I recently started on a 351w for a 79 ford f150. Convertions are as follows: holley 650 4 bbl with a ford 351w iron 4bbl intake, 266 / 488 comp cam, heads by JCS (hich I believe if jesus had a hotrod it would have these heads on it). The problem..it runs like crap. I set up cam timing notch to notch and tried ignition timing 6 ways to sunday. I am using stock ignition set and a dual vac distr. I am getting a bad case of pre-ignition detonation under load. Exaust is clean and compression is good (stock cylinder, ring and piston size). I am going to crack back into the timing cover and see if anything jumps out. In the meantime, any ideas out there?

Lose the iron 4 bbl intake, they are terrible for distribution.

Im wondering if you are running the correct firing order. you Check the firing order on the cam card, and make sure you are running the correct one.
As for the stock 4 bbl intake, they arent the greatest, but they will get the job done.

...And I don't have the data card for the cam. Is it presumtuous of me think the stock firing order would be incorrect? I have done this before with my 66 mustang (289 hipo)...just change the cam, intake, carb and exaust for a little performance...and it runs like a raped ape. As for the old iron intake, lol, I hate it when aluminum warps when it gets too hot....lol.

Well as far as the firing order being changed, its not really presumptious, but the sad fact is a lot of cams that are sold for 351W do have the 289/302 firing order. Ive made that mistake myself, and I am far from no genious on that stuff. That is why I brought it up. It is an easy mistake to make.
What is the grind number on that cam? I dont see it in my Comp Cams book, at least not with that advertized lift and duration.

Ok, I pulled the timing cover and valve covers off and checked valve timing to ignition...13726548...they match. I am thinking of ditching the dual vac dist in favor of a single vac and going to points instead of electronic (yes, I am an old man). At this point I am pretty sure this is an ignition issue...anyone second this opinion?

All you need to do it just disconnect the vacuum hose nearest the distributor cap and plug off the nipple, and also plug the vacuum line nipple on the vacuum manifold the hose ran to. The rear vacuum line only works when the enigine is cold, allowing it to prevent the vacuum advance from working, thereby causing the engine to warm up faster. One of those genious ideas for polution control that all the auto manufacturers foisted on us back in the 70's to buffalo all the idiot lawyers writing silly regulations.