Thread: GT 40 P heads Biggest cam with stock rockers

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Here are just a few variables that come to mind and the reason nobody can give you a definitive answer....
Piston deck height
Piston crown configuration
Piston valve pocket placement and size
Valve size
Gasket thickness
Valve seat location relative to the deck of the head

When you first think about my explanation, you might think that you should just check it with the piston at TDC. The thing is, at different piston locations in the bore, the valve might drop down into a pocket, whereas it missed the pocket in the position before or after. That's the reason I said to check at different piston locations in the bore.

Valve to piston clearance will normally be tightest on the exhaust valve during the overlap period when the piston is chasing the exhaust valve back onto its seat.

Ok some info I have stock pistons , 1979 block . valves on the P heads are 1.84 and 1.60 pistons are super cut for low compression .

Are going to convert it to a roller motor? I did a bunch of mods a few years back with a roller 302 block.. it had stock crank and rods, 306 probe pistons that were .030 over with 8.5:1 before the blower. The p heads were worked and had 1.6 ford motorsport roller rockers. I went with a custom ground cam that was equivelent to the lift of an "X" cam. ( about .540 lift) my pushrods were not stock length and cannot remember the little specifics of it.. I built an 83 nonroller motor and had nothing but problems with that one.. it wasn't worth the money.. and to tell you the truth... either was the GT40P heads.. the explorer heads were okay back in their day.. they are a far cry from the GT40 heads. today I would have went with a set of RPS cast irons for the same price. Don't take this as gospel.. I had a lot of heart ache with this combo.. I wanted to build a race motor for the street.. I broke more things than I care to write about.. I paid more cash than I would admit.. and have made friends with the local flatbed driver, all for the sake of the Need for Speed... The motor finally crapped out when I lost a valve keeper down into the motor and you can figure out what happened there..
The motor ran 12.90 in the 1/4 and just didn't have any more pull on the top end due to the heads.. Now I have a 331 with reinforced everything!! 210 cc flowing heads with a custom .600 lift cam, 8 lb supercharger and big injectors.. It has almost 600 horses and I am afraid to run the damn thing because everything is just so expensive if it breaks.. does it make sense? I have about $8K in this motor and now the car sits in the garage most of the time... Now my new project is an 86 Buick Regal with a BBC and an 8-71 supercharger.. Once that is done right.. I am guessing it will also sit in the garage.. go figure????

Bobby,
With the stock pistons you will be limited to not a lot over .500 lift even with the dished pistons and OEM fly cut - that is unless you do some more fly cutting of the valve reliefs. My last 351 I stayed right at .512 and it was fairly close even with the fly cut hypereutectic pistons. Of course if you choose to replace those OEM pistons with something else, then the sky CAN be the limit. I do remember that you are trying to build on a reasonable budget, so do understand that your options become somewhat limited as to where you want to go.

As far as stock rockers - an out of the box Performer Plus will sound nice, run decently http://www.edelbrock.com/automotive_..._ford_sb.shtml Of course, some roller rockers........

AS far as HP3445's comments, he is correct if were building a race engine, not a streeter with a nice idle.