org

I’ve been posting occasionally about my choice of an LS type engine for a small aircraft. I’ve finally settled on (and taken delivery of) a L92 crate engine. It makes the right amount of power in the right power band in stock form, but I’m thinking I’ll eliminate the VVT and replace the cam with something like the Lunati Voodoo cam.

The engine won’t be operated like a car engine, but will be more like a boat…a short period of wide open throttle with a RPM limited to around 4800, then 10 minutes or so at WOT and 4000, followed by up to a couple of hours at around 3500 for cruise, making 200 to 220 HP or so for cruise at altitude.

The only thing really different from a car or boat installation is that the exhaust will consist of 8 identical stacks of 14” length instead of conventional headers and pipes. I’d appreciate any opinions on what effect this will have and what cam specs (in general) will be best for this exhaust.

I’ll be using (probably) a SD setup of either a GMPP controller or a Megasquirt, since it seems O2 sensors won’t work with short stacks.

I have the L92 and a 6.0 LQ4 (both new) and also wonder if the LQ4 heads might be better than the L92 heads for the maximum power (torque) between 3000 and 5000 rpm. Any opinions will be welcome here, too.

To clarify: I don’t care about power above 5000 rpm. For this installation it doesn’t exist and is unusable due to propeller limitations. I don’t really need a particularly smooth idle below about 1000 rpm. Throttle response off idle isn’t important except that the engine needs to smoothly accelerate into the 3000+ range. I don’t want to change anything but the cam and oil pan, and possibly swap the heads if it makes sense.

I’ve always gotten some good information in other discussions, so thanks in advance for your thoughts.

Black02SLPSS

iTrader: (5)

Out of curiosity are you going to be running a gear redution unit on the engine? Oh and is that an iron block engine or aluminum? Only reason i ask is i was wondering if that was going to throw your weight and balance off. What plane is it going in? Thanks

org

I have a 2.43 to 1 Geschwender reduction drive, it will be aluminum block. It's going on a SAL Mustang, a scale P-51. At least one has flown with a LS1, quite a few with small block Chevy iron block engines.

old motorhead

iTrader: (10)

Interesting. I remember Mooneys having a Porshe engine option a few years back. It had a belt driven reduction drive if memory serves. Aren't all LQ4 blocks iron? I know mine is. How much HP do you need for take off and cruise? That answer would dictate cam heads etc. Running straight pipes off of each exhaust port sure might complicate things. No room for even shorty headers or exhaust manifolds?

3fingas

iTrader: (16)

get life insurance

narcszm

Your goal here should be valvetrain reliability. Focus on the lifters and springs, and find a cam grind that doesn't even push the envelope of the valve springs, and find the best valve springs money can buy. I think it is a given you go with an LS7 or Cadillac racing lifter, and a cam with no more than 0.575" valve lift. Given your engine speed goals, the only thing that could really fail is some cheap spring giving up the ghost, and you don't want it doing that at altitude.

Richard@WCCH

iTrader: (3)

Stick with the L92 heads. You can extract all the torque you need with .500"-.525" lift. It'll go easy on the valve train. Factory LS6 yellow springs will do nicely. If running pump gas look for a cam duration of approx. 214º with a 110ºlsa.

Good luck,

Richard

Ryne @ CMS

iTrader: (10)

i agree

org

[QUOTE=old motorhead;11510774]Interesting. I remember Mooneys having a Porshe engine option a few years back. It had a belt driven reduction drive if memory serves. Aren't all LQ4 blocks iron? I know mine is. How much HP do you need for take off and cruise? That answer would dictate cam heads etc. Running straight pipes off of each exhaust port sure might complicate things. No room for even shorty headers or exhaust manifolds?[/QUOTE

You're correct about the LQ4 block, it is iron. I'll be using the L92 short block regardless of which heads I end up with, it's aluminum. Anything over 200 hp for takeoff will do the job an the airframe will take up to 450 or so. I'm shooting for 350+ for takeoff and 200 + for cruise. Since cruise will be at around 8000+ feet the power will drop off about 25 per cent. The L92 should do the job, power wise. The cowling is only about 27" wide, so no room for exhausts. My drive uses a 3" chain.

