89 360

Well I'm glad this is over, here is some info thats very useful to all. But keep this as a reference as these are for allout racing engines. Superflow states that the maximum valve size for a given bore on the intake is .52 X the bore size. Then on the exhaust you would X the intake valve by .72-.75. Thus the maximum size for a 318 with a 3.91 bore would be 2.03 and 1.52 respectively. But we all know that we don't have allout racing engines here so most cars are aprox. 20% less in efficentcy. So for the average bracket car this has to be reduced, without getting into a bunch of detail here these are the factors that I have come up with.

318-360 use 2.1
383-400 use 2.05
440 use 1.95
500-572 use 1.9
The idea here is to keep the port volume and the flow in a reasonable aspect, the #s that you will come up with here is the cc's of the port, then multiply by 1.6 for all mopar engine for the air flow.
Example: 318 divided by 2.1= 151 cc's this is very close to a stock 360 head volume which most are 150 cc's. Then multiply this by 1.6, 150X1.6=241.6 or 242 cfms this will get you in the ball park and satisfy most engines. Now this isn't to say that this is the most efficent head, thus if the port is smaller like the 318 heads with only a tiny 124 cc port then you also have to reduce the size of the valve for this to keep efficentcy up, it would look like this.
Example: 124 divided by 150=.826 or 83% of the bigger port, so now you have to reduce the valve size by 17% which is the difference between the two ports. This would look like this, 2.03x.17=.345, then subtract 2.03-.345=1.685 valve size to be efficent. Then the flow would also have to be reduced by the same amount which is like this. 242x.17=201 which is represents the heads from the factory.
Then if you have a mildly ported head thats 134cc's then the new valve size would be 1.807 for the intake and would need 215 cfms of air flow.
So with this we tried this out on a race car, and here are the results. The engine is a std. bore 318 with a .501 comp cams cam, a M-1 intake and a 750 vacume sec. carb, it also has 1 5/8 hedders and race mufflers it runs on 87 octane gas. The car weighs in at 3100lbs with the driver (70 Duster) The car ran a best with the 360 heads of 7.93 1/8 and now runs 7.68 1/8 with the smaller but more efficent heads with smaller valves. This is just some food for thought.



BJR Racing