It's no secret that if all other things are equal, more displacement will generate more torque and power. As any Mountain Motor Pro Stock racer will tell you, there is no substitute for cubic inches.
That premise will be on display as we set to build a 347ci Windsor engine from our stock 302ci Ford platform. As came to light in a test we did in Muscle Mustang & Fast Fords some years ago when we compared a 306ci Ford to a 347ci, we know that the additional cubic inches were highly beneficial for power generation. In that classic test the 347ci engine made 44 more horsepower and 39 more lb-ft of torque with increased benefits throughout the usable rpm range.
Our Engine Decision
Over the years, the Ford Windsor engine has been cut up and modified in about as many ways as imaginative engine builders can dream up. But with all the testing, there are certain configurations that seem to be the most popular for this classic engine. The Ford 347ci engine is extremely popular since it is easy to find and our 1987-1991 model year, E7TE-code engine includes the very cool and highly efficient hydraulic-roller camshaft design. In this case, we upped the 302's game with added stroke to generate more cubic inches and that all important, get-you-down-the-track additional torque. For a limited amount of additional cost, the 347ci engine does a great job of delivering for both street and race-bound vehicles.
But it's not only a matter of additional cubic inches that equates to making it a "better" engine. For engine owner, Saul Gutierrez, he originally felt that for the 302ci platform he would opt for the shorter stroke 331ci engine; the change to the 347ci engine came about after discovering K1's very strong and very affordable forged crankshaft that opens up the stroke to a full 3.400-inches.
As Gutierrez rationalized, "while the 331ci engine would see peak rpm in the 7,000 range, the 347ci engine would deliver additional torque which would really work for the street/strip plan I had for the engine. While we had to notch the block to clear the increased stroke of the connecting rods, that was really the only serious modification required. With my plan to potentially add nitrous or a supercharger, the additional 16 cubic inches would be exponentially beneficial with a power adder."
The move to the larger stroke also brought about a discussion about rod/stroke ratios. For the record, rod/stroke ratio is a calculation determined by taking the center-to-center rod length and dividing it by the crankshaft stroke dimension. Most engine builders figure that the best ratio is between 1.55:1 and 1.70:1 to achieve the best durability and other engine characteristics.
What does rod/stroke ratio mean to me?
Quite simply, the lower the ratio, the greater the side forces applied by the pistons and also the piston skirt pressures on the cylinder walls. In their worst form, these issues can manifest as increased internal engine vibration and higher piston skirt wear increasing oil and coolant temps. On the positive side, the shorter connecting rod length (lower ratio) allows for shorter, lighter engine combinations and engines that will generate more vacuum at lower RPM for better throttle response (increased timing advance) and low end torque.
In contrast, a longer rod (and higher rod/stroke ratio); the piston dwells at Top Dead Center (TDC) slightly longer for more efficient and thorough combustion, which equates to slightly more power. As a general rule, engines with longer connecting rods generate slightly more power in the mid to upper engine rpm range. These engines have lower intake vacuum for reduced rpm and torque making this system the better choice for racing engines rather than street use.
Parts is Parts
Most things equate to the sum of their parts and with this engine build that adage was never more accurate. The parts list used for the short-block portion of the engine build features parts from Automotive Racing Products, ATI Performance Products, JE Pistons, K1 Technologies, Clevite Bearings, and Comp Cams.
The camshaft was the recommendation from the Comp Cams tech line, who spec'd out our camshaft, including all of the accessories such as the hydraulic roller lifters and timing chain setup. The green epoxy paint applied to the galley was a signature touch of our engine builder, Tim Roberts, who is the engine specialist at Gear Driven Automotive.
Follow along as we walk you though the basics of building up this 347ci engine for Gutierrez. In the end we will dyno the engine to determine just where we came in with regards to performance and power - because all of this engine stuff just can't be measured by just looking at it on an engine stand. And we wouldn't do that to you!
