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First I want to apologize to Joe P. 😉
While I won’t argue that a 403 may be better suited using big block heads, they still do pretty well with small block heads too;
4.375 Racetec piston 9.8:1
Molnar SBO Rods
N crank
My Halo
Hyd roller 227/233@.050
#5 heads, real good bowl blend, everything filled and welded, 2.00”/1.62 valves
HS 1.65 rockers
RPM intake, divider cut, no other work
Brawler 750 VS
Pertronix HEI
Dyno headers 1 3/4
Nice Mark, but didn't the one with E heads still do better?
More horsepower and torque with less compression, 9 and 9.5 to 1, both C heads, searching on here. The cam profiles are a bit different but similar and one has a 3.4" stroke. Both have 450+ HP and over 500 ft-lbs of torque.
Last edited by olds 307 and 403; Oct 18, 2025 at 07:19 AM.
I did one with Edelbrocks, but I don’t remember doing one with iron E’s.
And yes the Edelbrock one made about 15 more with less cam.
You know, I would have sworn you did one with E heads, but I went back through the forum and there were two builds with C heads, one in 2018 and one in 2016.
I don’t remember the combo on the second one, but the first one is one I dyno’d for a build headed to CA I believe. That had bowl blended big block heads with 2.07/1.68’s, more cam and a port matched intake as well, I’m pretty sure..
Very nice !!
for additional info, I built a .030” flat top piston 403 with C heads with bowl blend. Hydraulic roller, 9-6-1 compression RPM 750 vacuum brawler. Most all part came from mark. 470/494 on pump. Mark can explain what it really makes after dyno correction and fuel testing that was from a pump on the dyno. Those numbers we agreed are more in the 495/510-520 range. The big block heads are definitely what these things need.
