Refreshing A Dart 9-Degree Super Late Model Small-Block Chevy

Buying a used race engine is not an easy task. Race engines are rather class-specific so trying to find something you are looking for in “used” condition is a tall order. Then, when you do find one for sale there are all kinds of questions that can come to mind. For example, “What’s wrong with it?” Or “What kind of shape is it in?” Or “How much is it going to take to rebuild it?”

We all are familiar with the scenario. You don’t want to sink a lot of money into something that may not be worth rebuilding. Sure, you do not mind putting a little money into something worthwhile, you just don’t want to end up spending more than you would have, just buying new. Additionally, you want to find something that isn’t outdated and make sure you’re going to be competitive once you freshen it up.

Real-World Experience

This is exactly the scenario I was recently placed in. I had a customer that wanted to try Dirt Super Late Model Racing. They were currently running a Limited Late Model Class but wanted to step up and try a few of these “super“ races to see how they would like it. The truth is they wanted to feel more horsepower in the same car and be legal. Trying to find a used “super” engine for a decent price that would both be competitive and not require a ton of money for a rebuild was going to be somewhat of a task.

Dirt Super Late Model engines make a lot of power. Depending on the combination they can make anywhere from 850 to 900 horsepower on the engine dyno. If you talk with any of the drivers you will find that this amount of power is used for a great qualifying position. Then, most of the time, after qualifying is over and the track starts to dry out, the teams spend most of their efforts trying to “detune” the engine for the dry slick conditions. So our goal is to find something that could be affordably rebuilt and make 850 to 900 horsepower when all is said and done.

Even in cast form, the 9-degree cylinder head was a very potent piece for dirt Super Late Model racing. Several championships were won using these cylinder heads, but like everything else, racers trended to newer things.

After looking for several weeks we happened to run across an aluminum 434 cubic-inch small-block Chevrolet with Dart 9-degree cylinder heads. This engine was used for “super” racing and was built back in 2010. It was not a wide bore-space (4.500-inches) like they use now, but rather the stock 4.400-inch bore spacing. The find was rather interesting, largely because the Dart 9-degree cylinder head is not currently produced and there wasn’t anyone currently running them. The good news was that the engine was reasonably priced and the owner of the engine had documented all of the expenses on the engine since it was new.

My curiosity was killing me as to why this cylinder head was not produced anymore. Remember, I didn’t want to get something that was outdated and not going to be competitive. Before I purchased the engine, for the customer, I was able to get in touch with Dart and got some history on the cylinder heads. They were actually first produced in billet form by Don Lasito at Ultra Pro Machining. After talking with Don he enlightened me to the concept behind the cylinder head design and extremely shallow valve angle.

The Dart 9 cylinder head is only offered in “raw” form meaning that the head has to be fully machined. Our build sheet on the engine listed that this set of cylinder heads was prepped at Ultra Pro Machine by Don Losito. This included the CNC ports, guides, seats, and valves. On the right, the exhaust ports display major changes compared to that of a conventional small block. The ports are raised and roll out over the head bolts. A water outlet is also tapped between the two center exhaust ports to help in cooling and formation of hotspots. The header bolt layout is only offered in a “stahl” bolt pattern.

The Journey from 23 to 9

For the Chevrolet, the small-block started out with the factory 23-degree valve angle. Later, a more popular upgrade was the introduction of the 18-degree cylinder head which is still around today. Eventually, the valve angles moved to 13 degrees and engines were making good power. There were some cylinder head manufacturers who took the valve angles to 10 and 11 degrees but it was found that with the shallower valve angles the horsepower had dropped off.

The shallower valve angles were causing fuel distribution problems. With the design of the ports, the radius of the turn was so tight in the port that fuel and air were having a tough time making the turn. Don at UPM was able to take the shallow-valve-angle concept and produce a billet version in a raised-port design, with a 9-degree valve angle. The heads were a success, and with the right valve sizes could flow up to 440 cfm on the intake side. The intake runners were still a little long compared to the SB2, but that helped in producing better torque and lowered the RPM range of the engine. After some time, UPM worked with Dart and a cast version was produced.

The Dart 9-degree cylinder heads still uses the typical inline valve formation as a traditional small-block Chevrolet. The valve sizes are 2.200 inches intake with a 1.625-inch exhaust, with a 43cc combustion chamber.

Even in cast form, the 9-degree cylinder head was a very potent piece for dirt Super Late Model racing. Several championships were won using these cylinder heads but like everything else, racers trended to newer things. The good news was that if we purchased the engine, we could at least be competitive and not have something that was totally outdated. I also learned from Dart that they were planning to reproduce the cylinder heads for 2021.

Making An 11-Year-Old Engine Competitive

After purchasing the engine and tearing it down, everything was found to be in good shape other than the typical parts that were going to need to be replaced due to wear and tear. After looking at several of the internal components and parts, we realized that the engine could be updated with better, more modern components, which would hopefully make some more horsepower. According to the paperwork with the engine, it had been freshened several years ago and had made 850 horsepower. With that as a baseline, we could hopefully make it just as good and possibly a little better.

