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pre ignition on a 172.. piccy.. dont run lean !!!

herea pic of the head from the 172 engine I am stripping for the turbo build.
this head is ALREADY showing signs of BAD pre-ignition which can often lead to detonation.
the pits in the squish area of the chamber are NOT caused by debris.. these are caused by tiny explosions.. they are infact mini craters...

the piston (this is on no. 3 pot) shows exact corresponding marks..

left for much longer and the piston could well have been holed !..

The car the engine came from (Mk1 172) had 8k on the clock.. and an induction kit...

if you get an induction kit.. make sure its not running lean at top end WOT !!!.

Nick Hill - Hill Power, has the only kit and mods to sort this afaik..

Joe - ps, tell him I sent ya lol..

Lo Capt,

I had my fueling at the top end checked when the superchip was installed. The guy said it was spot on Is Nicks solution a proper chip ?.

  Mk4 MX-5, Smart 451

im not one for the technical know how about engines, but what does it mean to be runing your engine lean?, and is this sort of thing happening on bog-standrad 172s mk1/mk2s?


2 questions then....

my mk1 172 has been "superchipped". (not my choice, the garage had done this previous to me owning the car)

anyhow... does this affect the lean / rich side of things ???? or does it not ???? i.e am i potentially doing any damage just by driving around on a day to day basis with this remapped ecu??

2nd question, as i see induction kits are mentioned here, does this apply to all cars ????

a friend of mine has just bought a nice vr6 highline like my old car and straight away got an induction kit fitted... fair enough... makes a nice noise... blah blah blah

but can / will this affect the fuel mixture enough to cause problems ??? the car is running a standard exhaust system...


vr6 man,,

yes it certainly can apply to all fuel injected cars.. especially the later ones that have to be more fuel efficient and emissions efficient.

safest way is to have it rr tested and exhaust gas analysis done at full bore.

re superchips etc, they tend to increase the fueling at wide open throttle (WOT) do should be fine. - still worth checking though ..

NEVER, EVER buy induction or exhaust kits unless the procider can show a GENUINE RR Graph for YOU MAKE AND EXACT MODEL before and after conversion, otherwise you are probably buying total crap.. that goes for induction kits from ALL supliers, and ALL breeds of so called performance exhausts. Most are total crap.

  clio 20v

has anyone got an air/fuel ratio meter in there car? do these take there info off your lama sensor or do you have to install a seperate one

I have ordered a Laser/Jetex Cup Racer exhaust aswell but it´s just the backbox, right??

Joe. Any need to worry if you have a BMC replacement filter in the standard box?

sh*t, i hope not!
why didnt i frikin check this! i was talking to them about the system so i hope its full, or im gonna be pissed!

anyway, back to ignition..capt. why or rather how do sparks bet blow out in turbo applications and what conditions attribute to this?....

the denser the air, the higher the voltage needed to ionise it...

they dont get blown out.. they just fail to fire correctly..

good quality ht leads are a must...

or.. COP.. coil on plug... thats what I a using...


I thoguht that Clio 172 has a detonation-sensor, that will reduce ignition advance if engine is going to detonate?

detonation has to occur before the sensor can take any action, the role of the sensor in WOT (wide open throttle) operation is uncertain on the Sirius ecu as fitted to the 172... the fueling on WOT is a simple table with no lama correction.

the dame here is pre-ignition or hot spotting.

a slight carbon build up on the piston edge, plus a lean top end causes the carbon to glow and act as multiple ignition source..

If you are medically inclined its a bit like ventricular fibrillation with multiple ectopic focii..

Medical head off lol..


i was gonna say that about the ventricular fibrilation!

During my A levels in bio, we got to play with a dead rat. We had to try keep its heart going for as long as possible....we tried all sort of stimulants and shock to de fibriate....haha...we were pissing our selves when we added the teahchs coffee!!!
i think we kept it goin for about an hr 1/2 or so......what a waste of a lesson.

still betetr than photosynthesis!

lol M8.. hee hee..

only trouble now is, I need to get the 172 head squish area tigd or ali sprayed and resurfaced.. ..

once this starts, it will continue to be a trap for carbon and future nasty events..

Did you not try to shock the rat ??.. .5 joules with 2 pin heads shold a sorted it...


yeah, we shocked it!!! but i think we went overboard!! it was bouncing off the table....we weer just young and having a laugh! it was horrible for a while though, killin the rat was kinda freaky....cause we drowned it...hehe

Your gonna tig the chamber then grind it down again!?
wouldnt i be easier just to get new pistons and save all this work on the head!?

to re-use this head at all - on any application.. it needs tig n surface plane. - note the damage is on the squish.. the area that is closest to the piston edge..

I dont intend to do any other work on the head.. it will all be in the pistons..

if it is not repaired, the head is scrap !


OH! didnt realise there was anythign wrong with the head! my bad..whats wrong with it?
172 or turbo head?

me thinks you are still asleep lolool..

the head, as in the first pic, has crators in the squish face..

it is a 172 head..

the squish face is the area that comes closest to the pistons, the idea is that a greater pressure area (and the squish is all around the edges head chamber ) is formed between the piston rim and the head chamber at these specific areas.

the higher pressure acts as a burn inhibitor and causes the compressed mix to be flowed to the centre plug area in a controlled way.. this increase power potential by massively reducing detonation potential.

It is also sometimes caused the quench area.

the last thing you need is pitting in this area.. carbon will become trapped and act as a future ignition source.. this if uncontrolled will lead to detonation.

it HAS to be repaired.

ps.. this is why the thicker head gasket route often quoted to reduce cr is a load of bollox ..

if you put a thicker gasket on, you will lose the squish effect between piston and head.. the engine is more likely to detonate with a lower cr and reduced quish than a higher cr WITH squish.

I know its late there m8


ak, I wouldnt think you would have done any long term damage at all - or even short term.. this one was obviously abused by its owner but shows what can result.

I wouldnt worry about it at all.. I think if you had run thousands of miles with sh*t petrol, the story may hae been different, but not in such a short time.



Was chatting to NH today and it seems the lean running problem has been sorted. I didnt ask how he had sorted this out - did you have any input, i.e. is he using the method that you were guarding?



Was chatting to NH today and it seems the lean running problem has been sorted. I didnt ask how he had sorted this out - did you have any input, i.e. is he using the method that you were guarding?