Hi Paul,

Embedded comments:

I set up Tracy's system in the hangar to measure the injector  pulse
widths using my oscilloscope. I removed the drive gear from a crank
angle sensor and chucked it into the drill press. Powered the whole rig
using a 12 Volt adjustable power supply. At 1200 RPM the whole system
drew about 2 amps. Ignition and EFI system. The current draw will go up
with RPM. In theory it will be about 4 amps at 2400 RPM and so fourth
and so on. 5800 RPM 8 amps.

Which component in the system is responsible for the current draw
increasing linearly with RPM?  I would have guessed that the system draws
a certain current at 0RPM.  The total current would be the 0RPM current,
plus that which is required to run the injectors at whatever RPM was being
used.  Are we on the same page?
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The injectors and the ignition coils. The computer is probably less
than 100 ma PL

I bought a vacuum pump at the auto parts store and plotted default total
injector pulse widths from about 5 inches of Hg to about 30 inches of Hg
or full atmosphere pressure. The hanger is 245 feet above sea level and
it was about an 85 degree day. Don't know the humidity but in SOCAL it
is generally below 25%.

I don't think I understand what you mean by pulse width..  At 12000RPM,
the frequency in hertz (cycles/sec) = 12000revs/minute * 1min/60sec =
200revs/sec = 200Hz.  The period of a system running at 200Hz:  period =
1/frequency = 5ms...

7500RPM = 125Hz, period = 8ms.

It looks like you just plotted the period in ms of each revolution, which
doesn't seem to have a direct bearing on how long the injector needs to
stay open to deliver fuel.  I guess you can see that any injector can
operate at 12000 RPM, because it would only be required to cycle in 5ms -
plenty of room for the 1ms minimum pulse width.
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The 8 ms is how long it takes the engine to make one revolution
at 7500 RPM. Since tracy pulses the injector once per rev
and the pulse width is limited to 80% of that or so that means
max stock injector pulse width is 6.4 ms. Given its max flow specs
that is not enough fuel for 250 HP. PL

Does it hurt an injector to leave it on 100% (duty cycle)?
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Yes I think it does but I am not sure. PL

This is total pulse width.

Isn't how much total fuel that an injector will flow (pph) the key spec?
How long it has to be open to do so seems less relevant.

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Well it is a combination of both. PL

Below about 15 inches of Hg only
the primary injectors work. Above 15 inches both sets of injectors fire.
Tracy adjusts the pulse widths so there is a smooth transition at 15
inches of Hg.

The three curves represent what happens when you change
the injector size in Tracy's Mode 3. The stock injectors default pulse
widths is the middle curve. When you increase or decrease the injector
size or flow rate the curves shift right or left.

Note; with the stock injectors you will run out of max pulse width
around 7500 RPM. That would be about the upper limit using the stock
injectors default pulse width. If the stock injectors will not flow
enough to provide the necessary fuel for your HP generated at that RPM
you will have to go up in injectors size or flow rate. This is why I
chose higher flow rate injectors for the P-port engine.

Paul Lamar

That is true, but don't forget about the other RPM end - at idle you
might have a problem with larger injectors because injectors will not
open reliably below 1 millisecond pulse width due to the mechanical
inertia of the pintle valve.

Chuck

Good point Chuck. I need to get some of those new skinny Bosch
or RX8 injectors and test them for dynamic range down below
1 ms or so. Anybody got one they can send me? Either that or I need to
talk Tracy into supporting six injectors like the high power
RX8 engine uses. Obviously Mazda ran into the same problem
with the high power RX8 engine that has a 9,000 RPM red line.

I think it might be easier for Tracy to mod the system to handle a small
primary injector and a firehose sized one for the secondary.  Ala the 4bbl
carb.  That would allow nice idle response, and plenty of total fuel at
high MAPs.  Seems like that might be possible with just a software tweak.


Regards,

Matt-