Menu toggle

Back firing on over-run

plhorner

plhorner

Moderator
Right,
I think I might have problems! I had SSI's fitted last year along with a sports back box, its always been quite 'burbly' especially on over-run but recently its started 'popping' (lightly) and is quite lumpy on light throttle openings.
Is this normal behaviour? Anybody else had similar issues?

In addition to this, again on over-run, I'm getting a little vibration between 2500 and 2900rpm!! Any ideas? Engine mounts??

Cheers,
 
I had exactly the same problem when I had my suspension updated. One of the air hoses had come loose (at the back of the engine so you couldn't see it!). If you cant see any cracked or loose hose then spray some WD40 around the houses, if the idle speed changes you have found your leak. (great sound though init),

Not sure on the vibration though. Is this felt through the gear stick? Or through the body / floor?

Paul
 
I think the overrun is normal, though you don't hear it with the std exhaust unless you sit in the passenger seat and really listen for it. Its not really big overrun like the Turbos that overfuel on lift off or the MFI cars that like to run rich, in fact the DME cars shut off the fuel entirely when you lift right off to save fuel, but you still get some overrun popping IME.

Don't really have too many ideas on the vibration but the lumpy light throttle stuff sounds a lot like a tired AFM. Does it also hunt up and down at idle when cold?

RB
 
I intentionally introduced some popping on overrun into mine when I had Ian fit his H&S exhaust system with the sports pre-silencer...very childish[:D].

However, I filled up with some Tesco Super Unleaded a week back to give it a try as my local Optimax price had reached 105p/litre..ouch!

The popping and banging went up alarmingly on lifting, really very noticeable. I've now gone back to Optimax and once it had flushed through, everything returned to normal.

As an aside, the pick-up was definitely much worse on the Tesco's fuel than Optimax. Maybe Shell do have a formula that improves pick-up.
 
Phil,
I think its a characteristic that exists but as RB advises with standard exhaust systems you struggle to hear from in the car. Mine is a Targa so with the lid off you can hear it more.I had SS back box and pre-silencer fitted last year and find that I can induce the effect which is great fun if you feel a bit hooliganish( buildings on each side or through bridges) Twinny is obviously a real Hoooooooooooligan.[:D]
Dunno about the fuel as I have always run on Optimax.
Vibration etc sounds like something else.
regards
Graham
 
Well, after a prolonged period of inactivity I've finally got my car sorted, turns out that the mixture had gone to cock and was running way too lean. The car now runs like a dream and sounds fantastic, however it now pops and cracks when hot at tickover, the lads at Zentrum suggest that all is well and its just due to the low back pressure provided by the SSI's and Sport Back Box. Has anybody else had this? I was wondering how easy it would be to modify the rear box to add a little back pressure without loosing the sound / performance.Are many of you running SSI's on a 3.2?

Regards,
 
Hi Phil, I fitted a Dansk stainless sport system with twin mersey tunnel sized outlets a couple of months ago, I ordered the one piece crossover pipe which was a mistake as the heat exchanger needs to come off to get the flange in[&:] so thats now propped in the corner of my garage. the exhaust sounds wonderful and i no longer need to drive in third all the time to make the engine sing so im saving the world!!I too get a little popping but not very loud so am not overly woried about it.
 
Ray,
Funily enough, my back box is also a Dansk but I opted for a single outlet! They do sound really good but I must admit that it makes me drive like a holigan under bridges and through tunnels.....6000 rpm in third through the Dartford Tunnel does sound good [:D].
The popping I get does upset small animals and children and I must say that it does get a little embarrasing in traffic jams! I'd imagine the difference between our two cars is due to the pre-silencer and the added back pressure.
 
Phil,

I live in Northern Ireland and have no real tunnels to holig through ( new word!! someone right that down[:)]) the pre scilencer i have is a straight through one, i seem to get the popping from 4th to 3rd[&:] only any idea how to get more !!?
 
Phil,

As RB says its not uncommon with SSI's and Sports boxes due to lack of back pressure, mine with SSI's and
H&S backbox was like a machine gun but only when the revs were dropping from 2000 down to 1500, my mixtures from idle to OTT were spot on as well, after my AFM packed up completely a few weeks ago I put another one on and now it hardly pops at all, ( very disappointing [:D]), so I think AFM / mixtures do have an effect on how bad it is.
 
You must log in or register to reply here.

Posts made and opinions expressed are those of the individual forum members

Use of the Forum is subject to the Terms and Conditions

Disclaimer

The opinions expressed on this site are not necessarily those of the Club, who shall have no liability in respect of them or the accuracy of the content. The Club assumes no responsibility for any effects arising from errors or omissions.

Porsche Club Great Britain gives no warranties, guarantees or assurances and makes no representations or recommendations regarding any goods or services advertised on this site. It is the responsibility of visitors to satisfy themselves that goods and/or services supplied by any advertiser are bona fide and in no instance can the Porsche Club Great Britain be held responsible.

When responding to advertisements please ensure that you satisfy yourself of any applicable call charges on numbers not prefixed by usual "landline" STD Codes. Information can be obtained from the operator or the white pages. Before giving out ANY information regarding cars, or any other items for sale, please satisfy yourself that any potential purchaser is bona fide.

Directors of the Board of Porsche Club GB, Club Office Staff, Register Secretaries and Regional Organisers are often requested by Club members to provide information on matters connected with their cars and other matters referred to in the Club Rules. Such information, advice and assistance provided by such persons is given in good faith and is based on the personal experience and knowledge of the individual concerned.

Neither Porsche Club GB, nor any of the aforementioned, shall be under any liability in respect of any such information, advice or assistance given to members. Members are advised to consult qualified specialists for information, advice and assistance on matters connected with their cars at all times.

Porsche
Lockton
Pirelli
Officially approved
Oracle Finance
WEX Esso
Collecting Cars
Archant Dialogue
Back
Top