Dr.Jeff
True Classic
Lately I've been going through several SOHC engines I have, deciding which ones to rebuild and use. Currently I'm looking at four heads. All are 1500, one a carb ('79 Calif smog spec), the other three fuel injected (one '80 and two '85s). Here are some random observations and resulting questions.
The '79 is the healthiest of them by far, but had the most carbon build up (a lot more). Likely in part from carburetor issues (vs FI), but also I'm sure due to the emissions stuff; EGR, AIR, you name it. This head has the internal passage connection to all four exhaust ports, although it was disconnected and plugged at both ends. Interesting how much volume that tunnel has. When filling one exhaust port with fluid (checking for leaks at the valve, etc), it also filled the other three and required a lot of fluid to do so (much more than the volume of four exhaust ports). I cannot help but think this design has a negative impact on performance. Consider how much goes into designing a exhaust header for impulses, pressure waves, etc. Now put a large connection to all four cylinders directly beyond the valves. With the paired compression strokes, there must be an effect on the other two cylinders, and vice versa. Not to mention how it negatively influences gas flow to have this big gap sitting along the port at a critical point.
Another difference in the '79 head is the obvious improvement in casting quality compared to the three later FI heads. The material has very little porosity (the others are very porous). The casting lines are clean and small (the others are huge and rough). And overall the shapes, forms, edges, surfaces, etc all seem much cleaner/truer than the others. I do not know where any of them were made or what changes took place between the late 70's and the mid 80s, but the result is significant.
Something I see on all of the FI heads are small lines in between the exhaust and intake seats in all four chambers. At first I thought they were cracks, but looking closer I don't believe they are. One of the heads was severely cooked - extremely warped and something like 18+ easily visible cracks all over the chambers (some going through the seats) and on the flat surface. With that one you can easily see the difference between cracks and the lines on the others. Actually on one head there is one chamber with an actual crack between the seats; it has a different irregular shape, open sharp appearance, and you can easily feel it with a pick. It's not the same with these other lines. They are straight and directly at the narrowest point between all of the seats, with no real indication of being a open crack. They appear to be some sort of electrolysis or erosion in the aluminum? Or maybe it was a casting thing? Has anyone else seen this and know exactly what they are? Seems common to all three of the FI heads I have (not the carb head).
The '79 engine does not appear to have been opened up before, while the other three definitely have been. Two of those were recently rebuilt, however they had failed already. Probably speaks to the work that was done more than anything. Regardless, as I said the '79 was in the best shape of them all despite being older, never rebuilt, and earlier technology.
I appreciate any comments on the various questions I raised, thanks.
The '79 is the healthiest of them by far, but had the most carbon build up (a lot more). Likely in part from carburetor issues (vs FI), but also I'm sure due to the emissions stuff; EGR, AIR, you name it. This head has the internal passage connection to all four exhaust ports, although it was disconnected and plugged at both ends. Interesting how much volume that tunnel has. When filling one exhaust port with fluid (checking for leaks at the valve, etc), it also filled the other three and required a lot of fluid to do so (much more than the volume of four exhaust ports). I cannot help but think this design has a negative impact on performance. Consider how much goes into designing a exhaust header for impulses, pressure waves, etc. Now put a large connection to all four cylinders directly beyond the valves. With the paired compression strokes, there must be an effect on the other two cylinders, and vice versa. Not to mention how it negatively influences gas flow to have this big gap sitting along the port at a critical point.
Another difference in the '79 head is the obvious improvement in casting quality compared to the three later FI heads. The material has very little porosity (the others are very porous). The casting lines are clean and small (the others are huge and rough). And overall the shapes, forms, edges, surfaces, etc all seem much cleaner/truer than the others. I do not know where any of them were made or what changes took place between the late 70's and the mid 80s, but the result is significant.
Something I see on all of the FI heads are small lines in between the exhaust and intake seats in all four chambers. At first I thought they were cracks, but looking closer I don't believe they are. One of the heads was severely cooked - extremely warped and something like 18+ easily visible cracks all over the chambers (some going through the seats) and on the flat surface. With that one you can easily see the difference between cracks and the lines on the others. Actually on one head there is one chamber with an actual crack between the seats; it has a different irregular shape, open sharp appearance, and you can easily feel it with a pick. It's not the same with these other lines. They are straight and directly at the narrowest point between all of the seats, with no real indication of being a open crack. They appear to be some sort of electrolysis or erosion in the aluminum? Or maybe it was a casting thing? Has anyone else seen this and know exactly what they are? Seems common to all three of the FI heads I have (not the carb head).
The '79 engine does not appear to have been opened up before, while the other three definitely have been. Two of those were recently rebuilt, however they had failed already. Probably speaks to the work that was done more than anything. Regardless, as I said the '79 was in the best shape of them all despite being older, never rebuilt, and earlier technology.
I appreciate any comments on the various questions I raised, thanks.
