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Original Message
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| RE: "Canadian Cobra Jet" SK Heads |
| By Travis Miller - 10/16/2001 8:21:46 PM; IP 64.12.102.154 |
When you say Canadian Cobra Jet and SK heads, you are talking about two totally different heads.
The SK heads were developed for the 427 Medium Riser and were used prior to the introduction of the Tunnelport heads. To give you an understanding of the SK heads, you must first understand the regular Medium Riser heads. There were two different versions of the regular MR heads. The first was the C5AE-F which had a intake runner volume of 153cc's and an exhaust runner volume of 115cc's. The 2nd version was C5AE-6090-F which held 164cc's and 124cc's respectively in the runners. The 2nd version holds more volume because it used a larger bowl under the intake valve. It can be identified by a large C5AE cast at an angle between the middle exhaust ports and a large 6090F cast between the outer exhaust ports toward the right end of the head. As for the SK heads, there were two different casting numbers, SK 35369 and SK 31635. These heads differed from the regular MR heads because they used the huge bowl under the valve that the Hi-Riser head used. They also had no heat riser passage. The SK, the C5AE-F, and the C5AE-6090-F heads all use the same intake gasket. The exhaust port is in the same place and the ports measure the same at the exhaust manifold mating surface on all three heads making them appear the same without looking at the casting numbers. Ford knew how to play the game. For drag racing, all three heads are legal for S/S with the SK being rated higher but the SK's are not legal for Stock.
The Canadian head was used on the 428 Cobra Jets. Externally it is identical to the regular 428 Cobra Jet head. Some people say that there is a difference in the clarity of some of the casting marks but I've never seen it when comparing the two. Both use the same casting number of C8OE-N. The difference is in the intake runner. The intake runner goes straighter back into the head to a larger bowl under the valve. The intake port also has a dip cast into the floor of the runner. The only way to learn the differences is to put a regular CJ head next to a Canadian head and actually compare the two. Then you can see the difference. The biggest problem is that most of the rare Canadian heads have been used up in S/S drag racing where porting and welding is legal.
One thing that I do find interesting is that every Canadian head that I have seen or asked anyone about has a casting date of 9H20, 9H21, or 9H22. If this is the case, then they were not cast until August 20-22 in 1969. That was just before the NHRA Nationals at Indy that year. So how did the '68 428 Cobra Jets have Canadian heads in 1968, or did they? The story goes that NHRA caught Ford with them on the earlier 428 CJ's in 1970 and made the 428 CJ's run at a different horsepower rating when claiming the Canadian heads.
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