turbo vs super charging

[Dale Harris]

Yes, but you did notice I said "unless there are retrofits out there". Of course you would agree that you get less fuel burn, because you are making less horsepower, wouldn't you? It's no misprint, to get 350 horses out of the TIO 540, you pretty much need 2575 and 42" You'd be getting something in the region of about 300 to maybe 310 hp at that rpm. Check the lycoming engine handbook that someone mentioned earlier. It'll show you the hp you are producing. If I can find it i'll have a look at it tonight.

[Capt W E Johns]

Seems to me that the TIO-540 needs a lot of inches and a lot of gas for not many extra horses... I fly a Lycoming IO-540 which is benched at over 300 BHP with around 28" and 2700 RPM, using about 100 LPH.

Is the TIO-540 compression ration much lower without supercharging? (forgive the ignorance, I have only flown a couple of types)

[DirectAnywhere]

Capt. Johns, Compression Ratio doesn't change as it's the ratio of the cylinder volume with the piston at BDC compared to cylinder volume with piston at TDC. Turbocharging itself won't change this basic characteristic of the engine.

[Woomera]

The "new" piston engine Cessnas have Lycoming engines. Textron, Lycoming parent company, bought Cessna from General Dynamics in January 1992.

[Jamair]

Jeeez, I dunno Dale; I ain't any sorta expert at all, but 330lt/hr seems AWFUL rich for a Chieftain........I've never seen more than 220 total flow at takeoff - thats full power, full fine, full rich, at SL. I don't have my Chieftain PoH handy, but next time I'm in the thing I'll look those numbers up.

[1McLay]

Hi Capt W E Johns

Seems to me that the TIO-540 needs a lot of inches and a lot of gas for not many extra horses... I fly a Lycoming IO-540 which is benched at over 300 BHP with around 28" and 2700 RPM, using about 100 LPH.

Probably to some degree that is quite right but the main advantage is the T engine will continue putting out that power for many thousands of feet in an upwards direction. Basically the turbo charged engine will work as though it is at sea level up to around 20,000ft. Obviously somethin' no N/A engine will ever achieve!

regards

1M

[nomorecatering]

Everyone should read John Deakins articles on Engine Operation, better still attend the workshop run by Advanced Pilot Seminars, Jointly run by John Deakin.

[Dale Harris]

Jamair, All references to Lycoming Operator's manual, TIO 540.


Full Rated power, (350 h.p) TIO 540 J series, requires 41 U.S. Gal/Hr. X2 = 82 U.S. Hr. = about 320 L/Hr. I would respectfully suggest if your engine is only using 110 L/Hr, it isn't producing 350 h.p. Remember, we are talking about Takeoff power, we average 155 l/hr block time. Remember guys, the TIO 540 series can be had in many different versions, many producing different rated H.P. They vary from 250 rated h.p to 360 rated h.p. The fuel burn at take off and in cruise will obviously vary accordingly. My figures are for your average everyday Chieftain, with the L/TIO 540 J series. As a check last night, on take off, the a/c I flew indicated 42 gal/hr R/h eng and 40 gal/hr on the L/h. Fits nicely with the average I gave above, although given the OAT and Air pressure, I think they are underboosting slightly.

Direct anywhere,
Compression ratio does vary amongst Turbo and Non Turbo charged engines, even amongst the turbo charged varieties. In the TIO 540 series, they vary from as low as 7.2 to 1 up to 8.5 to 1, depending on the amount of boost allowed. A non turbo charged engine usually has higher compression ratio than a turbo.

Just out of interest, I used to fly a Queenair with the original geared supercharged 540's. IGSO 540's to be exact. Rated H.P. was 380. It achieved that at 3400 R.P.M. Or maybe it was 3200? It's been a while. Anyway it also produced 47 " of boost. Required, If i recall correctly, something in the order of 300 L/hr PER ENGINE at that power. Of course, the engine was probably really producing something closer to 450 or 480 H.P. really, as the supercharger is notoriously H.P. hungry, hence the big rpm and boost/fuel flow numbers.

[DirectAnywhere]

Thanks Dale.

I presume this changing of the compression ratio is a design compromise by the manufacturer.

The act of merely bolting a turbocharger onto an engine won't change the compression ratio unless the manufacturer makes a design decision to change the length of the piston/ length of the con rod/ anything else - to change that ratio though will it?

[Dale Harris]

Yes it is a design compromise, DA, usually based on the detonation margins existing for that engine design. Fuel octane, quality etc all have a part to play, plus ultimate output from the engine. Any time you drop compression ratio, you lose power and efficiency. Manufacturers use different "tricks" to change compression ratios, including piston deck heights, but sometimes they will also vary the combustion chamber size too. Another trick is to use "dished" pistons rather than flat topped ones. All methods vary the combustion space available, at TDC, not the actual cylinder volume in any appreciable way. If you want to vary the cylinder volume you either have to change the bore or the stroke. That's much more expensive!!!!!

Cheers.

Actually, that is a bit simplistic. I am of course referring to the static compression ratio. Turbo or Supercharging does change the dynamic compression ratio, it has to, since you are compressing a bigger volume of mixture. In a dynamic sense, the compression ratio in every engine varies somewhat in practice, according to many variables. Static ratio is what is normally quoted as a comparison. That is of course as you said, the comparison of combustion space with the piston at TDC compared with the cylinder volume at BDC.

[Jamair]

Well, like I said Dale, I ain't any sorta expert at all, so next time I'm in the thing I'll check those numbers. Cheers.