One of the important upgrades to our engine combination were the valvesprings. Instead of using the ordinary 1.55-inch diameter springs we were able to use a 1.300-inch diameter valvespring. You can tell by the spring cups how big the original springs used to be. This upgrade was able to reduce mass, which will also help in controlling harmonics in the valvetrain.

Starting from the top, the intake manifold was a Dart two-piece cast design, built specifically for the Dart 9-degree cylinder head. The two-piece design was made for ease of porting, and the intake had already had some extensive porting modifications. We decided that we would keep the intake as-is and see what would happen on the dyno. Moving to the valve covers, one odd thing was that they did not have the option for valve spring oilers. Most of these engines came equipped with valvespring oilers so that was something we could possibly upgrade.

The rockers are a T&D aluminum shaft-rocker system with a 1.75:1 ratio on the intakes and 1.60:1 on the exhaust. They were sent back to T&D for a rebuild to make sure they were ok. The valvesprings were Isky 1.550-inch OD dual springs with an internal damper. Upon teardown, you could see where the damper of the spring had eaten into the 8-degree titanium retainer. The intake valves are 2.200 inches in diameter and made of titanium with a 7mm stem. On the exhaust were 1.625-inch Inconel valves with a 5/16-inch stem. It was stated in the paperwork that the valves had been recently replaced. When inspected the valve stems had very little wear and they all measured the same length. In most cases when titanium valves start to fatigue, they tend to stretch indicating that they are in need of replacement.

To accommodate the large intake ports the cup of the intake lifters were offset .150 inch. This allows the pushrod to clear the intake port. To give some stability to the valve train the pushrods were 3/8-inch diameter, .140” wall, and 8.900” long. Because of the size of the lobes of the 55mm camshaft, the lifters have to be .937 diameter bore in order to accommodate a .850-inch roller wheel. The lifter bores were bored and bushed with bronze sleeves to accept this size of lifter.

Because the valvespring retainers had been damaged and the valvesprings were fatigued, we wanted to upgrade the entire package. We reached out to Joe Hornick of JHE who specializes in racing valvetrains. If the diameter of the spring could be reduced then we could reduce the mass. By reducing the mass we could also reduce the harmonics. After taking several measurements for JHE they came up with a valvespring, locator, retainer, and lock package with a 1.300-inch diameter and no damper. They were able to reduce the mass by 62 grams per valve which will benefit the engine in the higher RPM range.

The camshaft is a solid roller with a 55mm roller-bearing cam journal. Even though the cam was a roller the lobes of the cam were getting worn down. After contacting Comp Cams and researching the serial number, it was found to be the original cam, ground for the engine at the beginning of its life. We worked with Comp Cams in redesigning the lobes with the company’s new “low-shock” design.

The rockers were custom made by T&D Machine with the intake offset to complement the pushrod offset in the lifter to miss the intake ports. The intake rocker ratio is 1.75:1 and the exhaust is 1.60:1.

The “low-shock” design changes the way it opens and closes the valves, while maintaining intensity, to reduce shock loads on the valvetrain. The camshaft was ground with a lobe separation of 107 degrees with a 265- degree intake and 275-degree exhaust duration at.050 inch of lift, with a .750-inch of valve lift. The lifter bores were bushed for .930-inch diameter Crower solid-roller lifters which have a .850-inch diameter wheel. The lifters had been replaced in the last refresh, so they were reused.

Getting Into The Guts

Moving into the bottom end, the cylinder sleeve bore measured in at 4.157 inches. They did have some wear but cleaned up with a .001-inch hone. That gave us a final bore of 4.158 inches, and saved us from having to re-sleeve the block. The original pistons were manufactured by Diamond Racing Pistons, and Diamond was able to make us another set for the .001-inch-larger bore. We also took the opportunity to make some additional changes to the pistons.

Because the old Diamond pistons were worn and needed replacing, we reached out to them to see if they could custom make us the same pistons with some changes. They were able to move the ring lands up with the use of Total Seals 0.9 mm compression rings and get the wrist pin out of the oil ring land by using a 2.0mm oil control ring. They also provided a anti scuff coating for the piston skirts. To achieve 14.5:1 compression the pistons had a 16cc dish with intake pockets that would accommodate a 2.25-inch diameter valve with a .250-inch depth. The exhaust pockets would accommodate a 1.625-inch valve and the depth was .220 inch.

The pistons had a 1/16-inch, 1/16-inch, 3/16-inch ring pack and had a support rail because of the 5.900-inch rod length pushing the wrist pin bore into the ring lands. We opted to switch to a set of modern Total Seal rings with 0.9mm top and second compression rings with a 2mm oil ring. This allowed us to move the ring lands up on the piston and get the wrist pin out of the oil ring. The piston skirts received an anti-friction coating and the crown was designed with a 16cc dish. With the cylinder heads having a 43cc combustion chamber, the compression ratio would come in right at 14.5:1.

