I snipped out most of the quote but thank you for all of that. Helps a lot with knowing what combos I should research before making a decision.
Truck is a 2001 with a 4.3 and NV3500 5 speed.
If I do the L92, the plan is to buy it as complete as possible so I can drop straight in without opening it up and letting out the factory magic dust. I'm assuming I'll need the matching ECU but I plan to get in touch with CPW before hand to see what they recommend.
One of the reasons I was homing in on the L92 was that I thought the VVT could actually be a good thing. I had read a couple comments on LS1tech about good VVT cams being available so it seemed like a good idea for a street only truck. But as I read more it seems like just about everybody does away with the VVT right away. So I'm going to do more research but I'm not as excited about it as I was just a week ago.
I know I don't want to trade low RPM torque for high RPM HP though.
I also know I want an aluminum block though as I really don't want to add additional weight to the truck and especially not up front.
As I see the cost of this creeping higher and higher I've started thinking some about picking up a running Camaro or Trans Am with a complete LS1 and T56. I'm sure that would create a whole new set of issues to research and pay for though.
Camaro's and trans-am's are boring. Camaro's from the 98-02 vintage are especially boring. The new ones are a bit more interesting.
Anyway, about the VVT- what you need to understand is that GM's VVT in the LS engine works by adjusting the retard or advance of the camshaft. This has a disadvantage to other manufacturers that use dual overhead cams, or cam-in-cam designs. In total there is around 20 degrees of advance/retard, I forget the exact number, maybe 22? Anyway doesn't matter as much someone can look that info up.
What matters is GM essentially takes a very mild cam, and moves the intake & exhaust events forward or backward. In doing so they use up most of the non-PTV swept room available for the valve. If you think about the cylinder bore as a 3D volume, at any given time there is a finite amount of space not being occupied by the pistons. If you plot this on graph with time on x axis- it looks like sin wave, because duh, its a piston going back and forth, essentially oscillating. Valves do this too in that they occupy a 3d time & space in time with the movement of the piston.
If you were to fill in the area between 0 and the curves, you get basically "area under the curve", or time that the valve is open to flow air in, and conversely to flow exhaust out.
We want max area for both, generally, but we can't do it all the time... that's where VVT comes in. It allows the engine to run what would otherwise be a very rough cam, but do so with a lot of advance to make it run well at idle, or cold-start up, and then as the rpm climbs it can retard the cam back to benefit the higher rpm's.
Aftermarket VVT cams make a compromise- they generally require phaser limiters, to limit the range of retard/advance from say 22 degrees to say 12 degrees. Boom you lose half the benefit of VVT right there. Meanwhile they still can't provide the same lift and duration values because too much advance on the cam will result in valve to piston kissing.
This is in essence why standard cam's can't be used- they'd cause PTV issues like crazy. Finally tuning for VVT cam is more involved than tuning for a standard cam.
Hence, in performance application there really isn't a whole lot of benefit to VVT in GM's incarnation- its more GM being able to run a higher hp cam while still having a stock sound and good MPG at low rpm's.
Other manufacturers incarnations of VVT are inherently better due to the use of separated intake/exhaust cams, or cam-in-cam designs.
Frankly you probably want the sound of a nice cam anyway- so a non VVT cam will always be better. Which begs the question, why run a VVT cam, and why bother with DoD/AFM period?
Forgive me if I mixed up terms- trying to type it quick and get the general gist across, you're welcome to read more in depth into camshaft design. Anyway, with enough understanding of how the camshaft actually "works" and why it is designed the way it is, you begin to see that GM putting VVT in was looking for an every so slight improvement in stock, consumer driven vehicles, not a massive game changer in the performance world.
As for how to judge the condition of your engine- you can only do so much without tearing it completely apart. But first step is use a compression tester to test cylinder compression. Low comp = worn rings, worn rings = worn skirts and possibly worn bore. But if compression is solid and up near spec- then the rotating aspect of your engine is likely fine.
As for oil- the rear main seal tends to leak with age, it dries/hardens and isn't as flexible as it once was. Can also be the front cover or oil pan gasket. Slow leaks are not a sign of a worn engine- more of an old engine. Knocking, ticking, oil burning, rough idle, low cylinder compression these are more indicative of engine wear issues usually. I have a 4.3 that's got about 200k on it and still purrs like a kitten.
The L76 doesn't get as much love because 1. It is less common, originally used by Holden (as a variant of the LS2), domestically it had a pretty short run and was not a base RPO code engine, and 2. It's a 6.0 displacement, not the 6.2 of the L92, that's mostly why its cheaper.
As for Turboing something... boost and power are relative to number of cylinders... you can turbo your 4.3 and get up to 300hp maybe with the right cam, or you can get a 4.8 which at base level doesn't make a whole lot more than the 4.3, turbo the 4.8 and suddenly you're closing in on 400 pretty easy.
That is generally why more turbo a 5.3/4.8 than the stock 4.3. The L33 5.3 alum turbo'd is a pretty sweet little motor. Those who can generally go bigger displacement, ie 6.0 or 6.2, and those who really can go way big displacement and turbo it!