Six Appeal: Part 1
WE OUTLINE THE SHORT-BLOCK DETAILS FOR A 200ci INLINE-SIX ENGINE BUILD FOR TODAY’S DRIVING
Building a 200ci inline-six engine for today’s driving—in Part 1, we outline the shortblock details
THE DAY BEFORE I SAT DOWN TO WRITE THIS ARTICLE, A FRIEND OF MINE PURCHASED A VERY NICE SIXCYLINDER 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 sixcylinder 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, 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.
Prior to this story, we outlined the one mandatory part needed to build a better-than-stock six: the Vintage Inlines cylinder head (mustang-360. com/how-to/engine/1804-finallya-performance-cylinder-head-forford-six-cylinders). After that, 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 205225hp engine of the Fox-body 5.0L era—with the torque of the straightsix 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 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-1979. 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 bearings 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 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 engines 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 prob-
lems. 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.
With 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 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.
Conclusion, For Now
Part 1 of the engine build has shown what went into the bottom end
(short-block) of the 200. Come back next month for Part 2 to get details about the camshaft, cylinder head, and all the other parts required. We’ll finish up with Part 3 when we put this puppy on the dyno and see how much power it makes. But before we take it to the dyno, 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!
“Part 1 of the engine build has shown what went into the bottom end (short-block) of the 200. Come back next month for Part 2 to get details about the camshaft, cylinder head, and all the other parts required.”
The future of the Ford six-cylinder is here. You can now build a six-cylinder that will perform for today’s driving without sacrificing the economy and torque the straight-six was known for—possibly for cheaper than what you would spend converting to a V-8.
The bottom end of our 1967 200 is very rugged with its seven main caps, so we only did the standard machine work— we bored it 0.020 inch and had the machine shop check the align hone and deck; then they installed our camshaft bearings and core plugs.
The ARP studs torque more than the stock main cap bolts. ARP prefers the bolt-stretch method over a torque wrench, but most of us don’t own a stretch gauge. ARP instructs to torque them three times, which gets you closest to the true torque number.
Nothing special was needed for the stock crank, which was turned 0.020 inch on the rods and mains. It’s a solid piece and will hold up fine on our mild build.
We are using ARP main studs for the added strength needed for the dyno runs. Always use ARP assembly lube on all ARP studs and bolts.
We’re checking our gaps on our Sealed Power moly rings used with the Silv-O-Lite flat-top pistons. These pistons should yield around 9.6:1 compression with the 55cc chamber heads. If you don’t bore the block, check the ring gap at the bottom of the piston travel.
We chose a Clay Smith hydraulic camshaft with .450-inch lift and 224 advertised duration on 112-degree lobe centers. This high-lift, short-duration cam should give a good idle and still have good mid- to high-rpm response.
A comparison of an early camshaft thrust plate and our new aftermarket thrust plate. The 1965 plate does not have the small oil-feed groove, and the aftermarket plate has it on both sides and upside down, so you can’t get it wrong.
Don’t lose this small beveled spacer that is installed behind the cam thrust plate. It is not reproduced!
It is recommended that you do not use a high-volume oil pump, and that the standard pump works fine. We chose a quality Melling pump for our build. Don’t forget your distributor driveshaft.
Our oil pan was beat up, so we opted for a new one from Vintage Inlines. The stainless dress-up kit is also being used on this build.
With our bottom end assembled, we went ahead and painted the block and oil pan with a coat of Ford Corporate Blue (Omni # 13358). This will really set off all the polished aluminum planned in the build.