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Final attempts to reduce BEC noise
Toprivetguns - 9/7/16 at 06:47 AM

Morning all,

I'm looking for any tips that I might of missed to reduce noise on my BEC.

I measured 100db on my test hence a fail - items already include standard air box and standard ram air ducts, acousta fill and a decibel killer which has helped as my standard reading read at 105db

The exhaust is pretty asmatic so the remaining noise is purely intake. I have some sound buffler 20 to install under the bonnet today, also managed to aquire a sheet of dynamat.

Any other tips and tricks would be appreciated.

Bladerunner - 9/7/16 at 07:00 AM

I had the same problem, in the end it was going for a silencer that had a diameter considerably larger that did the trick.

Rosco86 - 9/7/16 at 09:29 AM

is this for your iva? what revs are you testing it at?

40inches - 9/7/16 at 09:36 AM

quote:
Originally posted by Rosco86
is this for your iva? what revs are you testing it at?


This. The test is based around max power revs, not maximum revs. I put my max power revs at 10,000 rpm and it only just passed
with a ZX12R silencer

motorcycle_mayhem - 9/7/16 at 09:40 AM

As above, nothing more to do except a larger Can, both in diameter and length.

105 dB at 3/4 throttle will just about scrape the static on a track day on a noisy day/circuit. The same will just about scrape through a competition entry at a quiet circuit (e.g. Combe).

However, with static levels this close, the drive-by will get you excluded/black flagged.

When I did the SVA (2002) with the Megabusa it was 101 dB, which the car just about scraped. That was with the factory catalyst-in-the-Can system, which was/is very quiet.



As I've said, I now have a very tired MX5 for trackdays.

Jeano - 9/7/16 at 10:10 AM

I have a ZX12R and have exactly the same issue, i put a muffler in the end and repacked the exhaust and at 8,500 rpm im at 106.8dB and 7rpm is 104.5dB

Not sure why i tested at those levels but basically its right on the limit. I want to reduce it further so i can deffo get under 105dB based in essex i think i want to find someone to put a new exhaust on it for me.

Jenko - 9/7/16 at 10:19 AM

How close is the exhaust tip to the actual engine. During my IVA, the noise test was picking up the engine noise also, so to solve the problem, I covered the engine bay in sound proofing....This made a big difference. Also, as you are through the emissions test, there is no harm in stuffing a db killer up the exhaust...

MOTORCYCLE EXHAUST SILENCER BAFFLE 53.5mm 4 STROKE DB KILLER TRACK DAY

Toprivetguns - 9/7/16 at 11:03 AM

The exhaust is identical to most 7 style cars - near side infront of the rear arch.

Currently installing engine bay sound proofing so fingers crossed.

The day of my test was extremely cold - I assume different temperature contributes to sound moving through the air differently for these type of tests.

adithorp - 9/7/16 at 11:32 AM

Test should be done at 3/4 of max power revs. That's the revs where the engine makes max power not the max revs. If MPR isn't known then it's done at 2/3 of max revs. 2/3 of you stated max would have you tested at 7800.
Did you state the correct figure on the IVA application? ...and it's not unknown for people to under-state MPR by the odd few revs.

[Edited on 9/7/16 by adithorp]

Toprivetguns - 9/7/16 at 12:17 PM

Cheers for all the advice gents - will report further once the sound proofing has been installed.

Toprivetguns - 10/7/16 at 03:51 PM

So after installing some decent bonnet insulation and pointing my exhaust tip down I am still tittering on the edge of 99-100dba.

Next is more insulation of the nose cone mounting, side panels.

Rosco86 - 11/7/16 at 07:49 AM

quote:
Originally posted by Toprivetguns
So after installing some decent bonnet insulation and pointing my exhaust tip down I am still tittering on the edge of 99-100dba.

Next is more insulation of the nose cone mounting, side panels.


so what revs is this at?

adithorp - 11/7/16 at 09:05 AM

How much accoustafil did you use? The online calculator is wrong and leads to overpacking.

russbost - 11/7/16 at 09:47 AM

quote:
Originally posted by adithorp
How much accoustafil did you use? The online calculator is wrong and leads to overpacking.


I would agree with this, but also everyone who's said "fit a bigger can" - it's fairly simple, not a black art, unless most of your noise is coming from the air intakes/underbonnet (which would be unusual) then giving the gases rom to expand & slow down is what it's all about, so either a bigger can or an "add on" that you can bolt on for trackdays etc. dB killlers & packing do work, but work a LOT better when the gases have somewhere to expand to, otherwise you just finish up strangling the engine. Adding an extra box has the additional advantage of moving the measuring point further from the engine bay.

Toprivetguns - 11/7/16 at 07:34 PM

I took everyone's advice and used the correct amount - no over packing.

Jeano - 12/7/16 at 08:26 AM

where did you get the bonnet insulation from, with a bonnect scope i guess it would be pointless for me.

Wonder if i overpacked now :

andyfiggy2002 - 24/7/16 at 08:23 PM

I find it frustrating that a motorbike with 2 wheels can bomb about with an ear piercingly loud exhaust but stick another 2 wheels on it & for some reason with the same engine/ exhaust it has to as quiet as a church mouse!

Toprivetguns - 30/7/16 at 02:33 PM

Solution found - issue resolved !

After checking all things mechanical on the engine I noticed the air switching valve pipe work. Being nosey I investigated what sounds it made connected and disconnected from the air box. I read a few bike forums Curious about this part. It sucks air through the induction box and dumps it directly into the exhaust port within the head helping reduce emissions and carbon build up (quote me if I'm wrong)

I know a few guys on here have it blanked and now I know why. I blanked off the pipe work (valve left in place, not to bring up a FI code) then tested with my decibel meter @ 3/4 rpm as per the engines max rpm and achieved 96.9 dba.

Persistence paid off - cheers for all the suggestions.