LS engines are great, but they’ve got a couple of weak points when people start boosting them.
Pistons are the most common failure (we’re looking at you #7) and rods are the next common failure point.
Starting with the pistons, the ring end-gaps are tight from the factory and weren’t intended for the heat produced with boost or nitrous.
When the gaps go solid, the ring tacos, which can break the top or second ring land.
A solution for that emerged earlier this year when Summit Racing introduced its line of 2618 alloy forged Pro LS pistons.
Those pistons are packed with technology, but priced affordably. Built for boost and nitrous, they also come in multiple compression ratios.
Some details on the Summit Racing Pro LS pistons:
- Pro LS 2618 forged pistons
- Made in the USA
- Ultra-modern 2618 alloy forgings for boost and nitrous, with maximum ring land thickness
- 4.8, 5.3, 5.7, 6.0, 6.2 liter standard bores and multiple oversizes
- Variants for each of the three common connecting rods
- Pressure fed pin-oiling with durable chromium steel wristpins
- Specially profiled and coated piston skirts for stroker applications with tight piston-to-wall clearance
- Generous valve reliefs for extra piston-to-valve clearance accommodates both cathedral and rectangle cylinder heads
These are complemented with Summit’s made-in-the-USA piston rings.
- Pro LS premium steel piston rings
- Steel top rings designed for maximum life with boost and nitrous
- File-fit rings for maximum ring seal, reduced friction, and tensions optimized for wet-sump engines
- Martensitic ductile Napier-hook second rings for strength and maximum oil control
- Made in the USA
Summit Racing Pro LS 4340 Forged Steel H-Beam Connecting Rods
Next up, let’s look at the connecting rod issue:
The Gen. 3 rods were thinner than the Gen. 4 rods and the pre-2001 models had weak bolts to boot. The Gen. 4 full-floating rods were tougher, but tuners need to pull timing around peak torque to keep them from bending under boost. That’s no fun!
Enter Summit Racing’s new Pro LS 4340 steel forged H-beam rods. Before we get into how they’re constructed, let’s take a look at the loads they are designed for.
On the power stroke, the connecting rod is seeing extreme compression forces. At the end of the exhaust stroke, it undergoes extreme tension trying to slow down the combined weight of the piston, pin, rings, and connecting rod. To combat this, Pro LS rods use ARP bolts exclusively.
The ARP 2000 bolts are rated at 200,000 psi.
At 7/16 diameter, they’re also 23-percent bigger than the factory’s 9mm bolts. The bolts and beefy double-ribbed rod caps keeps the big end round under extreme loads. The bearing’s oil-film remains intact and proper clearance is maintained.
RPM is often used to rate connecting rods, but it’s not the best way.
At the same 7500 rpm, a long stroke crank is exerting far higher loads on the rod than a short stroke crank. The best way to compare is by looking at piston speed. Pro LS connecting rods are rated for average piston speeds of 5000 feet per minute in drag racing and street applications, and 4750 feet per minute in circle track or road racing applications.
What does this equate to? 5000 feet per minute is the equivalent of a four-inch stroker crank turning 7500 rpm, or a 3.622 stroke turning 8285 rpm.
Piston speed is horsepower, and Pro LS rods give you more of it.
The Pro LS rods fit the Pro LS pistons perfectly, with minimal side clearance between the piston’s pin towers. This maximizes shear strength and gives the pin far greater resistance to bending.
Here are details on the connecting rods:
- Pro LS 4340 forged H-beam connecting rods
- Designed for 5000 feet-per-minute average piston speed in street and drag applications
- 7/16 ARP 2000 rod bolts with 200,000 psi tensile strength. They’re 23-percent bigger than the factory’s 9mm bolts.
- Dual-ribbed caps for maximum strength
- Added stroker clearance allows up to a 4.250 stroke crank to clear a standard base circle cam
- Balanced to within +/- 1 gram per end
- Full-floating and precision-honed in the USA to +/- .0001 in.
- 6.125 in. with .927 pin, and 6.098 with .945 pin variants available
A side note on the .945 pin version: A side benefit of using the 6.098 .945 pin version is the extra strength of the pin versus common .927 pin pistons. The larger diameter standard material pin is stronger than a .927 pin and will hang in there a little longer before switching to expensive (and heavy) tool-steel pins becomes a good idea. Pro LS pistons have a .945 pin variant that includes Spirolox and grooves for correct clearance.
Summit Racing Pro LS 4340 Forged Steel Crankshaft
With the connecting rod program on track, it made sense to continue with 4340 forged steel cranks. These are offered in standard 3.622-in. and 4-in. stroke versions along with your choice of 24X or 58X reluctor rings. Here are some details on those:
- Pro LS 4340 Forged Steel Crank
- Core hardened to optimum strength, tempered and nitride hardened
- Lightening rod journals, gun-drilled mains, profiled counterweights for lower windage and better engine acceleration
- Maximum journal tolerances of +/- .0001 to ensure consistent bearing clearance
- Straight-shot oiling for maximum oil film strength at the maximum load angle
Summit Racing Pro LS Rotating Assemblies
With the Pro LS pistons, cranks, and rods all currently available; the next logical step is complete Summit Racing Pro LS rotating assemblies.
It’s not uncommon for rotating assemblies to be limited to a single bore size and a couple of compression ratios.
Our friends at Summit Racing got to thinking “Why stop there? Why not make a rotating assembly for every one of the pistons, along with each over-size?”
The result was 227 different assemblies.
It’s pretty quick and easy to drill down to the right combination of bore, compression ratio, stroke, etc. on SummitRacing.com.
Here are the basics behind the lineup:
- 4.8, 5.3, 5.7, 6.0, and 6.2L combinations.
- 2618 Alloy Forged Pistons
- Mid-compression pistons for nitrous
- Slightly reduced compression pistons for boost
- Standard bore and multiple over-sizes
- Premium 1.2 and 1.5mm steel top, Napier second piston rings
- 4340 Forged Steel Cranks
- Standard stroke or 4 in. stroker.
- 24X or 58X reluctor rings
- 4340 Forged Steel H Beam connecting rods
- 6.098 length with a .945 pin
- 6.125 length with a .927 pin
- Premium Main and Rod Bearings
- Clevite H-bearings are designed for high-rpm operation in racing applications
- Tri-metal bearings are designed with high bearing crush for maximum retention
- Medium eccentricity shells with precision wall tolerance of +/- .00015 in.