HIGH PITCHED SCREECH AT 0.5 BAR BOOST

[Enright]

Fairy nuffski.

It IS a tad indiscreet, but I never follow myself anyway so it's not too big an issue, and it does make tunnels or crowded bus stops fun, especially when I can make it backfire with a quick stab of the gas.

Now where did that reverse-baseball-cap smiley go...?

[ailwyn]

but I never follow myself anyway

Except on roundabouts?

[JIMBO]

Hi everyone,
I still have the "mother in law" of a screach over 6000 revs. It has really spoilt the car in my opinion, as it atracts too much attention. The "boy racer" sound is ok pottering around but gets very wearing on journeys.
Has anyone taken theirs back to Peco for an assesment ? It's too far for me, but surely they are aware of this and should offer to put ALL the screachers right.
As I have only covered 2000 miles in the last 18 months( including 500 to get the exhaust fitted) it seems a waste of a good car, so I shall probably get round to selling it in the near future.
Regards to all
Jim

[Enright]

Jimbo,

Where are you? Your profile doesn't say.
Maybe it would be worth considering an ESM switcher module like the one I have, which allows you to change between boost profiles.
That could provide a setting where the volume of air quickly goes through (or stays below) the one that causes the resonance which makes it screech.

Alternatively, I too have a 2 1/4" system, as well as all of the 2" bore components to make a complete standard system. In other words if you want to do a deal that wouldn't take you off the road, get in touch.

[algirdas]

Dear Jimbo:

Don't you think selling the car because the exhaust screeches is a bit extreme? We have half a dozen or so people afflicted with this problem plus a bunch of other very bright people who are willing to help us get it all sorted. Plus, Dave at PECO is an M100 owner and, if the exhaust truly is the culprit, I seriously doubt he will just flip all of us the bird and tell us to go buy earplugs.

Instead, let's all put our heads togther and figure this out. Its not like we are trying to land a man on the moon.

Geoff-Check your PMs tomorrow. I have yet another silly idea on this.

Sincerely,

Algirdas

[ailwyn]

Is there a way to "pressure test" the system whilst stationary or off the car all together in order to prove or disprove the leak/poor weld theory?

[Enright]

Al, I read it that he was going to sell the exhaust rather than the entire car. I could be wrong, but I hope I'm not.

I have another theory about this:
My system uses the standard 2" downpipe, and then joins onto it just near the cross-piece of the prongeron.
The Peco systems all dispose of the downpipe and are 2 1/4" right up to the join between the bottom of the pre-cat and the downpipe.
But the lower hole in the pre-cat is still only 2".
This means that you are trying to funnel air through a 2" orifice, only for it to immediately open out (with a noticeable 1/4" difference in diameter step) afterwards.
It must be like blowing through a flute!

My theory is that if the bottom of the pre-cat was ported to 2 1/4", and the join filed so that the air saw the smoothest transition possible from pre-cat to exhaust, it could eliminate the screech.

I have a pre-cat already split. Anyone with a Screecho want to borrow, port and fit it?

[philip_sloper]

The problem appears to be caused by some slight dimensional variations in the tailpipes. Peco are studying this and have promised to post something on this thread as soon as possible.

[algirdas]

Dear Phil:

Have you been in contact with Dave at PECO?

Also, for whatever it is worth, mine only whistles in first, second and third gears from 5,500 rpm. It gradually begins to whistle at 5,500 and reaches its highest volume at 6,000 rpm. Curiously, it whistles in first gear most of the time, but not all of the time. In second and third gear it whistles all of the time.

I have not tried fourth or fifth gears because of the speed involved.

Neil-Good catch on selling the exhaust. Did not consider that as an option. But then again, it is us lawyers who noticed that Godiva rode a horse!

Sincerely,

Algirdas

[Monty]

I have another theory about this:
My system uses the standard 2" downpipe, and then joins onto it just near the cross-piece of the prongeron.
The Peco systems all dispose of the downpipe and are 2 1/4" right up to the join between the bottom of the pre-cat and the downpipe.
But the lower hole in the pre-cat is still only 2".
This means that you are trying to funnel air through a 2" orifice, only for it to immediately open out (with a noticeable 1/4" difference in diameter step) afterwards.
It must be like blowing through a flute!

My theory is that if the bottom of the pre-cat was ported to 2 1/4", and the join filed so that the air saw the smoothest transition possible from pre-cat to exhaust, it could eliminate the screech.

I have a pre-cat already split. Anyone with a Screecho want to borrow, port and fit it?

a possiblility i suppose, but then wouldn`t all the peco`s screetch as the pre-cat housing and the downpipe will all be identical + then other makes off 21/4 systems would do the same thing. Thats why i still go with the welds or maybe something in the rear silencer

[David]

Hi all,

sorry to hear that the high pitched screech still exists. Have been giving it some thought & there is a modification I would lik to try on the tail pipe.
If one of you could send me a rear silencer that has the problem I will try the mod and return it to you asap for testing.

