# GM LFX V6

Discussion in 'General Auto Conversion Discussion' started by pfarber, Apr 26, 2019.

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1. Apr 27, 2019

### pfarber

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LY7
The 3.6 L; 217.5 cu in (3,564 cc) LY7 engine was introduced in the 2004 Cadillac CTS sedan. It has a 10.2:1 compression ratio, a bore and a stroke of 94 mm × 85.6 mm (3.70 in × 3.37 in). Lower powered versions only have variable cam phasing on the inlet cam (LEO). Selected models also include variable exhaust. The engine weighs 370 lb (170 kg) as installed.

The LY7 has a lower compression (10.2:1 vs 11.5:1) but sequential port injection. Unclear what models have VVT, but it seems that some do not.

Still less than 400lbs, so 250hp is still obtainable without the DI or VVT.

2. Apr 27, 2019

### pfarber

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Cam phasing is a 15+ year old tech. My 2004 F150 has phasers on it (intake only) and its a very simply system. If you know how a constant speed prop works then you know VVT. A solenoid allows oil into a chamber to advance/retard the cam in relation to the fixed cam gear timing.

Some VVT systems are dead simply to delete. The LS1 has a $120 delete kit, but requires remapping the ECU. Until recently most aftermarket standalone ECUs didn't do VVT. Now most do. But I have no read about ANY modern (say 2010 or newer) motor being put into an E-AB. Everyone sticks with carbs and solid cams. 3. Apr 27, 2019 ### pfarber ### pfarber #### Well-Known Member Joined: Feb 21, 2019 Messages: 433 Likes Received: 34 Location: Pennsylvania Yes. Your google fu is weak. This forum is dead and worse, full of people stuck in the 1990s. Your definition of 'productive' is odd. 4. Apr 27, 2019 ### Toobuilder ### Toobuilder #### Well-Known Member Joined: Jan 20, 2010 Messages: 4,566 Likes Received: 3,402 Location: Mojave, Ca The forum is not "dead". But some of us require more than the dubious technical content of various manufacturer's sales brochures. It you want to break new ground, we're all for it. But we need hardware and data before we're ready to abandon a century of proven performance. BJC likes this. 5. Apr 27, 2019 ### poormansairforce ### poormansairforce #### Well-Known Member Joined: Mar 28, 2017 Messages: 733 Likes Received: 212 Location: Just an Ohioan How does a V6 weigh half of a V8? I'm guessing that you'll be at the same weight or more than a 540 with less reliability and the close to the same money.(if your lucky) 6. Apr 27, 2019 ### mm4440 ### mm4440 #### Well-Known Member Joined: Jan 14, 2012 Messages: 185 Likes Received: 40 Location: LA area, CA Hi, 378# with heavier cast intake and exhaust manifolds. Listed weight of 415# for LS3. The 4 cam heads are big and add weight to the the V-6. If you can compare actual equivalent fwf weights, they will be closer than you think. More cylinders = less problems with PRSU and you can get your 250 hp at 3300 rpm not 5000. http://www.kemequipment.com/manuals/pdf/kodiak-power-curve-62LS3.pdf The Corvette engine was putting out 191 hp on 4 cylinders. If GM had made an all aluminum pushrod 60 degree V-6 of 4 L. + that would have been great but they did not. The 4.3 L , 90 degree V-6 has a balance shaft and split pins so is not as good of a choice as the V-8. You might want a constant speed prop with the V-6 that would not be needed with the V-8. I've been through this in the early 1990's with a Mustang replica project before all aluminum engines were readily available. Simpler is better. Murry 7. Apr 27, 2019 ### TFF ### TFF #### Well-Known Member Joined: Apr 28, 2010 Messages: 12,038 Likes Received: 3,468 Location: Memphis, TN What kind of fuel are you going to run? If 100ll is an option, you can’t run synthetic oil. The lead and synthetic do not like each other. The modern GM engines really need synthetic oil because of the close clearances and heat they run at. All the airplane oil manufacturers found out the hard way by having to pay a bunch of claims. That is why you don’t see full synthetic in piston aviation. Race cars change oil after each race so It’s not a factor. These modern engines seem to be quite a consumer of oil. They tend to foul sensors. You have to evaluate each problem. What happens if one sensor or combo fails. You don’t want to be put in the dirt. If it was easy, it would be the predominant choice in homebuilts. Great for experimenting, but nothing has been a breakthrough to break the status quo. 8. Apr 28, 2019 ### pfarber ### pfarber #### Well-Known Member Joined: Feb 21, 2019 Messages: 433 Likes Received: 34 Location: Pennsylvania I have been looking for ages to get a good weight for an LS engine.. everything put it at 500-700lbs. So when I saw v6 at 345 (possibly less as complete means AC/power steering/cast iron exhaust etc) complete I was very intrigued. If the v6 weight is less than 300 for the long block I'll use it no matter what. I'd still have to do a W&B on the bigger motor (more weight farther forward) and take a W.A.G. as to the moment arm it creates. My E-AB is a tail dragger so forward CG is a concern and not having to add lead in the tail would be be great. https://www.autopsrus.com/about-the-ls3 "GM lists the 6.2L Chevrolet LS3 engine as weighing in at 411 lbs right out of the crate. We remove the cast iron exhaust manifolds and other accessories not utilized in aeromotive application and end up with an engine weighing 376 lbs. Once we add our engine mount, ECU and harness, radiators and all accessories, PSRU, oil and water, we end up with a ready to fly weight of between 489-493 lbs depending on the airframe application." Some quick math shows about 100lbs added to the LS motor to get it in an AC. If the V6 LFX is 300 lbs + 100lbs of extras (I'll say less as the V6 is smaller, needs less liquids etc) you're still ~100lbs lighter. More than an O-360 but significantly less than an LS1,2,3,4 engine. I am concerned about a PSRU and the ratio needed to spin the prop. Once I talk to some PSRU manufacturers I'll get a better idea. I have no doubts about the V6s ability to operate at those RPMs (de-rated to 250hp, about 5000rpm). There is an example of my E-AB running a v8. ONE. Its a monster. Not an LS but a custom aluminum race block. Its a BEAST. I don't need a beast. Just to flesh out my thought process, not modifying the engine is a priority. So I don't want to drill holes or do anything that deviates from factory to much. Next would be weight. 50-100lbs in a 1100lb empty E-AB is SIGNIFICANT and I don't want to lose that cargo capacity. My lard butt is taking up enough capacity as it is. Next would be initial cost. last would be operating cost. So right now the V6 wins in all categories. It would not require any modification (other than removal of useless/heavy parts). Is significantly lighter (right now 100lbs seems to be the difference between v6/v8) and cheaper. A v6 core, rebuilt to new is less than$2k, a crate motor is $6k. An LS1/3 core, rebuilt to new is$4k. A crate motor is \$8k. Fuel wise I think the v6 would have a lower GPM than the v8, but rebuild costs would be about the same.

