Effect of atomisation on required ignition timing

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Quagmire
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Effect of atomisation on required ignition timing

Post by Quagmire »

Morning all,

I recently swapped out the standard Lucas injectors on my old Rover V8 for some later Bosch EV6 style ones.

The Lucas injectors give very poor atomisation and deliver a thin pencil-point stream of fuel compared to the fine mist produced by EV6 units.

I was wondering if anybody had any experience of what this change in atomisation might mean for my ignition timing? The spark table I am using at the moment is one I built some years ago based on the distributor data. I guess my concern is that the better atomisation will result in a quicker burn and so I could need to retard things slightly?

I know a rolling road is the only real way to know for sure, but wondered if anyone had been here ahead of me and got some idea of the impact, if any.

Cheers
DaveEFI
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Re: Effect of atomisation on required ignition timing

Post by DaveEFI »

Could you keep us updated on any benefits of this? I'm going to change from MS2 with the original RV8 Lo-Z injectors to MS3 sequential this winter, so will need to get new injectors. Are they a direct fit to the later (Hi-Z) injector holes in the hotwire or Gems manifold?

BTW, my Lo-Z injectors produce a conical spray as seen on blotting paper.
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Yves
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Re: Effect of atomisation on required ignition timing

Post by Yves »

Fuel atomisation has a more noticable effect on idling quality. That said, the injectors are one part of the story, injection timing being the other.

At higher rpm it progressively means less as the airflow is stronger and more turbulent. Time is also less, which means most of the fuel atomizes in the cylinder.
BigBlockMopar
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Re: Effect of atomisation on required ignition timing

Post by BigBlockMopar »

My first thought would be the engine could probably do away with less fuel because of the better distribution/mixing of the air & fuel.
Not sure if that would have much effect on the ignition table, as a leaner mixture could again like some more ignition advance.

Why not advance or retard the timing table say 3 degrees in the lower kPA area and see/feel how it drives, presuming this is not a racecar that can't be street driven?
Daily driver: 1973 Dodge Dart - 360ci engine - 11.3:1cr - MS3x - ignition only. 42RH/A500 OD+LU transmission / 3.23 gears
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Yves
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Re: Effect of atomisation on required ignition timing

Post by Yves »

Reason being that better atomized fuel leads to faster and more complete burn.
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