I am building a 351w from a 1983 F350 with about 50,000 miles on it. I bored it .030" and had to deck the block about .052" to get the pistons about .0005" below the surface. Using a .040" gasket. I have a bigger cam, Not much more than stock , same crank and connecting rods. I have Gt40 Heads that have been surface ground and are 62cc.Using 7.2 Crane Bolt down roller rockers, and 8.100 pushrods. I have an aluminum Intake Manifold and Ford Motorsport Headers. I see that a stock 351w has about 8:5:1 ratio, and I am ending up around 9:7:1 ratio. How is this going to run, will it ping and will i need to run 93 octane??? It would be a big help if I could get some Info From you guys, THANKS

 

Here try this .You got flat tops? You got to now the dish of your piston in cc's.https://mustangforums.com/m_782863/tm.htm

 

WOW that's a lot of math! 9.7:1 compression "might" be able to get away with regular octane, but has a lot to do with how much timing advance you're gonna use. Or meaning, how power greedy you gonna become lol

Once it's built start with premium for break in, then reduce octane till you hear trouble brewing, then either up the octane or retard the timing.. My $0.02

 

+1 to GreyStang's recommendation. 9.7 isn't too radical, but won't like el cheapo gas. I run 91 octane on my 10:1 engines, generally.

 

Correct me if I'm wrong, a big block with higher compression is probably going to need higher octane to begin with before any timing advance...Sort of a question on my part too...

 

That's an interesting question,, but I would think 9:1 is the same be it a big block or small.. Combustion chamber shape probably has more to do with issues than does combustion chamber volume

And,, a 351W isn't a big block if that's what you're referring to

 

Block size won't determine the octane, but compression ratio, compression chamber shape, and materials will all play their part in determining what kind of octane would be needed.

 

bb/sb dont matter guys..9.7 wont need 91 oct unless ya adv it too much//10.1 will run fine on 89 if flat topa are used ..domes usually need more octane to not detonate..10.5 in flat tops can run lower oct over a dome with 10.5...with out gettin into all of it..its a quench,space(more n less) thing...i have domes and 10.5 with just 9* adv and can rum 89 but isslugish...if i run 91 its ok,93 better,and 104 perfect.. i had 10.3 with ft once and i could run 87...he has no prob with lower oct,if its just a mild build..