318 or 360 heads

[Mr. 6pak2go]

alot of people have told me that 360 heads on a 318 will hurt it more than help in does anyone have any sugestions i have a 67 318 block stock no ob or anthing completely stock bottom with keith black flat tops a 340 6pac cam and a 340 intake wiht a holly 625 what would be the best heads!?

[Challenger6pak]

I have run 360 heads on 318's alot.  I don't know of any problems if you run a matching manifold.  The ports are larger on the 360. 

[Jacksboys]

The main problem with running 360 heads on a stock 318, is the compression ratio.  Since the 360 heads have a larger chamber, then your compression will decrease, which will hurt the performance.  If you use aftermarket pistons that have the compression ratio measured with the larger chambers, then the 360 heads will flow better with the larger valves, and thus give you better performance.

My father did this head swap on a 318 and the engine would not pull until it was over 2500 rpm and after that point the power band still felt weak.

[Mr. 6pak2go]

thanks iv heard that the compression was the problem you think the flat tops would be enough to fix that problem or would i need to shave the heads block intake etc?? i have a 360 block that needs to be built i may may bulid it i cant decide!

[Jacksboys]

I am not sure of which flat top pistons you have, but here is some info about a good KB piston I found at www.hughesengines.com

Part No.   Part Description   
2005       318 Flat Top 8.9:1 With 70cc Heads/ Keith Black Hypereutectic

For 318 V8 and 3.9L V6 engines.
Compression ratio with head CC size.
58cc = 10.2:1
62cc = 9.7:1
70cc = 8.9:1
74cc = 8.5:1

636 grams w/ pin
Effective dome volume -5cc
Compression height 1.810"
Deck clearance .011" 
 
All compression ratios are based on a .030" oversize and a .039" compressed gasket thickness. Piston deck clearance is based on a block, crank and rods with factory perfect measurements (which, due to poor factory quality control, never happens). All Keith Black pistons have generous valve reliefs to clear most high-lift camshafts. However, always check piston-to-valve clearance prior to final assembly. All Keith Black pistons can be used with either press-fit or full floating wrist pins. All pistons use 5/64", 5/64", 3/16" rings, except for Diamond Racing pistons which use 1/16", 1/16", 3/16" rings, unless ordered otherwise. 

[Jacksboys]

Using the 360 engine would also be a good idea, since they can be rebuilt fairly cheap.  Plus the added torque is very nice.

[Challenger6pak]

Using the 360 engine would also be a good idea, since they can be rebuilt fairly cheap.  Plus the added torque is very nice.

I've always used aftermarket pistons in the 318 when I rebuilt the motor so I never gave compression much thought. It makes sense that the stock 318 compression would be low with the 360 head.  If you can use a 360 motor use it.  They are good motors.