Dropping 2db

[Jordy32]

Hi all

Long story short I got pulled over and police escorted to an RTA Inspection / defect station as well as having my car tested for noise by the EPA on Friday night. While this may sound incredibly scary to some, I made it through the RTA inspection / defect station without any issues and they were actually quite nice and in the words of both the 4 highway patrol officers who were looking all over the car as well as the 2 RTA inspectors they said "Mate this is a mechanically great car, there's nothing wrong with it at all and it shows that you know what you're doing and that you care" which I will take as a compliment!



After that lovely ordeal I was directed to take my car to the EPA man who did the exhaust noise test, he was actually a really nice guy and explained the law/rules/bullshit that governs the legal limit of noise a car can make. After revving my car with the microphone he explained that the legal limit was 90db, and that throughout the whole rev range my car was under the limit (hooray!) until he backed off the throttle, and each time he did this it would spike to 2db. He also took the time to run me through the rev range and let me watch the computer/device which showed a db reading and showed that every time he did it it would spike.. After a good 20 minute chat about exhausts and mufflers he decided not to fine me for exceeding the limit, however I will need to go to the EPA and have it tested again after I "fix the problem".

My main question is how can I permanently stop the noise from spiking so much when the throttle is closed. I'm well aware I can bolt on a stock system and go to the EPA and pass so please don't suggest that, I'm not interested in a band aid, I want to be confident that if ever get pulled over again it will pass AND I honestly hate loud cars too.. Does anyone know of a certain muffler style which will help this, or would mild steel sections perhaps be the answer? The EPA guy also mentioned that they do not care how thick the exhaust's diameter is, nor do they care about the material it's made of, they just want you to adhere to the noise limit.

I am currently running a Kakimoto 3" stainless steel system from the cat back which has 2 mufflers in it and is quite quiet until you jump off the throttle.. does anyone have any thoughts about how I can modify this system to suit my needs?

Appreciate it!

[Ben C34]

The over run noise might be able to be tuned out.

[Ben C34]

And that guy is a wanker

[AngryRB]

Maybe twin pipes from the diff back into a large twin tip muffler.

[GTSBoy]

Kakimoto are famously a bit raucous and raspy on over-run. Perhaps you had best get some photos of the mid and rear muffler into this thread. Blu-tac your phone to a stick, put it in video mode and pass it under the car a couple of times. if the mid muffler comes up as an obvious fix (ie it's really small) then we could point you towards getting a bigger replacement. But without actually seeing what's there, it's going to be a bit of a fool's errand trying to come up with suggestions*.

* I can come up with several, including putting in a 2" section, putting in an orifice plate into one of your flanges, stuffing steel wool up its arse, etc etc. But of course, these are the ones that we know will work regardless of what else is there, but that you do not want to do.

[Jordy32]

"over-run" that's the term I was looking for, cheers!

When I'm next with my car ill take some pics of the mufflers that are there, I know the question kinda left you all in the dark but appreciate the help so far

I had a 3" mild steel system on my R32 which was great which had 2 straight through mufflers which came out to a 3" tip but im almost sure the kakimoto would be the same, the only difference being that this system is stainless.. If i was to get a mild steel system do you think the over-run sound levels would drop at all? I know stainless is certainly more raspy but how does that translate to db.

Sorry for all the questions lol

[GTSBoy]

Got to be easier just to put a bigger muffler in place of one that is (assumed to be) too small.

[Dose Pipe Sutututu]

It you're running an aftermarket ecu, just enable the fuel cut on decel earlier.. There's a lag time which allows fuel to be injected after TPS of 0% the lower you set it, the less fuel is injected on decel reducing the over run crackle/farts/pops another way is to introduce another resonator, muffler, etc.

[GTRPSI]

Go to one of the flanges of the exhaust, undo it a little and slip in a gasket made of tin with a 1.5"-2" inch hole in it.......remove after test.....

[V28VX37]

Go to one of the flanges of the exhaust, undo it a little and slip in a gasket made of tin with a 1.5"-2" inch hole in it.......remove after test.....

Or easier still, a removable external exhaust silencer: http://www.ebay.com.au/bhp/exhaust-silencer . Good in theory at least but not much $ to test it out.

[Trex]

I believe for db tests you can't use a bolt in silencer.

A lot of people just cut up a coke can or similar and drill holes in it and put that between a flange to pass db limits.

[GTSBoy]

Problem is that he wants the system to be good all the time. Effectively he wants to be able to pass a roadside test, should one be inflicted on him.

[Trex]

Yep. Your post was spot on gts. Just letting v28 know

[Jordy32]

It's a real shame exhaust valves are illegal really, I watched a guy with a varex get his ass handed to him by the EPA right next to me...

Thanks for the tips though, coke can gasket oh boyyy love it!

[Jordy32]

It you're running an aftermarket ecu, just enable the fuel cut on decel earlier.. There's a lag time which allows fuel to be injected after TPS of 0% the lower you set it, the less fuel is injected on decel reducing the over run crackle/farts/pops another way is to introduce another resonator, muffler, etc.

That's a great idea, unfortunately I'm only running a Apexi SAFC on a stock computer..

I know it's a dinosaur!! but for a stock car it's fine for now

[Dose Pipe Sutututu]

that's probably why it's popping and farting more unfortunately

[Trex]

The safc has an over run feature from memory. You can add and subtract fuel during throttle off.

[V28VX37]

It's a real shame exhaust valves are illegal really, I watched a guy with a varex get his ass handed to him by the EPA right next to me...

Thanks for the tips though, coke can gasket oh boyyy love it!

Cheers Tom

It's a real shame exhaust valves are illegal really, I watched a guy with a varex get his ass handed to him by the EPA right next to me...

Thanks for the tips though, coke can gasket oh boyyy love it!

Umm wat, I thought HSVs and most late model performance euros and exotics ran bi-modal/valved systems from factory, fully street legal? Or is just that they never get selected for 'random testing'?

[zebra]

Oem is very different to aftermarket when it comes to epa shit.

Current Hsv gts also has a supercharger...doesnt mean I can fit a blower to my v8 commodore and be legal

[NISR32.5]

Go to one of the flanges of the exhaust, undo it a little and slip in a gasket made of tin with a 1.5"-2" inch hole in it.......remove after test.....

^^^ this lol

Done that before to pass a full inspection in SA, worked like a charm. Car drove like shit tho. Stopped down the road after the inspection and dropped the 2 bolts from the flange and left the gasket on the side of the road. Happy days