Oops, i've knacked my engine

[Steve Cargill]

I've always run Optimax. Was running on stock plugs without 2nd cat with mutated stock exhaust at 14PSI for the first year.

 

Last summer decatted, stock plugs were left in and misfired, keeping the boost to 15/16PSI. Got BKR7E's put in and boost to about 17/18PSI.

 

In Feb had cat back exhaust fitted - Leons own - and the plugs checked. Boost would flutter around 17-18PSI,

 

A few weeks later at TSC - BANG. Search for "5 cylinder supra" for the full story.

[MONKEYmark]

doom n gloom in here

 

is it the lack of fueling or the heat thats the killer.

 

got most smallish jobs done on mine

blitz nurspec,dumpvalve,induction,fmic

hks cams n gears + eht + boost gauges

rltc

trl fuel cut

ngk colder plugs

cw decats

 

dont know what smallish jobs to do next. wanting a T/convertor

and some sort of fueling mods

need to get fueling checked out too

 

think someone wants to write the do`s n dont`s about tuning for everyone to try learn from

 

its not nice seeing an engine go south.

 

hope the lad gets it sorted.

 

feel for ya mate

[Thorin]

I think it's a case of running too much boost on the turbo's and the fuelling not being up to the job. The fuelling on J-Spec's is on the limit at 1.2/1.3 I think. It seems that some people don't realise that they're not just risking damage to the turbo's running any higher, they are also risking running lean and going boom.

[Adam W]

Mark, my understanding is this. As you turn the boost up the fuel system can't supply enough fuel to match the airflow that the turbos are pumping in. The engine starts to run lean, and the combustion temperature of the fuel/air mixture goes right up. The sparkplug tip starts to heat up, melt, and become incandescent. This heat source is enough to ignite the next lot of incoming air/fuel mixture well before the sparkplug actually fires (hence the name pre-ignition), when the piston is at the bottom of its stroke. Now when the piston accelerates upwards it's having to push against an expanding, red hot, burning mixture for the whole length of its upstroke. The centre of the piston can't dissipate this heat so it weakens and melts, and the forces exerted by the gas mixture blow a hole right through it.

 

Solutions are - make sure your air/fuel ratio is correct (12:1 or lower for turbo engines), and run "colder" plugs which can radiate the combustion heat away more quickly.

 

 

The other issue that can occur, even if your fuelling is sorted, is detonation. This is caused by too much boost forcing too much mixture into the combustion chamber, which then gets compressed by the upstroke of the piston to the point where it explodes spontaneously like a bomb going off, rather than being ignited by the sparkplug and then burning smoothly. This can be tackled by running higher octane fuel or less spark advance.

 

Lots more info here:

 

http://www.streetrodstuff.com/Articles/September_2000/Engine_Basics_I.php

[Adam Kindness]

any update?

[jjgage]

Adam,

 

Not really any update as yet as I've been busy trying to get my run-around Renault 19 back on the road - i think it'll be a slightly cheaper to get back running again....

 

Anyway, cyl no. 6 if definately knackered - haven't had the compression tester on the car yet but there is compression on number 1 because you can hear it when the car turns over, hardly any compression at all on no. 6 when you turn it over. And the spark plug gets completely covered in oil after a couple of seconds even when its cleaned beforehand. So i'm guessing there is a whole in piston 6, and maybe a slight loss of compression in no. 1 Am seriously considering stripping the engine down with my mate who is a mechanic, theres 4 of us that built a westfield from scratch with no assistance so we'll have a good go! I haven't got a penny to my name just now so I've no other option. Obviously i'll have to get parts from somewhere but will cross that bridge when i know whats wrong.

 

Will keep you updated anyway........

 

Jonny