1970 340 heads on a 73 318

[chardart]

Hi
I have a set of 70 340 heads that I was going to put on my 73 318.
But now I am confused with all the different opinions. I have read that I will loose compression with the 340 heads because of the larger combustion.
I have been told to put thin head gskts on and it will be ok. I also noticed the combustion cc is smaller on the pre 72 head. Will this setup work. I really don't want to deck the heads. I just go to car shows and want more power than the 318 gives me now. I am currantly running edelbrock performer intake and edlebrock small 4 Bbl carb. Dual exhaust (no headers and stock cam)
help! :munky2:

 

[moper]

If you are running factory manifolds, with no plans to change even to HP manifolds (the 68-71 340 HP manifolds..), I'd leave the heads alone. A cam change, will accomplish what you want, without causing more issues. The head swap, is a double edged sword. You get better intake ports, bigger exh ports, and larger valves, all of which help in power production at higher operating ranges , especially ona small displacement engine. You loose port velocity on both int and exh, and static compression. Both of which lend themselves to power production at lower rpm ranges where stock gears, convertor, and manifolding dictate the egine run at. You cant ram air thru those log manifolds. So, any extra flow cant get anywhere easily. And, you'll loose idle quality and response becuase of the compression loss. Compression enhances power from 200rpm up to redline. any loss there is significant. My suggestion, would be to install a small hydraulic cam in the 318, as the current one isnt even designed for a 4bbl engine, much less the 318 ports (which really are not that bad for a small displacement engine). Any new cam should be degreed during installation, so you really get what you expect form it. MP cams especially..

 

[chardart]

thanks for the help.
so you are saying to leave the stock heads on and install a cam. Do you know what power increase i could expect from this?

 

[73DartSport340]

If you are running factory manifolds, with no plans to change even to HP manifolds (the 68-71 340 HP manifolds..),

Even if you run the "HP" manifolds you would only most likely gain a whopping 3-4 HP over your 318 manifolds(even after a cam swap). So a step above stock cam would be my suggestion becuase without going with a bigger cam,headers,something like a RPM manifold so if your sticking with the manifolds jsut pick a bit bigger/stronger cam to "wake it up" a bit.