4 Cylinder Turbo Lyc/Cont

[patterson]

Hello engine guys (girls)

I'm building a new version of the F1 Rocket. A 4-Cylinder Rocket now being named the F4 Raider. But, here is my question? Which 4 Cylinder might be best for higher altitude cruising? I have just about decided on using a Turbo-Normalized Lycoming, but have second thoughts for a number of reasons.

I like the idea of flying up around 15-16,000', with O2, and get long range cruising, hopefully at 70-75% power. There are lots of turbo'd air cooled engines to choose from, but the question is which might be best for the F4 Rocket?

Considerations are: 1) weight, including turbo and required waste gate and exhaust. 2) Horsepower , at 14, 15, 16 thousand feet
3) Fuel Burn, Using a TN-4 cylinder should (yes?) result in fuel savings over the 6 cylinder normally aspirated Lycoming 4) Cost, maybe I should have put this first.

I'd like to see sea level HP of around 210 (75% of that T-normalized at altitude) but what about configuration and weight? If it ends up to about the same as a 6 cyl Lycoming in weight, I wonder if I would be better off doing a 6 cyl normally aspirated Lycoming instead?
Thanks for your thoughts and advice
Ron
Currently flying an RV-4 with 204HP angle valve IO-320.

[BobTurner]

One more thing to consider: cylinder head cooling at altitude.

IMHO you are on the fringe: at 15,000' you won't see much gain over the normally aspirated six. At 18000' the turbo will win.

[Marc Bourget]

Something to consider -

John Thorp was Rajay Turbocharger's consulting engineer in the 60s & 70s (and maybe longer). I recall his opinion that such installations were a trade-off, and less - due to maintenance issues, unless the air frame was designed to operate at the selected altitude.

Another interesting aspect was a normally aspirated Lyc, for example, would run hot on, say, the #1 cylinder, but in the turbo version, the #4 would run really hot - sufficient to require changing the baffles, etc. (#s for example only, my memory isn't that good).

There might be some value if always operating high (based in Denver, for example). John's approach was to install an 0-360 in an air frame where a 0-290 was sufficient, then by careful selection of prop, achieved decent performance at altitude and better BSFC than 0-320's at the same cruise speed.

[rv6ejguy]

It will be pretty much a wash below 15,000 feet as far as cruise hp goes between a 260hp 540 and a turbo normalized 360.

You need to look at up front costs, reliability and complexity of the install.

I doubt if engine cooling will be a big issue if you're starting with the 6 cylinder cowling. But be aware of the extra heat loads and cooling required for the oil and induction air (intercooling) on the turbo engine.

Lycoming had a nice Experimental turbo version of the 360 a number of years back but I don't know if that's still available. Had a well designed turbo system compared to some of their older certified attempts.

[BillL]

Ross - question - do variable nozzle turbos hold up in an aircraft application? A waste gate just seems like a really heavy and inefficient solution to boost management. Also, does your company do controls/algorithms for modifying timing, A/F etc depending on critical engine monitoring information? Like inlet temps, CHT, knock etc? Would that be an option for a turbo application in an RV?

On the turbo normalizing, it would seem that EFI w/spark control, lower Cr with a heavier piston (maybe with keystone rings), piston cooling jets, and aftercooler might be a good starting point. A good understanding of rod/main bearing loads with higher pressures, head and barrel cooling, and understanding of the typical parallel valve head/barrel cylinder pressure limits are would be in order to evaluate the basic hardware's suitability for turbocharging. I admit to thinking that higher boost (as opposed to only normalizing) is a better package just due to the weight, cost, packaging, and maintenance with very little advantage for the first 12,000 feet altitude. Detonation limits would need to be understood. "Understood" means quantified.

Remember, just flowing air through the compressor and turbine cost something. 60% overall turbo efficiency would be a good goal, but that requires more boost than normalizing.