A buddy of ours has a '68 Valiant that he takes out to track days at the local road course whenever possible. His Valiant is fairly quick with a cast iron 360, but the new Z06 Corvettes were beating him on the straights, so he's ready for more power. The Valiant is a four-speed car with a 2.94 rear end ratio, so the new engine needs to make loads of torque. After thinking it over, we decided the best way to make a small-block act like a Viper engine was to increase the displacement. In our search for displacement, we uncovered some tips and tricks as well as stubbed our toes a few times. The purpose of this article is to show everyone what we've learned on this engine project so far, to help you guys when you decide to go big with a small-block.
Given our power goals, we knew that we needed to build a short-block with at least 420 cubic inches. Going that big with displacement requires either a much larger bore size than stock, or a much longer stroke. Most production blocks are limited in possible bore size to just a 0.030-inch overbore, but they will physically accept a lot of stroke. However, the production blocks were not really designed to handle the stress put out by a really long-stroke engine, so we decided it would be safer to start this project off with an aftermarket block. Fortunately for us, Mopar Performance has a selection of race blocks available for the small-block engine builder. There are a lot of options available including different deck heights, different lifter angles, dry sump or wet sump, and siamesed or non-siamesed cylinders. We reviewed the various block choices and eventually decided to purchase a 340 restoration block from Mancini Racing.
Our 340 restoration block weighed 211 pounds as delivered from Mancini Racing. That makes
The 340 resto block that we ordered was a non-siamesed, wet sump block with a 9.60-inch deck height and 59-degree lifter angle. Non-siamesed cylinders means that the cylinders have a water jacket all the way around them, just like a production block. These full water jackets provide better cooling, but they also limit the maximum size of the cylinder bores to 4.080 inches. Had we selected a siamesed block, we could have used a 4.125 bore size and increased the displacement to 440 cubic inches, but we didn't think we had enough cylinder head to handle that many inches.
The 340 resto block we ordered from Mancini was part number P5007552AB. It was delivered to us finished honed at 4.040-inch bore size, and came complete with cam bearings, ARP main bolts, and freeze plugs. In theory, these 340 resto blocks are ready for assembly right out of the box, but we knew right away that our first stop would be the machine shop, not the assembly line.
Fixtures cut from heavy gauge sheetmetal were used to hold the block in a Bridgeport mill
Block Machine Work
The MP race blocks are designed with four extra head-bolt lugs on each side of the valley. Even though those extra bolts aren't required on the 340 resto block, Mopar does not machine them away. These extra lugs stick out between the lifter bores and consequently prevent the use of tie-bar-equipped roller lifters. Because we wanted to run a roller cam, we knew that the block needed some serious machine work before we could start the assembly process.
Shady Dell Speed Shop in Shady Dell, Pennsylvania, offers a super nice CNC package for these race blocks that removes the extra head bolt lug, as well as other excess weight from the block. In hindsight, we should have had our new block drop-shipped to Shady Dell for their CNC package. but being inexperienced at this, we just assumed that we could do the machine work ourselves. We knew it wouldn't be too difficult to machine away the extra material in the valley once we had the block in the machining center, but we underestimated how complicated it was to fixture the block. Engine blocks are heavy and awkward to hold on to, and our local shop wasn't fully equipped to handle this type of work. To make things even more complicated, our machine work needed to be performed at the same 59-degree angle as the lifters. We eventually figured out how to build a set of custom fixtures, to hold the block in a machining center at the correct angle for the necessary machine work. Our homemade fixtures worked perfectly once we had them constructed, but it did cost us a few weeks of time to design the fixtures and to get them fabricated-lesson learned, just call Shady Dell.
