There’s nothing new about building an LS engine — we’ve all seen it done many times over. But, what about an aggressive, yet streetable, naturally aspirated combination? Today, we travel the path less taken to see if we can make well over 700 horsepower at somewhere north of 8,000 rpm. And, we’ll do it with non-extravagant and mostly off-the-shelf parts. We headed to QMP Racing in Chatsworth, CA to get started on this LS engine build.
Pouring The Foundation
The foundation for any engine combination is the block. If you want to go with a large bore — larger than 4.060 inches — then an aftermarket LS block is in your future. The one that suited our needs was Dart’s SHP LS Next Pro iron block. Dart’s “Pro” version of the block comes standard with 7/16-inch main studs instead of bolts and carries a 220 Brinell hardness. That puts the hardness about 25-percent greater than a standard LS Next block, and thus, more rigid. Furthermore, we upgraded the cylinder head bolt-holes to half-inch diameter to provide better clamping force against the .625-inch thick deck surface.
Priority main oiling is something you will find in every Dart block. It does exactly what the name implies. Oil is first channeled to the main bearings before heading up to the cam and through the rest of the valvetrain. The LS Next cylinder barrels have been extended by .375-inch, providing additional skirt support on long-stroke applications while still providing enough clearance for an eight-counterweight crankshaft. A full-skirt block design accepts standard LS oil pans, while steel main caps provide all the needed support. Best of all is that everything bolts up to the Dart block as it would to a stock LS block.
We utilized Dart’s block prep service, which includes a final hone along with all of the block’s plugs and caps installed. We originally spec’d the block out to a 4.165 bore but later decided to go with Dart’s max recommended bore of 4.185 right out of the gate. To achieve that final bore, QMP Racing Engines performed its full “hot hone” service on the block.
The service entails the block being honed normally until slightly under the desired final bore diameter. From there the block is pumped full of 150-degree coolant, bringing it, as well as the honing stones, up to temperature, in order to induce thermal expansion prior to honing. The block is final-honed at the elevated temperature to ensure the bores are as straight as possible when the engine is at operating temperature.
Eight Is Better Than Six
Residing between the main caps, also from Dart, is the trick, eight-counterweight 4.000-inch billet-4340-steel crankshaft. A standard LS crank has six counterweights — none of which are on the center of the crank. What happens is that the crankshaft will want to “jump rope” in the middle at high-RPM. Since we want to spin our LS over 8,000 rpm, the extra center counterweights help alleviate that problem. Combined with a 4.185-inch bore the crankshaft’s 4.000-inch stroke means we ended up with 440 cubic-inches of displacement.
Hanging off of the crankshaft is a set of K1 Technologies 6.125-inch LS connecting rods. We wanted an affordable but light H-beam road to reduce our reciprocating weight and the K1’s checked all the boxes. The forged 4340 steel rods come fully finished and weigh-in around 660 grams each. Due to the expected RPM range of this engine, we opted to swap out the ARP 2000 rod bolts that come standard, for a set of high strength ARP Custom Age 625-plus rod bolts. These stronger bolts will provide peace-of-mind above 8,000 rpm and require a whopping 100 lb-ft of torque to achieve the proper bolt stretch of .0058-.0060 inch. Upgrading to the 625+ bolts did require us to have QMP rehone the big ends of the rods.
The last component of our rotating assembly is a set of ultra-trick custom JE pistons. Designed for a 13.2:1 compression ratio, these pistons are built on JE’s Aligned Grainflow Technology forgings — the same forgings used in JE’s Ultra Series line. The Aligned Grainflow means that the way the piston is forged aligns the grain structure in critical areas of the piston. That enhanced grain structure allows areas like the piston crown to be machined thinner than normal without a loss of strength. That means that these pistons will withstand the rigors of street driving, while only weighing a scant 378 grams.
A combination of attributes is required in addition to the forging to make the piston that light. A fully machined crown eliminates sharp edges and promotes flame propagation, while the thermal barrier crown coating reflects heat back into the chamber. The undercrown of the piston is also machined to provide a perfectly even crown thickness.
An asymmetrical skirt design reduces the skirt’s contact patch with the bore which both reduces piston weight and friction within the cylinder. Lateral gas ports provide increased ring seal with the 1.0mm/1.0mm/2.0mm ring pack. Holding the rod and piston together is a Trend Performance Diamond-Like Carbon (DLC)-coated wrist pin. This coating procedure reduces friction and wear in the most stressed part of the short-block.
The Heart Of The Short-Block
When you hear “8,000 rpm” and “streetable” you probably have some conflicting emotions. Sure, you can make a naturally aspirated engine spin to the moon, but the real challenge is getting it to make power up there. The key to that is the camshaft. When it comes to selecting a camshaft to make power at high-RPM, there’s one phone number at the top of the list.
We enlisted COMP Cams’ camshaft design guru Billy Godbold, and his suggestion is the company’s line of MGZ lobes. “The MGZ series has a very interesting story. After about a week of testing new designs on the Spintron, we went to the dyno with these lobes and were quite impressed at the performance in an 8,000-rpm turbocharged cathedral port application,” says Godbold.
“About the same time, another good friend was building an LS7-based engine package for circle track applications. For his combo, we kept the MGZ on the intake, but tried the EHX/ESX series lobe that was mainly used in Factory Shootout style applications on the exhaust. The results were awesome. He was making more power everywhere and it was stable 1,000-plus rpm higher than the more typical hydraulic roller lobes he tried. Peak to peak comparisons were even better than the average numbers as the large head loved to put in the work upstairs.”
Godbold continued, “Since then, we have used the new MGZ package on a number of more race-oriented applications. They probably are not the best lobes for an engine that will never go past 5,500 rpm, and they are likely not as quiet as you would want in a near-stock CTS-V. However, if you want a camshaft for a ‘ringer’ LS race engine, we have something perfect.”
On the intake side, an MGZ 23502 lobe measures 250 degrees of duration at .050-inch of lift with a gross lift at the valve of .684 inch, with a 1.8:1 ratio rocker arm. For the exhaust lobe, an EHX-series 12701 lobe was chosen. It has 267 degrees of duration at .050-inch of lift. With .675 inch of valve lift.
The best camshaft grind in the world isn’t worth a hill of beans if it isn’t kept in proper time with the crankshaft. To ensure that, we used a COMP billet single-roller timing set. Not only is it a reliable timing set, but it allows us to ensure the camshaft is installed exactly where the cam card calls for.
One trick of the trade when it comes to freeing up horsepower and reducing windage is a dry-sump oiling system. Aviaid manufactures several kits designed specifically for the LS platform, including direct-fit oil pans and pumps. We opted for Aviaid’s three-stage LS “C” Series 2 kit. Dual pan pickups scavenge the oil out of the pan and route it to the kit’s 2.5-gallon tank. The ATI damper included in the kit has a splined hub to drive the oil pump off the backside, minimizing accessory overhang.
That wraps up the short-block build on our high-winding streetable LS build. Stay tuned as we finish the long-block and strap our mill to the dyno!