few that actually concentrated on HP performance not just sound and weight reduction. Others don't even make any claims and I suspect it's because there is no actual HP gain.

ESS= +8hp
Dinan= +6hp
Eisenman= +3hp
Akra= +4hp

If these companies try so hard to squeeze a few HP, it seems like it would be real easy to lose 4-5hp without even trying, just so you can have more volume and in the process decrease airflow. I guess all we can do is speculate until someone actually does a before/after dyno. I'd be interested.

My point was more along the lines that you have this really nice expensive car but don't want to spend the money on an exhaust, so then you hack up the OEM exhaust and basically do the equivalent of those high school kids that poke holes in their civic exhaust to make it louder, and in the end lose HP?

[duvinclunk]

Originally Posted by Mr.Metak2you

My point was more along the lines that you have this really nice expensive car but don't want to spend the money on an exhaust, so then you hack up the OEM exhaust and basically do the equivalent of those high school kids that poke holes in their civic exhaust to make it louder, and in the end lose HP?

I'm not sure I agree with this. Sure, the intention is to make it loud and sound better. But with the prices of these aftermarket parts for our cars and the price jack from most companies its no wonder why people search for other means. I mean I've seen some exhausts go for $6k+. That's absurd. Sure they make them excellent and put research into them, but its still hard for me to believe they're not making a killing on those because they know "M car drivers have money to blow" and thus they're so expensive. I even called a reputable company for lowering/coilover springs to work with my adjustable damping shocks. They said for an E90 335i they are $80 less than the M3. These springs are almost identical, no notable difference (besides rate) that the representative could come up with. They offer coilover springs in varying rates all at the same price so a different spring rate would be hard to believe for the price hike. It's just the M tax. Sometimes a $200 exhaust mod is easier to swallow than $6k for something that's only going to do +-4hp and all we're looking for is that V8 rumble.

Aside from the fact that we still don't have anyone to PROVE that it looses power. If I could find an exhaust mod exhaust to purchase I would do this test.

[STooK]

I had the oem mod on my e93 and didn't notice any difference in power. But even if I had an aftermarket exhaust would I really notice the bump in power? I don't think so. To me the awesome sound you get from the oem mod is easily worth the few hp you "might" lose.

[ASBSECU E93]

...and with the top down...that sound tho

[MattM3SVT]

Interesting video. I think it may also depend on the type of OEM mod done. Refer to the image below. If you do the 2-pipe/4-pipe perforated method, air still flows through chambers 5 and 6. Therefore I can see how that may slow down the air when you eliminate the perforated section. But if you do the bypass/ACM method, you completely bypass those chambers reducing the length of piping within the muffler (Bypass only uses the two outer chambers. Straight through design). So essentially the air has less pipe to go through and air can flow quicker. So I believe this method would actually increase air flow.

Regardless the changes in HP will be so minimal. And if you are worried, buy a drop in filter to make up those minimal loses and call it a day! Awesome sound for under $500