Hi,
gotta short question about my compression ratio.
Currently I'm trying to figure out if I need different spark plugs 'cause I got different heads. I know how to calculate things like that, but I'm short on tech data's about that. ;-) And I don't know whats cc means. Well I know that it descripes the size of the combustion chamber, but in which semantics.
So, I got an LG4 V8, I got in mind that these heads has 76cc stock, my new ones has 58cc. So do I need spark plugs with a differnet heat range? Or can i run stock?
Hawk

 

Stock LG4 heads were usually the 416 casting, which is 58cc nominal.

76cc heads were used on 350s and 400s through the 70s. I don't know that they were ever used on 305s.

cc = cubic centimeters

The stock heat range will work with those heads. However, pay attention to the seat of the plug, where it seals against the head. The stock LG4 heads would have used a "tapered seat". Some aftermarket heads require a washer seat. Check World's web site for the spec for your model of heads.

 

The S/R got straight plugs. Is that washer or tapered?
My english isn't that advanced ;-)

 

http://www.worldcastings.com/catalog/18.pdf

Look in the "technical specifications" section.

They call for tapered seats, which is the same as stock. The stock plugs would have been AC/Delco R45TS IIRC. Start with those, see how they work, adjust from there if necessary.

 

Thank you very much...

 

The S/R 305 WP head is supposed to be 58cc. Often the chamber is a little bigger than that. Its up to you to CC the chamber to get its actual volume.
You can flat mill the head to get the CC you want.
These heads are a very good 305 head replacement. They don't really flow much more than a stock 305 head does. The S/R heads are intended as quality "Stock replacement" head. But you can really make them into a high flowing, high performance head with some porting as there is lots of meat there to play with and they already have a larger valve.
Dart/ World products heads have very big intrusive valve guide bosses in the valve bowl that need a serious contouring and streamlining to kick the flow up. They need further bowl/pocket and shortside radius smoothing under the valve to enhance the airflow. use long shank cutters to avoid contacting the valve seats with the grinder. Work from the port flange side as much as possible when contouring the guide boss to a streamline teardrop shape.
Thats up to you.
For a high compression motor that sees a lot of WOT use I use a slightly cooler than stock heat range spark plug to gain some detonation tolerance.
AC/R44TS or AC R45TS is stock. Good for daily commuting in a stock application.

A high performance motor that sees a lot of WOT use creates more combustion chamber heat at WOT.
Can use a slightly cooler than stock plug heat range.
I use a AC R42T or a Champion RV8c non projected tip plug for racing, with high(er) compression ratio, moderate nitrous or supercharging.
These hi-perf plugs are no so cool in heat range as to cause fouling in normal driving. Just a little cooler running than stock for "performance driving" They are actually a common SBC Hi Perf Marine specification spark plug.