LS Engine Rebuilds: Break-In and Tuning Guide

Congratulations on a job well done—you’ve got a newly rebuilt LS sitting on an engine stand! Though the work of this book is basically over, we wanted to leave you with some final information that will help ensure your engine enjoys a trouble-free reinstallation and startup, followed by a long useful life.

 

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Engine Reinstallation

We finished Chapter 8 on an open-ended note, stating that you would need to reinstall all remaining engine accessories (like the exhaust manifolds and water pump) either while the engine was still on its stand or at the appropriate time during reinstallation. This may be easiest with the engine on its removable subframe (if applicable), or you may have to wait until the engine is already under the hood.

 

 

As with engine removal, reinstallation of your LS engine into your vehicle is beyond the scope of this book. There isn’t much to say here except to use patience, take all appropriate safety pre-cautions, and refer to any photos and notes you took during engine removal to sort out what goes where. Use all fastener torque specifications specified in your GM service manual and have someone else helping you throughout the process—engines and vehicles (along with their chassis components) are heavy and can do serious damage if not handled correctly!

 

Final Preparations

With your engine successfully rein-stalled into the vehicle, it’s time to stop and double-check your work. Carefully examine every inch of the engine bay to make sure you haven’t missed any electrical plugs or forgotten to reconnect any hoses. Once you’re certain everything checks out, use factory-specified procedures to replenish and bleed all fluids (as necessary). These vary by vehicle, but the two fluids you unquestionably will have to refill are coolant and engine oil.

Because the oil galleries of a newly-assembled LS are dry of oil, all engines should ideally be “prelubed” using special equipment. Unfortunately, the design of the LS oil pump does not allow an easy way to do this. In the old days of the Gen I small-block and its distributor-driven pump, prelubing was a simple matter of inserting a drill-operated tool into the distributor hole. But because the pumps of Gen III/IV engines drive off of the crank snout, the oil pump can’t turn separately from the rest of the engine. You should not be overly concerned about this issue, though; most of the time, the assembly lubricants used during final assembly should adequately protect the friction surfaces in the engine during the initial seconds before oil pressure builds.

 

 

This brings us to an important topic that we’ve alluded to earlier, but never had the chance to fully explain: the type of oil to use during initial startup is critical. It is recommended that you use the thickest weight oil you can find that will still work with the bearing clearances you’ve set on your rods and mains. For most engines, the same SAE 30 you used to lubricate parts during final assembly will provide the best protection during startup and the initial miles of operation before your first oil change. Also, this must be a conventional oil—do not use synthetic oils until you have accumulated at least a few thousand miles on your new engine; more on that momentarily. Also, if you have used all the right assembly lubricant in all the right places inside your engine, no fancy oil additives will be needed at startup (although as laws and regulations force oil manufacturers to alter their formulations to include less anti-wear additives, this may become necessary one day soon!).

 

   
 
 

Start-Up

It’s about that time! The moments just before your new motor is started for the first time are easily the most nerve-racking in any engine build. Rest assured, though: if you have taken the time to carefully pre-assemble your engine, been meticulous during final assembly, and double-checked everything under the hood after installation, chances are that you won’t have any problems at startup. Take one last look that oil, coolant, and other fluid levels are topped off. Turn on the ignition, but do not engage the starter; look and listen for anything suspicious. Do this a few times to cycle the fuel pump and build pressure in the fuel rails (they’re probably dry, having been disconnected for so long). This will allow you to check for any fuel leaks. In the exercise of complete caution, you should have a fire extinguisher and battery disconnect wrench close at hand—you can never be too safe!

With the above final items checked, the moment of truth has arrived. Turn the starter; the engine should begin to run almost immediately. Watch that oil pressure comes up within the first few seconds, and do not operate the throttle pedal—your EFI system should command the engine to idle for you. (For high-performance rebuilds that will require extensive custom tuning, you must at least install a “rough” computer calibration that will enable the engine to run for the first time—we’ll discuss more about tuning in a moment.) As the engine starts to warm up, listen for any possible mechanical issues inside the engine (for example, lifters that have failed to pump up), and watch for fuel or other fluid leaks that could arise without warning, at any time. Sight, sound, and smell are all important here, and if you notice anything odd, shut the engine down immediately and figure out what’s wrong.

When the coolant reaches full temperature (indicating that the thermostat has opened), turn the engine off and let it cool awhile. You will then want to top off the coolant; some vehicles require special procedures for this, so refer to your service manual if you are unsure. This may need to be done a few times, as air bubbles may take a few run cycles to find their way out of the system. You should also inspect the oil at this time to make sure it’s still at the full level and to ensure no foreign substances have found their way into it (this could indicate a number of problems, so call your machine shop if you see anything—they’re a good source of advice for pretty much any startup-related issue you might experience).

