Head
- 4L has larger ports in the head standard and repond better to turboing if used totally unmodified
- 4L has larger inlet and exhaust valves standard, 4.1L has room for bigger valve but this get expensive doing new valve seats etc
- 4L will flow around 430 hp, the 4.1L around 410hp when ported to the max virging on hitting wter jackets, with big valves etc.
- 4L has a bigger chamber so you only need 11CC dish to get 8.5:1 compression where the 4.1L needs the 27.9cc dish piston
- 4L valves are more canted so they need valve reliefs cut into the pistons, 4.1L engines have plenty of piston to valve clearance

Inlet manifold
- 4L have better inlet manifold design. Either EB-ED style or EF-AU multi path manifolds are better than the XF banana manifold.
- Turbo fords either 4L or 4.1L really responds to custom short runner manifolds with big plenums
- XF right through to AU engines use a similar size throttle body

Block
- 4L has slightly stiffer block but the 4.1L block is proven to handle 900 hp so doesn’t matter unless you want 900+ hp.
- 4L has the start motor on the passenger side which allows more room on driver side for exhaust. Free flowing exhaust is critical on a turbo engine so this is quite a big advantage. You can however fit a 4" dump out of a 4.1L engine in a Cortina so again this is something you can work around. Again 4L might be advantage if you need a 5" dump (1000hp region)
- 4L block has a BW40 bellhousing pattern so a $400 adapter and different flex plate and converter is needed if you want to run a C4. 4.1L came standard with C4 in XD falcon towing packs.

Crank
- 94DA 4L has the fully counterweighted crank although this can be grafted into an 86DA crossflow block anyway

Conrods
- 4L and 4.1L have essentially the same conrods although 4.1L are imperial bolts so ARP bolts from 289 windsor fit easily. ARP now do rod bolts for the 4L but they are harder to get
- No one makes off the shelf aftermarket conrods for either engine. The aftermarket, Atomic, PAR or Spool conrods for BA engines can be used with custom pistons in either engine.

Pistons
- 4.1L happily take the 27.9cc dished ACL duralite which esily get you 8 - 8.5 compression you need. 4L has a bigger chamber so the 11cc dish ACL race series piston gives about the same result.
- No one makes off the shelf forged pistons for either 4L or 4.1L engines, 4L is a bit harder to get custom for as the valve reliefs complicate it slightly.

Fuel System
- No differences here stock fuel pumps, injectors and regulators are not much use for a turbo engine regardless of what engine they were on.
- The fuel rail used on both engine is pretty good and with minor mods can support 1000hp fairly easily.

Cam and Valvetrain
- A stock 4L cam is around 114 lobe centres standard so works quite well on a mild turbo engine. When you want to go chasing 500+ rwhp the 4.1L has a lot more cam profiles available right up to full roller cam setups with very aggressive lift rates. The 4.1L valve train is identical to the 351 cleveland and roller lifters from a 460 big block ford engine can be fitted in the lifter bores. The 4L is limited to about 230 degree duration @ 0.050" lift on a 114 lobe centre cam which is good for around 550 rwhp engine combination.
- Both 4L and 4.1L have pretty poor valve springs that should be ditched. 4.1L engine have readily available double valve springs and retainers available fairly cheaply, I am pretty sure 4L are easy enough to get good springs for also.
- 4L have roller rockers standard which are good for reasonable sized cams. If you get to the stage the 4L is breaking rockers then there is no billet items available. 4.1L use Cleveland rocker gear and Yella Terra roller rockers are readily available but these are around $400 - $800 a set depending on what type you get.
- 4.1L have a pretty ordinary timing chain standard but a rollmaster double row chain is only about $90 which allows the cam to be dialled in with the multi keyways etc. 4L have a double row chain standard but being OHC the chain is a lot longer and has the hydraulic tensioner. The 4L chains have been known to break on cars racing the Saloon car series. There is no stronger chain available for them. Cam adjustment can be done buy using a vernier cam wheel on the cam sprocket. This is convenient as it can be adjusted by only removing tappet cover.
- Both engine use the same oil pump. 4.1L drive off the cam, 4L have a dummy shaft in the front section of the block where the cam used to be just there to drive the dizzy and oil pump.

The Crossflow blocks changed four times.
First was the 76DA,
then the 80DA,
then the 83DA
then the 84DA,
then the 86DA.

The first 76DA was a cast iron x-flow, nigh on bomb proof.
It runs the same time honoured rope seal found on the US 250, and earlier post 1970 Log headed Aussie 200 and 250's.

The first of the 80DA's were Honda alloy head x-flow, higher compression, sensationally economical.
Prone to head gasket failure due to foolish people not following the corrosion inhibitor anti-freeze spec.
The block had locating dowles to stop the aloy head fretting ,and minor ( tiny) changes to the water galleries.
The 2-bbl Alloy Head II engine came out in mid 1982, and was the same engine with an intake swap.

After 1983, all Alloy Head II and EFI Falcon XE's got blocks with the 83DA code, the first block without a drill hole for the Cortina dipstick.
The rear main seal was still the rope seal, and the engine had a new HF5 cylinder head with cut-outs for the EFI injectors, even it the carby was still found in the base model.
There were some other changes that justified the 83DA label, possibly to allow the EFI.
Valve sizes were the same as the first Alloy Head XD and XE engines.
There is still a boss for the rear moutn Cortina dip stick, under the 83da-6015-AA part number.


The 84DA had the new neoprene seal, a 360 degree affair which was easy to change.
The bad point was that it tended to leak rather a lot.
It's not worth worring about, though.
It was a concession to the need to ease service and warranty claims.
The block no longer had a boss for the Cortina dip stick, under the engine casting number.


The 86DA was designed to run the Dec 1987 run of OHC crankshafts.
The two engines were fitted side by side on the same Broadmedows line.
The 86DA engines were initially stockpiled for use, and then drip feed using OHC inventory for the next 5 years.
The Falcon Utility was a huge success, with Ford having introduced it in 1979 from a reheated 1972 design.
The x-flow engines were used because they expected to axe the old ute, but the rampant inflation made Jap utes very expensive, and Ford just kept churning them out at about 10,000 units a year.
The big change was the so-called dog turd OHC crank seal.
This made both the 3.3/4.1 x-flow and 3.2/3.9 OHC cranks the same.