How to Make 1,300 HP From a STOCK LS Block!

Racers have a very cool habit of finding competition in the most interesting ways. We know of guys who have the world’s fastest leaf spring car, the fastest electric car, heck even the fastest tri-fuel burning car (gas, methanol, and nitro). We suppose that if you wanted to cut the floor pan out of your race car and have the fastest Flintstone-powered car, somebody would grab the cutting torch and try to race you for it.

And although it may seem like a perfect recipe for catastrophic engine carnage, there’s a group of characters out there competing to see who can be the fastest using a stock LS block. As we went to press, the current record was somewhere in the 4.550-second range in the eighth-mile. Drag racer Jason Halam thinks he can top that in his Fox-body Mustang, and contacted engine builder Pete Harrell of Harrell Engine and Dyno to help him get there.

Instead of starting fresh, Harrell felt he could simply rebuild the existing 6.0L iron-block LS engine in Halam’s car. It was already making 1,200 horsepower with a turbo and burning E85, but the engine was at its limit and was having problems with the engine lifting the heads and burning head gaskets.

Harrell regularly builds ridiculous engine combos and is a master track tuner. You can see more of this particular build in the accompanying photos, but what we found most interesting was the steps he took to get a stock iron block to withstand nearly 1,300 horsepower on a preliminary dyno run with plenty more to come at the track once they turn up the boost.

Block Fillers

The LS block is already strong, and choosing one cast in iron helps even more, but it still has its limits. That said, the old-school method of adding a block filler is hard to beat, so that’s one of the first steps when making and OEM block withstand big power.

A block filler is basically concrete that is poured into the engine’s water jackets while wet and allowed to harden. Despite what some may think, you can actually use block filler in high-horsepower street applications. By filling the water jackets only as far as the bottom of the water pump holes, you can still move coolant through the heads and upper portion of the block where all the heat is created. On race-only applications, Harrell says he’ll often completely fill the block. If you are burning methanol or E85 for fuel, which produces less heat than gasoline, things get even easier.

Besides keeping a block from splitting right down the middle, a block filler also helps make power by strengthening the cylinder bores so they stay round despite the incredible pressure created by combustion. “We used to see that with the old 4.6 Modular Ford blocks,” Harrell explains. “To get them to hold power without warping you had to put in the high-dollar cylinder liners. But then when we would add hard block and ARP head studs, the stock cylinder liners could take just about anything. That’s because the block is now hard as a rock; there’s nowhere for the cylinders to move.”

Of course, not all block fillers are created equal. “I like to use Rokblock,” he adds. “Not because it’s really any stronger than other products. I like it because it is machinable, and if I screw up or get a little too much somewhere I can cut it back out. Concrete is permanent. I’ve made enough mistakes in the past and learned that once it is in there, it’s not coming back out. Rokblock is a little more forgiving but does just as good a job at strengthening the block and keeping the cylinders round.

Better Cylinder Sealing

When designing engines, the OEMs are obviously more concerned with efficiency and longevity than how well the blocks will hold up to quadruple-digit horsepower. So even if you can keep them from splitting in half, few have enough—or large enough—head bolt mounting provisions to keep the cylinder heads secure to the block.

As a result, the head bolts will stretch, allowing the head to lift ever so slightly from the block, and you blow a head gasket. Modern multi-layer steel (MLS) gaskets are an improvement over the traditional stuff, but Harrell found they still aren’t enough for this application.

Instead, he turned to a unique design of head gasket from Athena that uses a steel O-ring which cuts into the deck of the cylinder head to create an incredibly strong seal. Athena says they’ve done dyno testing up to 1,950 horsepower with no problems. The Athena gasket works better than cutting an O-ring groove like is common with race engines because on a street engine that is expected to last for long periods between teardowns, it can allow water to leak into the oil. But, because the steel ring in the Athena gasket does bite into the aluminum cylinder head, the heads will have to be decked every time the engine is torn down and rebuilt. Also, these gaskets are a bit pricey at over $400 for a set, but when combined with a set of tool-steel ARP head studs they should cure for good the blown head gasket problem.

Stud Girdles

One of the many ways the modern LS engine is superior to the first-gen small-block is its skirted block design significantly strengthens the crank case, helping the block hold more power.

That negates the need for a stud girdle, but we couldn’t help but ask Harrell how much a stud girdle can help an unskirted small-block or a Ford Windsor. “For a while there, we were really big into building Ford motors, and we tried a lot of different things,” he says.

“When it comes to stud girdles, in my opinion after years of using them, not using them, and trying all different styles, the only thing they are really good for is keeping everything in a nice neat pile when the engine splits.

“We used to split them with and without the stud girdles,” he adds. “It really didn’t seem to matter.”