347ci Engine Parts List
Factory 302ci V8 Ford Mustang engine
Main Studs, PN 154-5001
ATI Racing Products
Dome Volume: -22.00inch
Weight 415 Grams
Top Ring, PN S14030-5-116DMB
Second Ring, PN P24030-5-116IPT
Oil Ring, PN H34030-0316FCUF
Piston Pin, PN 927-2750-15-51S
K1 Connecting rods
K1 SBF 5.400-inch center to center
Forged 4340 Steel, H-Beam design
Shot Peened, Bronze Wrist Pin Bushings
Housing Bore: 2.225
Bearing Width: 8.310-inch
Bearing saddle width: 0.740-inch
Clevite Rod Bearing, PN 22387
Clevite Main Bearings, PN MB 529SI
Forged and 4340 Steel construction
Nitride hardened for improved strength and bearing life
Straight hole oiling for improved lubrication
L1 SBF 3.400-inch stoke, forged
Main Journal Diameter: 302 Ford
Total Weight: 47 pounds
Camshaft: Comp Cams Hydraulic-Roller
Gross Valve Lift: 0.544-inch lift intake & exhaust
Duration at 0.050-inch lift: 224-degrees intake & 230-degrees exhaust
Intake Centerline: 108.0-degrees
Lobe Separation: 112.0-degrees
Comp Cams Hydraulic Roller Lifters, PN 851-16
Comp Cams Double Roller Timing Chain, PN 2138
Comp Cams Lifter Retaining System, PN 8135-LR
Clevite Rod Bearing, PN 22387
Clevite Main Bearings, PN MB 529SI
Our 347ci engine took shape under the guidance of Tim Roberts and Gear Driven Automotive owner Saul Gutierrez (shown here).
The engine block was a fairly common 1987-1991 vintage E7TE 302ci Windsor small-block, featuring a hydraulic- roller camshaft and two-bolt mains. These blocks are plenty tough and should be able to handle both normally aspirated and limited levels of power adder performance.
Our JE Pistons were 0.030-inch overbore to match the machining done to the cylinder bores. These lightweight forged aluminum pistons generate a final compression ratio of just under 10:1. These pistons worked perfectly with the high strength 4340 steel H-beam K1 Technologies connecting rods.
Keeping it all in the family we selected a K1 forged crankshaft with a 3.400-inch stroke. When combined with the 5.400-inch long connecting rods the final displacement is 347ci.
The bearings we selected were from King and designed to work with the factory crankshaft specs. Other than washing them and wiping them dry, no special prep was needed.
After making sure each bearing saddle was clear of all debris, we tapped the bearing in place, making sure to align the tangs to the notches in the saddles. Make certain that the ends of the bearings fit flush with the surrounding edges.
We lubricated the bearing at this point using a 20/50 high zinc content oil. Note here that the holes in the bearings are lined up with the oil feed holes in the saddles. If you put the solid bearings here, there will be no oil flow to the crankshaft.
To the point previously made, note that the solid bearings fit into the main caps like this. Also note that the bearings with the side bearing material (called thrust facings) fit only on the number three main. You can see the outline for the bearing on the side of the number three saddle and bearing cap.
To get the main caps to fit in their tight recesses, we used this small brass hammer to lightly tap them in place. If they don't fit completely flush with the surface, find out why before locking them down with the main bolts.
ARP Bolts are the best in the business and were used in place of the original factory bolts. Never reuse main bolts as they stretch and will not keep consistent torque.
It's critical to make sure that the connecting rods clear the bottom of the cylinder bores. With the increased stroke and long rod length, we had to notch the bottoms of the cylinder bores in this manner.
Always use ARP's Ultra-Torque fastener assembly lubricant to achieve the proper torque spec with the bolts.
We torqued the crankshaft by first securing the bolts with a speed handle, then torqued them all to 35 ft-lb, and finally to 70 ft-lb, and then rechecked them all again.
We checked the endplay of the crankshaft by placing a micrometer in line with the crankshaft movement and carefully using a screwdriver to snap it front to back. Our endplay was 0.004-inch, which was just about perfect. A range of 0.003-0.005-inch would be fine.
The K1 connecting rods are a thing of beauty with its shot peened exterior for added durability. The high strength ARP bolts thread into bosses within the rod structure, avoiding the need for rod nuts. We also ordered up a set of Clevite rod bearings (Division of Mahle Aftermarket).
