This has been discussed at length before. Very good to discuss and debate the details, you will find the answers before you spend money with the advice from people here.
I'm very serious about the 30 thou lift duration figure, it governs how much overall cam duration your combination can handle, and still idle. Port injection engines are more governed by cam window area, to fit in with maximum piston speed and the cam timing needs to phase in with that. For non independent runner, 2 or 4-bbl cars and CFI systems where there isn't one port per piston, you can get away with a
lot more.
The 200 vs 250 is the most different combination. Despite the fact that 240's and 300's, 200 and 250's, 302C's and 351C's in there base application used the same cam on the small version compared to the bigger,
the 200/250 engines with different heads should not be considered similar in any way. One good thing is that the same cams were used on different headed 200 and 250's all over the world, and a factory 256 cam works fine on any kind of 250 engine, iron, log, 2v, x-flow or Classic Inlines.
The 1985-1987 162 to 164 hp XF Falcon ran a special upgraded cam because people complianed that the stock 82 to 84 149 HP EFI engine was so tame. The last 85 to 87 EFI cam spec copes with early 2v heads and there huge 1.65" ports just fine, so a stock Aussie EFI 264 cam grind on a non crossflow camshaft balank would be a good start with a CI head and 250 engine combination.
events 24, 60 exhast, then 60 exhast, 24 intake
advertised duration
IVO 24
IVC 60
EVO 60
EVC 24
LSA 109
Duration at lash for hydralic cam 264/264,
50 thou 196 in /196 ex
total lift at valve with 1.73:1 rockers was .439"/.439"
On the small 1.33" port head, power from 900-3400rpm on an EFI port injected engine
The Clay Smith 264 is
much more agressive than this, the most aggressive for 50 thou duration you can buy, and since it copes nicely with any 200 or 250 log head, it would be my best first option for a 250 CI headed engine.
The 300 carb or efi cam grind would be good as a perfect minimum starter cam, too
Advertised Duration
IVO 18
IVC 70
EVO 58
EVC 30
LSA 110
stock 300 cam is around .400 lift and 192 duration @ .050
In general, the rule is that as you become increasing under square and your capacity increasses by stroking the engine, you normally just run a more radical cam, and you can expand the LSA. The problem is that the CI head is a big port, high flow head, and even with a 250 cube engine, it doesn't like big cams when you use stock converters in an auto application. If its manual, you can get away with much more duration. When Ford designs a cam, it often makes a single grind which suits auto and manual, and then customises the converter if the cam is used ibehind an auto. This was what they did in the 351 C 4V HO dayS, and again in 1983 with the 5.0 HO engine. With certainty, Ford always ensures its engine cam combination suits the clylinder head flows. So its very like comparing a Cleveland 351 to a Windsor 351, or a Boss 302 to a Windsor 302. The bigger flow and port area head always kills low end torque when the same cam is used with a smaller flow rate, smaller port and intale runner head. In the killer HO Mustang engine options of 1969 to 1973, and again in 1983 to 1985, Ford ensured the manual and auto engines got very specific camshafts to suit the heads.
A 250 2-bbl log head with 278 solid lifter cam will idle much nicer than one would imagine, but a 250 with CI head and 2-bbl and even a 264 cam might idle with more chop than the 278 cam. It all depends on what stall ratio, power options and restrictions you have on common use. The Holley 2-bbl carb is very influenced by high intensity camshafts when intake runners are big and low lift cfms are high like they are with the CI head. Old 2V heads on 250 engines tended to have problems with 500 cfm carbs and higher than stock 256 degree cams. The problem is that its very easy to over cook the 30 and 50 thou durations, and if the lobe separtion is too great, the car won't idle properly. Cam designers know just how much you can push the friendship.
The 250 has a long stroke design, a very short length of rod to stroke ratio, and the CI head has a large port area. A cam that works on a 1-bbl log headed manual, non power steered 200 wont suit a 2-BBL ci headed auto with power steering.
Converter stall ratio, carburation, engine capacity, a/c, p/s, brake booster, diff ratio, effective compression of combo before mods verses effective compression with the cam retarted or advanced on the crank of a 250, everything influences evertything else. Intake runner volume, and if the the engine is running port on port or a large intake volume influneces maximim duration.
See again
viewtopic.php?f=1&t=68948&p=528890#p528890
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