Selecting The Perfect Pistons With United Engine & Machine

The performance automotive aftermarket latched on to the LS platform as soon as it was released in 1997, and by doing so it elevated the status of GM’s masterpiece and has since become one of the most attractive and available powerplants of all time. We certainly can’t think of any engine that has made its way into more applications than the LS. To date, we’ve seen this platform power thousands — if not millions — of classic cars and hot rods, along with imports and even a few motorcycles and airplanes. It seems that this engine will fit in just about anything with little effort and is a vast improvement over any Gen I small-block Chevrolet. And due to the cost and ease of swapping, this package makes sense.

Big-Block versus LS

Since summer is coming to an end, we decided to start another project with our 21-foot Baja boat. And while we need another project like we need another high-mileage 4L60e in our arsenal — which we don’t—, we think this swap will be attractive on many levels. For starters, the craft came with a 454 cubic-inch big-block, and a robust Bravo One outdrive. Over the years, we’ve continued with the big-cubic-inch theme with several variations of BBCs, with the latest being a 489 cubic-inch engine with a cast-iron block and heads. This combination makes decent power at 605 horsepower and 600 lb-ft of torque on pump gas, however, this engine weighs around 680-pounds according to the internet. So the question is, how would the boat perform with an all-aluminum LS engine nestled in the engine compartment?

While we know we’ll be hard-pressed to make the big-block power numbers with a 5.3-liter LM4 LS engine on pump fuel, we will lose at least 220-pounds with the swap. This thought was enough to get our brains churning, and we needed something to do over the winter anyway. So, out with the old big-block and in with the LS.

As we started to plan for this engine swap, we knew that the block needed to be cleaned up and bored. So, we decided this would be the perfect time to punch the aluminum 5.3 to 5.7-liters. This move would get us a few more cubic inches, 325 to 347 to be exact, and without breaking the bank, because these pistons should be readily available from the manufacturer. And our assumption was correct as we found what we needed on the United Engine & Machine (UEM) website.

We reached out to Marko Glush, Sales and Tech at UEM, to tell him about this ridiculous plan, which will include a supercharger at some point, and get his professional recommendation on the best piston for our application. Right out of the gate, Glush said cast pistons were not the first choice for applications with power adders. “A cast piston would be the weak link in any application that produces high cylinder pressures such as boosted or a nitrous application. This is because the chance of detonation increases with the higher pressures, the detonation shock waves, and increased combustion chamber temperatures force the piston to flex. The factory pistons are high silicon cast that handles the job of lasting for well over 100,000 miles, but they don’t flex well without cracking or breaking ring lands. Also, the factory ring end gaps are too close together for the increased combustion temperatures that a power adder can produce.”

Forged Pistons versus Cast

After talking with Glush, we knew that we needed a forged piston, since we plan on adding a power adder down the road. But, you might be wondering what makes a forged piston better. Sure, we’ve all heard that they’re certainly stronger and can handle more abuse than cast, but there’s more to it than just that.

“Forged pistons have a higher ductility rating, allowing them to flex without fracturing under detonation conditions,” Glush explained. “They also offer ring groove sizes to accept an upgraded ring material package that will live with high loads and temperatures.” And that’s not all…Glush also told us that the ICON forged pistons offer direct pressure-fed wrist pin oiling for increased heavy loads from higher combustion chamber pressures.

If mechanical failure should occur with a forged piston, it will stay intact better than a cast unit. So let’s say, for example, a valve strikes a piston; the forged piston will likely deform but not break. If a cast piston is used in the same scenario, it may break apart, allowing the rod to swing freely in the cylinder bore and destroy the engine block. Now instead of just having to replace one piston, you might need to build a new engine.

When it comes to disadvantages with a forged piston, it’s safe to say that there are not many. Admittedly, they are a little more expensive than the cast counterpart, but the peace of mind with the added strength is worth it, in our opinion. The only other downside is forged pistons may have a heavier gram weight, meaning the rotating assembly balance should be checked by the machine shop.

ICON FHR versus Premium

Once we knew we needed forged pistons, we needed to decide which one would be best for our application, the ICON FHR or the Premium line. Glush said, “Our ICON Formed Head Relief (FHR) Series is forged from a 4032 alloy, with most numbers having ‘As Forged’ valve reliefs. These pistons come with UltraWearM42 anti-scuff skirt coating and are targeted for street, strip, and marine applications and can be used with mild power adders.”

