Complete text from the article, I'll follow up with better scans of the images along with their captions after I receive my copy of this issue of Super Ford Magazine.
Building Ford's Big Six
Text and Photos by Greg Koesel.
Industry insiders and devoted six cylinder racers generally agree that the 240/300 cubic inch Ford six cylinder engine is one of the most durable inline engines ever made.
Introduced in 1964 for use in light trucksand the Ford Galaxies, the engine has plenty of potential for performance applications of all sorts, from drag racing to off road vehicles. The engine has many features which make it suitable for racing -- seven main bearings, four inch bores, and a twelve port head. Forged steel crankshafts and rods were used in the heavy duty 300 inch versions. Another point to consider in this age is that the 300 inch six engines are falling off Ford's Cleveland Engine Plant assembly line as fast as they can build them, ensuring an abundant supply of engines for years to come, while many of the performance V-8 engines were phased out of production years ago.
Most of the engines I have built have been used in drag cars but many of the steps I go through in building one of these sixes are used for other applications also. Let me also say now that I have learned a lot by talking with other prominent six cylinder Ford drag racers such as Bob Huettman, Bruce Sizemore and John Peto. They have helped me keep pace with the high technology racing going on in the 80's.
I am going to limit the scope of this article to engines using the production type head, because I feel this information will be beneficial to the most people. Those racers who are using hybrid V-8 heads on their 300 cubic inch sixes are pulling close to 600 hp out of them, but how many of us can afford the five figure bank roll needed to set up the hybrid head, induction system, valve train, etc. needed for one of these exotic pieces?
No, we'll concentrate on building an engine to put out a reliable three hundred plus horses without having to mortgage the farm. Before you get the impression it is inexpensive to build an engine such as this, it isn't. It will cost about as much as building a small block V-8. But if you like six-bangers you can build a durable powerful racing engine by following the procedures outlined. I'll also touch on that which works well in a street machine and towing and R.V. applications.
The engine blocks are virtually all the same, 240 cubic inch engines will accept the 300 crank and vice versa. The early blocks ('64-65) have smaller thrust face on the number of five main bearing insert so check the block for the proper thrust bearing size before ordering new bearings. I prefer to use a used block, but I don't go out of my way to seek out any particular year. All of the blocks have the same cylinder wall thickness. De-burr the block in the main web area and in the camshaft cavity to remove all remaining casting flash. Run a bottoming tap down all the threaded holes. Chamfer them slightly also. I like to install hardened cylinder head studs to pick up as much thread enlargement as possible and minimize bore distortion.
Keep the amount of overbore to a minimum as the cylinder walls are rather thin. The wall thickness is only about .160 to .178 inches, however the quality of the casting is quite good. I rarely see any evidence of core shift. For compression ratios of 10:1 or higher, install stainless steel o-rings in the block with about .006 inch stick out above the deck. Make sure the o-ring will contact the fire ring on the headgasket. Ultra-radical race motors and turbocharged motors require a metal head gasket made from a sheet of dead soft copper stock. Otherwise use Fel-Pro #8168-PT head gasket.
Most serious drag racers use the C6TE-6303-G (3.98 inch stroke) forged steel crankshaft with rod journals ground for the small block Chevrolet bearing sizes (2.100 in). The crank throws are reground to permit a large fillet radius at the corner of the journal. The generous radius reduces the stress concentration in the crankshaft at this point, ensuring longer crankshaft life. Check the crank throws for signs of cracking whenever you have the engine down to inspect or replace the bearings. The number six rod journal fillet radius is where the crankshaft will begin cracking. I have talked with a couple of circle track racers who claim to be using the cast iron 300 inch production crankshaft successfully ("They'll last one season"). But since I can't speak for the kind of power levels these guys are making with their engines I don't want to personally endorse using the cast iron 3.98 inch stroke crank. My plans for a new motor include using a cast iron, heat treated 300 cranksaft.
The 240 cast iron crank, on the other hand, is suitable piece to use in a race motor. Because of the additional main-to-rod journal overlap with the short 3.180 inch stroke, there isn't a strength problem with this crank. The crank that is currently in my car is a standard stroke 240 crank that Moldex Tool has ground, balanced, and heat threated. It uses the standard Ford journal sizes and i have over 120 full passes on it. I would also like to point out that a 240 sized motor offers advantages over a 300 incher in any type of racing where you are handicapped on the basis of cubic inches to weight. The port sizes in relationship to the cylinder displacement are more favorable with a 240 than a 300 and also connecting rod angularity is less severe because the 240 has a longer rod with a shorter stroke.
For a bracket racer the 300 incher is the way to go. It has more torque for consistent launches and a broad power band that makes this engine very forgiving of a minor driver inconsistencies.
Cylinder head preparation is important for pulling good power from any engine. The flow through the head is definitely the most limiting factor in getting any performance out of these engines. Smooth out the sharp corners and enlarge the ports by raising the roof of each port. Cut the exhaust guide back so that it is flush with the roof of the port. Cut the intake guide back .100 inch and install a set of bronze valve guides.
I use small block V-8screw-in rocker arm studs after milling and tapping the rocker arm bosses. Ridgeway Racing Associates makes a stud girdle which I use in conjunction with Crane roller rocker arms. (By the way, the 230-250 Chevy six arms also will work and they have a 1.76 ratio versus 1.61 for the Ford. this is a cheap and easy way to pick up about 10% more valve lift on a street machine, too.) Use .194 inch diameter TRW intake valves (#V235IN) and 1.60 diameter exhaust valves (#S2469) with a 30 degree back cut on the intake valves and a good 30 degree-45 degree-60 degree valve job on the valve seat.
Open up the combustion chamber around the valves out to the cylinder wall to promote breathing. The combustion chamber should hold 70cc when complete.