The connecting rods were manufactured by Dyers with a 5.900-inch H-beam design and checked out fine. To give some added insurance we replace the rod bolts with fresh ARP2000 pieces. The crankshaft is a Bryant billet 4.00-inch-stroke piece built with 400 SBC 2.650-inch main journals, and a rod journal size of 2.100 inches. Most of the time when you see high-horsepower, high-RPM applications you automatically assume that the crankshaft journals will be small, as it’s not uncommon to find racing crankshafts with 2.300-inch mains with 1.850-inch rod journals.

The crankshaft is a Bryant billet 4.00-inch stroke using a 5.900-inch Dyers connecting rod. Even though the crankshaft is billet, the main journal sizes used were 2.650 inches with the rods being the traditional 2.100 inches in size.

In the dirt track world, this really depends on the driver, as some prefer to have more rotating mass so when they come into a turn and back off the gas, the engine doesn’t decelerate as quickly. When they get back on the gas the engine can accelerate through the turns and not lose much engine speed. But some drivers prefer to have a lighter rotating mass because they drive the car with their own style of throttle control.

For the reassembly, we used coated rod and main bearings from Clevite and a set of DLC-coated wrist pins. When using a dry-sump oiling system on this design of cylinder block. The dry-sump system tends to suck the oil out of the pan which is what you want, but there isn’t much oil shedding from the rods and crank throws because of the block and oil pan design. The cam tunnel is cut off from the bottom end, so only the oil drains to the front or rear of the engine, which causes the wrist pins to suffer from under-lubrication. By running the DLC-coated wrist pins, the lubrication issue doesn’t become a problem down the road.

As we were wrapping up the engine, we found out that Don at UPM makes a set of billet valve covers that incorporate valvespring oilers. Oiling for the top end is very important. Not only because it lubricates the valvetrain, but it also helps in two other distinct areas. First, it helps remove heat — especially from the rockers at the two center exhaust valves. Because more heat is generated in this area shaft rockers can gall because of heat. The second benefit is the dampening effect caused by putting oil on the valve springs, which can reduce harmonics.

For the initial start up and all of the dyno runs on this engine, we used VP Racing’s 10W-40 Break-In Oil. VP says that when using the break-in oil, it’s good for 15 to 20 dyno pulls, or 50-100 street miles before changing it out to standard, non-break-in oil. The high ZDDP levels and anti-wear package in a conventional oil base allow for enough friction between surfaces that need it, while protecting those surfaces which don’t. The dyno’s 16-quart dry-sump tank is similar to the one in the car, but not exactly the same.

Spinning The Rebuild Up

Once everything was buttoned up, we took the engine to the dyno and bolted up the in-house dry-sump oiling system. For the initial runs, we filled the engine with VP Racing Oil’s 10-40W Break-In Oil. While VP Racing is typically known for its line of high-octane racing fuels, they have recently branched out into performance lubricants.

The VP break-in oil is a conventional oil base, fortified with increased levels of ZDDP providing 840ppm of zinc, and 1235ppm of phosphorus, along with a molybdenum disulfide-based anti-wear additive. The overall additive package in the oil allows friction where it’s needed to create “wearing in” but still protects under high-load situations.

Once the engine was off the dyno and fitted back into the Super Late Model chassis, the car owner refilled the large dry-sump system with 16 quarts of VP Racing’s Hi-Performance 10W-30 synthetic blend oil. Contrary to what a lot of people might think, these dirt engines work best on a semi-synthetic oil as opposed to a full-synthetic oil.

It’s designed to last for approximately 15 to 20 dyno pulls before being replaced with the standard semi-synthetic oil used in dirt Super Late Model engines. In this case, we used VP’s Hi-Performance Synthetic Blend 10W-30, which filled the engine once it was fitted back into the Super Late Model chassis, with the owner’s dry-sump system, taking a very healthy 16 quarts to fill. The Hi-Performance blend still contains elevated levels of ZDDP and other anti-wear additives, along with detergents and anti-corrosive additives.

After the initial break-in on the dyno, the power runs handily surpassed the numbers supplied from the previous rebuild. It produced 867 horsepower at 7,500 rpm and 720 lb-ft of torque at 6,000 rpm. While that’s not the 900 horsepower the wide-bore engines make, this is a very potent piece for a standard 4.400-inch bore space combination. After adding everything up, the total cost of the rebuild was right at $10,000. Not bad considering that brings the total cost of the engine to only $25,000. And with the 9-degree Dart cylinder heads slated to return to production, this could make for a new affordable combination for those wanting to dip their toe into the Super Late Model world.

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About the author

Bob McDonald

I have always had a passion for the internal combustion engine. I have been an automotive and diesel technician for over 30 years. I enjoy building high-performance engines and admire in-depth research and development.
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