[DML] Re: delorean fuel (David T)

["content22207" <brobertson@xxxxxxxxxxxx>]

No, "base timing" simply means the point in engine rotation at which
spark occurs without any additional advance enhancements -- in our
case the orientation of the distributor when you tighten it down.
That's why you set it at idle with the vacuum advance diaphragm
disconnected (unnecessary on a DeLo with proper functioning cutoff
solenoid). Only impacts starting insofar as too much initial advance
makes an engine harder to start.

And spark advance does not vary cylinder to cylinder. If the rotor is
moved ahead 10 or 20 degrees, EVERY cylinder will receive its spark 10
or 20 degrees sooner. Our engines are indeed odd fire, but that has
nothing whatsoever to do with spark advance -- the whole firing
sequence is simply shifted. Distributor itself, with its attendant
advance mechanisms, couldn't care less about odd vs even fire, or even
the firing order. That's determined by the cap (and wire routing
thereafter). Rotor button itself simply spins.

Base ignition time for all other North American PRV's is 10 degrees
BTDC (same for European Volvo and normally aspirated Renault models
BTW). Only DMC moved it that much closer to the bottom (and only DMC
removed one of the counterweight springs from an otherwise stock Bosch
distributor). Overall advance curve ends up flatter than other PRV's.
Of course it's there (engine couldn't rev up otherwise) -- it's just
not as aggressive.

BTW: there's a lot of controversy about whether the optimum point of
igntion is threshhold of detonation, or somewhere closer to TDC (can I
hear an "Amen" Martin?). My position, based on Ford's experience with
spark advance on the 460 throughout the 1970's, is that the optimum
point is NOT on the verge of detonation. At least not on a large bore
engine spinning 600-2500 RPM (moving base ignition time closer to
bottom not only lowered overall power, but required convoluted advance
mechanisms, such as double sided vacuum diaphragms, to ensure
detonation did not occur at full throttle). By 1978 -- last year of
passenger auto use -- base time had gone from 10 degrees BTDC to 16.
Impetus was emissions, not fuel economy.

Bill Robertson
#5939

>--- In dmcnews@xxxxxxxxxxxxxxx, "David Teitelbaum" <jtrealty@xxxx> wrote:
> 
> 
> The mechanical advance has 2 weights in it. They are different and
> only one has a spring. They BOTH work, it is just the one with the
> spring comes in a little later. It gives a "knee" to the advance
> curve. Also take notice that on the distributer cap the cylinders are
> not spaced equally apart. This has the effect of varying the advance
> for certain cylinders. It is very important that you wire the cap
> exactly to the cylinders as marked on the cap so as to maintain the
> correct timing for each cylinder. Base timing is mainly there for ease
> of starting and to minimize emmisions at idle. If you look at the
> advance curve (mechanical AND vacuum) you will see it advances quickly
> like most internal combustion engines. For best power and economy you
> want to try to get as much advance in as quickly as you can. That is
> of course up to the point BEFORE you get pinging! The problem is that
> for production motors all of this tends to be on the conservative side
> so that there is plenty of room to "cheat" and if you want to maximize
> things you could probably add even more advance. Going with a higher
> octane fuel will allow even more advance. If you do try this remember
> you are flirting with disaster. You can burn valves and pistons if you
> overdo this. In any case more advance is usually better than less. If
> your mechanical or vacuum advance systems are not functioning you will
> have poor fuel economy and low power. This is why going to a full
> engine managment system is so neat. You can change things like base
> timing and advance "on the fly" from the passanger's seat. Add a knock
> sensor and the system can run you right up to the edge for maximum
> performance without the danger of damaging the motor! This is the
> ticket for any serious performance gains.
> David Teitelbaum
> vin 10757
> 









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