EFI and Accidents...

[robert joseph dingli]

Hi Lou ,

>     I couldn't help but notice in one of you're messages you said to try and 
> experiment on a "cheap 4-cyl" that you don't mind blowing up. I have worked 
> with many high-perf V8's over the years, and short of RPM runaway, I haven't 
> blown one up yet. But I don't know all there is to know about engine 
> building, and I also get the feeling that I have been very lucky. What are 
> some of the things that can lead to engine destruction? I know that lean-out 
> can be a problem, but in a 4-cycle its ususally not destructive. (Unless 
> that lean out occurs when the Nitrous button in pressed....ooops!) 
> 
>     Any help would be appreciated..
> 
>                                       ----- Lou
Blowing up is a bit of a generic term I use for any type of engine damage.
I managed to partially sieze a couple of piston during some high speed and
load testing on a dyno.  A rebore and a new set of pistons solved the problem
but it was still a pain to have to strip down the motor.  BTW it's a Jag XK
4.2 which isn't the cheapest engine to rebuild.

Over fuelling can wash the oil film off the bores resulting in poor
cylinder lubrication while under fuelling increases the burn time and
results in more heat being transferred to the pistons, valves etc.  I've
encountered both scenarios in my testing and believe my test engine
suffered due to both.  Spark timing problems can obviously result in
knock for too much advance or high combustion temperatures for too much
retard.  All of these concepts are fairly basic to anyone who has
done any engine work.  I guess its just a bit easier when you can the
freedom of EFI to meter the fuel.

The other beauty of small engines is that there are less parts (eg injectors)
to buy and that they are generally easier to work upon (??).  In Australia
they are very easy to find already injected which makes manifolding much
easier.   (They also use less fuel during dyno and road testing).

I hope this helps.

Robert
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             Robert Dingli           r.dingli at ee.mu.oz.au

Power and Control Systems                 Thermodynamics Research Lab
Electrical Engineering                    Mechanical Engineering
   (+613) 344 7966                           (+613) 344 6728
  University of Melbourne, Parkville, 3052, Victoria, AUSTRALIA
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