Dart Machinery's Pro 1 Platinum Chevy 350 Heads - Top-End Teardown

Chevy motors have always been known as capable producers of strong, reliable power. They are an excellent base for any project vehicle, as the list of replacement and aftermarket parts for these motors is endless. Many times the first questions asked are, "How much power do you want, and how much do you need?" Really, the question that should be asked is, "How much power does your engine want or need?" Although we would love to build a motor capable of eating Porsches for breakfast, we wanted an engine capable of producing long-lasting, reliable power. You know; something that could get us to the trailhead, and then take us miles into the backcountry without fear of breaking down in some "Deliverance" type scenario.

A few months ago, we added a Holley Stealth Ram Multi-Point fuel injection system to the otherwise stock engine. While this did make our 350ci much more responsive, its overall performance was seriously limited by the otherwise stock motor. The vastly improved air and fuel flow of the MPI system was quickly restricted by the original cast-iron cylinder heads and cam/lifter combination. For aftermarket solutions, we turned to two highly respected companies, Dart Machinery and Comp Cams.

Once we had decided our engine was worth the upgrades (checking cylinder pressure, etc), we had to decide what parts were right for us. Cylinder heads are generally cast-iron or aluminum. Cast-iron is cheap, durable and can withstand a fair amount of power. Aluminum heads, while much more costly, weigh significantly less and are much easier to machine due to the softer metal used. Aluminum heads many times also allow for higher compression ratios. For most of us outside the racing industry, aluminum heads are more a status symbol than anything else. With that being said, the first thing we thought of when looking at aftermarket heads was "Oooo, aluminum!"

After a call to Dart Machinery, they suggested their new Pro 1 Platinum cylinder heads. Using wet flow technology to design the Platinum heads, they are said to achieve an extra 25 horsepower over the original Pro 1 heads! These redesigned chambers of the heads provide the ultimate fuel distribution. The spark plugs have been located as high and as close to the center of the chamber, while new five-angle seats are utilized to shear the liquid fuel and air mixture as it enters the chambers. Their heads come with either a 64cc or 72cc chamber, and offer four intake runner volumes from 180cc for mild street applications, all the way to 230cc high-horsepower racing engines. For those of you just looking to swap out heads on your power plant, Pro 1 heads have been designed to work with 'off-the-shelf pistons, valvetrain components, and intake manifolds'.

With heads on the way, we called Comp Cams to match up a set of cam & lifters those shiny new head, and nearly new MPI system. They suggested their XFI, or Xtreme Fuel Injection, hydraulic roller cam & lifters. Roller cams provide reduced friction, and thereby wear, over flat tappet ones. The rollers allow the cam to be ground with a more aggressive lobe design. The XFI set also comes with matched retro-fit hydraulic roller lifters designed for small block 265-400 cubic inch V8's originally equipped with a standard hydraulic cam.

With the cam & lifter matched to the valve springs and heads, we again turned to Comp to help us with some rocker arms. We are building a mild motor in terms of power, and while we would love to have a set of full-roller rocker arms, they suggested going with their Magnum Roller Rockers. They are not a full-roller, but do have a roller tip to reduce friction, providing smoother control of the valve opening. The rockers are a 1.52:1 ratio which is close to the original 1.50:1 rockers used in our small block.

Here are the set of Dart Machinery's...        read full caption Here are the set of Dart Machinery's Pro 1 Platinum cylinder heads. Notice the lack of an EGR port on the new heads when compared to the original. This was okay since our engine was smog exempt, and the MPI kit we recently installed didn't have one anyways. You can also notice the dual spring setup on the new heads. This was necessary since we are using a hydraulic roller cam & lifter set. Our heads used 2.02-inch intake and 1.60-inch exhaust valve diameters. Dart also suggested using a 180cc intake runner volume (the smallest available). This is probably more than we need for our application, but eventually we would like to boost power with a bottom end rebuild.	The ideal method for removing...        read full caption The ideal method for removing the cylinder heads is to use a breaker bar to break all the bolts loose. Then unscrew all the bolts, but leave the two end bolts on each head slightly screwed in. Take a bar or pipe, insert it into the head ports, and gently pry it loose. Remember, for all jobs, whether it is prying, pounding, loosening or tightening, only use enough force to get the job done. It will save a lot of skin and parts.	After the old parts have been...        read full caption After the old parts have been removed from the engine block, make sure to check it over for cracks, chips, major distortions and other damage. After a 128,000 miles on the original bottom end, a ridge had built up on the cylinder walls where the pistons rings stop. The ridge was fairly smooth, but will need to be machined when the bottom end is replaced in the next year or two. Had the ridge been more severe, it would have required attention before we put the heads on.
Regardless of the tools you...        read full caption Regardless of the tools you choose to buy, a quality torque wrench is absolutely mandatory for performing engine work. Cylinder head bolts need to be torqued in a specific order. Almost all heads' torque sequences will start at the middle head bolt and spiral outward in a clockwise manner until all the bolts are properly set. Check out the manufacturers' recommended torque values and sequencing. These Dart Pro 1 Platinum head & stud bolts suggest 70 lb-ft. When a high torque value is required, start with a low value, and increase the torque in 20 lb-ft increments. We started at 30 lb-ft, followed by 50 lb-ft, and finally ending with 70 lb-ft.	If you are going to reuse...        read full caption If you are going to reuse you old cam, tappets, or pushrods, it is very important to keep track of which parts came out of what hole. There are several plastic, aftermarket trays made specifically for this task, but we made this cardboard one at the last minute. Before you consider reusing any old parts, read the instructions to your new parts. The warranties for Comp Cams roller rockers and hydraulic roller cam & lifters are voided if you reuse your old pushrods.	We drained as much coolant...        read full caption We drained as much coolant as we could before pulling the heads, but there was quite a bit left over in the cylinder heads. When we pulled the cylinder heads off, coolant flooded into the cylinders. Being that this was our first rebuild, this was an unnerving sight. Don't stress; just do your best to remove all the solid and liquid debris that falls in. After you have sufficiently cleaned and dried the cylinders, take some engine oil and rub a coat over the cylinder surfaces to prevent rusting.