Mustang MonthlyHow To Engine
Six Appeal: Building a 200ci Inline-Six Engine for Today’s Driving
The day before I sat down to write this article, a friend of mine purchased a very nice six-cylinder 1965 Mustang hardtop for his wife to drive—a very good, solid car. His first question to me was, “Do you have an extra 289 or 302 lying around?” Ugh. The curse of the lowly six-cylinder Mustang.
More so in the Mustang world than in the Falcon/Fairlane and other realms, the six-cylinder Mustang has always been a target for an engine swap for more horsepower. Granted, the four-lug wheels and lightweight driveline components weren’t very robust, but the six-cylinder itself was not a terrible combination in the small Mustang platform. In the sixties, with 1960s driving, roads, traffic, and economy, the six was a good choice for a daily driver. Always overshadowed by the V-8 engine, Ford had to make a special promotion in 1966 with the Sprint 200 package to sell more straight-six engines. Even with no overdrive gears, the six was capable of delivering mid-20s mpg numbers in stock form.
V-8 conversions started almost immediately with the Mustang and continue to this day. But the cost of converting to a V-8 is starting to get pretty high, and some owners are still in love with the economy that the six-cylinder provides over the heavier and gas-guzzling V-8. So we decided to look at an engine build that would provide us with more horsepower for today’s driving without sacrificing the economy and torque advantages that the straight-six provides.
We contacted Vintage Inlines in Michigan and told them what we wanted to do—build a six with power for today and the torque and economy the six is traditionally known for. We didn’t want to build a high-horsepower, finicky-in-traffic overbuild you so often see in magazine builds; we wanted a build that made the straight-six an excellent choice for a car that is driven regularly. As a bonus, we were also looking for one-stop shopping to get the build done.
After thinking it over, we came up with an engine that we feel should get us into the 200-205hp range. That may not sound like much, but our target is one horsepower per cubic inch, which is more than the 205-225hp engine of the Fox-body 5.0L era—with the torque of the straight-six engine to boot. As the project unfolded, we started looking at induction systems. We decided that what we built would be used as the test mule to shakedown several different fuel induction systems: The two- and four-barrel carburetors and a couple of fuel injection options, which we are building for an upcoming project. Our plan is to dyno all these different induction systems so you can decide which one is best suited for your driving. But for now, let’s look at our engine and how we plan to reach our goals.
The BasicsThe Ford Thriftpower Six was introduced in 1960 in the form of a 144ci version. Early 1964 Mustangs were fitted with the 170 Special Six, and this was updated to the 200 in 1965. The 200 was used through 1969, when it was replaced by the 250, which was used throughout 1973. Ford re-introduced the 200 back into the Mustang in 1979, when the 2.8L V-6 was not available in quantity, so the straight-six was back as a replacement mid-’79. The last year of production for the 170 was 1972; the last year for the 200 was 1983; and the 250 ended production in 1980.
Besides the obvious bore and stroke differences, the big difference came in the 200 with the seven main caps instead of the 170’s four. This helped with not only making the bottom end more durable, but reduced some of the harmonic vibrations in the engine. The 170 had three core plugs on the passenger side, and some of the early 200s also had three. Ford began putting five core plugs in the block mid-1965. The 250 is about 1.66 inches taller than the 200 and around an inch wider.
The GoodThe inline-six was not only used as a reliable base powerplant in the Ford economy line, it was also known for the one thing all inline engine are known for—torque. “V” engines attach two rods to the same point, which drives the crank with two pistons at that point, increasing horsepower. Inlines connect each rod to a single point, and the push-pull characteristics increase rotational torque. So for the size, inline engines produce more torque than V engines.
The bottom end of the six was very good; the seven main bearings in the 200 and 250 help make the engine very durable. In most street builds, no real special work needs to be done to the bottom end—the rods and crank are very good and can handle a mild build with no problems. The oiling system is also very good and does not require any special alterations on most engine builds. According to my Bronco friends, the six is much better with cooling as well—where the V-8s overheat (according to them), the sixes remain calm, even with a good build.
