BBC head porting - need some comparative #'s

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David Vizard
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BBC head porting - need some comparative #'s

Post by David Vizard »

Just finished porting a set of 325 cc CNC AFR heads for this 632 that is being built at Terry Walters roanoke shop.
The reason I started with the 325 runner heads is that the guy already had them brand new.

For the target power (must be over 1050 hp) these heads were shy on flow and needed ports larger than the 325's offered.

Below are the figures for the flow - stock AFR Vs the ported ones.

The two columns to the right show the gains which start right off the seats. Having a high discharge coefficient though out the lift range has the same effect as having bigger valves. Unfortunately 2.3 and 1.88 valves are woefully inadequate for 500 inches let alone 632.

A while back I think I saw a post that talked about a 2.4 inch intake in a 24 degree BBC head. am I remembering correctly and if so what head was it that was able to accomadate that size?

When I get another break I will post the before and after flow #'s, CD, port velocity and port energy in graph form.
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RevTheory
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Re: BBC head porting - need some comparative #'s

Post by RevTheory »

Good morning, stranger. Did you ever get a chance to see if the 2.300 valve you installed in the EQ 225 head I did back in January brought the velocity up to a decent range? I got a little "happy" with the port for a 2.25 valve.
Joe-71
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Re: BBC head porting - need some comparative #'s

Post by Joe-71 »

Not scientific, but observations from past BBC heads I have ported over the years. CC of ports + ~120 cfm will be a "ballpark" flow number at .750" lift. For the 325 heads, the flow will end up around 445-450 cfm if every thing is right. I only have flow figures to the .800" on most heads from the past.
AFR 185 cc---flow 301-305 cfm
AFR 205 cc---flow 315-320 cfm
AFR 220 cc---flow 338-340 cfm
TFS almost identical
TFS R 225 cfm flow 350 cfm
Big Chief 2.350/1.94 492/370 cfm @ .750"
Big Chief 2.400/1.94 518/378 cfm @ .750"

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Re: BBC head porting - need some comparative #'s

Post by David Vizard »

Joe's post:-
For the 325 heads, the flow will end up around 445-450 cfm if every thing is right. I only have flow figures to the .800" on most heads from the past.

Joe,
Those are some righteous numbers for a 325 cc port!
Assuming our benches read the same I am seeing at best 430-435 @800 lift.
with a 2.3 valve I would like to compare your 200 and 300 lift figures with mine which are 177 and 258 cfm respectively. I am thinking I might be trading some hi-lift flow for mid lift.

Thanks
DV
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