9. Apr 28, 2019

### Toobuilder

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If you are looking for 250 HP, consider doing a trade study for a direct drive LS V8 vs the V6 PSRU. There is quite a bit of discussion (but not much action) concerning a DD LS in this forum.

10. Apr 28, 2019

### daveklingler

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I'm in agreement with most of what you've said, although I'm wondering whether you might keep the factory ECU with custom programming by a reputable aftermarket firm to ignore the unwanted sensors (there are actually only a couple that I can think of).

Having kicked this particular topic myself a few times, I'm wondering whether you looked at the LV3, and if so, why you chose the LFX. My own take is that the LV3 would give you much better torque at typical aircraft RPMs, but perhaps you've uncovered something different.

11. Apr 29, 2019

### daveklingler

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That's pretty interesting. Is there a study you might be able to point to?

That seems very strange. All modern engines have very tight machining, as you pointed out, but their frictional losses tend to be correspondingly very low compared to a couple of generations back.

I would think that's because of the allergy to 100LL you spoke of, not because of their tight tolerances and low frictional losses.

I guess I'd also think synthetic would be kind of a waste in aircraft engines, given how often the oil needs to be changed anyway and how much of it gets burned.

That statement runs counter to what I've seen - the factory oil in new cars tends to stay clean out to tens of thousands of miles before they get enough wear to finally make dirty oil, again because of the tight factory tolerances. Modern engines tend to last for 300-400,000 miles for that reason as well.

Given the wide variety of homebuilts, I don't think there's any one engine that would fit them all. That said, Hondas, Suzukis, Mazda rotaries, Subarus, VWs, GM Corvairs and GM V8 small blocks seem to be fairly popular these days. Then there's a certain snowmobile engine manufacturer that seems to have come up quite a bit in the market after its engines grew popular for homebuilts...

I suspect that the LV3 would make a pretty good aircraft engine, but I haven't tried it and I don't know anyone that has. It's fairly new, compared to the others, as is the LFX. If someone is willing to experiment and finds a winning combination, well, generally that's what's required for popularity.

