I've not done a full pre x-flow rebuild yet, but I have to work through the same cam and valve issues myself soon. I'm using every post here as a good foundation. The specifics have to be worked out with the engine builder. There is so much to deal with!
Q1
o I need a special piston to run 200 rods in a 250 pre-crossflow (i think i read that ACL make pistons to suit the 250 crossflow with 200 rods) or will any oversized replacement pistons suit?
A1: No, but I've heard tell from others that the 200 rods need clearance with the pistons to gudgeon pin and skirts. Normal linishing should help. I've not seen any confirmed cleance problems, although
Overdose has some evil pictures of side skirt breakage, which we thought was cam related.
Q2: If the car was to run on optimax what compression ratio should I be aiming to achieve?
A2: That's Shells 95, or is it 98 octane? The deal is that if the engine has a bigger cam, and runs the normal Aussie engines close piston to deck register, it should be able to hack high 9's. All engine builders tend to err on the cutious side by never going over 9:1, and maybe 9.5:1 on an cast alloy head. Its your call. If you go for those low load stress, long duration cams, it should be able to take a large amount of compression. I'd follow the best mean advance method for seting advance, and check the psi while being cranked. If its over 180 psi, then alter the cam timing to reduce the pressure to 160 psi. Then it won't knock. Last option is water injection. Yeah, poo-hoo it if you want but its got its place!
MustangGeezer's 200 with a single 500 Holley is on 11.2:1 with the Log head, are you game? He runs water injection, and a wilder 272 cam, from memory.
Q3:Are the larger stainless steel intake valves you mentioned avaliable in Australia, if not what else could be used for a similar result?
A3:The best option is to check out Chevy ones from the Ferras range, or do some local Yella Terra Bat 1200 Red/Blue L6 and XT5 V8 checks. You have to look at a more exotic material than the later valves, Nimonic, Iconnel are rare, but some early intake (21N material) valves can be used as exhast valves. The key is allowing the heat to be conducted without scuffing to take place, and a stainelss steel is the best option. The tuliped, Rimflo types are best, but it all gets very expensive quickly with valves.
The key is finding the critical height dimensions, and then doing the leg work. Sorry, can't help past that. In New Zealand, we find Sedgins has most of the details, and you can do custom valves if you know what you need. When Addo gets back, PM him, and tell him I sent you.
Q4:And finally you mentioned using XE cam and timing gear, can I also use an elctronic distributor from an XE in a pre-crossflow 250 or will it need to be modified to suit?
A4
o a search on the cam gear failures on this Aussie forum. The best option is getting a brand new Crow gear, and check that the dissy diameter is the same, that the distrubutor is well oiled with both lituim grease and half weekly doses of 10 mls on 20/40 when running in. The XE dissy needs a specail M8 or 5/16 bolt placed on the dissy flange to hold it tight, as per the stock XE item.
The end float must be within spec, and a new brass bush, 10 bucks from Ford, needs to be fitted. There are some details I can share some time on the rebuild. I haven't run a 200 or pre-log with an XD/XE electronic, yet!
Q5:This engine will be going into an XP falcon sedan with a four speed so I difinately think a brake and diff upgrade may also be needed as its running all the standard tiny four stud parts at the moment.
A5: Yep, you'll need it.
Sorry bud, out of my depth. The valves are the key to sucess. Don't go too big on the exhast, and don't settle for short valves, as the rocker geometry with small base circle cams is often not as good.
Best wishes,
Deano