Nightlife 0 compression found and cause.

I found this article by the Renault F1 team on header dynamics.

www.lesoft.co.uk/files/ASME_ICES_2006_1444_FIT.pdf

There are lots of areas I know little--I just keep my mouth closed in these areas. But you have to understand I've been collecting this data for over 40 years (since I came of automobile awareness around 16 Y.O.) I am a scientist at heart (needing to understand how the physics is transpiring) and built several race engines long times ago--imagine a FIAT X1/9 1300cc with 10.5 compression, 35/75 Cam, dual Weber 36 DCNF carberators, velocity stacks, and a 4:1 header exhaust system. I used to outrun 260Z cars with that thing (circa 1977) about 110-120 HP for 1850 pounds...

 

Just another reason to put test pipes on inbetween inspections. Of course for track use only.

 

I don't think the cats 'caused' the hole in the piston. There are several factors of which I can name a few, that will contribute to a failure as this. As far as I know the 348 ignition does not have auto knock retard (knock sensor), which could be unforgiving should the engine not be in great mechanical condition.

1. Carbon build-up in combustion chamber
2. Wrong heat range on spark plugs
3. Oil in the combustion chamber from worn intake guides or bad piston rings
4. Valves (probably exhaust) not fully seating/sealing
5. Low octane for conditions
6. Bad injector(s)
7. Driving the living crap out of your car with some or all of the above 'issues' will cause excessive heat, pre-ignition and or detonation ...... which can lead to a hole in piston

Sorry to hear about it Roberto ......... but at least you went down in a metaphorical 'ball of flames' ..................

 

Very, very sorry to hear this ended up being a serious failure, Roberto. I'm kind of a purist, so I would always rather have the original engine in the vehicle if at all possible. OK, with the possible exception of Sy's new engine! But I can understand the concern with expense of rebuilding the old engine. Too bad you don't have as many 348 brothers to help in the great north, but I'm sure everyone here will help as much as possible..... perhaps in exchange for more Nightlife pics Don't hesitate to ask for any help you need, and wishing the best for good progress at getting your car back on the road!

 

Well this thread has taught me a whole heap already and were only on page 2....

Just wanna thank these guys for sharing this tech info. Amazing stuff.

Still sorry to be reading this though.

 

Mitch thanks for the info!! :cheers:!

So the pressure wave is separate from the exhaust mass.. the pressure wave is acting more like a sound wave or ripple in water (but in this case the exhaust gas mass being the medium - i.e. pressure waves moving freely in that medium). It does make sense that they move freely without obstruction from the exhaust mass flow.. would the catalyst debris have to contend with the opposing force of the exhaust gas mass (i.e could the debris move in the same relative freedom of the pressure wave)?

It seems like a no-brainier to use a test pipe in lieu of the converters (off-road only of course) if this is a typical mode of failure.. didnt several car companies mount pre-cats immediately downstream of the exhaust manifolds (i.e. less than 6 inches from the exhaust valve). It seems like it was common practice for awhile late-90's early 2000's.. different than the header (as you mentioned above).. but so close it seems like pressure waves would be magnified..

I found this Porsche 997 exhaust system with cats immediately down stream of the headers.. Do you know if the P-Cars have similar issues?



It seems like this problem has been mentioned on the forum a few times.. engine knock also sounds feasible.. a exhaust valve not closing all the way could induce some raw fuel in to the exhaust tract pretty much cooking the converter in to a solid lump of crap. interesting stuff...

Nightlife: what was your mechanic thoughts?

off to read the ASME paper (thanks for that Mitch)!!!

 

Mitch - good read thanks for the info! In the paper they mentioned the pressure wave traveling down ref pipe 'A' caused an incidence reflection wave in adjacent primary pipe 'B' (and most likely at least two of the other primary pipes). That resonance happening through the collector chamber.. but wouldnt the cat be downstream of even the collector chamber? having a liner exhaust flow? thoughts?

 

of course!! I gotchya..[light bulb lit above head] hence the scavenging of the cyl... not just the primary pipe.. which would help the efficiency of cyl filling on the intake stroke.. gotcha.. during the overlap period it would actually help pull the intake charge into the cyl.. righto..

thanks again!

