Has anyone here replaced the LLT engine with a LFX?

JayTee2019 said:

Wow .. please do let us know how it all works out and any pitfalls along the way !

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I got 2 LFX engines delivered. Were supposed to have 40k miles, but both had double the miles they advertised and was not the same VIN as advertised. But I found out the injectors may (or may not) have been interchangeable. The LFX have rubber covers at the top, and the LLT does not. (Same diameter lower stem though) When turning the intake 180 degrees, you have to grind some support braces from the bottom. The aluminum intake adapter will switch from intake to intake, (the adapter and intake gasket are different and will not interchange) The intakes are the same, but the aluminum adapter (and gasket) for the LFX only fits LFX and the adapter (and gasket) for the LLT only fit LLT. I was able to return each engine sent to me and now have an LLT with 50k miles on the way. I gave up on the switch, mainly due to the extra exhaust work, and finding out I was "Mis-led" on the engine miles. I do suggest you check the VIN stamped on any used engine you buy (Last 8) and check the vehicle history. I couldn't have gotten the only 2 screw-ups.

mmaki said:

LLT engines are expensive and hard to find with less than 100k.

LFX engines are cheap and a improved design..

If it is only a matter of modifying the exhaust and other minor things, it seems like the way to go. Unfortunately I haven't found any posts from someone who has done it.

Anyone try this?

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Yes I have done several with a friend.. it's actually quite easy with junkyard parts
You keep the LLT injectors, rails, and pump.
LFX injectors are E85 capable and are too big
You keep the thermostat housing and water pump spout for the upper rad hose.
You keep the coolant temp sensor from the LLT

Use a GMC terrain 3.0 intake manifold, spacer, and throttle body
Use an air intake tube for a 2012 Acadia.
Lengthen the coolant sensor wires for the different location or pull from the harness like I did then retape it.
You need to monkey with the pcv hose. Just a cut and splice no big deal

I had a couple LFX flanges plasma cut and made up new down pipes to the stock cats.

It runs perfect on the factory ecm untuned but if you know someone who has HP Tuners you can make the best of it. Shouldn't be an issue to make 320ish HP (flywheel) with a tune.
All in all if you hunt an LFX is a few hundred dollars and the rest of the parts are peanuts.

Personally I prefer the LFX as it's higher compression and cam profiles give it a bit better throttle response power and fuel economy.

I'm finishing one now. 2012 Lacrosse LFX into 2010 Acadia. I used the LLT rails, high pressure pump, and injectors in the LFX. This required removing a small amount of metal from one intake port to clear the FRP sensor. I turned the LFX intake around and clearanced the underside for the same sensor. I had hoped to use the LLT intake, but it is not tall enough. It hits the cam covers. I was able to use the Acadia intake boot by turning it upside down and making a new PCV tube. I used the Acadia throttle body turned upside down to clear the manifold and lengthened the six wires. The LFX MAP sensor is independent, and the LLT is in the throttle body. As mentioned above, the 3.0 Terrain intake would work better. On the front of the engine I used the Lacrosse converter by trimming the aluminum engine mount bracket and moving the O2 sensor 180 degrees. With junkyard parts, it could be made to look closer to a factory installation. This is a personal vehicle. I wouldn't consider doing one for a customer.

Programming isn't required. Cam position sensors, crank position sensor, cam phasers, etc are the same part numbers between the two engines. The minimal bump in compression and the exhaust duration can easily be compensated for by the ECU.
I would rather mod the exhaust than start pulling heads off a perfectly good engine. Imagine if you spun a bearing the metal with be everywhere throughout that engine including the cam bearings, phasers and every orfice.
If you don't want to mod the exhaust than you can use aftermarket 2018 cats but they're expensive.
I've built 5 of these so far and it's really not that bad.
IMO Hands down the LFX is a better engine than the LLT and I have zero regrets. The integrated manifolds bring the engine up to operating temperature faster, it's far easier to do an oil change with the LFX. This last one I didn't even change the oil filter housing and it's even easier.
Unfortunately the first time you do it yes it can be a burden but now we can bang one out in two days without even thinking about it.
I'll see if I can get some pics of mine here so you can see the end result.