Michael Johnson
Technical Editor
July 11, 2018

As Mustang enthusiasts, there’s a certain pride when we can go on and on about our car’s modifications. Aftermarket wheels, performance tires, bigger blower, steeper gears, lowering springs, subframe connectors, short shifter, stall converter, heavy-duty clutch, adjustable shocks and struts, cold air intake, and custom tune are just a few performance modification we love to brag about to whoever will listen.

However, one key modification we purposely left off that list is a built engine. We did that on purpose…well, because this is an engine build article, and also since the one thing we love to brag about the most is our Mustang’s powerplant. We like to wax poetic about our built engine’s bore size, piston measurements, head gasket thickness, compression ratio, cam specs, and the like. Going on and on about this stuff is a lot cooler than saying, “Nah, stock engine.”

We know there’s a certain pride with running a quick number, or making gobs of power with a stock engine, but we all know a built engine is in every Mustang owner’s future when performance is of utmost importance. It’s just a matter of time before a stock engine will give up the ghost.

For us, we purchased a Terminator swapped 1994 Cobra, knowing there could be a cooling system or head gasket issue. Our hope was that the previous owner had simply overfilled the cooling system, or that it needed to be properly burped. Once we received the car, and ran a few tests, our worst fears were confirmed – at the least we had a blown head gasket, with potentially more damage in store.

Once we diagnosed the blown head gasket, we needed to find a shop to help take care of the repairs; when it comes to timing four cams, we thought it best to leave that in the hands of experts. Unfortunately, at the time when we purchased the car it was right before the holidays, and then once January hits, most Florida shops are getting cars ready for the upcoming racing season. In other words, it was going to be a while before the car would be ready for the streets. However, we also wanted it done right, as well; we chose Power by the Hour Performance in West Palm Beach, Florida. Based on their schedule, they agreed to remove the engine and send it to MPR Racing Engines in Boynton Beach, Florida. Once the engine was removed, MPR found a couple questionable pistons - what started out as a head gasket replacement turned into much more and we decided to have MPR tear it all down and start fresh.

MPR machined our existing 2004 Cobra iron block back into fighting shape by adding fresh bearings, ARP fasteners, JE pistons, head gaskets, and valvetrain components before putting the long-block back together. This installment covers the short-block assembly, but we will have the long-block assembly, along with dyno numbers, and elaborate on the cause of the head gasket failure in a future issue. Until then, here’s the short-block build.

1. This is what we started with at MPR Racing Engines. The 2004 Cobra iron block was down to the bare bones after an align hone to make sure the main bores are square, along with a slight cylinder bore to 3.5593-inch. A stock 4.6 bore measures 3.552-inch so our new cylinder bore size is roughly .007-inch over stock. Therefore, our engine now displaces 282.02 cubic inches.

2. We relied on MPR’s Tim Eichhorn for our piston specs and ordered up a set from JE Pistons that featured a 3.558-in diameter, -10cc dish, 1.220cd, Four-Valve reliefs, and a corresponding set of piston rings. Most of those measurements are self-explanatory, but one that may need some explanation is the 1.220cd. This measurement is known as the compression distance, or compression height. This is the measurement between the center of the piston pin bore to the top of the piston. This measurement is important in any engine, but perhaps more closely scrutinized with stroker engines. Also shown here is the factory set of Manley forged H-beam connecting rods, which are being reused.

3. The basis for many modular engine builds is the legendary Cobra forged steel 8-bolt crankshaft. MPR polished the journals on our Cobra crank and balanced it to make sure it was good as new.

4. To keep our engine bolted together we chose ARP main studs, head studs, camshaft bolts, and rod bolts. MPR’s Tyler Eichhorn already has our engine’s main caps lined up and ready for installation.

5. Tyler started off the build by installing new Clevite main bearings, ARP main studs, and main caps. The ARP main studs were coated with ARP’s Ultra-Torque assembly lube to provide a more accurate torque reading.

6. Tyler holds the bearings while he taps the caps into place on the block. He’ll tighten the caps without the crankshaft in the block, and then measure to make sure everything is perfectly round. First torque sequence in 20 ft-lb on the mains, and then a final torque to 65 ft-lb. The sides will be torqued to 30 ft-lb with ARP assembly lube.

