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I would not recommend running tighter main clearance on high hp engines period and certainly not on one with a stock crank flopping around in it. They can and will touch down. I would personally run more clearance and a standard weight non-synthetic oil especially anyone running methanol. The Lucas Plus line of racing oils is an excellent choice. They do make it in a 20w-50 and I personally use the straight 50wt Plus oil. I also run pan/oil tank heaters prior to running the engine too. The "plus" is a very high zinc additive package that was developed when Lucas was the title sponsor for NHRA TAFC/TAD. I'm not saying just dump it in and its a cure all. The engine needs to be planned out before building with things like what fuel, what weight oil etc determined and alloances made for them. It can obviously be done other ways but IMHO this is the correct way to go.
I think you're right. Especially for a track only setup. My idea was that with how much heat a half filled block will create if hot lapping, with too much clearance on an alu motor, you're just going to have no oil pressure if you start with like 30 thou on the mains. That has to grow over 45 thou after a few runs... I personally think something like 17 thou is really tight, and wouldn't go more than that for a turbo car probably ever... I know how I have mine set up and it's pretty standard, which is IMHO tight compared to non LS engines, or even iron block ls's.
I have been back and fourth about what oil to run. I think you're also right about oil, but maybe with the wrong reasons behind the thinking.
Data shows zinc lowers oil film strength. But that's actually a good thing, hear me out here.
Data shows that a thicker oil, distributes the load across a greater surface of the bearing radius. A thicker softer, zinc oil, will basically become a wider cushion to absorb the load. Rather than the bearings.
A stronger oil film will distribute that load to the bearing more directly. Like jumping onto a memory foam mattress vs jumping onto carpet.
And this makes sense from what we know about oil weight. Higher weight, we get more heat, more shearing, and more friction inside the oil its self. Which again, makes sense if we approach it understanding that higher weight oil will distribute the load further across the bearing radius.
Now with that in mind the bearings are important to also consider. Depending on the setup, like oem bearings are real soft, they just suck up anything you pound them or slide through there. Then use a thin film to reduce friction, there by reducing heat or energy loss. To improve emissions and mileage (that whole thing is a crock of shit btw, cars really aren't our worst source of emissions).
And we know race bearings are usually really "hard." But that's where we should pause.
A synthetic oil can withstand tremendous temperature, and still contain plenty of zinc. Zinc breaks down during shearing, which is how it actively cushions during the hydro dynamic wedge. But, the thick oil/heavy weight and wider bearing radial load distribution happens when the weight is "fat" enough, not necessarily exclusive to an excessive clearance, or excessive weight.
Because something like a 10w40 can be "too thick" for stock clearances (obviously dependent on the engine specifically). A 60wt in that kind of ultra tight clearance could be bad! Because the journal surface speed is way too high for the oil to continually flow and distribute through such a small window/passage (which is what our oil clearance really is).
So, I think a good synthetic and running more "standard" clearances and something more reasonable in terms of weight is the way to go. There are a lot of synthetics out there that have plenty of zinc in them still readily available, and cheap.
I know of one car (don't want to be too specific out of respect) that runs 200 1/4's, see's street duty, and runs a basic synthetic rotella oil in their LS turbo car. Clearances are not at all big. Bearings always look really good.
I think the other thing to point out is that too loose, and too thick oil will not be good for like hydraulic lifters. Like johnson's would not be good with a 50 or 60wt.
But if you just run the car to do the burnout, the hit, and then go back to the pits pushed by a go-cart... then yeah I would run extra clearances to not have to wait for the block to grow.
A car that can do "it all" can be done with an Aluminum ls. Will go real fast on the 1/4, be totally fine in traffic, be able to take a long cruise in, then beat on some people at the grudges. And the synthetic oils I think enable that.
Furthermore, I know that when you go from like 20 thou to 30 thou you don't get that much increase in film thickness, and continues to have diminishing returns past 30 thou, can't remember what the flow amount changes are in clearance...
There's some data by king for this. But I can't find the site that had a great write up on the loading distribution. You really have to pick the oil, and clearance, for how you want it to work and what you prioritize.
I'm going to try a super high psi film oil and some that are half that have a ton more zinc
