Hello newish CTS owner and I have very recently been having very harsh misfires on multiple cylinders. I have been toying with the idea of getting a newer LFX for the added power gains and hopefully a better timing chain and I was wondering if there is anything, besides a tune, that would be required to swap these engines.
Swap LLT for LFX
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dschom8123
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You're actually upgrading quite a bit with an LFX bottom end. It's a lighter rotating assembly and a touch more compression. You shouldn't need a tune as the LLT/LFX is very, very close as far as the ECU is concerned. If you run premium (91) then there shouldn't be an issue whatsoever.
I had to make a correction toward the end of post #12 where I mistakenly stated the LLT piston was heavier than the LY7 and GM shortened and tapered the pin in the LLT piston to compensate. The LY7 pin is the heaviest of all of the 3.6L builds. The LFX has a slightly lighter rotating assembly as a result of the single groove harmonic balancer, but that's negligible as far as performance is concerned, particularly when you bring inertia into the calculation. The connecting rods between the LLT and LFX are the same. The pistons are only slightly different in that the LFX pistons have no exhaust valve relief, which is probably what accounts for the slight bump in compression.
The LGX has the heaviest piston at 400 g, the LLT and LY7 are 390 g and although I don't have an LFX piston on hand, I'd expect its wt to be 390 g also.
The LGX piston pin weighs 116 g, the LLT and confidently the LFX weigh 120 g with the LY7 pin coming in on the fat side at 142 g.
The connecting rods for the LY7, LLT and LFX weigh 639 g, although the LY7 rod is shorter and the small end is not tapered.
The LGX has the heaviest piston at 400 g, the LLT and LY7 are 390 g and although I don't have an LFX piston on hand, I'd expect its wt to be 390 g also.
The LGX piston pin weighs 116 g, the LLT and confidently the LFX weigh 120 g with the LY7 pin coming in on the fat side at 142 g.
The connecting rods for the LY7, LLT and LFX weigh 639 g, although the LY7 rod is shorter and the small end is not tapered.
Magoo—2012 Cadillac CTS Luxury, Opulent Blue, plus many more, see signature.
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More good information has been posted.
Just one other thing that's already been stated in the earlier post from @Joseph Upson , but to draw attention to it again in case you missed it, you use the fuel system from the LLT with the LLT PCM. The LFX has a different high pressure pump and different injectors. Using those would require some changes to the PCM calibration maps (a "tune" for the LFX stuff).
All the more reason you should swap the components matched to the crank as well. GM may have changed, or improved the balance on the rotating assembly (trimmed more from the bob wts), requiring a different part number. If the ring packs are lighter that may factor in as well given the LFX has a higher rpm limit than the LLT at about 7200 rpm.
Magoo—2012 Cadillac CTS Luxury, Opulent Blue, plus many more, see signature.
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Based on everything I've seen, including some good information on this thread, I'd swap the short block.
If you're really concerned with the slight compression bump, you could keep the LLT block and pistons and rings (that have already been "mated" and run together), and change out the crankshaft with all the rods from the LFX. But swapping the short block is so much easier without disassembling all the bottom end stuff. Fewer opportunities for mistakes that seriously shorten the remaining service life of the parts that way.
If you're really concerned with the slight compression bump, you could keep the LLT block and pistons and rings (that have already been "mated" and run together), and change out the crankshaft with all the rods from the LFX. But swapping the short block is so much easier without disassembling all the bottom end stuff. Fewer opportunities for mistakes that seriously shorten the remaining service life of the parts that way.
We have completed 2 short block swaps so far, one was an LLT, the other an LY7. Joesph has more data on the actual components than I do but the LFX is superior to the LLT (even if only slightly on a technical level). The biggest upgrade reason from a LLT to an LFX short block is the fact that you're putting in a much newer, lower mileage engine. Because you're only using the short block itself, you can harvest the engine from a transversely mounted car which make the cost of the engine drastically less than one that came from a longitudinally mounted vehicle (CTS, ATS, Camaro, etc.).
The wrecking yards price the Camaro / ATS / CTS engines at a much higher price point because they're going to assume you are swapping the engine directly in. Those are much more valuable cars so the engines are priced accordingly. GM was still making the LFX engine all the way up until last year (maybe they still are). So you'll want to find the newest, lowest mileage engine from something front wheel drive. Impala, Terrain, Equinox, LaCrosse, etc.
You're going to swap in your front timing cover, oil pan and heads. You'll need a top end kit as well (head gaskets, head bolts, etc.), I would consider getting your LLT heads looked at as well to check over the valves and guides and any other wear you might have.
The wrecking yards price the Camaro / ATS / CTS engines at a much higher price point because they're going to assume you are swapping the engine directly in. Those are much more valuable cars so the engines are priced accordingly. GM was still making the LFX engine all the way up until last year (maybe they still are). So you'll want to find the newest, lowest mileage engine from something front wheel drive. Impala, Terrain, Equinox, LaCrosse, etc.
You're going to swap in your front timing cover, oil pan and heads. You'll need a top end kit as well (head gaskets, head bolts, etc.), I would consider getting your LLT heads looked at as well to check over the valves and guides and any other wear you might have.
None at all. 2x fully working engines on the road still. GM is the great recycler
Why, the reliefs would be the same size on both sides of the piston and the intake valves are larger in diameter than the exhaust valves, so there should be considerably more clearance for them. Four valve reliefs may have been a hold over from the first design piston in the LY7. Two less valve reliefs to cut improves production efficiency.
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Any suggestions on the down pipes??
So, I swapped the LLT top end for the LFX short block about 10,000 miles ago. Recently sounded like I head detonation and started using the highest octane gas I could find. It decreased what sounded like detonation/knock, had no way to test it. The octane was 91 to 93 as that is the highest I can find. Last week the car going up a hill lost power and the check engine light started flashing. Needless to say my mechanic said #4 cylinder had very little compression. Any ideas what I should do, this is the second Māoris and I am tired of the car. Just want to get some money out of it and be done and not sell a piece of junk to someone else. I ah e thought about even just making a race car out of it and going that way as well.
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