Kendalls ideas rock.
Where the x-flow has one huge key advantage over the better 1988 to 2007 Ohc engine, is its ability to fit any car which first had a 144 to 250 US engine. The percentage of US parts needed to get an X-flow going isn't much more than ignition, efi, and perhaps the pushrods, valves and any number of cheep ACL pistons.
The OHC is serverly crippled because of its engine mounts, the bellhousing incompatability, its wacky starter postion, its length, its width with the normal EFI intakes, and, in some versions, its sump. Yet again, people in the US have understood that its better to have a drop in an X-flow engine which can fit the US T5 gearbox with an adaptor plate, than have to cobble up a dumpster load of spare ignition, EFI and special mounts and bellhousings to suit the X-body Fords.
I got an XF EFI. 164 HP and somthing like 247 lb-ft. Stock engine has as much power and torque as the US 4.9 EFI
Any kind of Waste spark ignition (V6 Explorer, EF, AU Falcon), the simple Megasquirt for 225 US bucks, and its proper MAP sensor rather than the air vane are the best first ideas. Best of all, the Aussie CPU and air vane can be hurled over the nearest riffle range for skeet shooting practice. The Bosch LE system may have been cutting edge in 1982, but its old stuff now.
The hp limit on the EFI is the stock vane air meter. That is what sucks in the EFI....the lack of adjustability. According to enginers in the late 80's, 196 hp is all there is with cams below 280 degrees /215 at 50 thou. According to info in 1995, 185 hp is possible with no mods to the EFI, but relocation of the air vane to allow a better exhast header...the stock one is dreadfull.
The XF EFI cam was a good one at about 264 degrees, way up on the piddly 256 degree carby camshaft. The only difference between a 200 to 230 hp 4.0 OHC 2003 engine and your X-flow are the much smaller valves and intake ports, the 1.73:1 rockers (rather than 1.9:1 or 2:1 the OHC used), 5.88" rods rather than the later 6.06" ones, and the nature of the camshaft and the EFI and ignition. The OHC has a better crank and balancer, but if you really want to, you can fit an EL crank to you XE.
So if you focus on
1. just the EFI,
2. exhast and
3. ignition first,
your well on your way to nirvanna. In stock form, the torque from a good 250 X-flow is great, and the power from 4000 to 4500 is not bad, enough for a 16.5 second quarter in a 4-speed 3200 pound car.
4. Do a bare minimum rebuild of the bottom end and the stock head. Add the ACL shallow 1.163" tall pistons with the 8 cc dish to the 6.27" 3.3 Xflow rods, and look at getting an EF or EL crank and balancer and flexplate. Ever since 1966, the Aussie Ford Sixes have used the US spec 160 tooth 289 flexplate from the early Five bolt SBF block. The rear seal in the X-flow block has to be reworked to suit the EF to EL crank flange.
Then tune it up with a proper modern EFI and ignition system.
5. After that is done (it'll take you a year), make up an XE head, slap a set of 1.96" intakes and a 1.64" exhast valves (ex 351M or 400 Ford, in stainelss, and cut down from 2.05 and 1.71 to the sizes above). Open around the valves and cut back the valve inserts. It'll cost you a lot in machining bills, but the bits will be great. Then use Boss 351 studs and roller rockers and custom pushrods with guideplates. The intake ports form the rocker pedastalls for the exhasts, so just ask your machinist to be carefull installing the screw in studs so they don't break through the exhast port. You can find some 1.8:1 lifters and get a custom cam to suit. There is around 230 hp in that if you use a 280 degree cam.
Best part is, you still have a stock looking EFI, and a heap of grunt. The later cranks are awesome, the distributor gear is gone, the EFI is adjustable, and the better Boss 302/351, 351m, 400 replacement valve gear is really good for 6500 rpm.
Your 250 X-flow may almost match Mikes stock alloy head on a worked 250.
