This has been a great engine! It has tremendous torque, gets terrific gas mileage, and has been as reliable as an anvil. The only noticable flaw has been the inability to run in extremely hot weather (95+ degrees) on pump gas due to detonation caused by the high compression ratio. We've been using octane boosters and slightly retarded timing to get by. In spite of that, we racked up over 62,000 miles in nearly six years on this engine as of October 2000. It's starting to show its age, but continues to provide great daily transportation.
The log head suffers some design shortcomings that are difficult to address. We've seriously considered radical machine work to allow the addition of a decent fabricated intake, EFI, lots of combustion chamber reshaping, but ultimately it would really not yield much more power. The basic head design is very limited and you can only do so much.
The problem lies in the design of the cylinder head. The combustion chamber is a simple wedge design with little swirl or turbulence built in. The quench area is small. The spark plug location is too near the cylinder wall which increases the distance the flame front has to travel. The valves are shrouded by the chamber walls, but the small cylinder bore only allows so much additional valve relief to be added. The 1.75" intake valve and 1.38" exhaust valves can be enlarged, but then cylinder wall shrouding really becomes a factor.
On the bottom end, however, are seven very solidly webbed main bearings. The cam is well supported and the oil pump/distributor drive is near the front of the cam to reduce cam twisting from those loads. The oiling system is simple and direct, with a generous oil gallery providing the mains and the cam plenty of volume even with just the stock pump. The block is a thinwall casting and is very lightweight for its displacement. The 250 water pump is generously sized and provides a great deal of coolant flow for an engine of this size. What we have is a very good block in need of a much better head!
Ford of Australia developed a better head with a detachable 2bbl manifold in the mid seventies. They are a direct bolt on for the "integral manifold" head, but they are rare and expensive, even in Australia, and never came with EFI.
The ultimate solution for me was to skip ahead to the next generation of Australian six cylinder engines: The Alloy Head Crossflow. Produced in great numbers since the mid 70's, it is inexpensive and has plenty of aftermarket support (albeit all in Australia). This is a viable option to produce over 200 streetable horsepower! For more info on this engine, photos, our plans, and our progress, see the article on the Aussie 250 Crossflow Swap!
My 250 Engine Specs
- 1973 Maverick 250 C9DE block, .030 overbore, decked .040
- Stock Cast Crank, turned .10/.10
- 255 V8 Pistons, 9.8-1 CR, 1.585" compression height
- Hastings cast iron rings
- Comp Cams 260 hydraulic camshaft, springs, lifters
- DSII Distributor Swap & MSD 6A
- Adjustable rockers on shimmed stands
- D8BE 200 cylinder head, mild porting
- Clifford headers with 2" dual exhaust, Dynomax Turbo mufflers
- 14" Hayden electric fan
- '91 Lincoln AOD transmission
- 1 bbl Motorcraft (Carter YF) carb from 78 Granada
This engine turned a best of 15.98 @ 86 mph. Based on the curb weight of car and driver of 3100lbs, I guesstimate it produces 185 hp at the flywheel and puts about 145 to the black top.
Because the 250 has the same bellhousing pattern as a small block Ford, the AOD was an easy addition using the following parts:
- A 1991 Lincoln MkVII transmission
- Flexplate from an AOD equipped, 300 ci, 1987 Ford F-150
- A Windsor-Fox crossmember
- A custom TV lever and rod hooked to the original C4 kickdown linkage
- Original shifter and modified linkage rod
- New transmission coolant lines
- 1" shortened driveshaft
- Original C4 yoke, driveshaft shortened 1"
With 3.55 gears, the engine turns 2350 rpms @ 70 mph. Gas mileage ranged from a low of 19.2 to a high of 27.7 mpg. On average, I got 22.5-23.5 mpg in daily driving.
|Written by Forum Member: "MustangSix"