The 200-250 Engine Swap

The 250 is in the same family as the 200 making the swap relatively straightforward. Nevertheless, there are some items which need to be addressed in order to make the switch.

These comments apply to the swap performed on my 1966 Mustang. Later model Mustangs, Falcons, Fairlanes, and Mavericks may differ in details, but the same items should be considered.

Engine similarities and differences

The 250 was developed from the earlier 144/170/200 family of engines.

In order to accommodate the large increase in stroke from 3.126" to 3.91", the block deck height was increased and the cam location raised. Outwardly the engines appear very similar, but measuring the deck height (crank centerline to top of deck) shows that the 200 has a 7.808" deck height and the 250 has a 9.469" deck height. The cam is repositioned higher in the block to provide for crank clearance. At the rear of the block, the 250 was redesigned to accommodate the same bellhousing pattern as a small block Ford V8.

The flywheel to crankshaft bolt pattern is identical to the small block V8 and the 300 ci six cylinder. Although Small Block V8 flywheels will fit the 250, the balance is incorrect. 200 flywheels will not fit because the bolt pattern is smaller. The 250 and 200 oil pumps and pickups are different and the oil pans are different due to the 250's added width. 250 rods are longer than 200 rods. Valve pushrods are different due to length. 250 water pumps are larger as are the crank and water pump pulleys.

The 200 and 250 do share the same pistons, fuel pumps, valve covers and camshafts (although the lift and duration vary over the years). All 144-250 cylinder heads and rocker arms will physically interchange, but there are variations in combustion chamber size, carburetor mounting pads and pushrod ends. The motor mount mounting bosses are identical and in the same location relative to the bellhousing face. Exhaust manifolds will interchange across all years, but there are variations for emissions and exhaust pipe size.

Things to consider when swapping the 250

Height, width and length

The 250 is 1.66” taller than the 200. On early Mustangs this poses a hood clearance problem. The original early air cleaner is too tall to clear the hood. However a Maverick or Late (79-82) Mustang air cleaner is lower and will provide needed clearance. Because the carburetor is now higher, the throttle linkage also needs to be raised either by bending the linkage or extending it. The original lines from the 200 fuel pump and the vacuum lines from the carburetor will also be too short and new ones need be made.

The 250 is approximately 1.5” wider at the motor mount bosses. The original Mustang mounts can be used, but they will place the engine higher in the compartment because of the way the brackets are angled. Elongating the bolt holes in the engine mounts to allow the engine to drop slightly will help, but the proper solution is to use Maverick 250 mounts and brackets. The Maverick mounts are designed differently and will require new bolt holes in the frame.

The harmonic balancer and pulleys make the engine about 1” longer overall. This makes it difficult to install an engine driven fan. Even if there were adequate clearance lengthwise, the water pump on a 250 is higher which reduces clearance between a fan and the top radiator hose. The easiest solution is to add an electric fan.

Transmission options

The bell housing is the same as a 289/302/5.0 V8.

Manual options
An original 65-66 2.77 non-synchro 3-speed cannot be adapted because there are no suitable bellhousings and the torque of the 250 would quickly shred that tranny. The same applies to the 4-speed Dagenham transmission.

The 67-up 3.03 3-speed and 4-speed toploaders can be used by employing a 250/289/302 bellhousing. The Tremec 5-speed will also fit using this bellhousing. The late model 5.0 bellhousing and T-5 transmission will bolt on and standard T-5 swap procedures apply. For the really ambitious, it's even possible to adapt a T-56 six speed using the same procedure as used to install one on a V8. The bottom line: if it will fit a small block Ford V8, you can adapt it to the 250.

300ci flywheels and bellhousings will also fit the 250, but since most of these came in trucks, you will have to check for clearance and release mechanism compatibility.

The 250 flywheel is has "0" imbalance since the engine is internally balanced. The stock flywheel is 13.25" in diameter and has 157 teeth, just like the 289/302/5.0.

Automatic Options
Although the original C4 tranny will not bolt on without a bellhousing and torque converter change, it opens the door to a number of other transmissions. If you are determined to keep an original 200 C4, you will need to change to a V8 C4 bellhousing and torque converter.

Late model AOD/AODEs can be used behind the 250 as can any other automatic (C4, C6, FMX) which has a small block pattern. To use an AOD, a 164 tooth flexplate from an AOD equipped 300 ci six must be used.

Other items

The starter position is different than a 200. On most 200's the starter is above the oil pan alongside the block. The 250 starter location is identical to the V8. It is below the block alongside the oil pan. Although the 200 starter will bolt on, the orientation of the engagement cover is wrong. A proper 250 or small block V8 starter should be used. A 3.8 V6 starter will also fit and is smaller and shorter if header clearance is an issue. Tilton or Ford Racing gear drive starters for a small block V8 will also work.

If using a stock exhaust manifold, the 200 exhaust pipe is bent wrong and will not clear the 250 starter position. The stock exhaust pipe from either a 69-70 Mustang 250 or a Maverick 250 will clear the starter. Headers designed for a 200 may not fit for the same reason, but because different designs may work on multiple applications, you will have to trial fit them yourself to make that determination.

Accessory brackets from the 200 will not fit. The mounting bosses are located differently. Cars equipped with AC and PS will need the brackets from the 250.

The 250 water pump is larger and the outlet is larger than the 200. A Maverick lower radiator hose fits most applications.