hey guys i recently was given a set of 416 casting heads for free so i figured i would port them freshen them up and throw em on the ole 305. any way just wondering after looking over the posts i could find on these heads the flow numbers for the stock 184 intake ported are still 200+ cfm , so im thinking would i be better off sticking with the 1.84 intake and going to a 1.6 exhaust?? desktop dyno showed only a small increase from 1.84 to 1.94 but showed much more when the exhuast was enlarged.... what do you guys think????????

 

probably just need to "hog em out"to get better intake flow.the larger intake valves are shrouded by the bowl area and you get restricted intake flow.i have a set of those,but don't know how thick these heads are.if you do go thru a water jacket,all is not lost.lots of guys are using epoxy to fill small holes nowadays.
smooth the intake ports with 80 or 60 grit rollers,blend the base of the guide boss to look like a cross section of an airplane wing,and you're on your own with the exhaust.a flowbench would be way better than messing something up there!
Eric

 

Follow Standard Abrasives' Do-it-yourself Porting Guidelines, available on their website.

Don't "hog them out". You want to smooth and blend. Port matching can be justified, but the big gains occur by smoothing the valve bowls and short side radii.

1.94's and 1.60's can be justified for a 305, with cam, induction, and exhaust to match. Valve shrouding isn't that bad, at least not so much that the 1.94's don't help.

New springs, guides machined down for positive sealing type seals, pinned or screw-in rocker studs, you should be in for a nice ride.

 

Actually you have it backwards.

You will see a modest gain in port flow by just porting the intakes without upping the valve size to 1.94 from 1.84"

With 1.84's you'll get to about 210cfm. with 1.94's and good porting you can get 240+cfm.

You can get all the exhaust flow you'll need on a 305 with the 1.5" valve and good porting. But a 1.6" won't hurt.

The valve shrouding on a 305's bore is more than it is on a 350's bore but you'll still be way further ahead with the larger 1.94" intake valve.

Desk top dyno will lie to ya if you lie to it. (enter the wrong choice to model your heads.

stock 305 heads model best using the "Low perf" selection.
If you were to just port them but retain the stock valves you would then model it best with the "stock ports and valves" choice. ( remember "stock" refers to a decent *high performance* "stock head" like a camel back or L98 aluminum. Not a base low perf head.

Then if you were to further port the 305 heads and increase the valve size, then you would choose stock pocket ported to best model them with the approprate valves size.

If you open up the different cylinder head modeling choices and look at the flow numbers shown for each level of modification you'll see the default flow numbers for each choice. You can also enter your own flow numbers from a flow bench test and save these models.