The Mopar block comes with massive four bolt main caps on the center three locations. The
The oil passage that usually feeds the oil filter was tapped for 3/8 pipe thread for a fit
The 340 resto block is cast with provisions for additional head bolts as well as 48-degree
The same fixture used to drill the oil passages holds the block in the correct orientation
The small-block Mopar engine was blessed with a tall deck height, which makes it well equipped to handle an extra long-stroke crankshaft. While the factory engineers didn't go larger than the 3.58-inch stroke used in the 360 engines, the aftermarket has been making 4.00-inch stroker kits for many years. The 4.00-inch stroke crankshaft provides 408 cubic inches when used in a .030-inch over 360 block, and up to 416 cubic inches in a 340 block. While the four-inch stroke setup has become a very common small-block combination, we felt we needed even more displacement than that for our project.
A little bit of research on the internet found several options, including a Callies crankshaft with a 4.250-inch stroke, a Hughes Engines crankshaft with a 4.180-inch stroke, and a K1 Technologies crankshaft with a 4.125-inch stroke. While any of these would've worked for us, the K1 crank was available with the 340 mains and smaller, early-Chevrolet-sized rod journals. We wanted to use the smaller rod journals in order to use less expensive connecting rods, as well as to tap into a wider selection of rod bearings.
To arrive at 427 inches, a 4.125 stroke crankshaft with 2.00-inch rod journals from K1 Tec
Because the 4.125-inch stroke setup is a fairly new combination, we had to order custom pistons. Of course, custom pistons aren't really a difficult task for the industry these days with all of the CNC equipment and CAD files on hand. Our combination with the rods we chose was a little unique, but the folks at JE Pistons were able to provide us with a set of pistons that matched our requirements. The pistons needed a 20cc dish to keep the compression at a pump gas friendly 10.5:1, and we asked JE for their special Tuff Skirt coating. The finished pistons weighed 450 grams, while the piston pins weighed 130 grams.
The bob-weight for this rotating assembly with the small-journal rods and custom pistons was 1,780 grams. The K1 crankshaft had a natural bob-weight of 1,950 grams, so we needed to remove weight at each end of the crankshaft to balance properly. On a crankshaft like this, reducing the counterweight radius by 0.10-inch will remove about 100 grams of weight. A large lathe was used to take material off of each end counterweight, leaving a few grams for the engine shop to remove during their final balancing process.
....K1 also supplied the 6.200-inch-long small journal connecting rods. These are high-per
Our block came with ARP main bolts, but we wanted to use studs rather than bolts. Unfortunately, ARP does not offer a main stud kit for these Mopar race blocks, so we had to piece our own kit together. You can duplicate what we did by ordering a standard ARP main stud kit, then buy six individual studs and six washers and nuts.
Our original concept for this engine was to use a hydraulic-roller camshaft. We felt that with the long stroke and small heads that our horsepower would peak before 6,000 rpm and that, therefore, we wouldn't need the higher rpm capability of a solid roller camshaft. Our other thought was that a hydraulic roller setup would be fairly quiet and reliable, which sounded like a good fit since the car does see its share of street miles. With those thoughts in mind, we went ahead and ordered a hydraulic-roller camshaft and matching lifters from Comp Cams. We did understand that Mopar Performance doesn't recommend the use of roller lifters with these race blocks, but we had already machined away the extra head bolt lugs in the valley, so we assumed the lifters would fit. As we found out, even with the head bolt lugs machined away, the block walls are so much thicker on the 340 resto block that the lifters just could not be installed. We tried to grind additional clearance in the valley with a 30-grit sanding roll, but the amount of material that needed to be removed really had us worried. Even the constant use of a sonic checker didn't provide us with enough reassurance, so we eventually stopped grinding clearance and started to look for an alternative.
JE also provided us the latest in lightweight, low-friction piston rings. Their recommende
Lucky for us, we learned that Comp Cams was in the process of introducing a brand-new solid lifter that is designed to work with the Mopar race blocks. The design change with these lifters was to move the link bar from the outside of the lifters to the inside in order to provide more clearance with the valley wall. The 59-degree lifter angle in the small-block Mopar allows the inboard link design to work because the pushrods exit the lifter at such a steep angle. The new Comp solid lifters dropped right in place in our block without any interference, and the pushrods easily cleared the in-board link bar. Comp Cams engineering told us we could run the solid roller lifters on our hydraulic roller camshaft by setting the hot lash at 0.006 inch.
