Compression ratio

[jeffnoel]

I know there are charts that show what the compression ratio would be if you take say a 78 302 (8.4) and install 69 351W heads (goes to 9.5). These charts are assuming your keeping the stock 78 302 pistons. What if you changed to flat tops and did the head swap? Any ideas on what the compresion ratio would be then? The only reason I'm referring to 351W heads is that they have the same 60cc combustion chamber which the aluminum heads I want have.

 

[Northern J II]

If the flat top pistons are level with the top of the bore, use a 85-93 302 H.O as a refferance. happy head hunting
Remember not to give up too many CC's to raise the compression ratio, you may be better off with less compression and larger ports. 302's do not breath much. I picked 58cc heads in hopes of raising the compression ratio to build more power. My car kinda drops off at 4500. Edelbrock Performer heads Rev cleanly to 6000RPM. Thats my next step. My current heads breath really well, but only when the nitrous is flowing

 

[Blue Thunder]

All factory 289, 302,(excluding the massive 69-70 BOSS, and the GT-40P 5.0 Explorer) and 351W(excluding the 69-74 castings, which are superior) heads have virtually identical CFM airflow values. The only real difference in ANY of the small block Ford castings is the volume(in CCs) of the combustion chambers. Increasing compression is of course the easiest means of increasing power and efficiency. However, if you use castings with very small CC chambers, some of the benefit you're gaining from the higher compression is being lost because the smaller chambers also tend to shroud the valve's flow ability. The idea situation is a chamber that's large enough to leave the valves unhibited by the chamber wall. For this reason, it's better to use other means to manipulate compression ratio. Start with a casting with a fairly large chamber, and then have them milled to decrease the CC. A shallow, wide chamber will make more power than a deep narrow chamber. Of course, if money is a big factor, then slapping on a set of heads with small chambers will still give you higher compression, and will make you more power, but the motor wont be as efficient as it could be.

 

[Blue Thunder]

I'm still in the process of writing a virtual dyno program for market. It's partially operational at this point and I can use it to plug in whatever numbers you list to quickly calculate compression ratio. (Figuring it out manually is time consuming)

No combination of parts seems to be identical in any engine, so you really need to measure the pieces you plan on using and list the specs for proper mechanical compression calculation.

These are the related measurements you need to take:

Deck clearance of block:
Combustion chamber volume in CC:
Compressed head gasket thickness: (.038" is usual)
Number of eyebrows per piston: (2 or 4)
Engine Bore:
Engine Stroke: