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Originally Posted by nickd
I wondered if this step would have some anti-reversion benefit but isn't it too close to the valve head for that? Also, some of my heads have the step on the short side radius, and some on the long side. I can't imagine anything good coming from that?
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Based on extensive flow testing, it really doesn't have a significant impact until HP levels are above 360 BHP.
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Steve, thanks for the clarification. I feel like I would need to hunt for heads that have the ceramic 100% intact. Any amount of flaking could theoretically end up under the valve. Seems that would be the siren song for almost all 3.6's if they were that sensitive? Can't argue that it looks like a pretty badly implemented engineering idea.
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Its not easy to find GOOD used 964 heads now as most have many miles on them and suffer the same maladies.
The ceramic liners actually work quite well for what they were intended to do: help the cat get up to temperature and reduce high cylinder operating temps caused by that very cat. You must remember how much those heads expand & contract during every drive cycle and during all kinds of weather. Frankly, they hold up better than I would have thought, based on the hundreds of heads we have rebuilt for people over the years.