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      05-18-2015, 02:50 PM   #1
anom3
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AFE Rasp vs BMC Rasp - BMC Wins (Caveat)

So one of the first things I bought for my M3 when I purchased it about a year ago was the AFE air filter. I dont recall the exact model #, but its the one with the plastic elbow + filter combo.

Installed it, and right away I noticed at about 3000 RPM for a few 100 RPM there was a rasp noise. No I am not talking about the overall increase in sound the filter gave the motor, but a specific noise only around those RPMs. Almost a sort of rattle. I checked the fitment myself twice, and had the shop check once when they did some other work on the car. Fitment was not the issue.

So I removed it, I found the rasp quite annoying. Even had my friend (the previous owner of the car) ask "whats that sound" when I let him take the car on a little rip when I visited him.

About 2 weeks ago, I ordered the BMC filter from ebay. Installed it just now. No rasp! I have not had a chance to go WOT as I just went around the block, but its not there.

So I can highly recommend the BMC filter. In my setup, its the winner.

Now, here is the caveat:

AFE:

AFE Filter
BPM Stage 1
Akrapovic Rear End (NO XPipe)
Adaptations adapted (I had the AFE on for a couple 1000 KM)

BMC:

BMC Filter
BPM Stage 2
Akrapvoic Rear End + Akrapovic XPipe
Adaptations recently reset (They were reset when the Akra XPipe + BPM2 went in, about 400KM ago)

So yea, perhaps its the combination of the changes done to the car since the AFE was removed (and OEM put back in)... Or maybe the adaptations? Who knows... All I know is that with the combo I have now (BMC + Akra Full + BPM Stage 2), there is no rasp at all. Just a nice louder linear growl all the way up the RPM range (at least up to 5500RPM...).

BMC, Recommended!
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      05-18-2015, 03:02 PM   #2
Shredicus
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Hmm I rather like the raw edge unfiltered intake resonance adds. Definitely noticed an increase going from MS stg. 1 to stg. 2 filter. Are you saying you went from a full afe intake back to the stock elbow + bmc? That could explain the difference in resonance as I think the stock flex section is actually a resonator of sorts.
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      05-18-2015, 03:30 PM   #3
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You can get the 3000 RPM intake rattle with other brands of filters, too. I find it annoying as well, almost like a tip-in throttle ping or any other engine or exhaust related rattle. Just doesn't sound right. There are times when even minor mods have their drawbacks on these cars. Intake system must be susceptible to a resonance at that RPM, especially at wider throttle openings.
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      05-18-2015, 03:36 PM   #4
anom3
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On phone so will point form:

Akra rear end + bpm stage 1 go on
Afe air filter goes on
Rasp!
Removed afe, went back to oem
Akra xpipe + bpm stage 2 go on
Bmc goes on
No rasp

As far as liking the sound... I like the increased growl the air filter upgrades give just as much as most on here. What i found annoying with the afe was the metalic / rattle around 3000 to 3200 rpm. Reported by many on here (not just w afe btw, others too...). I dont get the rasp as its commonly called on here with the bmc i just installed today.

U may be right though, it could be the fact the bmc is a straight drop in, no new elbow... The afe had the hard plastic elbow.

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Originally Posted by Shredicus View Post
Hmm I rather like the raw edge unfiltered intake resonance adds. Definitely noticed an increase going from MS stg. 1 to stg. 2 filter. Are you saying you went from a full afe intake back to the stock elbow + bmc? That could explain the difference in resonance as I think the stock flex section is actually a resonator of sorts.
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      05-18-2015, 03:39 PM   #5
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Agreed, that said as mentioned w the bmc i dont have the 3k-ish rpm rasp. I specifically did a number of 1500-4000 accelerations and had the window down. Nothing, just a beautiful purr.

Just thought now... Maybe as the adaptations take hold it will come back? I hope not.

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Originally Posted by Beemdog View Post
You can get the 3000 RPM intake rattle with other brands of filters, too. I find it annoying as well, almost like a tip-in throttle ping or any other engine or exhaust related rattle. Just doesn't sound right. There are times when even minor mods have their drawbacks on these cars. Intake system must be susceptible to a resonance at that RPM, especially at wider throttle openings.
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      05-18-2015, 03:46 PM   #6
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Quote:
Originally Posted by anom3 View Post
Agreed, that said as mentioned w the bmc i dont have the 3k-ish rpm rasp. I specifically did a number of 1500-4000 accelerations and had the window down. Nothing, just a beautiful purr.

Just thought now... Maybe as the adaptations take hold it will come back? I hope not.
Since the "rattle" is a mechanical resonance, it could appear later when the filter and it's rubberized end caps have softened or become more compliant over time. Who knows?, time will tell. I would tend to doubt any changes to your adaptive tuning will affect this, but again, just a hunch.
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      05-18-2015, 04:03 PM   #7
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Ill update this thread in 500 KM or so, or sooner if the rasp comes back.

I am no expert by any stretch, but the BMC looked really solid just by visually looking at it.

Quote:
Originally Posted by Beemdog View Post
Since the "rattle" is a mechanical resonance, it could appear later when the filter and it's rubberized end caps have softened or become more compliant over time. Who knows?, time will tell. I would tend to doubt any changes to your adaptive tuning will affect this, but again, just a hunch.
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      05-18-2015, 04:23 PM   #8
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I should have my Macht Schnell stage 2 intake tomorrow. After I install it, I will let you know if I hear said rattle.
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      05-19-2015, 04:22 AM   #9
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I have a distinct filter "rattle" even with OEM between 3400-3800 ish. Not crazy loud but initially when I got the car it made me wonder. Changed filter which made it a tad better but since got used to it instead...

Tips on how to improve the OEM are welcome.
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