Does anybody know what the recommended octane rating for a 357ci SBC w/ 11.5:1 to 12:1 compression. This is for a street car not a drag racer. The engine has World Sportsman II heads, domed ROSS forged pistons with -15.20 cc head vol. and 1.268 in comp. dist. And a Crower solid roller cam #00431 258/262 dur @ .050 and .626 lift w/ 1.5 roller rockers and 105 lobe seperation. It has a forged crank and crower forged connecting rods with ARP head and main bolts.
I don't know the head gasket thickness. Will this engine run off of pump gas 92-94 octane or am I going to have to run race fuel of 100-105. I know the engine would be happier with the higher octane but I'll like to drive it not just race it a few times a year.

 

Those are iron heads which doesn't help any...but with a large cam and a loose converter, it might run ok on pump gas. It's really a trial and error situation. I'd keep the timing around 34 degrees and take it for a spin. Check the plugs for signs of detonation which would be small black specs on the porcelin area of the plug. Spark plug is also a factor. I'd run a 6 or 7 heat range plug. That's 2-3 ranges colder than stock.

It should be pretty mean sounding too.. I have a cam that size in a stroker and it turns heads...I'd guessing yours will want to idle around 1200-1500rpm and it will appreciate being shifted just past 7000rpm if you have a decent intake/carb/exhaust setup. At the track, it would make a great deal more power if you ran a race gas like VP113 and jetted the carb up 2-3 jet sizes all around and it would also guarantee that it will run safe. Goodluck and report back if you can.

 

Thanks for your input. What plugs would you recommend. Brand? part #'s For the time being, until I can afford a better one, I'll be using a Holley 750 3310 w/ vaccum secondaries. I personally think the carb may hinder the potental of this engine. But hey, use what ya got.

 

NGK V-Force 739-UR6 is what I'd try. (UR6 for short) it's 2 steps colder than stock(UR4)

V-Power Resistor Spark Plug
14mm x .460" Reach
5/8" Hex
Projected
Tapered seat

(you'll call it a UR6, the LS guys would call it a TR6, gasketed would be called a FR6 basically..it's all in the seat/reach design, etc)


Your carb shouldn't be much of a problem. I run a 780cfm carb and yeah it MIGHT be giving up 10-20hp, it drives like EFI so it's worth it. Hopefully yours does the same. Goodluck!

I'd also install ALL of the plugs and turn the engine over BY hand 2-3 revolutions to make sure the pistons don't touch the projected tip plugs. I don't know what you have now or what kind of interference the World heads might have with a domed piston and if they suggest a projected or NON projected tip plug. Odds are they want a projected tip like the UR6 but turn it over slow just to be safe...remove them and make sure they aren't "bent" or touched at all...haha better safe than sorry.