Failed EPA by 2db

[Guest Robo's]

Just been back from the EPA, and with the boost almost stock it still turned out 92db instead of the approved 90db. He would not pass it and i don't consider my car loud.

So i need to take 2db off it, so whats my best options??

I might replace the 3 inch cat with the standard 2.5 inch cat and try and turn the boost down even further, would this do it?

[predator]

dang.. if its nearly at stock boost levels there probably isn't much else you can do to reduce it further by playing with the boost. You could try and make it spool up very late, so its making maximum boost later on, and hence less noise down low.

Did you put the standard box back on? if anything you want to restrict the airflow the best you can, generally the opposite you'd usually want to do.

Stock cat should be a bit quieter, but might not get you under. I passed with full 3" hi-flow cat, but i think mine was a bit of a freak passing with absolutely no exhaust modifications.

Do you have a resonator in there? (its like a bulge you might see in the pipe). Bends in the pipework i think also tend to reduce the noise a bit.

Otherwise its time to borrow a stock exhaust off somebody.

[Guest Robo's]

Yes full 3 inch and 3.5 after the cat, i have a hi flow cat too, its running around 8psi.

[pentae]

Use the old trick of stuffing your muffler with steel wool. I heard someone on the s13 y! group say this is a good temporary way of reducing the sound.

[Pva_Glue]

Originally posted by Robo's

Just been back from the EPA, and with the boost almost stock it still turned out 92db instead of the approved 90db. He would not pass it and i don't consider my car loud.

So i need to take 2db off it, so whats my best options??

I might replace the 3 inch cat with the standard 2.5 inch cat and try and turn the boost down even further, would this do it?

THat's farcked!!! Go and ask them how do you know your machine is not farked!!!

ask them to test on other machine...

2db come on that;s nothing compare to harley davison Bikes.

[akeenan]

when talking about sound 2db is a fair bit actually! ... but...... 92db isnt too loud... do the steel wool.. if it was heaps over id say change the exhaust .. but its not to bad

[GZ R33]

What revs was that at, for a 6 cyl it is 4,500rpm.

[sky^rkt]

thats bad man, i failed mine by 8db i just put on a pea shooter and i stil got 88db!!! mayb just get another muffler and put it on or b nice to em and make em pass u

[Guest Robo's]

4800rpm it was done at, and it is angled at 45 degrees of the car, but my exhaust is angled also, making it inline with the exhaust rather than the car, damn!!

[Zane]

This story sounds familiar.

I got done for 2dB over the limit nearly 18 months ago now. I fixed it by adding another resonator under the car. Originally I had a hotdog style resonator and barrel type s/s muffler at the back of my 3" system and recorded 92dB. Had another box type resonator installed inline with the hotdog and it brought the reading down to 89dB, just enough to get the EPA off my back.

As long as you use straight through type mufflers and resonators you shouldn't loose too much power, but honestly, I wish I had just borrowed a standard exhaust for the test. It would have saved cutting up a perfectly good exhaust.

Z.

[PTR33]

Seeing that dB is a logarithmetric scale and that 3dB represents a doupling of the sound pressure energy, 92dB is about 50% louder than 90dB.

But I agree with you, even that's not loud man.

[Steve]

OK, if you go the steel wool, good luck. I tried this on rumour and all I managed to do was shoot flaming pieces of steel wool out of the exhaust - was pretty funny actually.

If you have the standard Jap type muffler - sounds like you have an N1 type or similar, most will have a small hole right near the tip at the bottom. This is so you can attach a muffler to the exhaust 'for street use', as a loud exhaust should only be used on the track:)

Autobahn sell the muffler inserts.

[Guest Robo's]

Alot of people are saying stuff chicken wire up there with a broom stick. I will try the smaller cat, or possible maybe get a smaller exhaust gasket on the cat, say 2 inches to restrict flow.

[CrazyGTR]

You can cut a thin plate of metal to a 3 inch circle shape, drill heaps of holes in it so it flows and put this between the cat and the rear pipe, it will shut it up.

[pentae]

flaming peices of wool! I bet they dont have that in the Fast & Furious 3 script..

[Warpspeed]

CrazyGTR is spot on, get a piece of thin sheetmetal and put a single smallish hole in the middle, maybe 15mm diameter and put this between the cat and the pipe flange.

If you are clever, it will not be seen, especially if you spray it with black muffler paint around the bright cut edge, before you fit it .

[Guest Robo's]

Cool, sounds easy, Bit of sheetmetal here i come, i'll make it into a cat gasket.

[Warpspeed]

Yeah, just make the hole so it knocks the edge off the noise.

If you make it too small, the exhaust will just hiss, and the guy doing the test will know you have done something shifty, and start looking underneath. So don't be greedy, just enough to pass.

[Guest Robo's]

Maybe make it 1.5 inch in diameter, ive got 2.5 inch gasket but i think that will be minimal from my normal 3 inch