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Old 03-13-2007, 01:17 AM
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Porting BBC oval port heads HELP

anyone ever ported a set of BBC #781 oval port heads?? how to infromation??

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Old 03-13-2007, 10:24 AM
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heads

What CI engine are they going on??

Intended usage???


Keith
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Old 03-13-2007, 02:58 PM
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Hi Keith.. the heads will be going on a 468 BBC, 8.5 cr, full roller hyd roller Comp cams ,CCA-11-414-8 adv dur is int 298 ex310 lift 566 int 575 ex with 7.1 rocker lobe sep in 113*
The blower is a B&M 420, with 6-9 # boost..
the heads are GM 781 oval port open chamber, susposably good flowing to 7K rpm,, all new parts , valves, 2.25 int
turbo 400, winters Q/C with probably 378 detroit locker,,

going in a 48 Anglia panel.. will probably weigh 16- 1800 # just a mean HOT ROD,, probably won't see any strip duty,,

This link works now,,,,,
I read a article at ,,, http://www.maliburacing.com/patrick_budd_article.htm polishing a set of sneakers
. just no infromation on how to port them,,
thanks Bill

Last edited by Bad Rat; 03-13-2007 at 05:39 PM.
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Old 03-13-2007, 05:09 PM
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Another great link is [below] flow charts for BBC on comparison of rec port vs oval port
when site comes up click on teck on upper desktop and then click on to BBC oval port vs rec port BBC head comparison



http://www.maliburacing.com
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Old 03-14-2007, 10:30 AM
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Heads

Ok..I'll give you what i know and then the fire storm (wizzing match) can follow...

First thing don't even think about touching the exhaust ports,except to polish them up...They are allready to big.....

I would not do anything to the intake ports except the short side radius,,just lay it back a bit...

Now, Where you will find 95% of any typ of increase with these heads is the valve job and the bowl right under it...

For the intake i would run valve angles of 60,45,30
exhaust 52,45,30

When you grind the bowls bring the intake up to the 30 and let about .187" (3/16")of the 30 stand

Same with the exhaust open it up to allow about .187"(3/16") of the 52 stand...

Back grind the intake valve,,,doing the exhaust valve will probably not gain anything...


If you run thses heads across a good flow bench right now and then after the work i describe and record the results.....You should be pleased.... Then if you feel like wasting a bunch of time.. try doing all the trick grinding to them. You will find you wasted a bunch of time for just a few cfm... and maybe even a loss if you get to moving metal at the wrong place..


Thats my .02 from what i have found with these heads


Keith
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Old 03-14-2007, 11:36 AM
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THANKS K-STAR Thats what I was wanting to know,, when the machinest did the heads,, he was suspose to do the bowl work,, but didn't do anything to the rest of the chamber, I have not taken the valve out to see if anything was done to the bowls,, The angles you listed.. are the samre angles he noted on the work order he gave me,, he is one of the best engine builders around here,, and he races BBC, Thank You ,,, Bill
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Old 03-15-2007, 01:03 PM
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what the estimated H/P could be ??????

I know this is a stupid question,, but it seems to be the most asked, when building a engine, what would be the estimated H/P be?? Just curious I guess,,,
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Old 03-15-2007, 07:42 PM
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K star is sort of right about the exhaust ports.They are pretty big and require a good 2" header or at least a 1 7/8" tube with a flare at the flange to properly match,but there is power to be found there.The best way to work the exhaust port is to open the bowl area up,then widen the short turn where it transitions into the bowl.Back cutting the valve and narrowing the guide boss a bit seems to help on the exhaust too.The downside to all factory bigblock exhaust ports is that they need to be raised,and if anything they could stand to be a bit smaller.

As for the intake side,if you insist on installing 2.19" or larger valves,make sure you cut the bowl out properly,and have a top cut done on the seats,then blend the job by hand.at the port entry there is a slight taper that can be straightened out as long as your intake is wized to match the port entry.With 2.19" intake valves on heads that came with 2.06" valves,you need to open up the chamber a bit,but if you cant do this with a machine then focus your hand work on laying back the chamber where it meets the quench area,and along the cylinder wall side of the chamber,Opening the cylinder wall up a bit to match the chamber helps too.Given the port cross section of those heads,even with the blower,unless the seats are beat to death,I would kerp the stock size intake valves,and invest in the best valve job you can get,and blend everything in by hand.Back cut the intake valves and you will have gotten 90% of the way there for half the investment.Even with the stock sized valves,you can benefit from sitting the heads on the bare block and marking the chamber outline from underneath to investivage how much the chamber overhangs the bore on the intake side.If nothing else with a camshaft of over .600" lift I would at least bevel the edge of the bore in that area.

Good luck.
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