7. The side bolt adjusters are torqued to 8 ft-lb of torque before installing the ARP side bolts. The initial torque on the side bolts is 8 ft-lb, but then a final torque rating is made to 30 ft-lb.

8. Then Tyler mics the crank journals to check tolerances.

9. Tyler went over the clearances with his dad Tim to make sure everything looks good before assembling the short-block. From there, Tyler gets to take it apart and put it all back together; at this time, Tyler removed the bearings, debur them, and placed them in the hot tank (“Basically a huge dishwasher, Tyler says.”) before putting them back in with the crank. He will also number the bearings to make sure they go back in the same spot.

10. Checking the thrust, Tyler is happy the crank comes in at .006-inch.

11. Tyler uses assembly oil on the factory ARP studs and arrives at 50 ft-lb of torque. Tyler numbered the connecting rods when he removed them from the engine. He also makes sure to keep the bolts with the corresponding connecting rod, as well. He then measures bearing clearance with a Sunnen micrometer. Tyler engraves the cylinder number into each connecting rod, as well.

12. Tyler checks the piston pin for any burrs and uses assembly lube to insert the pin into the rod. He then inserts the pin halfway to get assembly lube on the connecting rod and pin before putting together the piston and connecting rod assembly. To finish up the assembly, Tyler uses the C-clip to join them together.

13. Tyler gets a little help from dad Tim inserting the C-clips, then putting the piston and rod together, and finally inserting the C-slip on the opposite side.

14. Tyler makes sure the oil ring is the correct spec; any gap with the oil ring would lead to excessive blow-by. He places the piston ring into the bore using an ABS Products piston ring squaring tool, then checks the gap.

15. To check oil ring tension, Tyler starts with #1 cylinder, cleaning each piston ring of any residue from shipping or during the trimming process. Tyler installs the piston rings with the gaps offset from each other. That is done to make sure the engine has adequate compression on start up before the rings have fully seated. For our boost level, Tyler has set ring gap at .022-inch on the top ring, and .024-inch on the 2nd ring. He then uses a fish scale to check oil ring tension. Yes, we said a fish scale. In a nutshell, Tyler is using the fish scale to measure resistance. Ours came in at 14 pounds, which is ideal for our boost level of between 15-20 psi. A higher boost level Tyler would like to see a higher number, but for our combination, 14 pounds on the oil ring tension is perfect.

16. Before inserting the piston/connecting rod for the last time, Tyler cleans each cylinder with lacquer thinner on a paper towel. Tyler makes a couple passes in each cylinder until the paper towel is basically free of residue. Then he’ll follow up with WD-40 on the same type of paper towel, which cleans each cylinder further, and also to help with corrosion. He’ll let each cylinder dry while he loosens the connecting rod bolts to ready the piston and connecting rod assembly for installation.

17. Prior to installing the pistons and connecting rods, Tyler makes sure #1 and #5 crank journal is pointing straight down, then spreads Total Seal assembly lube throughout each cylinder. He coats the connecting rod bearings with assembly lube prior to placing each assembly down the cylinder.

18. Tyler then tightens the ARP bolts to 50 ft-lb of torque. Then he moves to cylinders #2 and #5 and repeats the process. Tyler had a problem with something getting on the #6 connecting rod bearing so he took that one apart to remove a small piece of aluminum that had gotten on it, which caused it to bind on the crank journal. Tyler was able to remove the piece of aluminum and get everything back together properly. Tyler stresses the importance of keeping your engine build area clean to prevent this from happening, but as you can see, that stuff even happens to the best.

19. With the connecting rod/pistons installed, Tyler will check the side clearance on each, and piston-to-deck height on each cylinder. Each cylinder was between .009-inch to .010-inch negative deck height, which is good so we won’t have to run a thick head gasket.

20. With that, the short-block is done, and it looks amazing. It’s almost a shame to cover up this masterpiece, but in order for it to run, it still needs the heads, intake, exhaust and supercharger installed. During the next installment we will cover the rest of the engine build and its installation in the car. Stay tuned.