JE built us a set of custom pistons. The 20cc dish is required to keep the compression dow
The crankshaft was about 200 grams heavy on each end, so we had a local machine shop take
Only a small amount of clearancing was required at the bottom of the cylinder bores to cle
Even with a 4.125-inch stroke, the rotating assembly fits neatly between the oil pan rails
The car that this engine is going into is equipped with a remote oil filter, so we needed a way to connect the external oil lines. The previous engine used an adapter on the oil filter pad to direct oil to the external lines, but the adapter was bulky and prone to leaking, so we wanted a different solution. After a little investigation, we decided to drill and tap the engine block itself, so we could attach the oil lines directly to the oil passages in the block.
The main oil passage that sends oil from the pump to the filter-pad area is accessible from the side of the block. If this oil passage is drilled slightly oversize and tapped, an oil fitting can be screwed right into the side of the block. There isn't much room in this area, so a 3/8 NPT fitting was the largest that we could install. When tapping the block for this fitting, we learned-the hard way-that the oil passage in the block was not drilled exactly parallel to the back of the block. Fortunately, we didn't ruin anything, but we did learn that it's best to verify the angle of the existing hole before trying to drill it oversize.
The Milodon 7-quart street pan fit perfectly over the rotating assembly without any interf
The 3/8 pipe threads in the block were smaller than what we wanted to use for oil lines, but there wasn't enough room to use anything larger. After a little research, we found a set of special fittings from Bo Laws Performance (BLP) that gave us a smooth transition from the pipe threads in the block to our -12 AN oil lines. On the return side, we found that a -10 to -12 AN O-ring fitting could be installed directly into the oil filter boss without any additional machine work.
As one would expect, the rear main cap on the 340 resto block is designed to use a 340 style oil pan. While it seems obvious that a 340 block should use a 340 oil pan, it isn't necessarily the best design choice. The newer 360 style oil pan is less likely to leak than the original 340 design, so an argument could be made that the race blocks should all come with the later design. Of course, if Mopar wanted to do us all a favor, they would make these race blocks compatible with the one-piece oil pan gasket used on the Magnum engines.
Milodon pickup 18346 cleared the rotating assembly without requiring any modifications. So
We originally wanted to use a Milodon windage tray on this engine but we quickly found out that a windage tray was not compatible with the four bolt main caps. Our attempt to modify the windage tray for clearance around the main caps wasn't pretty, so in the end we just left the windage tray out. We also noticed during the trial-fit stage of the engine build that some oil pans were too narrow to fit over the big main caps. The Milodon pan that we eventually settled on fit just fine, but one oil pan that we tried had to be knocked on and off the main caps. Evidently, the aftermarket hasn't fully embraced these Mopar race blocks quite yet!
At this point the short-block is fully assembled and ready for the top end. We have CNC-ported heads from Hughes Engines on order, as well as a ported intake from Shady Dell and a custom roller cam from Comp Cams. We certainly learned a few lessons about the Mopar race blocks during this project, but overall it has been a lot of fun. With any luck we'll have the engine finished and strapped on the dyno in time for the next article. Stay tuned as we finish assembly and hook our 427 to the lie detector.
One main stud had to be cut down to clear the body of the oil pump. ARP supplied us with a
Unfortunately, the Milodon windage tray would not fit over the four bolt main caps. We pro
We designed this engine around a hydraulic-roller camshaft but came to find out that the h
We thought we might be able to get lucky and use an older set of lifters that we had on ha
....We then thought we would be clever and use a set of lifters from a Magnum engine compl
Comp Cams saved the day with their brand-new 8043-16 lifters. These are solid-roller lifte
Once we had the lifter situation under control, we were able to quickly finish up the shor
The short-block assembly was finished up by installing a set of ARP cylinder head studs. W