The really critical issue for a lot of automobile conversions is PSRUs, but thankfully there seem to be a few good ones out there right now and that particular problem area might be improving.

12. Apr 29, 2019

### rickofudall

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You might want to consider Burt Rutan's advice about alternative engines. Do your testing in a production aircraft. One, you've eliminated all airframe issues from your testing and two, should you find yourself having to do an off field landing the morons on the evening news don't go fretting about those awful EXPERIMENTAL aircraft endangering God and everyone.

Rick

13. Apr 29, 2019

### TFF

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I have no study for the leaded fuel and oil. The study was in the pocket book of Shell oil. There is only semi Synthetic on the market now; they had to remove full from the market years ago.

As for oil burners, these and any type of the low tension oil ring engines are a crap shoot on how good they break in. Not going to run bad for most consumers, but they end up taking a quart every 3000 miles so it’s like two quarts between oil changes. GM lowered the intervals so the engines would stay in warranty. In something that is running high power, that can be either more consumption or maybe detonation. You can see in adds for GM cars with their complicated engines owners selling stating only synthetic used, and then google that model engine trouble and it is many times traced to second or third owners not wanting to put the expensive oil in the car, and they just crust up inside. My wife’s Odyssey is running synthetic because it will eat oil if I don’t. My Tundras have never needed an extra quart no matter the oil used. I use synthetic just because I don’t want to be fixing one of those engines.

My status quo was about auto engines in general. They are the hard row to hoe. In the 90s I dreamed of a Buick 215 in either a MGB or aTailwind. Have the engine. Had the B. Have Tailwind plans. It will be a airplane engine if I build it. Wittman put a good bit of time on his. It’s in the Oshkosh museum on a stand so you can look at it. But if you read all the articles on it, he flew it but he babied it a lot more that he did the airplane engine versions. Not against them, but for all the trying, no one has come through with a breakthrough combo that would do 90% of a Lycoming. They are their own hobby. Tip my hat, but in general it’s a lot of work if it fails. None of that is saving money. It’s only fun if you like playing with guts. Airplanes do weird things that defy reason. Buggs Bunny and the Gremlin. William Shatner and the Gremlin. No wonder AMC had such problems. They let Gremlins in their factories.

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14. Apr 29, 2019

### pfarber

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Evidently its quite easy to get the LFX running just on the ECU:

https://ls1tech.com/forums/conversions-hybrids/1753035-new-gen-v-project-5.html

No talk about weight though... most guesses are putting the LV3 at LESS weight that other 'High Value' v6's as the LV3 has a less complex valve drivetrain.

Its actually a VERY interesting motor. The 90deg V means its not as tall as a 60deg, but a 60 deg is said to run smoother.

Thanks for the info!

15. Apr 29, 2019

### pfarber

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For the cost of a certified AC and red tape to legally put an experimental motor into it I'll smile for the camera and hope they don't mention 'experimental' to loudly.

In his hey day I think Rutan could call just about any manufacturer and get something for free. Me? Not so much

16. Apr 29, 2019

### mm4440

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Hi, a big cubic inch LS based direct drive engine with a Whitman type inverted conversion would save about 50# and be even simpler. An excellent suggestion for the 250 hp needed.

Murry

17. May 4, 2019

### pfarber

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As mentioned before by others direct drive seems to go nowhere.

Save 50# how? Installed the v6 is lighter with the PSRU than the V8 without.

Any links to this 'Whitman type inverted conversion'???

18. May 4, 2019

### BBerson

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19. May 4, 2019

### bmcj

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Pfarber, this seems to me to be an important point that you missed when you read Billski’s post. I suspect that high torque at low RPMs can bring problems when applied to a prop.

20. May 4, 2019

### pfarber

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The O540 angle valve (300hp) produces 583 ft-lb at 2700

I don't see the problem. I would apply less torque that this. Yes, there might be more torque at a lower RPM as I haven'e seen a O540 torque curve.

Any auto engine is a compromise. And the work to delete VVT would fly smack into the reliability/return argument. Delete VVT, reprogram ECU, deal with internal oil rerouting and make the cam/cam gears work or keep it and *possibly* have 'to much' torque?

Explain to me how the VVT delete is a better option? No, not far flung 'what ifs'.. but compare the ACTUAL work to be done vs just keeping it stock. I'm all ears if there is a beneficial case to deleting VVT that can be made