Cracked Piston

[david nelson]

I know of one sprinter that had his 1.6 ss rebuilt on recomendation that all the engine the engine builder had ever seen showed some sort of problem. Well it was fine.

 

Some club members have run standard eu2 pistons upto 190 bhp with no problems. The will be examples of those that have failed and those that have not.

 

i would not be worried about it.

 

David

[Steve, Carol and little Cl]

With respect to using EGT to detect detonation, I´m afraid I don´t think you would have. When det occurs, the EGT do indeed increase.However, it´s never such that you would realise that det was occuring. it´s usually the pressure that does it. Also, consider a fully functional active knock system. When it eetects the occurance of det, it retards the spark. If youretar the spark, the combsution mixture burns later. A later burning combustion mixture means higher temperatures in the exhaust manifol, which leads to a higher EGT reading. So you wouldn´t actually know whether or not your det sensor is working or not. Use EGT to protect your exhaust system, especially your catalyst (if you´re running one). It does give an indication of the fuelling (and therefore the possiblility of det), but it is influenced by many other things. Really, if you want to monitor det, use a det sensor (a proper fully functioning calibrated one which is integrated into the ECU and has been set up on a test bed). If want to protect your cat, use an EGT sensor. If you want to monitor your fuelling, use a lambda sensor.

 

BTW on production cars, the det sensors aren´t matched individually to the engines. It would be way to expensive. They´re delivered in a big box, and someone takes one out and screws it in place.

 

Steve

 

Having survived another evening - only had to change her once

[Roger King]

I have to agree with Steve re knock sensors. Getting them to work properly is the work of many hours with the availability of much expensive test equipment. Believe it or not, but some very respected engine builders have been known to use what is effectively an ear trumpet attached at one end to the engine to listen for det while mapping. This is regarded as more sensitive than a poorly set up electronic version and serves well when dyno testing different engine types.

 

The point of a knock sensor it that it allows the engine to be mapped to within an inch of disaster, knowing that there is a 'backstop' to catch the ball if problems arise (note to self - must switch off metaphor mode). This is fine if you have large and expensive facilities, lots of time, and a need to meet emissions legislation, etc. It's probably not applicable to self mapped engines where a certain amount of safety margin should be left. In fact, one of the problems with engine management is that it allows the fuelling and ignition to be taken to the ragged edge of safety and this often goes horribly wrong when a marginally worse batch of fuel is used. In the old days of carburettors and distributors, you simply couldn't push your luck like this because everything was so imprecise.

 

Edited by - Roger King on 4 Nov 2008 12:51:32

 

Edited by - Roger King on 4 Nov 2008 12:52:07