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Gents,
What will melt the piston? lack of fuel or extra timing?
What will break the piston? lack of fuel or extra timing?
I heard some people say if the piston is broken at the edge that means.... and a lot of other says. If someone has ideas about this subject plz teach us.
I dont quite understand how, but lean mixture melts pistons, how ever if i'm not mistaken petrol burns with the highest temperature at stoich???
Lean mixture does 2 things:
- increases combustion chamber temperature (extra fuel has a cooling effect)(stoich is too lean at WOT),
- increases ability to knock/ping.
Both of those will damage pistons, and knock damages head gaskets, rod/main bearings, and rods.
Timing that is too advanced (even by a few degrees) also does both of those things (temp. and knock).
Quote:
Originally Posted by odd boy
So far I have learned, and I hope this helps:
A hole burned through the top of the piston in only one cylinder usually means that specific cylinder was running lean in comparison to the rest (usually a failed fuel injector).
Inspect your pistons, if the ring lands are cracked, you have detonation issues.
Inspect your rod bearings on the big end of the rod (crank attachment). If they have low mileage but are worn through in the center past the outside coating...then you may also have detonation issues.
When tuning, most people are only checking AFR. I wonder if any of these setups are running too hot EGT (exhaust gas temperature) that causes damage.
I wonder if some of these extreme setups need to have EGT sensors put in the headers while being tuned or at least check the EGT while doing an extended highway pull in 80-90F heat and see what REALLY happens. Too much heat in the motor and then jumping on it again=popped motor.
But compress air/fuel 10x and the rules of the game change I believe. The properties are different when compressed, no?Quote:
Originally Posted by Gelf VXR
Compression doesn't affect AFRQuote:
Originally Posted by Stealth97
I mean that petrol might burn it's highest temperature at stoich (which is 1bar, 14.7psi/atmospheric), but take compressed air/fuel, and it may have a different burn temperature. I'm not totally sure on this but just thinking out loud.Quote:
Originally Posted by Gelf VXR
I'll have to do some more reading in my Heywood.
Petrol/gasoline doesnt burn hottest at stoich. The leaner it is, the hotter it burns. It burns most "efficiently" at stoich.
Leaner = hotter = higher Nox / lower HC. Higher Nox because more nitrogen is oxidized. Lower HC as HC's are burned more effectively by the higher temperatures.
Knock will hammer a piston, lean mixtures weaken the piston, increase tendency to knock. Generally with GenIII/IV, to much knock breaks the top land (weakest area).
If it is too lean and knocking, likely the hottest part of the piston, the centre, will weaken and get a hole "knocked" through it.
They generally fall apart before they get hot enough to really melt. At least cast pistons do. Forged resist the extremes much better!
:)
Yes, Heywood says exactly that... leaner than stoich burns hotter (provided there is sufficient fuel, otherwise it won't burn at all... but that's pretty lean)... and the N2 (nitrogen molecule) requires quite a high temperature to oxidize (...lol... otherwise our 79% N2 atmosphere would oxidize with each and every open flame...).
Lucky for us so far.....a % or 2 more O2 and we are in deep doo doo. :(Quote:
Originally Posted by joecar
Glad my memory is serving me well after countless ales......:cheers: :grin:
The lean/rich scenario is used a lot in go-karting. Hand on the needle entering the straight, lean it out for power, then turn it back in before the piston and the bore become one! :shock:
Whats a Heywood?Quote:
Originally Posted by joecar
:shock:
John Heywood is the world's authority on internal combustion engine technology... he also teaches Mech Eng ICE classes at MIT.
See this book... it covers ICE theory/operation and is very mathematical and is considered an advanced engineering text.
mmm...thanksyou! My memory is still mostly working. Must track one down and see how it improves on Ricardo, Irving, Yunick, Jenkins and McInnes. Must have some good up to date stuff on VVT/DI/Emissions etc. The Bosch blue book is a good little source of info too.Quote:
Originally Posted by joecar
:cheers:
I don't think Heywood mentions VVT/DI (I might have not read far enough...)... he is a "traditionalist"...
he covers he underlying physics by which combustion occurs and how it is affected by cam/spark and anyything else...
VVT and DI still use the same underlying physics.
My understanding is also this:
It is easier to "light" a lean mixture and when it's too lean and you hear knocking it is because the compression is firing off the fuel (like a diesel) as the piston is on the upward travel - not good. That is why higher compression engines are more prone to knocking. Todays higher temperature engines have the added heat to make the problem worse. When you fire the fuel too early you expose more of the cylinder to the combustion which again generates more heat.
It is the same when the timing is too far advanced.
David Vizard is worth listening to. :)Quote:
Originally Posted by gmh308
Yes, he is very hands on.Quote:
Originally Posted by Sid447
Right on! David is pretty amazing. He has been consistently at it now for 25+ years producing very well researched, highly technical and objective books and articles. Certainly a pinnacle in the performance car space.Quote:
Originally Posted by Sid447
:cheers:
I have a collection of his books... good content and good writing style easy to read... :cheers:
Does he do any books that cover header design well?Quote:
Originally Posted by joecar
And does Heywood get into this? My notes on this are long gone, and so is that part of my memory where that info was.......:cheers: LOL
:cheers:
Vizard does talk about headers in his books, and there is a website where he goes deeply into header design (I have to look for it again).
Heywood does not talk about headers... he talks about engine theory in a theoretical manner (heavy in maths).
Vizard talks empirically about engines and engine modifications based on his/others experiments, in a very hands-on manner, and he does bring some theory into it as the need arises.
A website,
Pretty much full of DV and some others, who are into serious "stuff."
http://www.gofastnews.com/board/
DV went into headers, exhaust and muffler design quite a bit in this book:-
http://www.google.com/products/catal...tle#ps-sellers
Exhaust tuning article (amongst other things)....
http://www.geocities.com/motorcity/t...92/vizard.html
Whilst getting back to the thread....This was caused by detonation, possibly too much timing on a cylinder that runs hotter than the others in an LS1. Right under the exhaust valve.
Oddly enough, that particular cylinder had previously cold-cranked @ 190psi which was ~15psi higher than the average of the other seven which experienced no damage whatsoever (good old GM production tolerances).