Build an LS for 350hp@2500rpm
 

Ok guys, I'm interested/mildly involved in the experimental aircraft scene.....alternative engines are always a fun topic. Problem is with auto conversions is that they need to be run through a speed reduction unit to get the prop rpms down to 2300-2700. This comes with a huge amount of problems that no one seems to have truly figured out. There's a couple outfits out there for speed reduction units but the weight, harmonics, complexity, reliability, packaging and cost are all issues.

Now, if a guy were to build an LS specifically for direct drive, and your limitations were: less than 450lbs, and able to provide a continuous 300-350hp at mid-2000's rpms.

So, LS1 or L33 block? 6L rotating assembly? Cam? Heads?

Obviously there are other challenges such as cooling, redundancy, etc, but lets just talk about power@rpm@continuous use.

The engine this would replace would be Lycoming O-540's and Continental 0-470's, which are upwards of 40 grand to overhaul now, they are 235-300hp engines at approx 2500rpm.

So for that power level you are going to need 735 ft/lb of torque. Doable, but you will want some stout connecting rods and will need some sort of forced induction. What altitude do you want to have the rated power, or whats the max altitude you want a certain amount of power?

Off the top of my head you are going to want a pretty small duration cam with big lift and heads that can support big lift. A 454 lsx with some LS3 or aftermarket head would be good...turbo selection will depend on altitude. I would not recommend a supercharger for this setup...turbos were originaly made for exactly this purpose.

Also, LS engines are not meant for aircraft, so you are correct in the cooling system is going to have to be impressive, as well as a mandatory dry sump setup.

OK, let's be a little more realistic then.....how about 250hp@2500rpm, that requires 525lb-ft of torque..........that's almost got to be in the realm of an N/A motor with some stock-ish components? Let's assume this will be for a VFR machine, so 12,000ft ceiling. 93 octane auto fuel.

Im not smart at this so its purely my speculation, but i dont think cooling would be that big of a deal. Its cooler the higher the altitude right? Maybe only on takeoff, landing and taxing would heat build up. Running that low of rpms shouldnt build up that much heat tuned properly. Again i have never flown before so its alla guess. Sorry if im way off. Seems like a cool idea though.

The first cam on this page is a high liftshort duration cam Chevrolet V8 Gen III & IV (LS-Series) 3-Bolt 4.8L 5.3L 5.7L 6.0L 6.2L 7.0L 1997-Present


Or maybe a vinci cam with some 1.8 rockers.

The cooling is an issue because generally piston aircraft engines are air cooled. So figuring out where to put the radiator is problem. It can definitely be done, as there are flying examples. The interest in LS powered airplanes is growing, but as far as I know no one is using a direct drive, only through speed reduction.

A side note on cooling.........liquid cooling does have a pretty big advantage concerning shock cooling.......if an air cooled engine does a rapid power off descent, the cylinders can cool significantly faster than the pistons, therefore contracting faster than the piston and cracking a cylinder. Liquid cooled engines are in more of a steady-state temperature environment.

Would need to be a beefy cooling system for sure. Even at 250hp, 100% duty cycle with forced induction will overheat quick unless you put some thought into the cooling system.

Wondering if this is doable with NO power adders, N/A only.......FI adds a whole pile of complexity cost problems into the mix

It can be done, with lots of cubes... But its not going to reach 12000ft.

Maybe at sea level, but forget about it at altitude.

Air density at 12000ft is something like 69% of sea level, so 250hp at 12000ft you need to make 362hp@2500rpm at sea level, which is 760ftlb....which is doable with a properly set up turbo system, but ive never seen an LS make that kind of torque NA at ANY rpm, much less 2500. Thats big block territory.