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Old 12-04-2004, 05:16 AM
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help porting 305 h.o. heads

hi guys , i aquired a set of 416 casting 305 high output heads from a friend who ownes an auto salvage yard. they seem fine (lots of carbon though)and i need to get them tanked and checked.
they are 58 c.c. chambers,1.87 intake and 1.5 exhaust.
i learned a bit about 882 casting 350 heads from porting them at home. things like those heads were lacking on the exhaust side .
I have no knowledge on the 416 casting head though.
ultimately i would like to fit them to a 350 but i hear you all about choking itself to death at 4000 rpm.therefore i would like to make them the best 305 heads they can be.
what i need to know is what are the areas of these heads that need the most attention? do i gasket match the intake , exhaust,do i unshroud the valves?do i need to clean up the short turn radius much? what about the area where the exhaust comes around the valve,(i widened this area out in the 882's since it lacked in the exhaust.)
If anyone has done these heads over and had them flow benched please let me know where to attack.
if there is anyone with good knowledge of porting please let me know where to begin .thanks in advance , mike

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Old 12-04-2004, 05:35 AM
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I have never done anything with those particular heads, but all chevy heads have about the same problems. The main area that needs attention is the bowl area. Bowl porting including the short side radius are where the most benifit can be found. Gasket matching will certainly not hurt any thing. I also like to completely remove all the casting rough and polish the exhuast ports. On the exhaust port I also like to just open up the port a little bit all the way around when I am smoothing it. There are pics in my album of heads I have done.

Chris
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Old 12-04-2004, 06:20 AM
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in the first pic (i think),there is a lump it seems , is there a purpose for it?just wondering.
forgive my stupids , but ,by the bowls do you mean where the spark plug is ?or where the exhaust valve passes thru the exhaust port.
i'm still an amature,so to change the volumes on the heads to say 60 or so c.c. would be a formidable task.i would be able to unshroud the valves all the same or the like , but i wouldn't want to start to "drill" down and grind away, and then the measuring fun to get them all the same . no thanks.lol.
on the exhaust side i plan to take away all flash, take about 1/16" to 1/8 "off around the outside circle where the valve passes thru the middle ( ][ )<---- there.gasket match it to the header gasket , do the short turn radius (1/16 to 1/8 ")and polish.
what do you think of the plan so far. mike
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Old 12-04-2004, 07:00 AM
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how to port
http://www.sa-motorsports.com/diyport.shtm

There is more info in the Knowledge base from other numerious postings on the same.
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Old 12-04-2004, 08:00 AM
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got that link earlier today, thanks. i was wondering if there was something particular to these heads, thanks mike.
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Old 12-04-2004, 09:45 AM
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The only "bump" I can think of is where the valve guide boss passes through to the port. The bowl area is the area just below the valve inside the port. The chamber is the area that the top of the valves sit in.

You probably do not want to remove 1/16" and for sure not 1/8 inch anywhere on the heads other than maybe the bowl. In doing that with no experience you could easily grind right into the water passage and ruin your new heads. 1/32" inch of material removal in the exhaust port is plenty for what you are doing. That will get all of the casting flash out and enlarge the port just slightly.

There is not alot of need to port match the exhaust to the gasket. Headers will not line up real great with the ports unless you go with something high end. Some header gaskets are way larger than you want the port on a set of those light castings anyway.

Chris
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Old 12-04-2004, 02:06 PM
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thanks for the info, it's going to be a project for the winter . i'll study more up on the link i got(it's on my favorites) when i get the heads cleaned and checked first.thanks again for the knowledge.mike
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Old 12-04-2004, 03:04 PM
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news to me

i came across a set of these heads a few years ago and didn't think much about them. i still have them and am getting ready to build an engine. i did a check on numbers and found about the valves but didn 't realize they were h.o. that is nice to know. i will have mine checked and possible do some polishing on them. i will use that link also. thanks
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Old 01-27-2007, 06:51 PM
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The last set of 305 (416) heads I ported and flowed came out to 233cfm@28" at high lift and 218cfm@28" at .400" lift.
Ex flow is typically 180+cfm. (1.94x 1.60" valves) after deshrouding, chamber size is 61cc.
Get the David Vizard S/A book "How to build Max performance Chevy Small Blocks on a Budget". read it know it, there will be a test. Everything in there about porting SBC heads is relevent to the 305 heads. They need a full work up.
it's all in there. Don;t bother with 2.02's in these heads. (decreased valve C/L spacing)
More reading here
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