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Old 03-18-2009, 11:00 AM
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BBC aluminum head questions

Ok, some of you may or may not know but i am building a 496 BBC.I know and understand that some of you have do not like PRO COMP but for what I'm doing they are the better deal since I will have around $1200 in to a set of 781s i might as well go with pro-comp because of the benefits of aluminum and ill have around the same amount maybe a few hundred bucks more into the pro-comps but here is my issue

pro-comp has a

rectangle ports heads with 115cc chamber and 320 intake runner

oval ports with 110cc chamber and 300cc intake runner

I have heard that rectangles don't like lower RPM and my engine will be a street engine id like to go wit the ovals will the difference in chamber and intake runner be a huge differnce, and can they be made for 115/320 ??

please don't reply with remarks on the namebrand trust me if I could afford some eddie's or dart ..etc I would

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Old 03-18-2009, 04:07 PM
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From what I've read about your plans for the motor, I would definately go with the oval ports. The 110cc chamber is good for your compression ratio and you should have no problem getting to 9.5 or 10:1 with flat tops. Many people say that you shouldn't run rectangle ports on the street, and for some very valid reasons, however you can get away with them if your engine is set up right. The rectangle ports like to move a lot of fuel and air and enjoy living in a higher rpm range than the ovals, their bottom end isn't great on the street but they excel down the strip.
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Old 03-18-2009, 09:31 PM
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Once agin brain you come throguht for me and I greatly appreciate it , but I have another question. I was under the idea that I was going to need to run domes pistons is this true or will I be able to flats

also with lets say 10-1 and aluminum heads what octane will I be running... just guessing ?
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Old 03-19-2009, 12:01 AM
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With 110cc chambers, .04" head gasket thickness, zero decked flat top pistons +/-0cc's, I came up with 9.5:1. If you put a tiny 7cc dome on the piston it puts you at 10.03:1 which would be perfect for pump gas and a little timing with the aluminum heads.
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Old 03-19-2009, 10:23 AM
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well See from what i was told from several people is with 9.5-1 with iron heads ill need to 93... so i have 9.5-1 with aluminum head shouldn't i be able to run 89?
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Old 03-19-2009, 01:26 PM
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Camshaft timing has a huge effect on the amount of compression that can be used with a certain octane.

with a BBC, try running around 7.5:1 dcr (dynamic compression ratio) if you want to run 89 octane.

for example, 10:1 static compression with a little cam (say 260 degree cam) will have detonation issues with 89 octane. But that same engine with a cam with 290 degree duration will do ok.
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Old 03-19-2009, 01:33 PM
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that cam i plan i running is the comp solid roller xr274r with 274/280 duration
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Old 03-19-2009, 01:53 PM
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sounds like a good setup.
I actually went against the grain and put stamped steel head gaskets on my 496 because my chambers were 113cc and I wanted at least 9.5:1 compression. But my pistons were also down .018 in the hole, so with the .022 head gasket thickness I got a good quench depth of .040.
A lot of people will say not to use stamped steel on aluminum heads because they will brinell the heads but I have had no problems with my canfields.
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Old 03-19-2009, 02:27 PM
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9.5:1 would work well with that cam and a 496.

should have 7.5:1 dcr with 274 degree intake duration with 110 lsa.
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