The BadWith the exception of the weight, most of the problems with the six are from the deck up. The cylinder head was originally designed with an integral intake manifold, which was designed as a simple tube running the length of the cylinder head. With a single one-barrel carburetor, the center cylinder had a much shorter runner length than the outer two cylinders, which resulted in uneven fuel flow. The incoming air charge had to make 90-degree angles to get into the cylinder head, which was also not good for performance. The carburetor was located right over the center exhaust port, which meant it was susceptible to heat from the engine and vaporlocking issues.
Speaking of heat, the central port on the cylinder head combines the No. 3 and No. 4 cylinders together to make one big port. This, of course, made the exhaust output uneven, and worse, it heated up the cylinder head more in the most inopportune place—right under the carburetor. The aftermarket came up with a spacer to insert to try and solve some of the problems, but it is still a continuing problem on all builds with the original head. The original exhaust manifold was very constricted, not intended for any real horsepower usage, and often cracked.
The head is cast for one carburetor—a one-barrel. Performance enthusiasts have made converters and machined for multiple carbs and bigger carbs for years, but combined with the three 90-degree turns, more carburetor is not always enough to help a bad situation. The Autolite 1100 one-barrel carburetor was used in most applications (some Holley and Carters were also used), and the Autolite had some hesitation issues that some carburetor builders were able to engineer out.
The block itself is heavy, in terms of cubic inches. Ford wasn’t too worried about weight like they were with the V-8s, and the block was made for reliability, not performance.
Ford AustraliaFord Australia was deeply committed to the inline-six design, and in the 1970s they developed a two-barrel head with a removable intake made to mount a Bendix-Stromberg 2V carb. Now we are getting somewhere. They also made improvements to the exhaust, and this allowed for increased horsepower in the six and retained the torque numbers. Their work is where most of the engineering for our build comes from.
The Bottom End
To get to 200 hp we really don’t have to do a whole lot of special things to the bottom end. Our block is a 1967 200 that has been bored 0.020 inch. With the seven main bearings, the only thing we added was a set of ARP main cap studs to help with the dyno time this engine will see.
The crank is the stock crank and has also been turned 0.020. Rods are also stock and fitted with ARP rod bolts. Using these rod bolts does require some machine work to be performed to fit the bolts, but it is straightforward for any machine shop.
We selected a flat-top piston for our build, which should yield around 9.5-9.6:1 compression with our head selection. This is higher than a 250 at 9.0:1 or the original 200 at 8.1:1, but we should still be able to drive it on decent gasoline. We had our machine shop press the pistons on for us and balance the rods to the assemblies, and then we were ready to go. Rings were Sealed Power plasma-moly rings.
Vintage Inline sells a multi-index timing chain that is a double-roller design, and if you will be indexing your camshaft (you should), it allows for plus or negative 2, 4, and 6 degrees of indexing. Using the index gear, we were able to set our intake centerline at the 109 degrees that the manufacturer recommended.
No special bearings are required for the build, but good quality Clevite bearings were selected for the mains, cam, and rods.
As noted before, it is not necessary, nor is it recommended, to run a high-volume oil pump on the straight-six, so a stock Melling pump was used (MEL-200-OIL-65B). No other oiling modifications were needed on this build. Make sure you use the correct pump on your engines—170s use a different pump than the 200, and both differ from the 250.
We chose a Clay Smith hydraulic grind. It’s a good mid- to high-rpm range cam, and it is the high-lift, short-duration camshaft we were looking for in this build. Duration is 224 advertised (222 actual) degrees on both sides, and the lift is .450. We are installing it at around 109 degrees as per the manufacturer, and with a manual transmission this should run well. An automatic may require a little bit in the stall converter to run well on the street. Matching hydraulic lifters were chosen to work with the valvetrain.
