[DML] Re: delorean fuel (Bruce B)

["content22207" <brobertson@xxxxxxxxxxxx>]

Slight clarification:

13 degree BTDC base time is due to the hobbled DeLorean ignition
distributor (one centrifugal counter weight disabled), not PRV engine
design. Exact same engine (B28F) is base timed at 10 degrees in a
Volvo. DeLorean has a flatter advance curve, which requires moving all
sparks closer to cylinder bottom.

I'm guessing DMC did this for emissions. North American Volvo's used
EGR and air injection, both missing from Dunmurry's design.

Bill Robertson
#5939

>--- In dmcnews@xxxxxxxxxxxxxxx, "Bruce Benson" <delornut@xxxx> wrote:
> 
>  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
> >









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