I also replace the 5/16 inch diameter pushrods with 3/8 inch Clifford Research pushrods. Doing this necessitates enlarging the pushrod guide slots in the head to .380-.385 inch. When you do this keep in mind that the pushrods are slightly angled toward each other and the top of the guide slots are further apart that the rocker arm studs. As a final step to ensure good sealing. I resurfaced the deck and install six head post studs through the top of the cylinder head. These studs bear against the quench area of the combustion chamber roof and minimize chamber flexing. Four of the six studs are fairly easy to install because you can use the existing threaded 3/4-14 core plug holes in the top of the head for installing four center plugs. The two end studs must be installed by spotfacing the top of the head and drilling and tapping the head surface itself. use sealer on these studs to prevent water leaks.
All of the modifications to the head took about 80 hours of work, but the end result is a trouble free cylinder head.
Piston and rod combinations will vary with each application. There are several ways to go here. If you are on a tight budget you can use the stock rods and an aftermarket piston designed for small block Ford or Chevy V-8's. The 240 has the same bore and compression height as 289/302 Ford (4.000 x 1.605 inches) so a forged small block Ford piston will work well in a 240. TRW makes these pistons in both flat top (L245OF) and pop-up (L2249F) design. Fit the pistons with .0045 to .0055 inch skirt clearance.
The standard rods can be used in circle track and bracket drag motors after polishing the side beams, replacing the bit end bolts and nuts, and reconditioning the rod journals. A 302 Chevy pop-up piston will work with the 300 crank and early 300 rods if you open up the small end of the rod from the .912 inch Ford pin size to the .927 inch Chevy pin size. The dome of these pistons can be trimmed down by cutting it at a 12 degree angle to match the valve chamber which has been sectioned through the ports. It comes in handy for checking piston to head clearance.
My latest 300 inch bracket motor has Bill Miller rods, 6.48 inches long (stock length is 6.21). The big ends are bored for the 2.100 rod journals as mentioned earlier. These rods are hung on TRW pistons (L2370) which have been extensively reworked and lightened. B&B lightweight wrist pins with .095 inch wall thickness have also been fitted. The valve train on these six cylinders is one area that you can save considerable expense compared to building a small block V-8. For example, I don't use titanium valves because they're expensive and I just don't think they buy you any performance in an engine that won't see service over 8000 RPM. When you build one of these sixes for competition always keep in mind that the fact that the cylinder head port size will limit the usable RPM range to around 7900 RPM for the 240 and 7500 RPM for the 300. My 300 inch bracket motor uses a GK flat tappet cam with 108 degree lobe centers .571 inch intake valve lift and .596 exhaust valve lift, GK tappets, Clifford 3/8 inch diameter pushrods, Crane roller rocker arms, and GK 2010 springs installed with 140 pounds of seat pressure against titanium retainers.
The 240 inch D/ED engine uses a Crane Hi-Low No Pop roller cam with 108 degree lobe centers, .665 inch intake valve lift and .687 inch exhaust valve lift, Crower roller tappets, Clifford 3/8 inch diameter pushrods, Crane roller rocker arms and titanium retainers working against Lunati valve springs installed with 180 pounds of seat pressure. A Ridgeway stud girdle is used to add stiffness to the upper valve train area.
Induction systems are always a source of puzzlement on an inline six cylinder race engine.. Should I use one large centrally located carburetor or several small ones placed near each intake port? Is a common plenum of an isolated runner (IR) system the best? The fact that there are so many systems being marketed suggests that there is no simple answer. My current choice is a 650 or 750 CFM Holley double pumper on an Offenhauser intake. On a street machine a 480 to 600 CFM four barrel with vacuum secondaries will work great with the same Offy manifold. The offy dual port 4V manifold is a good choice for towing and recreational vehicles. These induction systems are simple and give a very good middle to upper RPM performance even in the 240 motor. I have tried using three Holley 650 CFM, three 500 CFM, or three 350 CFM two barrel carbs mounted sideways on an intake manifold with a common plenum chamber but they still haven't run quicker than my tried and true 4V.
Headers should be made of 1 3/4 inch O.D. tubing, 36 inches long with 2 1/2 inch O.D. collectors. Primary tubes made from 1 7/8" inch O.D. tubing hurt my E.T.s. Also seal the crankcase and install a Vac-u-pan system tee'd into both collectors. The best oil pan design is one that has plenty of depth from the front to the rear. I make my own oil pans by starting with the mid-sump pickup truck style pan because it has straight vertical three inch high walls running the whole length of the pan. I also make a windage tray from sheet metal and fine mesh windage screen material available from Moroso. If you don't want to fabricate a custom pan then choose the rear sump van style oil pan and the accompanying long oil pump pickup tube.
Finally, if you are going to run one of these inline motors in a drag car, here are a few guidelines for setting up your car. use more tire and less gear than you might otherwise choose with a small block V-8 powered car. The reason for this is that you need lots of bite because of the great low end torque one of these engines makes. You also want the car to pull strong right through the lights so big motored bullies can't run you down at the top end of the race course. My roadster uses 11.5 x 33 slicks and a 5.43 gear, but going as low as 4.33 gear with the same setup will only hurt your E.T. a tenth or so.
If you are using an automatic transmission, choose a torque converter with a stall speed of about 2000 RPM less than your intended trap speed. My roadster uses a 5500 RPM Coan converter, a Powerglide, and a trans brake.
If you run a stick shift car, a wide ratio 4-speed with a low first gear ratio works well. First gear should be at least 2.78:1 or lower.
In conclusion, Ford's 240-300 cubic inch inline sixes are packed with performance potential. They run well and last a long time with minimum maintenance. If you like racing mroe than wrenching maybe you have been overlooking the six. Most racers who build one get "hooked" on them as the most logical engine to race.