Thorp Air Command - T18.net

I used aluminum tape on my sump to try to deflect some heat. I really can't tell you it works.
Cubes

If you want to make your own, I did a set on the Eagle using stainless hand rails for swimming pools. Mock up with PVC DVW fittings, Then cut & splice the stainless to match. Slightly heavier as wall is thicker

Jeff, the other thing you could do in that section is High temp header wrap.

We use it on the drag car with exhaust almost touching the transmission tunnel and it hasn't even discolored the pain on that aluminum body. Before I wrapped it we had the gopro under the car on the dyno and the pipe would glow red after the turbo which is more than I would expect from a thorp engine.

Might be an easy option although if it's super tight you would have to be creative at wrapping it or remove the exhaust. Mylar reflective tape for engine compartments has worked well for us around the turbo area too.

I went with gluing some shielding to the sump. I already had shielding and high temp silicone in the hangar. The exhaust builder did say I could wrap the areas I was concerned about. He also said it wasn’t necessary because I wouldn’t have any trouble with heat unless the exhaust was actually touching the sump.

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Thorp T18
O-320-B3B (160 HP)
68x74 Sterba Propeller

"The joke in aviation is, 'If you want to make a million, you'd better start with £10m.' " -Bruce Dickinson

My experience with exhaust, the exhaust temperatures about 10" from the cylinder flange is about the same temperature as the engine case and parts. I have flown 1500 hours with the exhaust about 1/2" away from the sump and no shielding, generally shielding holds the heat.

Well the shielding is gone. I got a hold of some bad silicone. It wasn’t even skinned over after 15 hours, let alone on its way to curing. I don’t think it got below 50 last night. I was never worried about high oil temp. Cooking intake hoses and burning paint on the sump were my only concerns. The Continental engines run deflectors on the intake hoses and they are much farther away. The primary concern on the sump is a spot on the bottom of the sump that is 3/8 of an inch from the exhaust. I probably wouldn’t have thought much about that except that I have read where guys were having trouble with paint closer than a 1/2 inch from the exhaust.

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Thorp T18
O-320-B3B (160 HP)
68x74 Sterba Propeller

"The joke in aviation is, 'If you want to make a million, you'd better start with £10m.' " -Bruce Dickinson

I just test flew the new exhaust. No shielding or wrap around the sump. I have a performance change I am not sure where it came from. When I removed the straight pipes I noticed I had been flying around with no less than 25% carb heat on. Anyway, instead of cruising 150 mph at 2400 rpm and 22 mp, I now cruise 155 at 2400 rpm and ~23.5 mp (fixed pitch prop). Temps seemed about the same. It may be the leaner mixture and/or cleaner airflow around the engine but I am just guessing.

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Thorp T18
O-320-B3B (160 HP)
68x74 Sterba Propeller

"The joke in aviation is, 'If you want to make a million, you'd better start with £10m.' " -Bruce Dickinson

Still flying with the carb heat on? Did you modify your carb heat for the new x over pipes? Maybe it's more heat because of 2 pipes. The other thing could be smoother exhaust flow freeing up back pressure. You went from 2 straight pipes to a x over system? From what I have read the x over is supposed to be superior to the 2-1 system on each bank.

Maybe it would be worth my troubles to get new exhaust if it's going to pick up 5mph. That's a pretty cheap hp increase!

Went from 4 straights to a crossover system. Lots more room up front than before. Properly rigged the carb heat so it would shut off before installing new system. I was pressed for time on the test flight. Only flew .3 and didn't think to play with the carb heat to experiment. Just flew over a brush fire we had fought by hand earlier and flew past a buddy's house to let him know I was airborne again. Wasn't even long enough to get the oil temp above 177. The aircraft sounded different and felt strange without the exhaust hitting the cowl and firewall. I have to build a new fuel line and reroute. The fire sleeve on the existing line was extremely hot to the touch. Shouldn't ever be an issue in flight but I don't want to risk a vapor lock when stopping for fuel (no primer system installed). I also need to make some tailpipe fairings. Will try to remember to post before and after pictures the next time I am at the hangar.

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Thorp T18
O-320-B3B (160 HP)
68x74 Sterba Propeller

"The joke in aviation is, 'If you want to make a million, you'd better start with £10m.' " -Bruce Dickinson

I flew about 45 minutes yesterday experimenting with different power, mixture and carb heat settings. I think the speed increase had to come from the cleaner airflow through the cowl. The decrease in power is only noticeable on the manifold pressure gauge. Below are pictures looking forward into the left cheek.

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Thorp T18
O-320-B3B (160 HP)
68x74 Sterba Propeller

"The joke in aviation is, 'If you want to make a million, you'd better start with £10m.' " -Bruce Dickinson

Jeff, is that a 320 sump? If so can you pm me where you purchased that intake box? Also, do you have a seal from the intake to the cowl to keep forced air from pressurizing the lower cowl?

I hate my huge round car style airbox and worn out carb heat system.

Yes, it is an O-320. From receipts it looks like the intake box came from aircraft spruce (50256). The bottom tube was removed and the hole covered. I think they sell one without the tube for less money. The air filter assembly is a Brackett BA-4106. Not running a seal between cowl and air filter. Intake scoop (05-22500) was grafted onto the cowl.

_________________
Thorp T18
O-320-B3B (160 HP)
68x74 Sterba Propeller

"The joke in aviation is, 'If you want to make a million, you'd better start with £10m.' " -Bruce Dickinson

bummer, I have a 235 sump so it won't fit.

Are you not worried about ram air coming into the lower cowl causing decreased flow from top of the cylinders to the bottom?

I had given airflow around the airbox some thought but there isn’t much gap and my CHT runs around 350 on the rear cylinders so I decided not to mess with it given the lack of options for attaching a decent seal. What surprises me is there is no evidence of the filter assembly hitting the cowl. When I first saw it I thought there was no way I was going to avoid cutting on the cowl but so far so good. There is only about 50 hours on this airframe/engine combination so I am sure I still have some bugs to work out.

_________________
Thorp T18
O-320-B3B (160 HP)
68x74 Sterba Propeller

"The joke in aviation is, 'If you want to make a million, you'd better start with £10m.' " -Bruce Dickinson

With those CHTs I wouldn't start changing things. Maybe it's not as much of a factor as I think it is. If high chts I would look into it but it seems to be working just fine. I like that setup.