Paul--
Sorry to be a pest, but I'm a bit confused. Does the list above
(By Jean Prudhomme, i.e., 4 each Sealing Blocks, Pressure Taps, Injector
Blocks, & Bellmouths) pertain ONLY to Rx8's or to Rx7's as well, and to
NA or to PP engines? (I currently have a 1991 Rx7 turbo engine but hope
to rebuild it as a NA PP engine.) Thank you for your patience.

Paul Vermillion


All parts will work with RX8 or RX7 p-port engines except for the
injector block. That will only work with skinny RX8 injectors. Now there
is no law that says you cannot use RX8 injectors on RX7 engines. In fact
it is a good idea. If you don't already have RX7 injectors and you are
going to buy some new injectors I recommend buying the Siemens skinny
type. To reiterate... the skinny injectors and block will work with RX7
or RX8 engines. It is simply a cost issue.


Paul Lamar
--

Hi Paul
Just a couple of questions on using the Siemens skinny injectors in a
3rd Gen. Does Tracy's EC2 care which injectors you use on a 3rd Gen and
what is the part number for the correct ones?

Mike C.

No! Tracy's system does not care. Tracy stages injectors so the short pulse
rate response of the skinny injector is of no value. In other words Tracy
fires only two injectors at power levels below 15 inches of HG and all four
injectors at power levels above 15 inches of Hg (50% power). Therefore
the wider dynamic range of the new injectors is of no use. Dynamic range
is the ratio of the widest pulse width to the narrowest pulse width.
Putting it another way the skinny injectors turn on and off faster.

Staging has been a tuning problem in the past as it is sometimes seems
difficult to get Tracy system to run smoothly around the staging area. To be
perfectly clear 50% power is rarely used in an aircraft engine while
flying except if you are low on fuel and too far to the next airport.
You might extend the range in that case by slowing the aircraft to its
best MPG speed. That varies with a lot of factors so it might be wise to
do a little testing and find out what that speed is for your airplane.
It probably is close to the best climb speed as that is the lowest
drag speed for the airplane. Hence the lowest HP required speed. For
an RV this can be anywhere between 100 and 150 MPH.

In the 555 system however all four injectors are fired at all power levels
so the low power/idle mixture can be controlled better with the skinny injectors.

If one injector fails on one rotor it can be compensated for somewhat by manually
richening the mixture on its companion injector. HP will be limited on that rotor but
it will get you to the nearest airport. In other words a limp home mode.

This is similar to what happens in Tracy's system in the limp home mode.

Another trick would be to put the fuel pressure regulator in an accessible
position so you could manually crank up the fuel pressure in an emergency situation
where one injector failed on one rotor or two injectors failed on two rotors.
One on each rotor.

If you have two fuel pumps wired in parallel you could try turning on both pumps
and that may also increase the fuel pressure.

I don't want to give the impression that injectors are unreliable.
Nothing could be further from the truth. When was the last time a
fuel injector failed in your car?

The correct injector for any EFI system is the one that gives enough
fuel at a 90% wide pulse at full power at about .65 BSFC.
BSFC is the pounds of fuel burned per HP generated. Point six five is a
number that is generally used when discussing the amount of fuel
needed for any engine when the mixture if full rich.

Lets say your engine is 200 HP side port. In that case you will be using
0.65 times 200 or 130 pounds per hour. Divide by 4 for four injectors
so each injector will be required to deliver 32.5 pounds per hour.

If 250 HP p-port the numbers go up to 162.5 pounds per hour or 41 pounds
per injector. It is a good idea to use a slightly larger injector
say 50 pounds per hour and it probably won't hurt the idle.

Here is a chart of injectors and the amount of fuel they can deliver.
Any of these will work with Tracy's system. The 555 system however requires
the so called high impedance injectors that have a coil resistance
around ten ohms. Recent injectors, and the skinny's included, mostly
have high impedance. It is easy to find what what your injector
impedance is using an ohmmeter.

Increasing the fuel pressure will increase the amount of fuel
injected at a given pulse width.

Paul Lamar

Hi Paul

My order is on the mail ,you should have it in few days from Canada

Jean Prudhomme

I'll let you know if there is an extra charge to ship to Canada.
I'll ship them as auto parts so there should be no duty.
Unless of course you have a shipping address in Florida.

Paul Lamar