Regards

Dave Jones
Head of R & D
A & I (Peco) Acoustics Limited
Sandford Street
Birkenhead
Wirral
CH41 1AZ

Tel 0151 647 6041
Fax 0151 666 1805

[JPGuillon]

Hello Dave , you have a PM .

[philip_sloper]

Dear Phil:

Have you been in contact with Dave at PECO?

Yes, please see his post above. I think his idea is likely to work.

[algirdas]

Dear Phil:

I save Peco Dave's post. I'm curious to see how it turns out. Please keep us all posted.

Sincerely,

Algirdas

[mikeydude]

Erm, It's a few days on..you have all gone quiet...well your pipes are still parpin I assume!?....

Anyone heard from Pico as to what's happening, I was hoping to get a PICO but I don't want a pinging!

[TomE]

Did Dave at Peco have any success with a fix? Garage called this afternoon to warn me that there is a screech above about 5,500 rpm now that the Peco exhaust is on. That must be the cause, as all the other work has been suspension and brakes plus a B service. They've also now double checked timing, sensors, plugs etc and everything's within spec.

My car's an SE with standard Peco tailpipe and standard factory downpipe. It's previously had a BBR conversion, K&N filter and Quicksilver exhaust and in that setup boosted to about 0.8 with no whistling across the revs/gears.

I won't get the car back until Thursday and am then on track at Goodwood on Saturday, so will be able to investigate in more detail there - assuming I don't fail the noise test! There'll be several other Lotus owners around who can have a listen and throw in ideas. Any local LECers very welcome to come for a listen too!

I've also got a rolling road session booked for Sat 8 Dec and can do some more testing if anyone has thoughts on what to test or tinker with. There are spare slots at the session (in North Surrey) if anyone else wants to join, either for exhaust trouble-shooting or the usual power measurements. £35-40 per session, details on the SELOC events page here.

[TomE]

Here's some more info from my testing at Goodwood on Saturday:

1. For me the noise is more of a whistle than a screech and isn't as loud as I'd thought it would be based on other people's comments here - disconcerting but not deafening.

2. Whistling starts fairly abruptly at about 5500rpm, with no gradual build-up in sound level or pitch below this. Also, only whistles if on full boost on the turbo (which in my case is 0.95 with the BBR kit and tweaks) - any backing off to reduce the boost (even slightly to 0.9) and the whistling stops even with revs over 5500. What conditions are present on full boost, regardless of whether your car boosts to 0.5, 0.8 or 0.95, but are not present on less than full boost?

3. Whistling starts at the same revs in every gear (checking this in 5th at full boost at 125mph was "interesting"!). The whistling continued from 5500 up to redline.

4. Contrary to some other posts, for me the sound level and pitch seemed independent of revs (once over 5500), gear or road speed. Confirmed by observers in the pits for 3rd and 4th gear runs.

5. Sound seems to be coming from the rear half of the car, behind the driver, rather than in front - so presumably it's the exhaust rather than the turbo or manifold.

6. No evidence of boost creep.

Consensus from others who observed is that it's some sort of standing resonance. People talked about the sound you get when you blow across the top of a bottle rather than the "finger on a wine glass" sound mentioned by others here.

On the plus side:
a) the PECO exhaust note pre whistle is great and really suits the car
b) as an Elise owner said on Saturday, the system is "inverse chav" - huge great drainpipe hidden under the car, with discrete tailpipe sticking out the back!
c) the increase in performance is amazing - +10-15% on the top speeds I could reach on each straight due to more power and acceleration. Back in May I was just breaching 110 on the fastest section with BBR but no PECO - now getting 125
d) I was still well within the noise limit for a Goodwood "quiet" day - 94dB measured versus 98dB limit.

'Scuse the long post but figured the info might be of use. Next stop, December's rolling road test.

[DeeAitch]

Kept out of this as most original posts said the noise came from the front. If from the tailpipe I suspect it is more of a 'Jet' noise than a screetch, coming from the tailpipe itself, a common problem - I have a bolt on tailpipe on my muffler which I can make a 'Jet' noise with at circa 4k RPM if it is not in the correct place
Can someone with a private test track try packing the gap between tailpipe and finisher with Glass wool? You will need to keep it in place with some tape - don't leave it there for more than one quick run

[philip_sloper]

My screech has been cured by removing the inner round pipe from the standard Peco tailpipe design, so that only the outer oval pipe remains.

I think the reason some screech and others don't is caused by a variation in the length of the inner pipe and thus it's relationship to the outer pipe. Dave at Peco is investigating this.

[JIMBO]

Hi TomE,
125MPH ? did you forget to take the handbrake off ?
Back in the late 70's and early 80's I was pulling just over 135mph in my Uren Comanche (modified 3ltr Capri), and having to lift of before the right hander before St Mary's so as not to over rev it.
Sorry to hear that you have joined the screachers, but it looks like Phil may have the answer.
Best regards
Jim