Sequential vs Batch Fire

[James Ballenger]

If you run sequential you will be able to get smaller injectors and get
better idle quality.  As an example

BSFC*Hp/# cylinders (just made up to work with) = .55*100/4 = 13.75lb/hr
fuel flow necessary

Sequntial at 12000rpm->60000ms/12000rpm = 5ms/rev
Firing once per cycle (2 revs) = 10ms
Assuming 1ms opening time -> Duty Cycle is (10ms-1ms)/10ms = 90%
Injectors = 13.75lb/hr/.9 = 15.3 lb/hr injectors

Batch at 12000rpm-> Firing once per rev = 5ms
Assuming 1ms opening time -> Duty Cycle is (5-1)/5 = 80%
Injectors = 13.75lb/hr/.8 = 17.2 lb/hr injectors

With the larger injectors required for batch, you would have to keep the
injector open for a smaller amount of time and end up with (if it's too
short a time period for the injector) poor fuel metering and inconsistency
at idle (I like to think of it as dribbling).

I have a 4 cylinder making the above numbers and will use "phase-sequential"
which is 2 batches of 2 injectors, just like you are running.  Because of
our setup, we could run either fire once per rev or once per cycle. For
injector sizing and general ease of use, I will be using the sequential
calculations and fire once per rev.  Yes I realize I could end up with
puddling at low rpm on the non-intake side, but I will have the benefit of a
dyno, UEGO, and possible individual exhaust temp sensors to check out both
methods.

I'm still learning this stuff so lemme know if i messed up,
James

-----Original Message-----
From: owner-diy_efi at diy-efi.org [mailto:owner-diy_efi at diy-efi.org]On
Behalf Of Nicholas Parker
Sent: Friday, October 27, 2000 8:35 PM
To: diy_efi at diy-efi.org
Subject: Sequential vs Batch Fire


Hi List,
For sequential injection you need big injectors as all the fuel has to go
through an open valve.  Does using big flow injectors have an adverse impact
on the efficiency of fuel atomisation and controlability at idle?
I have heard for instance that with my car (365cc/min stock injectors) that
someone using 550cc injectors (big h.p. application)  could not get a smooth
idle, -mind you that was with a 2-batches of 2 injectors E.F.I setup (on a
1600cc 4cyl supercharged engine).

Nick Parker.

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