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jpi
Dave
I had a JPI installed in our "P". I believe there was a hole behind the engine and about the middle of the firewall that was used rather than drilling a new one. Besides, they used a type of feed thru that was "split" and then it was cherry riveted to a backing plate. There are in the spruce catalogue as fireproof feedthru's. Make sure you seal from the inside carefully to insure no leaks and use fire proof sealant on the engine side of things.
Ideally it would be best to put a CANNON type feed-thru connector, however, this is not the best idea since the type of wire (nichrome) should not be cut or altered.
The wire JPI uses is rather small and I think the size of hole recommended is too large. I would think the hole for the front engine is about 1/2 to 5/8 inch. The hole for the rear engine was in the top left corner of the rear (looking from the inside) bulkhead and there is a lot of support in that area where other wires pass thru. There is quite a bundle of wires including the spoiler hydraulics and I don't think there should be a support issue. Running the wires up the window channel will be a chore as there is not much room.
I could take some pics the next time I am at the aircraft.
Two words of caution (then some)
1) keep the wires routed AWAY from any of the ignition wires.
2) use the CHT WELL probe where existing cht probes are located. The sparkplug probes are not as good as the well type.
3) Be careful where you drill the holes for the probes on the front engine exhaust. make sure they are uniform length from the exhaust flanges and I think we could only get them about inch away rather than the specified length. You will not get the TIT far enough away on the front engine so it will read somewhat different to the rear...... it is more a relative indication anyway.
4) be sure to add the oil temp sensors. they are very important.
5) I use the OAT probe to measure the intercooler exhaust temp so you can get a handle on boost limits.
6) Reset the limits so that CHT is 400 for the alarm.
7) take the alarm output and feed it to a LED on the eyebrow to get your attention. It is a great alarm system.
8) do install the jack for the computer serial port. Best location is down under the glove box on the lower right side.
9) connect the wiring close to the battery as possible as it can pick up interference on the radio bus. (my experience).
It is a great instrument !!!! Now you will find out how bad the Cessna instrumentation really is...... ARG!
hope this helps
now for your question. YES= it had to be approved by an Engineer and a 337 drawn up.
bob
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