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Now that I have your attention, I had a set of ported and polished AFRs heads installed on my 427 C5R to replace my LS6 Stage III heads with a leaking valve stem seal. The car dynoed at 512 rwhp and 492 lb-ft through the headers, x-pipe, cats, and Borlas and with no tuning. The folks at Thunder Racing expect that the engine will produce 530-550 rwhp through open headers, and no cats. The heads flowed a healthy 353 cfm on a flow bench. The compression ratio of 10.8:1.00 was maintained on both sets of heads. In a nutshell, I am very pleased with the performance esults of the AFR heads - they feel stronger and smoother in the mid and low end than the LS6 heads. I will need to compare dyno graphs of the old vs. new once the engine is retuned to be sure. In addition. the AFR heads look better in the engine bay and have substantially thicker side walls. I would definitely pick the AFRs over the LS6 heads and probably add another 0.2-0.5 points of compression - I think 11.2:1.00 is about the limit of compression if using 93 rms street octane.
 
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