Listen vewy carefully!
QUESTION 1. Ask your self, HOW MUCH MONEY DO I HAVE?
FACT 2. Know that if you just add a turbo, you can get 450 hp with a practically stock 4.1 X-flow. Why would you ever want a 350 NA car?
FACT 3. FOR NATURALLY ASPIRATED OR TURBO POWER FOR LOW COST YOU CAN'T BEAT A 265 CHRYSLER HEMI. Add a Turbo, and you into the 500's with just a Impco CA 425 and propane and 12-17 pounds boost, more if you run a better 4-bbl intake and big turbo. When it comes to power, the Mopar is a better engine than any small I6 Ford 250.
FACT 4. For naturally aspirated power at substaintial cost, you can't beat a DOHC Barra 182 or 190.
The cost of getting it to the 240, 245 or 270 Kw level without a turbo is huge, as the costs are 1500 for a custom computer which is no where near as good as Fords computer , and 1000 or more for dyno tested cams which will do the job. Remeber, its got vairable cams, and Ford spent 2 years remapping the Barra 182 engine just to get another 8 kw. Plus the cost of fitting the engine to a Cortina, which isn't so bad now that there are Territory sumps which clear the rack and pinion steering and little cross memeber.
FACT 5. For the Falcon 250, 2V or X-flow, you have a pretty bland vanila base, tragic valve gear, a lack of good quality stock valve materials , no really good rev range compared to a Ford OHC or DOHC over even a 265 Hemi, and a lack of good four stage autos to gear the thing for performance. 3 speed C4's are great for a weekend machine or turbo, but you can never run a 350 hp NA 4.1 Litre car on the street with a 3-speed auto unless you compromise on a 3.5:1 diff ratio. The 4-speed Toploader used from 1968 to 1973 are good gearboxes, and you find them in Cortinas and some Falcons, and later four speed F100 utes, but they then have awfull gear ratios. The 289/302W and 351C sedan ones are well geared, and are the ultimate economy option for strength and gearing. 4-speed Single rails (1973 to 1986) may hack the pace if they have the close ratio 351 gearset. The 1986-1993 T5 5-speed gearbox option has to be upgraded to suit, its the locally made version of the US World Class T5, but has a lack of good quality bits. It has to be upgraded th Barra T45 spec just to hack the loads of 350 hp. You can adapt a custom Toyota Supra 5 or 6 speed. But agian, unless you spend 3 or 4 grand on a gearbox, you are handicapped for ever making 350 hp streetable. That is not the case wih the dohc, as ever transimission is a winner.
FACT 6. Mathematically, based on simple BMEP calculations, to get 350 naturally aspirated hp from a 250, you are going to have to pull 6000 rpm, and get power at about 5500 to 5800 rpm. You'll have to use three IDA or IDF carbs or some aftermartket DHLA 48 Webers. This was done back in the early 70's on 2V's in Cortina by a guy in New Zeland. Such set-ups are awesome weapons, even with a 4 speed Toploader.
The real issue is that the cost of electronics and cams on a Barra engine prohibit developement. The Mopar is down right cheap, and the Ford I6 has to have a really good triple Weber or Dellorto induction system to make up for the design compromises the 250 has over a 265. No matter if its an X-flow or 2V 250, the valves, port sizes, head and piston and rod dimensions hold the Ford I6 back about 30% behind a 265.
If you decide to go balls out on a 250, you MUST use an independent runner intake, a great 4-speed auto or 4, 5 or 6 speed manual to make it work, a good 3.5 ot 3.25:1 diff, and you have to get a cam designer to build the cam to suit the specific combination, right down the the venturi sizes, ignition curve , gearing and mechanical valve train, valves, port sizes, head and piston and rod dimensions. You'll have to use custom Chevy 6.2" rods, and good custom Ross or ACL short deck pistons.
Such combinations have been discussed by an ex Ford SVE engineer who did work on the 2V and X-flow, and there are benchmark examples of 350 naturally aspirated Ford 250's in Kiwi sports sedans and Aussie drag racing, but you have to copy a known combination, and its very unlikely it will ever be streetable.
