Thorp Air Command - T18.net

Hello. I have started looking for a Lycoming engine core to rebuild for my project. Based on everything I have read on this forum the 320 is the optimal fitting engine, but the 360 would work as well - little more power, burns a little more gas. But there are numerous model designations that denote how the accessories are mounted for instance and with the Thorp's cowling and dynafocal engine mount, are there any specific configurations that don't fit well for the Thorp and I should stay away from?

I am currently thinking, Lycoming carbureted O-320, wide deck (suffix will end with the letter “A,” such as L-XXXXX-27A), with accommodation for a constant speed prop. Will stay away from the limited run and problematic H2AD models.

Appreciate any input the group has. Chris

There are a few sump configurations. The 'carb or injection servo on the back' won't work because a tube of the motor mount interferes with the carb. I have such a sump from a Grumman Tiger, which I thought might work to eliminate the bump on the cowl bottom.
There are front entry sumps, including aftermarket. I got a Superior Cold Air Sump for my RV-8. It would work on a T-18, but not with a standard cross-over exhaust. Vetterman Exhaust makes a special pipe for this sump, for RV-6 & 7 that *might* fit. The air intake would be higher on the cowl, just under the prop spinner. Could be limited space for an air filter.
There are 2 updraft sumps, I think the one with the most forward carb mount is the one most T-18s use. Its also the most common?
I caution against modifications from the plans because of the extra time these mods take. I put a Mazda Turbo Rotary on my RV-8, it only added about 5 years to the build. My T-18 stays stock. Any changes are limited to adding fuel computers, EFIS units, tailwheel upgrade, repositioning the battery and removing the vacuum system for better weight & balance. And now adding ADS-B...Jobs that won't individually take too long.

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Scott Emery
EAA Chapter 326
T-18 N18TE

I have a rear mounted fuel injection. It does take some modifications to the motor mount. My sister plane has a rear mounted HA6 carb. Likewise, it took some work to fit, but it can be done.

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Bob Highley
N711SH
SN 835
KLAL

I had the same .. rear mounted HA-6 .. right now I have a rear mounted FI on my IO-320 ... this is a custom built aircraft ... if something doesn't "fit" ... make something that will let it fit.

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Lee Walton
Houston, TX
N51863,N118LW
KEFD

I like my Lyc 0-320-E2D converted to fuel injection with an Airflow Performance system and their 90 degree elbow on the std up flow sump. Fuel injection pump faces the rear with a K&N air filter. Fuel divider feeds into priming ports. This past year I also removed one magneto and converted to SDS electronic coil pack ignition running MSD plug wires on Iridium auto plugs. Fabulous...easy starts, smoother running, and adjustable timing. Next I will be using the G3i magneto harness conversion to use auto plugs on the remaining magneto.

Terry
N51079 Thorp T18C
KSCK

Hello Terry,
You have setup your O-320-E2D exactly as I was expecting to configure my build, with FI and SDS ignition. Are you running only 100LL or have you ever used an aviation grade of auto fuel and if so, what is your experience with the auto fuels? If I am correct, the E2D can be configured to put out 150 or 160 hp depending on the pistons used and resulting compression, what horsepower are you making with your base motor, and do you think that moving to FI and electronic ignition has contributed to any power increase?
Regards,
Chris

One way to clear a rear mounted carb or fuel injection.

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Bob Highley
N711SH
SN 835
KLAL

First question, are you going to want to run mogas or strictly 100LL or whatever replaces it? This dictates what compression ratio
we can use. A 10:1 compression 100LL O-320 can be reliably built to 190hp. Dana LaBounty

Hello Dana, My build objective is to have an engine that will provide reliable and smooth power, with the flexibility of using either 100LL or mogas, taking advantage of all the latest fuel delivery and ignition options that are available to an experimental builder. Right now 100LL is readily available to me but that might not always be the case and wanted my engine build to be flexible enough to use either. Making maximum possible power is not my goal and my research to date tells me that when using the higher grade automotive fuels does limit me to 8.5:1 compression and whatever hp that generates. I am curious though whether I can expect any bump at all in hp if applying FI or EI to the engine?
Thanks, Chris

8.5:1 comp. and have your cylinders done by Performance Aircraft Powerplants. If optimizing the engine is a higher priority than budget go with injection and dual e-mags or like. Building to optimize power also makes the engine run smoother. Cylinders flow matched and dynamic balance rotating assembly. Thermal coat the piston crowns and dry lube the skirts. Have the cam profile optimized for cylinder flow and compression. Easy 180 smooth horsepower. Engine will run cooler and be more fuel efficient. D.L.