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GM 3.6L variants FYI

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maticulus

Member
Joined
Aug 11, 2019
Messages
7
Good day. Since I joined this forum specifically to offer some clarification in a thread it turns out I can not post in after the fact, I'll kill to proverbial birds with one stone by combining my intro along with the info I intended to share, here.

I am an Army veteran/heli mechanic from long ago, that loves the subject of flight and aircraft, although I have not transitioned over to the point of becoming a licensed pilot (yet). I am also an avid motor head. I stumbled across this forum while doing research for a future performance build on a GM 3.6L V6, where I found the thread discussing the LFX motor.

In that thread I read some valid points and respectfully, as much that was far off the mark. I'm providing information that I believe those interested in the idea of this platform will hopefully appreciate, those who are not enthused might become such and those who think it's upside down might lighten up a little, or not.

The now 3.6L is an impressive motor over the iterations, DI=direct injected;
2.8L, 3.0L and
3.6L LY7 242-275 hp,
LLT DI 281-304 hp,
LFX DI 301-321 hp,
LF3 & LF4 twin turbo versions, 420 & 464 hp respectively and the latest, a clean sheet design 3.6L LGX 305-335 hp with active fuel management.

With the exception of the LGX, the motors share several interchangeable parts, except those associated with the smaller displacement motors and all listed above are VVT on intake and exhaust. The Turbocharged 2.8L was a Saab application that I understand carried single camshaft VVT.

The 3.6L has had its struggles with timing chain elongation issues early on, mostly associated with an extended oil change interval (owners mistaking the oil life left monitor, for oil level & running it too low), an alleged defective batch of chains and the effects of cheap motor oil. That problem is a non issue now.

Although some engines used oil (not just the 3.6L), I understand it was mostly the result of the PCV system design causing the motor to ingest it as opposed to burn it. Add an extended oil change interval to an oil consuming engine and put an individual behind the wheel that doesn't bother to check the oil level after 5000 miles, because the oil monitor says there's 50% life left and yes, there's a good chance it will run low and ruin the motor as several did resulting in a recall and recalibration of the oil life monitor.

My 08 3.6L LLT in a CTS does not use oil that I have detected between 5k mile intervals. I replaced the timing chains as preventive maintenance at ~176,000 miles and it has about 195k on it now.

I read debate in the thread over the VVT usefulness in flight and can only say that anything that optimizes camshaft angles for efficiency should be considered in terms of fuel savings. Locking the camshafts straight up is easy, but efficiency varies more with a fixed camshaft over rpm changes vs. functioning VVT, which changes with engine rpm as well as other conditions.

There is a software program used by those who modify their cars called HPTuners. This software makes it possible to tune as well as adjust many important engine performance parameters, including camshaft angles. An aftermarket controller could be used also.

I stopped reading about halfway through that thread, one thing I try to avoid on the net is arguing vigorously with strangers over a difference of opinions, in the absence of documented facts, I'm married and get plenty of that up close and personal already.

Here's the thing, a lot of what I read were rules that applied to old technology being repeated, with little to no consideration given to modern technological advances. One statement that really shocked me was the suggestion that direct injection had little advantage over port injection under a set of common circumstances.

That was eye "popping" for me. The LFX and LGX have a compression ratio of 11.5:1 and they are rated and SAE certified on 87 octane gas. The LY7 with 10.2:1 compression and port injection is also rated for 87 octane, however, under some circumstances it may encounter spark knock and may need to use 89 octane here in there. The owners manual points that out. There is no such caution for the DI motors in the owners manual. I wouldn't be surprised to find, given the reserve GM often includes in their drivetrain applications, that the DI motors can be bumped to 12:1 compression and still run 87 octane. Either way, that is an exceptional accomplishment by old standards.


There are DIY turbocharged 3.6L LFX motors generating in excess of 700 hp, with ~550 wheel hp set as the limit for the stock motor and those who are fortunate enough to own the Cadillacs with the twin turbo production 3.6L motors (ATS-V) are tuning and tweaking them into 10s quater mile cars, without gutting them and turning them into track cars.

I would like to build, or own a plane some day, and several years ago before getting deeper into my education path, I acquired 4 part catalogs from major suppliers and purchased the book, "Fundamentals of Flight" to show my level of commitment, so I guess my visit here at this time is not too premature.

Whatever the case, I believe power to displacement potential makes this motor worth being considered and as for the theoretical speculation to the contrary that I read in that thread, I had to endure similar when I defied "ancient" performance rules stating that you must lower compression in order to run boost, along with other anticipation that I would fail, from individuals who had never attempted, or seen anyone attempt what I was planning to do.

I had actually thought the process through for feasibility after deciding to do it. I built an 11.5:1 compression, port injected GM 60 degree 3900 V6 and boosted it to 7 psi with the help of water/meth injection under boost. The motor was so powerful from the high compression that in a short while it destroyed the 6 speed transmission. It still managed 33 mpg hwy after I damaged it from being impatient while tuning it, by burning a few valves and dropping cylinder pressure in the affected cylinders. I have no doubts it would have done 35 or better had I tested it before the damage. I rebuilt it to 11:1 and ran boost pressure as high as 22 psi on 93 octane with water/methanol injection. I will never build a low compression motor for boost.

I applaud anyone thinking outside the "Box" to try something different in an effort to achieve an outcome that makes it all worth it, with respect to all safety concerns. Theory is just that, theory, but the proof is in the pudding. If we all adhere to the existing rules of the DIY "playbook", there will be no progress beyond those limitations.

Looking forward to surfing the forum and dreaming.
 
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