 

I'm not attempting to hijack this thread...but Roberto's situation got me thinking...

When I had my 30k done on my 355 in June and my cats and headers replaced, my left was had NO ceramic components inside of it--yes, you could see right through it with no obstruction.

Should I be worried about possible future problems because of this? Many of the ceramic pieces were inside the OEM exhaust muffler, which I replaced with a Quicksilver.

Any info would be appreciated.

 

Yes, by a few microseconds in time. It would be better for power to delay the positive wave created at the end of the expansion chamber (like headers from muscle car era), but *.gov regulations prevent this. *.gov wants the cat to heat up fast and clean up the exhaust gasses, and at the end of the header it goes.

 

I do remember some incidents in F1 where a header tube ruptured and the infow of air got into the cyclinder and so leaned out the mixture that the engine grenaded itself. So, yes there is a lot of mass movement possible.

But remember, exhaust manifolds and exhaust headers are different animals. One allows the exhaust gasses to flow out, the other utilizes the waste energy of the pressure wave to make more power.

The image of the Porsche exhaust system is somewhat between that of a manifold and that of a header. The collector (where the three tubes combine) are not properly organized (shallow angles into the common aft-pipe.) Althoug it probably has some of the properties of a header. It might have similar problems since the cat is that close.

This is one reason the ECU has so much logic devoted to learning and retraining the engine mappings to minimize knock, ping, and emissions--over time as the engine ages.

 

+1 This place has some amazing minds running around...




Roberto, I wish I could buy you a drink and we could talk. I wish you all the very best through this and I hope it finds a way to work out for the best.

 

Roberto, you should consider re-connecting the slow down lights.

 

RifleDriver,

Can you tell us what frequency you are seeing this problem? 1/1000 355's? 1/10,000 550's that kind of impression?

Do you think newer variable valve timing schemes are contributing to this problem in cars in general?

Do you think there is a service life either in time or miles that V-8's or V12's should be just changing cats out as a disposible item or do you think the real problem for cat death are up stream timing issues, electrical failures giving rise to misfires etc., or some other failure that you are seeing repeatedly?

Thanks!

 

Good point, but man, now I am really scared to start the engine on my car ... and forget about drive it hard !!!!

 

So shouldn't the slow down light have come on. Sounds like there's a bad cat ecu in there or a burnt bulb. If an injector went down there would have been no warning. A vacuum line off would not help either as the ECU will adjust rich and light off a cat but that would have also turned on the check engine light.

 

From an earlier post he mentioned that he thinks the slow down lights were disconnected:

 

Sorry I missed page two. I think a used engine is the best bet just check the compression and oil pressure first if it's possible. I was going through the numbers on rebuilding and it was getting up past $5k and I backspaced all my typing and changed my mind. You can take your time with rebuilding the original engine. A spare from a parted car would get things rolling faster. When the original is fixed put it back in the car and sell the donor.

 

Sorry to hear. I was thinking of adding some back on, as the car will make you stink without cats. Anyone know if aftermarket ones, like the hyperflows ever have this issue?

 

Holy ****, those are photo's I never wanted to see

I have fitted test pipes to my car, the smell is only minor IMO, I don't find it offensive at all...in fact, I sorta like that it smells a little....might be too much hair gel?

Really, it's not much different to having cats, but I think it will depend on the fuel you run, our fuel down here is quite good so I'm told....

 

I've run a few track cars without cats before.. the smell was quite unpleasant if the tune is off just a tad..

 

Mitch - Thanks for the detailed reply!!

Night train - might ask your mechanic about having the injectors flow tested and or replaced. I'm not sure what style they are (pintle, disc, etc..) but i think they are bosch units. should be easy enough to test and replace is needed. a flow matched set is always nice to have anyways..

Another area I'd be curious about is the fuel pressure regulator.. variations in fuel pressure alter the volume (and theoretical sizing) of the fuel injectors.. I'm not sure if these cars have on or two FPR... if they have one on each size that could cause one side to run very rich! a bad 02 sensor could also cause a bank of cyl to run rich or lean depending on which way it failed (or again - got lazy)..

good luck.. let us know what you find!