LQ4 into a 3rd Gen/1972 Nova by frojoe

4 minute(s) of a 891 minute read

Alright fellas, time for a bit of an update.. hopefully the subscribers to this thread haven't run off to bigger and more interesting things!

So after beating on this thing on the street for the better part of 3 springs summers and falls, it's time for an engine refresh. My oil pressure has always been 40psi cold and ~30psi hot at idle, spiking up to 80psi under rpm, but after a HOT day in early September with about an hour stuck in traffic, I noticed my idle oil pressure go down to 29psi, then 28, then 27, eventually settling around 26psi. I pulled over, waited about 30mins for the engine to cool down, then drove it home keeping out of boost. I parked it for a while, took it for a spin or two in the colder dense air, and it always idled at 30psi, but then dipped down to 27-28psi after one spirited drive. Parked the car and changed the oil soon after, and found some copper powder in the oil. I'm lead to believe this could be cam bearings, but either way then engine is coming out.. I need moar everything.

If the engine is coming apart, I might as well stroke it. As I've been doing research, I originally was going to go as big as 4.060" on the LQ4 block, depending on how it ultrasounded, but apparently that's good most of the time for N/A but is pushing it for even medium boost on an iron block that checks out thick. It seems 4.030" bore is good almost universally (of course I'd get the block checked first) and that would give 408cid. I would have a big range of piston choices between 15cc dish and up to 32cc dish giving 9.7:1 down to 8.4:1 compression ratios. The ones I'd be eyeing are Wiseco 25cc and 20cc dish which would give I believe 8.64:1 and 9.27:1 compression ratios (off the top of my head, I'll post my evaluation spreadsheet later). I already have this block, but would likely be into it for $500-750 CDN of machine shop time after checking, cleaning, bore & hone, and possible deck check as well (mains and cam bores were checked before last rebuild and were mint). There are few off-the-shelf deep dish piston options for 4.035" and 4.040" if I needed to rebuild again later on.

The other option is a new LS3 block. I'd be able to run it at 4.065" right from the start giving 415cid, and would have 4.070" and 4.075" to expand to in the future. Not to mention I'd be ahead in lighter weight, and the block would be reinforced so potentially same wall strength compared to a 0.030" bored LQ4. It would cost me probably $1800 CDN, but my brain could justify that for weight and newer engineering of the block etc reasons.

LSX block & 6-bolt heads is out of the question for both total cost as well as added weight.. this isn't a 25psi+ 1500whp drag racer, it's a street driver (eventually road track too) car that sees boost but also cruising and a bunch of idle.. I just don't see the need.

I'd keep my cathedral port 317 heads for now (71.06cc chambers), along with LS9 head gaskets (4.100" bore x 0.051" compressed) all of which dimensions I used for the above compression ratio calcs. I could potentially upgrade to LS3 or LSA/LS9 heads in the future for a stronger casting, but more importantly a likely better intake flow. Changing to a 70cc chamber LS3 head will increase the compression ratio of any combo I decide on by ~0.1:1.

I know that once you add boost you technically don't need to lose sleep over how free-flowing the intake/heads/piping/etc is, but me being an engineer I like the idea of eventually having all the individual components be as free flowing as they can.. I like to think they may all add up for non-boost low end or something, but if for no other reason than simply just on principle.

So.. who here has an opinion on: 1) keep what I have and make it a 408, or 2) buy new for ~$1000 more and have a lighter 416, all other details considered the same?