I was told by "Mac" that GM was worried about warranty issues with the longer stroke 250 OHC-6's and they used weaker valve springs on the 68 & 69 Sprints to limit them to around 5400 RPM by having the valves float at that RPM, the sorter stroke 66 & 67 Sprints will rev beyond the 6500 RPM red line. By putting stronger valve springs on 250's I have been able to get them to over 6800 RPM. but they don't rev as fast or freely as the 230's do.
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Jeff R
60 Jaguar Mark 2, 3.8L Automatic
67 Sprint Firebird 230 OHC-6 4-Speed A/C
1971 Fiat 130 Coupe 3.2L SOHC V6, ZF 5-speed
78 Catlina Safari, Pontiac 400 powered
77 Astre Formula, 215 Buick V-8 T-5
73 Lemans Safari, 400 4bbl 4-speed
71 Catalina Enforcer, 455 4bbl
05 Dodge Magnum 3.5L SOHC V6
06 Mallet Solstice #024 LS2, Now with a Tremec 6060 6-speed!
2012 F-150 Echo Boost (My local Ford Dealer SUX!!!)
2020 Dodge Charger Scat pack (recovered)
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