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.

Yes, 250hp at sea level, that's how aircraft engines are rated.

Heres basically the most badass NA LS engine out there, RHS Turn Key 502c/810hp | Golen Engine

And its still not even close at 2500rpm. However if you look at the dyno graph, it does make 550ftlb at 3500rpm. You might could make something like this work if you use a smaller diameter prop with a higher pitch or more blades so you can turn more rpm, but as far as your original goal of 350@2500rpm or even 250@2500rpm does not look doable with an NA LS...

how much are the speed reduction units?

you might get an alumnium LS engine and youll save 80lbs compared to the Iron block .

2500 RPM @ .75 reductun will give 3333 RPMs engine speed

LS motors can stay there for a along time and prduce a decent amount of power

LS7 would be the best to go with

dry sump ready , light weight rods , has the displacment , and with simple mods will get you close to what you want

here is the dyno

its almost 230hp at 3000rpms

and on 3500rpms it has more than 250hp

Dyno LS7 Engine (17802397) HP, Torque RPM Chart | GM Performance Parts


with 2" headers , a custom cam , and a good tune , you should move the curve where you want

I know a guy who thinks he's perfected an LS reduction drive. And he's wrapping an RV-10 around it. I have his card in my flight bag at work. I can not see a feasible way to make enough power, reliably, with that low of RPM. And I'm not up on FAA rules, but I know Transport Canada would never allow an STC for it, so you're stuck as Experimental. Which kind of sucks, because a 182 with an LS3 would be great.

An O-540 is roughly 440 pounds dry, I imagine an LS3 is not far off. Definitely under 500. But since the 540 only makes 300 or so, and the LS3 is 400 or so, you've already beaten the weight vs. power. Without throwing the W&B off too much.

Ya, I just wish I knew more about engine design, it just seems to me that an O-470 should be able to be outperformed with a little smaller modern engine (say an LS stroker of some sort in the low to mid 400ci range) especially from the efficiency aspect of modern injection and tuneability.

An RV-10 should be a rocket with that motor, there are several out there cruising at 200mph on 235hp. There was an RV-6 or 7 for sale in Canada recently with a 4.3 chevy v6, carbureted with a PSRU that claimed 175mph cruise on 7.5gph.

It just drives me nuts that a new cessna 172 is ~$350k and you are essentially getting the exact same thing from 1956, just some updated avionics. That's why I really like some of the stuff being done in the experimental world.

I was just talking about this the other day, that how much further ahead we'd be if the big companies would keep up to experimentals and home builts. The problem lies in the cost of something becoming certified by the FAA. However the FAA has delegated certification to the ultralight manufacturers to do in-house. It's on a trial run, but if it proves successful it may find its way up to Cessna, Piper etc.

The company I work for has six 172's, two are 69's the rest are 74's. You're right, you can hop in one of those, then go hop in a 2013 model and the only difference? Glass panel. Which shouldn't be in a 172, but that's another discussion.

I would go with a stroked 6.0 and top it with the smallest runner heads i could find. It would keep the velocity up at low rpms. A good intake and professional designed headers would get you close. Having some one build tuned headers for your engine setup would bring the torque curve down.

Just tossing this out there, but what about a reverse split cam? They've proven to make great power in the lower RPMs. Combine that with the small runner heads mentioned above on a Stroker an I'd think that would make pretty good power down low.