The JE Pistons wrist pins fit through the piston bore and hold the connecting rods in place. It is critical to make sure that the rod/piston combination for the bore you are filling is correct with regards to the valve reliefs in the deck of the pistons and the chamfer on the connecting rod, where it attaches to the crank journal. The chamfer must face outward rather that against the connecting rod it shares the crankshaft journal with.
Twin spiro-locks are used on either end of the full-floating piston wrist pins.
To work on the piston/rod assembly, you must correctly protect the sides of the connecting rods from the jaws of the vice; these protective covers are designed to do exactly that.
End gap is the measurement between the ends of the ring when they are placed into the cylinder bore. The ring must be perfectly square to achieve a correct measurement. Note the difference in end gap amounts is dependent on the type of engine you are building.
This "pip" on the piston ring denotes which way the ring should be installed. In almost all cases, the "pip" should face up.
Using a flat blade feeler gauge, we measured the end gap of our piston ring. Every ring should be test fit for proper end gap.
If the end gap is too little, you can grind the end of the ring with a ring grinder. Be careful to not take too much off or you could find yourself buying new replacement rings - after all you cannot put ring material back on a ring and excessive ring gap will reduce engine efficiency.
This oil rail support ring is in addition to the standard rings as it creates a "floor" within the oil ring land. This is necessary with this style of engine since the oil ring goes through the wrist pin bore.
When installing piston rings, it is important to oil up both the ring land and the ring you are installing. Remember, no metal-to-metal dry contact points and never drag the end of the ring across the surface of the piston or you will damage piston-to-wall sealing.
After installing the rings, we used a ring compressor to, appropriately enough, compress the rings around the piston so they would fit into the cylinder bore. Make sure to thoroughly lubricate the cylinder bore and piston skirts before installing.
These golden rods from Hawaii Racing screw into the connecting rods and align the rod with the crankshaft journal. Make sure that the crankshaft journal you are working with is in its lowest point of crank rotation, making it a straight shot downward to reach the journal. Also make sure not to scuff the journal when sliding the connecting rod into place or you'll be headed back to the machine shop to polish out the journal again.
Here is the chamfer we talked about earlier. The chamfer shown here on the side of the rod cap faces toward the outside of the crank and not towards the adjacent connecting rod. This is very important and will affect engine operation, oiling and overall durability. There is also a chamfer on the connecting rod itself, and the caps must match that design.
Torque the connecting rod bolts evenly after snugging them up with a speed handle. Ultimately you want 45 ft-lb of torque on each rod bolt.
Here is why we notched the bottom of the cylinder bores. Note how close the rod end and bolts come to the notch in the cylinder bore. What you see here is the optimum amount of clearance.
These oil gallery plugs were screwed into the channel around the front of the block near where the camshaft will be installed. This is important to achieve proper oil pressure.
We then liberally lubricate the Comp Cams hydraulic-roller camshaft with the same oil/zinc lubricant to avoid any kind of metal-to-metal contact. No other traditional "flat-tappet" camshaft lubricant is needed here.
The Comp Cams double-roller timing chain goes on in the traditional way. The circle on the top half of the crank gear is all the way up and aligns with the mark on the bottom of the camshaft gear. Make sure there is no slack in the timing chain.
This ATI Performance Products' Super Balancer was the crowning touch on our engine build. Designed exclusively for high performance Ford engines, the damper eliminates torsional crankshaft vibrations and exceeds SFI 18.1 specs for all forms of racing. This balancer is internally balanced with a 6.325-inch diameter, making it perfect for our application.
We lubricated the lifter bores and lifters and slid the Comp Cams hydraulic-roller lifters in place. The flat surface of the lifter should face out towards the center of the engine valley.
These links slip over the lifters, two at a time, and lock into the flat surfaces on the face of the lifter body to keep the lifters from rotating in the bores.
Holding everything in place is the lifter retainer that bolts to the center of the engine valley with two self-tapping screws. Make sure the arms of the retainer keep pressure evenly on each lifter link. That's it for now, but the next time you see this short-block, we will be assembling the top-end and getting this bullet ready for the dyno.
Photography by Cam Benty