 

Break-In

During the first miles of operation, the parts inside your new engine will mate to each other during the process we all know as break-in. Despite the fact that today’s engine parts are manufactured to more exacting tolerances than ever before, there is still a microscopic uniqueness to any one piece of metal that comes off of an assembly line or out of a machinist’s vertical hone. Think of this mating like the last step in machining: all surfaces that contact one another finish each other to the point they’ll operate at for the useful life of the engine. The problem is that if we try to rush this initial wear-in, engine parts will instead wear out prematurely.

Even though advents like the LS’s rollerized valvetrain mean break-in procedures are far less involved than small-block engines of decades past, the following tips should be followed to ensure long component life:

Use a variety of engine speeds

Frequently vary your engine RPM and load for at least the first 500 miles, and avoid high-RPM usage and full-throttle operation during this time. Conversely, don’t “baby” the engine constantly at very low-throttle, low-RPM conditions.

 

 

Keep the oil clean

A substantial amount of metal particulate (from rings, bearings, and other surfaces) will find its way into the engine oil during break-in, and this is normal. Keep the engine oil clean by using a high-quality oil filter and by changing the oil after 100, 500, and 1,500 miles. You can then switch to a normal oil change schedule.

No synthetics

Do not use synthetic oil for these first few oil changes. It is important that piston rings wear in the correct manner to form a proper seal with the cylinder walls; if this does not happen, it will greatly compromise efficiency and horsepower. If synthetics are used too soon, they may never allow full ring seal to occur; and in severe cases, they can even require tearing an engine down to deglaze the cylinders! Use of synthetics after break-in is not only perfectly permissible, but strongly recommended for long engine life and increased engine efficiency.(Please note that some LS engines received a “factory fill” of synthetic oil when new. GM and other OEMs specifically tailor cylinder wall finishes and piston ring types to allow use of synthetics from day one; because these characteristics in your rebuilt engine are most likely different, you should not do the same.)

 

   
 

ECM/PCM Tuning

The days of simple carburetor jet swaps and distributor twists resulting in a properly-tuned small-block are long gone. Today, the same parameters are controlled by a complex set of sensors and computerized control unit(s) that make up an electronic fuel injection system. While it takes a little more know-how to properly adjust such a system, there is little argument that modern EFI systems make high-output engines much more driver-friendly, fuel efficient, and—perhaps best of all—produce more torque and horsepower. We simply do not have the space here to discuss the ins-and-outs of tuning these systems, but here’s a quick rundown of the basic issues you may need to deal with.

While stock rebuilds will require no changes to ECM or PCM calibration (the possibility of a CKP Learn excepted), high-performance rebuilds are a different story entirely. LS engines that incorporate the likes of extra cubic inches, higher-flow heads, and/or larger fuel injectors will not run properly, or at all, without changes to the engine computer’s internal maps. Exactly how much recalibration you will need is a question of degree. Engines that incorporate minor internal modifications like small camshafts (or external bolt-ons like exhaust headers) may not require many changes, but some recalibration will still need to be performed. In this case, you may consider picking up a so-called tuning suite such as those made by EFILive or HP Tuners.

 

 

 

While the core features of most tuning tools are fairly easy to learn and will enable you to achieve satisfactory results (if you’re careful), highly-modified engines would require learning the tuning program in its entirety and constructing all engine maps from the ground up. The time commitment needed to do this would be immense, and the process would be fraught with dangers—one wrong keystroke could destroy your new engine! Probably the best option, then, for most high-performance rebuilds is to get a specialized shop to perform a full custom tune on your vehicle. See our “Tuning Shops” Workbench Tip for more information. Extremely radical engines can even eclipse the capabilities of stock engine computers, in which you may need to have such a shop install and tune a standalone aftermarket EFI system. Note, however, that the need for this type of system isn’t as common as it used to be on GM high-performance vehicles—LS engine controllers are much more intelligent and adjustable than earlier iterations from the 1980s and early 1990s, and so can simply be recalibrated to match the vast majority of high-performance scenarios.

Conclusion

If you’ve gone through this Work-bench book step-by-step, you will have a fully rebuilt (and properly tuned) LS engine at this point. But there is one final step to take, and that is to get out there and enjoy it! I sincerely hope you’ve found the process of rebuilding your Gen III or IV LS engine to be as rewarding as its end product. Thanks for reading. —Chris Werner

 

 

Written by Chris Werner and Posted with Permission of CarTechBooks

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