The rocker arms are stock 1.6-ratio adjustable rocker arms on a reconditioned shaft assembly. Pushrods are 8.230-inch-long ball-and-cup design. Adjusting the rockers is the same as any other hydraulic grind cam—turn the pushrod and adjust the arm until the pushrod just stops spinning, then give it a quarter-turn.
The Top End
Our top end starts with the new aluminum head from Vintage Inlines. You can read more about it online here: mustang-360.com/how-to/engine/1804-finally-a-performance-cylinder-head-for-ford-six-cylinders. Our aluminum head should cancel out all of the issues associated with the original cast-in intake design. The bolt-on intake improves flow and runner lengths and moves the carburetor away from the heat, and the dual exhaust port is eliminated. Our head has a 55cc combustion chamber (stock was 51.5-54) and comes with 1.80-inch intake and 1.50-inch exhaust valves (stock 1.642-1.657 intake and 1.381-1.396 exhaust). A free-flowing aluminum intake manifold and your choice of adapters for Motorcraft/Holley two-barrels, Weber 2V, and Holley 4V carburetors are included with the head. Valvesprings are single springs with a damper, and they use steel retainers and keepers. The head is designed to work with stock components (you could even bolt up a stock exhaust manifold). We are using ARP head studs to hold the engine in place.
Our plan is to test several different popular induction systems on this engine, which includes the Ford/ Holley 2V, the Weber 2V and the Holley 4V. The Weber is rated at 380-400 cfm and the Holley is rated at 390 cfm. The new intake will also allow for bolt-on central fuel injection units and both the intake and the head are cast with bosses for sequential fuel injection.
There have been several good headers made for the six-cylinder engine, and we are using a dual 3-into-1 header made from 304 stainless steel. The flanges use spring-loaded ball joints from the flanges to the extension, making fitment easier in some chassis. The extensions can be modified for use with O2 sensors or heat riser tube—we plan on doing the former. Big, thick mounting flanges should eliminate warping. The header comes with a gasket that matches the improved dual outlet on the center two exhaust ports.
Vintage Inlines sells the Performance Distributors HEI-style distributor, which makes horsepower gains over some of the more popular electronic ignition systems available. It is a one-wire design that only needs a 12-gauge power wire supplied to the HEI-style coil. It is teamed with a set of Livewire spark plug wires and loom set. It should be noted that this distributor is big and will not clear the stock power steering pump, but the pump sold by Borgeson will clear this distributor. Vintage recommends using the coldest spark plug to start. A plug that runs hot can pre-detonate and cause internal damage, whereas a colder plug will foul and can be replaced with a hotter plug if needed. Also, you should back off of your ignition timing at first to prevent pre-detonation and damage. Start on the reduced ignition timing and slowly add advance into the timing.
For mild carburetion like the ones listed above, a standard fuel pump will work just fine. The Weber carburetor likes 3 psi as opposed to most carbs at 5-7 psi, so the use of a pressure regulator for the Weber is recommended. Fuel injection requires more pressure, and you should move to an electric fuel pump (and no vaporlock!). A standard fuel block-off plate will work with the six-cylinder engine.
This is another place where stock components will work just fine. The six doesn’t appear to suffer overheating like the V-8s do, so a stock water pump will generally do the job adequately.
Other Build Notes
• We changed out the bolts supplied with the intake with stainless Allen-head bolts. The location of the bolts is very confined, and the curve of the mounting point made the smaller-head Allen bolts work better. We opted for the Stage 8 locking exhaust manifold bolts, which was a cost upgrade, but worth it.
• There are plenty of polish and chrome accessories available for the straight-six engine; just be sure your bolt kit (if you get one) works with items like the aluminum valve cover (the bolts were too short).
• When installing the rods and pistons and/or the camshaft, note that there are flats on the camshaft to allow for the swinging of the rods. Not a problem when the timing chain is on, but when you are rotating the crank for the next piston, you can jam the other rods against the cam. Keep the cam moving to clear the rods.
