The Merc 5.7L Vortec is a GM engine design that uses Vortec Heads. These heads are much more efficient due to improved flow. Some people go back and add these to older GM 5.7L and 350 engines for better performance and improved horsepower. Did you buy the engine or have someone rebuild it? In either case, check to see if the already did the initial break in..
For a never run engine, here is my break in process:
First, break-in oil is critical and should be used for the initial run in. I am using Gibbs BR30 break-oil but had to order it as it isn't readily available at most local auto stores. DO NOT use synthetic oil for the initial break-in as the engine likely won't break-in properly. I am in final assembly of my newly built (did it myself) and plan to start it up, set the initial timing at idle (may already be done on your engine???). I plan to run it at about 2,500 to 3,000 rpm varying it a few hundred rpm for the first 30 minutes but holding it steady in that rpm range (watch the temperature). At 30 minutes I will shut it down, change the filter and then do another 30 minutes or so at the same rpm but varying it from 2,000 to about 4,000 rpm briefly every 5 minutes or so.. After the break in, I will again change the filter and this time the oil. I would use a non-synthetic oil then for about the first 5 to 10 hours of run time. After that going to go to full synthetic..
This is just the way I plan to do it... I suggest you Google "how to break in a Chev 5.7L Vortec engine" and read through the various literature to find the way you think will work best for you... You will even find people of the opinion that you should "drive it like you stole it for break in". The argument there is that the new technologies don't require a break in the old way. I prefer to do it as above that I described...
Hope this helps....
