New GM 5.7 next Saturday

[RatherBeLucky]

I'm having a brand new GM 5.7 crate motor installed next Saturday in my 99(OBS) K 1500. I'm looking for break in advice, bolt on performance parts advice and any general information you guys can give me. I'm new to all this! It seems these engines should make a lot more power than the stock horsepower rating!

 

[slowburb]

You need to run it at varying engine speeds and allow the engine to slow the truck down by using your gear selector. IOW, put it in 2nd, and run up to 4000-4500 rpm, then let off the throttle and let it decelerate. Same in 3rd. Do that a few times and cruise for a while. You're trying to seat the rings by doing this. A replacement 350 for a '99 truck should be an L31 with roller cam and lifters so you don't need to concern yourself with this aspect of an engine break-in or run-in.

Bolt on performance for an L31...headers/exhaust, maybe pulleys, and maybe rocker arms. The best bang for the buck would be to have your computer flashed with a better "tune", that changes the spark and fuel maps, shift points, torque management settings, etc.

 

[RatherBeLucky]

Thanks a bunch, Slowburb!

 

[Ironhead]

By letting off on the throttle, you create a high vacuum in the cylinders, which draws a bit of oil by the rings, which helps the break in process. Some hard pulling helps seat the rings, but these newer engines are extremely well machined, and don't require extensive break in procedures as engines did 20 or more years ago.

As for the initial oil fill, I'd probably just go with 5W-30, even synthetic, as some new cars (BMW) come factory filled with synthetic. Some folks, though, figure that using dyno oil for the first fill helps the ring seating process. Opinions, opinions, opinions..