I had zero intention of further responding to you in this discussion but, this is flat out wrong. there are a ton of changes, some of which make certain engines unique to only their original applications.AngelMarc wrote: Thu Mar 26, 2026 3:13 pm And drawing a line between 3100, 3400, 3500, and 3900, is like saying an LQ4 isn't an LS.
LQ4-LS1 almost every single part can be interchanged directly with no modification whatsoever. even GEN III smallblock to GEN IV smallblock can largely interchange most parts without issue. The differences would be more similar to the differences between GEN I and GEN II (optispark LT1) small block Chevy engines, that said, they aren't even that similar. For context, I currently own a 2.8 gen 1, a gen 3 3400, 2 LX9 3500's, 1 LZ4 3500, and 1 LZ9 3900. I've swapped a LX9 3500 into a Fiero, (both with external crank triggers+a P04 and an MS3 pro) helped swap a 3900 into a Fiero with a 5 speed and a E67, I did a HCI+5 speed swap on a 3400 Grand AM, have developed and sold parts for these engines, 3d scanned+developed digital models of them/parts of them, and am even a moderator of 2 facebook groups related to these engines for whatever that's worth. I've also spent countless hours pouring over P04 PCM's from a application, wiring, and tuning standpoint, and tried to get further into the PCM code. note the differences I'm listing below are not all inclusive.
I don't consider myself to be a subject matter expert for every engine family out there, but these engines I'm very well versed in, so I again say your assumption is very wrong.
2.8's, 3.1's, and 3.4's have iron heads for gen 1, and aluminum for gen 2, all gen 1 and 2 engines have flat tappet cams, some use distributors, some have crank position sensors and distributorless ignition system that's effectively a solid state distributor. the iron head gen 1 3.4's have cam position sensor provisions. gen 2 aluminum head engines have high flow splayed valve ports and are very different from the iron head gen 1.
The gen 3 3100, and MOST 3400's are largely a direct interchange between one another, almost every difference can be addressed in the calibration without issue. and all use a distributorless ignition system that was similar to the gen 2. the heads are a similar design to gen 2, with improvements, some 3100's have different intakes, some of the heads have minor revision changes. most OBD2 applications use a P04 PCM.
the LX9 3500 is the most similar to a 3100/3400, but the block casting is specific to the LX9, it has a larger bore, piston oil squirters for cylinder 5/6, a different crankshaft with the LS1 style crank position sensor, heads with raised ports, and a matching intake manifold. the ignition system is a wasted spark setup with three coils driven directly by the PCM. the throttle is DBW, and controlled from the PCM directly. The PCM is not a P04, and last I checked is largely unsupported. there are a ton of parts that can be swapped between the LX9 and early 3400's, but many may require other modifications, like grinding the intake to clear a 3400 fuel pressure regulator when the upper intake manifolds are swapped.
The LNJ 3400 is a unique engine, with a ton of unique parts, it's similar, but uses a different crankshaft, and a larger diameter camshaft, the block casting has many bosses that the earlier 3400's do not and like the LX9 is a specific piece. the LNJ also uses a 3 coil wasted spark setup like the LX9. it also does not use a P04 PCM. LNJ and LX9 blocks are both cast with the sides of the block contouring the cylinders, the earlier engines all have flat sided blocks.
The VVT 3500 and 3900 use yet another different engine block, the cylinder bores are moved outboard of the crank centerline 1.5mm, piston oil squirters are incorporated onto every cylinder. the front motor mount boss is now a single bolt, and in t a different location than either of the two mount bolts used on the earlier engines, the timing cover bolt pattern is the same, but several bolts are smaller, the block side bosses are in similar locations to the LX9. The timing cover incorporate the thermostat, on the suction side of the water pump, like a gen II or gen III SBC. the crank position sensor is now a 58x sensor like the gen IV smallblock. The crank and cam position sensors are different than the LX9, early 3400, and LNJ. the cylinder hears have significantly enlarged ports, while the bolt pattern is the same, the combustion chambers will overhang the deck on the earlier engines, due to the later engine having a bigger bore. The exhaust flange has a different pattern, the coolant flows out of the front of the cylinder head near the timing cover, and through a coolant log on the front of the engine back to the water pump. the 3900 oiling system is revised with a larger oil feed to the first cam bearing and to support VVT and squirters. the oil pump is larger and not compatible with the earlier engines despite fitting the earlier engines main cap, the oil pan has a bump to fit the enlarged oil pump, and a cutout to fit the oil filter, due to the oil filter being on an angled adapter, it does not share the same bolt pattern as the earlier engines. the cam is the same diameter as the LNJ cam, but a physically different due to the modifications for adding VVT. the camshaft base circle is significantly larger and the lifter bores are taller on the block to keep the oil band on the lifter from exiting the bore. some engines have provisions for displacement on demand. the 3500's and 3900's use "E" series PCM's, IE E67, E40, E38 ect.
plenty of other engines have similar coolant flow strategies, the problem was not a coolant flow problem, it was a gasket design and coolant chemistry problem.AngelMarc wrote: Thu Mar 26, 2026 3:13 pm Some of them have VVT and the bigger 2 (later model cars) have a coolant crossover that isn't integrated into the intake manifold, to address the coolant in oil problem the earlier engines had.
