The two intake ports are very similar with the D3 intake's short turn radius crest being .100" taller relative to the deck and port floor at the entry. I have found that this helps higher lift stability.
In both budget ported small valve and large valve versions the intake flow curves are very similar.
The cross sectional area of the as cast exhaust ports favor the early castings.
We drop the short turn radius of the D3's and completely reshape it from bowl, over crest and out to the exit. This adds needed cross sectional area. In the end both exhaust ports when properly ported will flow with in 5 cfm of one another.
Seat width, bowl shape, short turn shape and width are everything on these exhaust ports.
I have a 1.8" exhaust valve D3 R&D piece that flows 200 cfm @ .500" lift gaining a bit at 6 7 and 8.
Long story short:
In your application I concur with Paul, Randy and Dave
We have done countless 380 to 550 HP small valve budget ported deals with both castings and the differences in output are with in the margin of error of the dyno we test on. All things such as c/r being equal.
We did a simple Budget ported D3 small valve (305/180 @ .600") stock rocker arm 460 with TRW domes, 219/227 voodoo, RPM intake, curved duraspark with 38 degrees total timing. 750 DP etc
3950 pound Torino GT, hooker super comps, 3.89 gears, C6 3800 stall etc which ran 12.50's @ 106-107 MPH
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Last edited by The Mad Porter; 01-24-2014 at 11:40 AM.