Probably a Dumb 318 Question
I'll chip this in before this thread turns into a complete **** show:
A lot of guys will jump on the "get a 340/360" bandwagon - which is good advice if you are shopping for a motor to build up BUT you already have the 318, so i say go for it.
Also God help you if dartswinger70 reads this - it will turn into endless posts about UTG (totally unrelated) and how 318s can only ever be the 200ish HP engines that they were from factory and its pointless to try to do anything with them :BangHead:
You might get more usable info asking how to build X HP per CI than how do I build a XXXHP 318. A 400hp 318 is 1.24HP/CI at a +0.030" bore (the equivalent of a 420hp 340 or 445hp 360 - been done plenty of times before)
Definitely not impossible to achieve but will take a bit of planning and parts selection vs just slapping something together.
So a little bit of info in no particular order:
318s are harder to get a decent compression ratio out of due to the short stroke and smallish bore - domed pistons are the "easy" button but generally don't play well with closed chamber heads (will run you $$$ at the machine shop with mock assemblies and machining of the crowns for adequate clearance). My 318 comes in around 9.8:1 CR with KB167 pistons 0.014" above the deck, 63cc combustion chambers and 0.051" head gaskets to set the quench at 0.037".
The wiseco or icon forged pistons will be more forgiving if you run into detonation. Also worth noting that most 318s have "340" rods just without the small ends bushed for floating pins.
It was cheaper for me to reco/prep the factory rods, set them up for floating pins and fit them with arp bolts but I'm in Australia - in the US it may be cheaper to just buy new rods.
Ported speedmaster heads will flow plenty for what you want to do - just make sure you are lifting the valve enough to take full advantage of the extra flow.
High volume oil pump, windage tray and baffled oil pan, some oiling mods are outlined in a sticky in this forum
Arp main cap bolts or studs
There are better suited cams than what you've got on hand - make sure your chosen parts complement each other
Get a good ignition & timing curve sorted for your setup
Spend money on getting everything ballanced
Spend money on a good valvetrain components and a B3 geometry correction kit
Spend money on a good intake, carb & headers
Spend money on a good modern torque converter, shift kit and making sure the trans is in good condition - no point putting a trick engine in front of a clapped out slipping gearbox
See the trend here? $$$
Don't be afraid to make it rev
Make sure the rear end, suspension & barakes are up to the task. ( if it has the factory diff for a slant 6 car you will probably kill it on the first drive)
There are likely a few other things I've missed here
Or there is this for a lot less money and effort:
460hp, well maybe not on a typical hot rodder's budget, but can it put out as much as a factory 340? you betcha and it would be a blast to drive, even on pump gas.