UAS downpipe - horrible sucking, hissing sound.

RichardH · Post by **RichardH** » Thu Jul 22, 2004 11:18 pm

Hi all.

My docile, purring little pet has just turned into a rabid hissing, spitting tomcat!

Just got the UAS downpipe fitted today. It was fitted using the existing three exhaust pipe gaskets, with high temp goopy sealant on each side for a good seal. It all looked in good nick. Otherwise stock exhaust.

But...

On throttle-off between 4000rpm and 3200-odd rpm, something is making a bleedin' awful sucking hissing sound. It was quiet as a kitten before, but from the first test drive with the new downpipe on, it's noisy as hell.

There's always a background hiss on full throttle, which I'd expected, and can live with. But the throttle-off hiss is something entirely different. I feel like I've spent a chunk of pay packet turning this car into something not so pleasant, hehe.

So. Anyone else installed the UAS downpipe on an otherwise stock exhaust? Anyone else have a hissy, spitty, rabid, feral cat noise on throttle-off, specifically as the rev counter moves between 4000rpm and just above 3000rpm?

If not, it's off to poke at exhaust manifold gaskets, downpipe flex joints, cat-to-rear-pipe joints, etc. to see what's been disturbed.

Cheers, folks!

- Rich

Post by **smorison** » Thu Jul 22, 2004 11:29 pm

the engine pipes help it breath a lot better, which means more noise.. unfortunatley we have noticed with some aftermarket exhausts the resonation is a liitle funny...

a hissing noise is normally a gasket from experience...

SilentBob · Post by **SilentBob** » Fri Jul 23, 2004 8:46 am

Hey
my exhaust is stock except for the uas pipe, and yep, there is that sucking noise(sounds somewhat like a BOV im my ears) during let off around that rev range...
never had it looked at so dont know if its a gasket problem exaturating the noise...

when i first got it installed, it annoyed me somewhat, but now....i think its not to bad

SilentBob

RichardH · Post by **RichardH** » Fri Jul 23, 2004 10:41 am

hehe. If I wanted a BOV, I'd buy a turbocharged vehicle with a BOV!

But I don't.

Any chance the sucking noise has lessened over time? ie. Due to a bit of carbon buildup around the new gaskets/pipe? Or is it just that you've got used to it?

It's just irritating finding myself "driving around" it - choosing my shift points so I'm not in closed throttle between 3k and 4k. I've got other stuff to worry about on the road!

- Rich

ruchi · Post by **ruchi** » Fri Jul 23, 2004 10:45 am

it's interesting that this occurs on backoff when the pressure is reduced, not on acceleration when the pressure would be increasing.

RichardH · Post by **RichardH** » Fri Jul 23, 2004 11:36 am

Thanks all. Esp. SilentBob, with same system as I have, and same symptom. Bugger!

I'll drop in to a good exhaust place I know today, and have a chat about it...

- Rich

PS. Torque graph has been produced from Home Dyno. Suffice to say I'm a happy man on that front.

I'll do an ftowa.com article on it asap...

FTO338 · Post by **FTO338** » Fri Jul 23, 2004 11:53 am

ruchi wrote:it's interesting that this occurs on backoff when the pressure is reduced, not on acceleration when the pressure would be increasing.

Is the same effect you get, when you swich off your car if you had a pod filter.

RichardH · Post by **RichardH** » Fri Jul 23, 2004 1:43 pm

Okay, here's the skinny on the hissy sucky...

(Hmm, never used that phrase before, and never will again)

I took it to an exhaust specialist just now - recommended as really knowing their stuff. They immediately identified the noise as being due to the type of flex used by UAS.

Apparently, the overwhelming majority of aftermarket flex joints are noisier than original factory flex. In the stock FTO pipe, the inside of the flex joint would have been extremely fine and smooth. This inner sleeve stops it breathing, hissing, whistling and generally carrying on.

