I wrote up a history of the LD8 Northstar and first posted on it'* own but after reading it back felt it was worthy of being in the sticky so reposted here and deleted the post
Post subject: History of the Northstar LD8 V8
The LD8(VIN Y) and the L37(VIN9) have been confused by many both here and other places and forums as well.
The L37 is the original V8 from Northstar in 1993. It came out as 295Hp and came in the Allante, Eldorado and Seville STS. The LD8 was brought out in 1994, a variation of the L37 and was detuned to 270 Hp by lowering the cam profile for the smaller Caddys. The L37 was offered in some upper trim levels on these smaller models and I think that lead to the confusion that the STS engine was specifically detuned for Pontiac to use. In 1995 refinements were done that added 5 Hp to each engine and both were made thru 2005.
Also in 1994 the L37 block was bored to 87mm (instead of 93mm) and given to Olsmobile to install in the Aurora. Northstar designated this new variant the L47 with 250 Hp.
The LD8 is a cast aluminum block and heads engine and uses a cast aluminun girdle that replaces the main bearing caps. It has four camshafts and four valves per cylinder. The intake valves are 33mm and the exhaust valves are 29mm. the valves have a direct acting lash adjuster over each valve. And three seperate hydraulic tensioners keep it tight and smooth running. If the one of the chains fail or if the engine is cranked over with a chain removed, the engine is destroyed.
The intake on the LD8 is made of a nylon thermoplastic to reduce the heating of airflow.
The ignition on the LD8 started as 4 coil packs and was changed to 8 coil on plugs in 2000. The crankshaft has two sensosr plus a camshaft sensor gives timing inputs. Also there is a knock sensors on rear head of engine between cylinders 1 and 3. This ignition coupled with fuel injector control makes the LD* do tricks. If the PCM fails or if vital sensors to the PCM fail the engine will stay running at a fixed timing of 10 degrees advanced to limp home. If the PCM registers an overheating issue, it directs the ignition module and injectors to fire only four plugs and injectors, alternating, (the air sucked into non firing cylinders cool the engine) and sets timing to allow it to limp home without any coolant in engine. ( I dont think I would trust this feature since you cant monitor the engine temp and there have been reports of the engine "never being the same afterwards.)
The altenators were liquid cooled for all the Caddys electric bells and whistles but went to air cooled in 2001 to rid it of coolant leak warranty problems.
The LD8 is a disposable engine and though a few minor rebuilders doing "cosmetic rebuilds", there are no major rebuilders for this engine . Critical internal parts are unavailableand the steel cylinder liners cant be replaced or overbored. Same with the heads which have the valve seats and guides hard powder coated and seats cant be reground or the guides replaced. It comes with 100,000 mile platinum tipped spark plugs and150,000 mile antifreeze. There are varied thoughts about this extended life antifreeze and some feel it degrades to gaskets. I'm not taking chances and trading it for normal green. Other than oil and oil filer changes the engine is maintenence free.
The diecast aluminum block of the Northstar has always had oil seepage problems. In the ealier models it was so bad it dripped out of the block. In 2000 Northstar invented a "squeeze casting process" to eliminate block porousity but to this day owners are reporting up to a half a quart or more gone at oil change.
The LD8 is a notorious oil burner and carbon deposit maker. They used to removed all the plugs and soak cylinders with a cleaning fluid, then vacuum out the garbage but have since resorted to doing WOT'* and putting the transmission into second gear at higher rpms to make rings rattle to seat better and scrub the uppermost area'* of the cylinders. The cleaner fluid they used in the old days was GM # 12378545. I'm not sure if it'* still available.
Also stripping bolts to acessory items on engine is common and GM offers a rethread kit J42385-2000