At this point, we were already sold, as the description sounded like the perfect piston for our needs, as Glush mentioned marine and power adder in the same sentence. However, we wanted to be sure and again got Glush’s opinion. He said, “The ICON Premium Series pistons are forged from either 2618 or 4032, depending on the application. These pistons offer fully machined valve pockets, drilled oil drain back holes, second land accumulator groove, and polished piston tops. Some “race” part numbers have lateral gas porting to improve the top ring seal — this series targets the race/street with high compression or high output power adders.”

The ICON Premium Series pistons were a little more than we needed for our LS boat project. Even with a supercharger, we’re only looking to hit the 600 horsepower mark, which is right in the FHR’s wheelhouse. The Premium line is rated at 600 to 1,500 horsepower, depending on the application, which is way more than we would require for this combination.

Coatings

Just in the last few years, coatings have become an essential part of the automotive aftermarket, and companies like UEM have found different ways of using them to their advantage. In fact, just a few years ago, a self-fitting abradable skirt coating was unheard of. But today, UEM offers its LINE2LINE abradable skirt coating, which dramatically stabilizes the piston during operation, limiting piston rock noise and aiding in optimum ring seal. UEM also utilizes thermal barrier coatings, which offer less heat migration into the piston.

“Adding a thermal barrier coating to the crown of a piston will increase the service life of any engine build but mainly benefits high output applications, Glush explained. “Although all forged pistons are heat-treated to increase the aluminum’s hardness, each heat cycle deteriorates the heat treatment. The thermal barrier coating helps maintain the hardness and reduces material fatigue by limiting the piston’s heat saturation. Another performance gain of a thermal barrier is that the combustion heat is reflected into the chamber, producing more power.”

On The Shelf And Ready To Rock

By now, you’ve probably realized that the current pandemic is wreaking havoc across the automotive industry with supply and demand problems. However, UEM has a vast inventory of ready-to-ship part numbers. So if it’s in their catalog, they strive to have it on the shelf. And this was the case with our pistons.

We ordered a set of ICON FHR LS1 pistons (PN IC9988CKTS.STD) per Glushs’ recommendation. This part number includes pistons for a 3.898 bore, wrist pins, 1.5mm, 1.5mm, 3.0mm ring set, and locks. The FHR pistons will take our compression up to 10.67:1 with a 61.15cc cambered head, which will be fine with pump gas in the tank. However, Glush did suggest using a thicker head gasket or swapping out the cylinder heads to drop the compression a little when we bolt on the supercharger down the road. And we will keep you posted on that project when we get closer.

Off To The Machine Shop

After a couple of days, the ICON pistons showed up at our door, and we couldn’t help but open them up and get a peek before heading off to Keeter Performance Engineering (KPE) for the machine work. As expected, the pistons were flawless with a coating to match. We were curious to see how much the FHR pistons weighed compared to the less durable GM cast pistons and asked Tommy Keeter, the owner of KPE, to let us know the differences between the two. The cast GM pistons tipped the scales at 603.5-grams with the wrist pins and rings. We were surprised to see the ICON FHR’s weighed 600.4-grams with the wrist pins, retainers, and ring set.

With the pistons in hand, Keeter went to work on the engine as he balanced the rotating assembly for us, decked the block, and bored the cylinders from 3.780- to 3.898-inches before honing it. Now, all we need to do is put it together and get it installed in the boat before spring arrives in 2022. And while that sounds like a simple task, for some reason, things never go as planned.

If you’re in the market for a new set of pistons and are unsure what you need for your application, you can visit UEM’s website for more information. Its website is up to date with the latest products, and offers unique tools like a compression calculator, distributors lists, and you can even “Ask the Pros” with the click of a button. For a personal recommendation call the UEM Tech line at 800-648-7970 or email the tech department at [email protected]. They will make sure you get the best piston and ring combination for your particular application.

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About the author

Brian Havins

A gearhead for life, Brian is obsessed with all things fast. Banging gears, turning wrenches, and praying while spraying are just a few of his favorite things.
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