LS6427

iTrader: (2)

Lancair has used Chevy V8's in there Lancair IV 420-P model. It has twin turbos though, just because its pressurized, but its been done for a long long time.

Should work out just fine. Jim Rahm built them for Lancair, he's a retired General Motors engine designer.

org

Narcszm, Richard, and Ryne, here are the specs for the Lunati Voodoo cam:
Advertised Duration (Int/Exh): 262/268
Duration @ .050 (Int/Exh): 212/218
Gross Valve Lift (Int/Exh): .531/.531
LSA/ICL: 113/109
Valve Lash (Int/Exh): Hyd/Hyd
RPM Range: 1600-6400

What do you think? Would reducing the LSA to 110 help with the short stacks? This grind looks like it fits other than the LSA. I'll be running pump gas mostly, but once in a while I'll probably have to use some 100/LL Avgas (another reason for no O2 sensors.) I assume no problems with valve/piston clearance with the stock L92 engine(?)

org

Yes, quite a few LSx engines flying on everything from SeaBee to fighter replicas. It's a natural for aircraft. The reduction unit seems to be the key, since the engines seem pretty bulletproof if run in a reasonable way.

Richard@WCCH

iTrader: (3)

Comp Cams has this lobe listed in their catalogue.
...........Lobe #.........Adv Dur.........@.050"............@.200".............l ift w/1.7rr
Both I&E 3301...........266º..............214º............. .129º................. .519"


With the straight exhaust you don't need the extra scavenging of a longer exhaust lobe.

Also I would suggest replacing the factory valves with stainless units. I don't feel the oem valves are aircraft worthy. There have been a number of oem valve failures near the valve lock groove.

Richard

narcszm

Good call, and whatever you do, don't get any two-piece hollow intake valves. Reliability is much more important than saving a few grams of valvetrain mass, especially at your relatively low RPM.

Old SStroker

Richard had some good advice.

I would add that VERY few folks have optimized cams for an LS engine running the rpm/power bands you need, especially with 14" exhaust stacks. Individual stacks are not a bad idea, BTW. The correct cam can be designed to complement your constraints.

I suggest that the optimum cam probably won't be on someone's shelf, unless perhaps it's one of the many OEM cams! I would also use the best endurance springs I could find running at a fairly low stress level. PAC nitrided springs "spring" to mind.

IMO, you really should get with an LS valvetrain specialist. You might be surprised how mild that optimum shaft might turn out.

Good luck.

Jon

Schwanke Engines

iTrader: (1)

Stock cams tend to make peak HP at 5200 or there abouts with gobs of torque before that. You could just get a tight center stock cam and save a bunch of time. Then, you could stick with the LS6 valvespring as mentioned before. You also shouldn't have to worry about crashing the valve into the stock piston either.

old motorhead

iTrader: (10)

How big of a prop is this bad boy going to swing? With your gear box, 3000 rpm cruise yields 1440 prop rpm. Everything I've ever flown has had prop speeds between 2000 and 2500 rpm at cruise. However, every picture I've ever seen of a P51 showed a small plane hanging on to a giant prop. Do they make props that are effecient turning that slow? Sounds like a neat project. I'm just a whole lot of time and money away from doing something similar!

Stock cam and springs sound good to me at the rpm levels you're considering. They'll last a long time and remove that as an issue to worry about. About the last thing you want is an "unscheduled" landing due to valve train trouble.

stroker_SS

Sounds like a pretty cool project, I dream of someday owning a p51 or corsair(the r2800 at school has got me laughing at all the guys that think there 540ci BBC is big) but the likelyhood of that happening is pretty slim, if at all. But i certainly wouldn't mind owning a scaled down replica.

A video of this beast once finished is necessary.

panterx1

iTrader: (22)

I hope you will keep this updated with your progress, I would like to see the end result.

oberth1

iTrader: (6)

well this thread is subscribed.... never thought of a lsx in a p-51... love to see some pics! good luck to you!