That hole is for an emissions pipe. You can either fab a small metal plate to bolt on or tap it for a pipe plug. Either way is fine. There is usually a gasket in a manifold set that you can use for a template. It looks kinda like a tear drop.
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| Cylinder Head Questions? https://slantsix.org/forum/viewtopic.php?t=31383 |
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| Author: | pemercie [ Sun Sep 28, 2008 11:46 am ] |
| Post subject: | Cylinder Head Questions? |
Hole at the end of the exhaust/intake mounting side of the head takes compressed air to the open valves. Has a threaded hole above for holding on a cover? What is this hole for? The original head on the car does not have this hole. The head ($1000.00) I got from Clifford has the hole. What gives? |
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| Author: | sandy in BC [ Sun Sep 28, 2008 12:47 pm ] |
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Clifford...... They just charged you a grand for a late/heavy head. You may have done better a different way.... |
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| Author: | slantzilla [ Sun Sep 28, 2008 12:50 pm ] |
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That hole is for an emissions pipe. You can either fab a small metal plate to bolt on or tap it for a pipe plug. Either way is fine. There is usually a gasket in a manifold set that you can use for a template. It looks kinda like a tear drop.
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| Author: | SlantSixDan [ Sun Sep 28, 2008 1:32 pm ] |
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Welcome on the board. Sandy's right; unfortunatel you did overpay — grossly — for that "special" (not) head from Clifford. These later heads are significantly heavier, especially with air injection, than the earlier heads. Slantzilla's right that the hole you're seeing is for secondary air injection. The factory blockoff plate P/N 3751 249 is still available from the dealer; it's quite beefy to deal with the thermal cycling and exhaust pressure. Blockoff gasket is P/N 4275 834. When installing the manifolds onto the head, it is very much worth your while to use the good gaskets. |
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| Author: | Dart270 [ Mon Sep 29, 2008 6:40 am ] |
| Post subject: | |
FYI, the 80s hydro heads are only about 3-4 lbs heavier than the early tube heads. 75-79 heads are about 10 lbs heavier, BUT they have more meat in port cross sections due to less core shift. 75-79 is preferred casting by at least two of the highest HP Slant guys out there, with 80s in 2nd place. Lou |
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| Author: | Doc [ Mon Sep 29, 2008 11:11 am ] |
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The air injection passageway acts like a long "gusset" in those heads to give it more stiffness. More metal and stiffness in the cylinder head is good when you are running astronomical cylinder pressures. (race engine) Lighter weight parts means a lighter weight vehicle which is better on the street or on the race track... as long as the engine holds together. In the end, it's a "balancing act"... if the combo runs well and I can save 5 to 10 lbs, I will shed the weight . If you are blowing head gaskets or need to port the head to the max... start with the heaviest head you can find. DD |
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| Author: | wvenable [ Mon Sep 29, 2008 4:15 pm ] |
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Pemercie, don't worry about the price. You are still on the right track. Talked to a local machinist and told him what I had spent on intake and exhaust manifolds and he told me that the money I had spent would damn near pay for a Nice (with a capital N) small block chevy! I reminded him about belly buttons and bungholes and he agreed 100%. The satisfaction for dollar of return on the slant is a great ratio. You have arrived at a great resource. Read, Read , and Read and then do like I do.. ask stupid questions! Welcome! 
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| Author: | Volare4life [ Mon Sep 29, 2008 5:15 pm ] |
| Post subject: | |
just some food for thought guys, I used a broken wheel stud hammered into place the splined end sealed perfectly in the head with no leaks to date !! and its a cheap trick !! -Mike |
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