They reckon they get whistling pipe issues every now and then, and it takes a bit of ferreting around to find the really good flex stuff to eliminate it. Even vehicles like landcruisers can suffer from it at particular rpm.

So there you go. The sound I have is the flex joints talking!

- Rich

ruchi · Post by **ruchi** » Fri Jul 23, 2004 1:47 pm

I take it that the flex joints is that mesh braid or is it something else?

RichardH · Post by **RichardH** » Fri Jul 23, 2004 1:59 pm

That's the stuff. The downpipe has two flex joints.

- Rich

ruchi · Post by **ruchi** » Fri Jul 23, 2004 2:32 pm

so is someone going to feed this back to UAS? I'm sure it could help to develop a better product and it would also be interesting to see what they thought.

G1 · Post by G1 » Sat Jul 24, 2004 9:49 am

yes mine isnt stock exhaust but i am getting the hissing as well.. it doesn't seem as loud to me anymore... either im used to it or it has actually gotten quieter over time... i'll double check next time i drive...

RichardH · Post by **RichardH** » Sat Jul 24, 2004 6:54 pm

UPDATE - Solution:

Hi all.

I did a bit of research, and found some interesting stuff. Here's the best one, by the way:

http://www.greghome.com/Greg's%20Garage ... Y-Pipe.htm

This morning, I purchased 7 metres of exhaust wrap (50mm wide) from Repco ($44 or something). I wrapped both flex joints (and only the flex joints) in this stuff, with a standard hose clamp at each end.

I've just taken it around the block, and... no more sucking, hissing noise on throttle lift-off between 4000rpm and 3000rpm!

I'm off for a real drive now, so we'll see if it's quieter all round. But a good result for the daily-driver side of things.

- Rich

Boris · Post by **Boris** » Sun Jul 25, 2004 5:45 pm

Hmm. it's funny this, good work...

I don't have the UAS pipe, and mine does this hissing, but mine appears to be higher up in the rev range, from 4.5 to 3.8 get's less louder by 3.5

If I shift exactly at 4.5, it sounds 100% like a BOV...

Richard, from what I read, this can happen on any exhaust that doesn't have good flew joints?

Would this hissing, also sound like it might be a valve or something?

So can anyone confirm, whether, they have this hissing, on their stock frontpipe? Cos yeah... I might not have a stock pipe then...

FTO338 · Post by **FTO338** » Sun Jul 25, 2004 10:50 pm

Hey Boris, i know you properly know this, but could it be your air-filter?

Boris · Post by **Boris** » Mon Jul 26, 2004 12:05 am

FTO338 wrote:Hey Boris, i know you properly know this, but could it be your air-filter?

Nah man, Although I do have a Blitz SUS airfilter, i have tryed replacing it with another K&N one... This hissing doesn't seem anything like airfilter, it's very mechanical, like a something opening/closing at 4000rpm... It's really hard to describe.... it's more of a "ZZZZZZ"....

fto12345 · Post by **fto12345** » Mon Jul 26, 2004 10:38 am

Hi Richard,

Why using the clamp for the hose wrap?
Is it for the temp to see how it goes?
Or you just wanted to do this?

Just asking as I'm sure there are a better ways to hold these then hose clamps?

hehehe......I'm sure you knew that though....hence the question.

Thanks,

Post by **smorison** » Mon Jul 26, 2004 11:18 am

hose clamps are pretty standard for this sort of thing....

RichardH · Post by **RichardH** » Mon Jul 26, 2004 2:52 pm

> Why using the clamp for the hose wrap?

erm...

* The same company that sold the exhaust wrap also sold "special" clamps. They were all-metal round clampy things that were stupidly expensive. And they didn't do up very cleverly.

* Hoseclamps are also all-metal clampy things that do exactly the same job, but are dirt cheap.

* They are nice and wide, do up tightly and have smooth edges.

Seemed to do the job just fine to me....

As long as they stay on, don't rattle and keep the exhaust wrap where I left it, I'll be a happy man!

- Rich