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#1
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906 vs. 452?
I would like to know if there is any appearance difference in a 906 casting big block head over a 452 casting? All I've worked with so far is the famed 906 head. So I don't really know if there is any difference at all. I have read in a recent Mopar magazine that as far as the airflow characteristics, all open chamber heads after the inception of the 906 head in 1968 flow essentially the same airflow. The difference is, the later years had the hardened valve seats for crappy pump gas.
Question 1: If I am after a stock looking appearance on my all original 1969 Road Runner but want the hardened seats, will any hard core purist be able to tell the difference between a 906 and 452 head aside from actually taking off the valve cover and looking for the casting number? Question 2: Is it recommended that I swap out my 906 heads to get the hardened seats of the 452 head? Or should I just have the hard seats installed in my 906 heads. What would you do? |
#2
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You would have to pull the valve cover to tell that it is a 452 head.
There are many things that go with question #2. If you plan on doing any valve grinding (bigger valves, radius the valve seats, etc) you will machine through the induction hardening of the 452. If the engine is properly tuned and it the car sees low miles and no racing, then you really don't need the hardened seats. If you put a lot of miles on it and/or it sees track time, then I would let price lead the way. If you go with the 452 heads, keep the 906 heads in the corner. |
#3
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My experience in P&P jobs and flow testing on these has given a little insight on this. In general terms, the 452 has a lower approach in the intake port, but flows better, with better swirl characteristics. A stock comparo is very close, giving a slight edge to the 452 on intake and 906 on exhaust, but with both ported, about a 5% benefit on 452 intake and 6% on exhaust. IMHO the 906 offers better crack resistance, though. :-)PCRMike
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#4
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How many heads did you flow? I mean, the exhaust ports are identical, besides casting variations. The intake ports are different, with the 906's having a small "short side", and way bulkier around the guide. It requires some experience and skill to get the intake short side right when porting, while the newer design that came in '71 is way easier to port for good results. Typically, in stock form the 915/906 intake ports have better low lift flow than the newer heads.
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#5
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Mopar Muscle online has a great tech article on this guys Look it up in their tech articles
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#6
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Normally the older heads have a little more core shift, so I am a little more conservative on the amount of material I remove. I only flow tested a pair of each. It is possible that the core shift made the dif, but yes, there is a lot more to do to make 906's flow well compared to the 452. There was a set of 906's I got once with about 1/8" shift that made it nearly impossible to balance out the port. :-) PCRMike
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