Re: [DML] Re: delorean fuel

["Bruce Benson" <delornut@xxxxxxxxxxxx>]

 The ignition process starts at the most opportune time to get the force of
the explosion to drive the piston down. In the DeLorean's case the
hemispherical head design, which acts to control the burn rate and direct
the energy produced, along with 87 octane fuel requires the ignition burn to
start at 13 degrees before top dead center. Thus, by the time the crankshaft
rotates the final 13 degrees and the piston is at top dead center the
optimum force is developed to drive the piston down. When a faster burn fuel
mix is introduced the whole scenario can change. The optimum force of the
explosion can happen too soon before top dead center. When, for example, a
turbocharger is introduced into the mix the intake temps rise simply because
of the exhaust element being used as a power source and the fact that temps
rise as the incoming air is compressed. When you mix that with a low octane
fuel you have a more volatile mix that will have an uncontrolled burn.You'll
put a downward force on the piston while it still needs to get to TDC. The
result is loud pinging and if you don't back off the throttle you'll soon
end up with anything from cracked rings to holes in pistons. Needless to say
this is all puts a lot of extra strain on the piston rods, crankshaft and
related bearings. Sometimes, if carbon deposits build up in the cyl head
compression is raised and the engine pings on low octane fuel. This can
happen if ,for extended periods, you've used high octane fuel in an engine
designed for low octane fuel. The slower burn causes the carbon build up and
in a way the car has developed a dependency on high octane fuel.

Bruce Benson
>
> I'm just curious to know how it ignites faster to the extent that it
> will ignite while the piston is still on its way up. If there is
> preignition then the engine has overheated valve or plug problems. If
> the engine is trying to ignite fuel while the piston is still on its
> way up-the engine won't run at all or kickback. -----Dani B.







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