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Friday, October 29, 2010

Reconditioning Big Mopar Iron Cylinder Heads



So as the title says today I am working on getting a set of '452 castings "Bagged & Tagged". These particular heads were used on a friends 452 stroker build that I originally built in 1999. Well the engine recently expired due to a failed rod bolt. Really what can you expect with stock rods / ARP bolts and heavy KB hypers + 10 years of frequent street use as well as dragstrip abuse? Anyways the heads survived relatively unscathed and are now back in my hands for repairs and refreshening. What was really neat about this job is back in '99 these were home ported in my garage and were my first real crack @ porting.  I remember how much work it was and how cautious I was about messing with the shortside (s.s) and how the pushrod pinch and port matching were "useless" to grind on. So I didn't touch either of those areas and just worked the bowl and guideboss into a nice radiused form. I even had the foresight to take these to a local "guru" that had built himself a flow bench and had 1intake port flowed. The results were very pleasing as his bench was later found to be about 30-35 cfm above what the standard of the industry SF-600 would read. Why am I telling you this? For the simple reason that I now have at my disposal a bonafide SF-1020 ProBench! Well curisosity got the better of me and I set a head up and checked it. Now, before I share the results I should make it clear that I had a pretty good idea of what kind of flow rate to expect due to the fact that the 452 was dyno'd twice with cams being the only real change and that it produced a best of 532 HP /559 TQ. So all along I figured flow to register around the 260-265 cfm mark. The first head before treating it to a modern valvejob (VJ) came in at a whopping 248 cfm @ .500". So knowing just how much of a difference a well executed VJ can make I went ahead  and chose some angles that I have found to work very well on these heads. Post VJ numbers are 261 @ .550" with no changes below .450"! Now I'm thinking all I need to do is take out the "Huber Hump" in the floor, open up the pinch, etc... Whoa! Lets not get carried away! Flow is not everything you know-But that's a whole other blog topic. These heads are being relegated to a spare engine and the premier engine will be getting some modern aluminum castings. For now here's some pics of our SCHOU resurfacer which I converted to CBN/PCD tooling for the latest and best surface finish. If the video works and you have never seen or heard a CBN resurfacer than take a look-you'll wonder how something that sounds so "lumpy" can produce a finish superior to a segmented grinder. J.Rob

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