stevieturbo

I dont know about LS1's specifically, but in general I was always under the impression an engine temp of around 160degF was best for producing power, and best economy around 195 degF.

I tried the shim mod, as per the LS1 book. Only real difference I noticed, is that it takes longer to warm up. On cruise in cool weather the temp will drop, but most of the time mine still runs around 190degF monitored via my ecu.

I have a proper 160deg Stat on its way to me now.

PREDATOR-Z

You Will Never See 160*

T/A rocker

There are a few things most folks don't seem to understand about thermostats.
1) the temp a thermostat is rated at (in this case, 160 deg.) is where the stat BEGINS to open. It will not be fully open until about 170-175 deg. So, just because it's rated at 160 deg. does not mean your engine will run at that temp, and also:
2) You have to adjust your fan temps by some means, either a manual switch or through reprogramming the PCM. If you don't adjust the fans, all you get from the lower stat is increased warm-up time, and slightly lower temps when on hwy.
I have a '98, and I tried the shimming mod, and coldest I could get the stat to open was about 160*. Any thicker of a spacer, and the stat would not fully close. So I just went ahead and bought the Hypertech 160.
My running tenps are usually around 180 to 190 on hot days, could be cooler if I programmed the fans to come on sooner, but it seems to run the best that way. I think to cold and maybe you do lose some efficiency?

PREDATOR-Z

You do. LS1/LS6 being a mix of Alum and other alloys need to reach close to 200* for optimum efficiency.