Before You Build

At Car Craft, we’re not too often in the habit of recommending pricey things like $400 head gaskets, so now we’re going to make up for it with two tips that are absolutely free. The first is to do your proper prep work before assembling anything.

“We spend a lot of time deburring a new block to remove any sharp edges,” Harrell says. “That includes around the mains and any edges where holes have been drilled into the block. Ninety percent of the time when the thing splits, it always goes down a hole—whether it’s a bolt hole, an oiling hole, or something. So anything you can do to relieve any sharp edges you find before you begin building the engine is a good idea.”

Avoid Detonation

Finally, Harrell says that the absolute most important factor when it comes to keeping an OEM block—or any block, for that matter—together despite how much horsepower you are making is to be sure you avoid detonation.

“The number one thing out of all of this has nothing do to with prep or the parts you buy. It is your tune-up. You can do all the other stuff, all the tricks, but if the engine isn’t happy and it detonates, you are going to tear something up. I don’t care if you have a billet block and all the best internals, if the engine rattles things are going to go bad. So the number-one thing is making sure the engine is happy with the tune-up. No exceptions.”

Pete Harrell of Harrell Engine and Dyno puts the finishing touches on the short-block that will be able to handle well over 1,300 horsepower.
This is a rebuild and upgrade of an engine that Harrell didn’t build originally, so the first step was to tear the OEM 6.0L LS iron block completely down and re-machine all the critical dimensions. At this point, Harrell’s crew also invested significant time with a carbide grinder smoothing down all the sharp or rough edges around the main bores and everywhere else on the block.
The crank is a forged K1 unit with a 3.900-inch stroke. That’s 0.278 of an inch longer than the 3.622-inch stock stroke, but still shorter than many engine builders will use because Harrell says the shorter stroke creates a broader powerband. Combined with the 4.030 bore diameters, that makes total displacement 398 cubic inches.
The pistons from the previous build are being reused. They are Diamond forgings that have been given an anti-friction coating from Line 2 Line and will use rings from Total Seal with a 1.5mm stainless top ring.
Aluminum connecting rods are used not only because of their light weight, but also because the softer material (compared to steel) absorbs shock and helps protect the rest of the rotating assembly. Connecting the rods to the pistons are a set of wrist pins with a super-thick 0.225-inch wall thickness to make them incredibly stiff.
The rod bearings are King’s HP bearings. The aluminum-based HP bearings are softer than King’s XP race bearings, but Harrell says this material is a better fit for use with aluminum connecting rods. Even with all the aluminum used, Harrell says that with a proper tune-up this engine should be good for at least 200 passes.
This 55mm roller LS camshaft is ground with 236 degrees of duration at 0.050 lift for both the intake and exhaust. It has 0.578-inch lift on 112.5 degrees of separation. Also, if you look into the water pump hole, you can see the white of the Rokblock used to harden the block and help it withstand ridiculous levels of horsepower.
Once complete, the engine will burn methanol rather than E85 like before. Generally, Harrell says he’d prefer to use a piston with a dome versus the dish of these with the slower burning methanol, but the old pistons were still good and reusing them helped keep the budget in check. The difference in power will be minor, plus it can easily be overcome by turning up the boost.
The Athena head gaskets use stainless-steel O-rings that are located by the composite portion of the gasket. The O-rings bite into the aluminum cylinder heads so that even if the heads lift a bit under the pressure created from combustion, the gasket can still maintain a good seal. Combined with a set of tool-steel cylinder head studs from ARP, the engine should now be able to handle well over 1,500 horsepower.
Sealing off the cylinder bores are a set of AFR cylinder heads ported by Tony Mamo Motorsports. They are cut with 60cc combustion chambers and use 2.050-diameter intake valves with 8mm stems. The springs are rated at 165 pounds on the seat and 385 at full lift.
Harrell pulls the tool steel ARP head studs to 110 lbs on the inners and 28 on the smaller, outer studs.
Once in the Fox-body Mustang race car, the engine is finished off with a Plazmaman LS Pro-Series intake, an 88mm Garrett turbo, a Holley HP engine controller, and all the other bits and pieces necessary to get it up and running.
During preliminary dyno tuning, the engine made 1,279 horsepower with modest boost. (Harrell prefers not to say too much yet.) We do know that he thinks the engine can handle up to 30 lbs of boost and make 1,500 hp or more. He says simply that when they are ready to go for the record they will just keep turning up the wick until they get what they need.


Diamond Pistons 23003 Diamond dr. Clinton Twp, MI 48035(877) 552-2112
Garrett (Honeywell Turbo Technologies) Torrance, CA 310-517-1981
K1 Technologies Byron Center, MI 440.497.3100
King Engine Bearings 327 Little Falls road, Suite 5 Cedar Grove, NJ 7009800-772-3670