Originally Posted by DARK SIDE
is the intake surface on a sbc head all on the same angle over the years or did the angle change. I have a 1974 350 with stock heads. I have a 89 TPI intake that I got to mock up for brackets and stuff but the intake dosen't quite fit flush. Its on a slight angle to the head. Some guys have done this intake swap here but mine just don't seem to fit right. Any ideas???
All production Gen I and II engines use 23 degrees. Bowtie and aftermarket heads are available in other angles usually either 18 or 15 degrees.
If you have "stock" heads and an intake where the angles aren't correct between the head and intake it more likely shows that the block has been milled across its decks, and/or the heads have been milled, with either case the intake was not milled the correct corresponding amounts. When the head or the block are milled the head is lowered in relation to the intake because the ends of the valley aren't milled, this holds the intake too high and since the heads have moved closer to the crank centerline they have also moved toward each other which pinches the intake up. Or what really changes this angle is if the head has been angle milled. This is done to take more material off the combustion chamber side than flat milling can, this substantially removed more material increasing the compression more than can be achieved with flat milling.
The other scenario is that the intake has been milled somewhere along the line for another engine that had milled heads, deck or both different from the engine you're trying to use the intake on.
The angle the valves make to the deck (ie 23, 18, 15 degrees being typical) has nothing to do with the angle of the manifold surfaces. Changes in this angle simply moves the valve in relationship to the port reducing the sharpness of the bend from the valve pocket to the seat.
One needs to realize that these things are never perfect fits which is what gaskets are made for. So you need to realize that some imperfection is normal.