• Degreeing the camshaft is a challenge. First, most components are designed for V-8s, not the six. We had to make a special spacer to center the degree wheel on the smaller six-cylinder crank bolt. On a V-8, the lifters are right there and you can get your dial indicator right on it. Not so on the six—they are down deep, and you will either need an extension on the dial indicator to get to the lifter or make a way to bring it up to your indicator. You can do it after the head is installed, which requires a light spring to replace the fitted springs, just like on a V-8.
• ARP bolts are amazing, and they have been doing this for a long time—DO AS THEY SAY. Clean your threads, use their thread lube, and torque your bolts three times if you don’t own a bolt-stretch gauge.
• Fall in love with assembly lube. If you wipe a camshaft lobe, then it is probably your fault—you aren’t getting a new cam and they aren’t paying for your trashed engine. Any point that has metal-on-metal contact needs break in lube.
• Although the engine runs great, it is going to be very close to the passenger shock tower in a Mustang with the new intake and carb. Some Holley installs may have to get creative with linkage and mounting to avoid contact with other components; the Weber fits a little better.
Conclusion, For Now
Our test mule motor is now complete. Before we take it to the dyno and see where we stand, we are going to step back and attempt to design and build a sequential fuel injection system for the straight-six. There have been several attempts to use junkyard parts but we are going for the whole package brand new. We may try to talk some other vendors into letting us test their existing EFI systems as well. Stay tuned!
Here is a list of all the parts used in this buildup. Make sure these parts fit your specific applications as variances are in place. Check out other build options online at the Vintage Inlines website.
1967 200 seven main bearing, bored 0.020, refurbished
200 crankshaft turned 0.020, refurbished
Stock connecting rods; refurbished, balanced, and machined for ARP bolts
Camshaft bolt and beveled spacer
Crankshaft bolt and spacer
Build Parts - Vintage Inlines P/N
Cylinder head Kit - FSP-250-AHP-DEP
(Includes head, intake, carburetor spacer of your choice)
ARP main caps stud kit - ARP-200-MS7
Clevite 77 main cap bearings - C77-200-MBM
Clevite 77 camshaft bearings - C77-200-CBS
Clevite 77 rod bearings - C77-200-RBS
ARP rod bolts - ARP-200-RBK
Engine gasket set - COR-250-COM
Silv-O-Lite pistons, flat top - SLV-1185-CPF
Sealed Power ring set - SPP-200-MPR
Clay Smith camshaft - CSC-274-HSP-12
Clay Smith hydraulic lifters - CSC-200-FEH
JP Performance double-roller timing chain - JPP-200-DRC
Camshaft dowel pin - CSC-200-PIN
Melling oil pump - MEL-200-OIL-65A
Oil pump pickup tube - MEL-200-PT-65BS
Oil dipstick - ACP-200-DST
Oil pan - ACP-200-OP
Reconditioned harmonic balancer - DDC-200-RB1
Reconditioned rocker arm assembly 1.6 ratio - RAS-200-HRR
Pushrods 8.230” - RAS-200-ANP
Weber DGS 38 swap kit - WEB-DGS-SWP-K
Weber carb base gaskets - WCD-WBG-PR
Dual outlet header - FSP-200-DOH
Optional upgrade Stage 8 locking bolts
ARP aluminum head stud kit - ARP-250-ACH
Alloy valve cover - FSP-200-AVC
Ford Falcon Six performance book - FSP-200-FSH
Alloy intake manifold gasket set - FSP-250-IGS
Billet single-groove water pump pulley - FSP-200-BWP
Billet thermostat housing - FSP-200-BTH
Chrome valve cover breather kit - SPT-200-VCA
Performance Distributors Street/Strip distributor - DUI-200-CIK
(Includes Livewire plug wires)
Wire looms - DUI-200-BWL
Holley Carburetor - 0-8007
Water pump stock - GMP-200-AWP
Fuel pump stock - FSP-200-MFP
6-Cylinder dress-up kit stainless - VIP-200-EFK
Camshaft thrust plate - MEL-200-CTP