I have to agree that you don’t need aluminum heads to make good low-end power with a 455…and keep it affordable. You can get great power from the cheap and readily available 6X-8 heads. As mentioned previously, you need more cam, like the Summit 2802 at a minimum. The only place a factory 067 cam makes more power than a 2802 is from idle to 1500 rpm.
Here’s an actual dyno comparison of two 455’s using the same short block and cam (Summit 2802 & lifters) with different top ends…the first is with the original 1970 small valve 455 #15 heads and log manifolds (the standard 1970 Bonneville engine 360hp/500 lb-ft). The untouched #15 small valve heads had 90 cc’s finished (9.94 to 1 compression) with 195/145 cfm approximate flow. It dyno’d at 390 hp at 4600 rpm and 512 lb-ft torque at 3400 rpm.
I later switched over to ’71 455HO heads/intake/carb/RA exhaust manifolds. The 455HO #197 heads were also untouched originals with 108 cc chambers finished (8.60 to 1 compression) with 225/175 cfm port runner flow. I was surprised it made a bunch more power with a 1.4 drop in compression, but better flowing heads and exhaust. It made 431 hp at 5000 rpm and 535 lb-ft torque at 3500 rpm. It made a little more torque down low than with the small valve higher compression heads. Both combinations had the Felpro 1016 head gaskets (0.039” crushed thickness) to provide 0.040” quench.
The same engine with stock 6X-8 heads (more common and cheaper than the 6X-4 heads) would wind up somewhere in between power-wise, or around 410 hp at 4800 rpm and 525 lb-ft torque at 3500 rpm. The 6X-8’s have 100-102 cc chambers uncut, and after a truing cut gets them down to 98-99 cc’s netting roughly 9.25 to 1 compression on a 455 that is zero-decked.
Dennis
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