My last update concentrated on the shortblock. Since then, I have received just about all of the other major components and have continued to mock-up the engine. I have spent a lot of time on matching the ports of the AFR 185s to those of the RPM Air-Gap intake manifold. The ports of these are not a great match. The ports on the AFRs are larger and the corner radii are larger than that of the intake. It's a little like fitting an oval and square together.
The first thing I found was that the manifold's ports were too high - the top of the RPM's ports were above the top of the head's ports, so an edge would be "seen" sticking into the port roof by the intake charge. That's bad news. I also noted that the end rails of the block and manifold did not sit parallel to each other - one side sat higher than the other by about .030" and the low side was bottoming out on the end rail. Also, bad news.
For those not famliar with how to go about checking port match "out-of-the-box", I'll explain. You need three measurements:
1. the distance on the head from the top of the valve cover rail to the top of the port.
2. the distance (with a fully torqued-down intake manifold now in place) from the rail to the top of the manifold at each port
3. the distance on the intake manifold from the top of the port to the top of the manifold (i.e., the thickness of the port roof on the manifold)
Take these measurements for each port (because they may all be different).
If the resulting measurements "2" + "3" = "1", above, then the top of the ports (intake to head) will match perfectly. Since these parts are not precision made, you will likely find each port will be a little different. In practice, getting the intake port roof to sit about .030" below the top of the head's port is about optimum. That's where I start.
From there you can mark the port width on each part (use felt tip marker and rule), assemble the manifold to the heads (i.e., to the longblock) and see how the ports mate laterally. You can also make measurements of the ports' depth and determine how the floor of the ports meet. the key is to register the roof of the ports, first and then work to the floor. It's not too tough, but it takes time.
If you find that you need to have the manifold machined, as I did, in order to lower the ports, the amount to tell the machine shop to mill off is the same amount that the port roof is too high on the HIGHEST manifold port. Let's say that the highest port was .020" above the roof of the head's port. The rest were close, but all a bit lower than this one. Now, I want the intake's port roof about .030" below the head's port, so I would remove .050" from the manifold's machined surfaces. You can use your judgement, depending on the variation from port to port - meaning that if all the others are lower than this one port, you might just take .040" off in order to have the one port .020" below and the other ports closer to .030" below. Hopefully, you won't have one port way higher than all the others, which might require some port work to get a better match.
Pay attention to the end rail gap. If you don't have much end rail gap before machining, machining material from the manifold port surface will reduce the end rail gap further. In my case, I had to have the end rails of the manifold machined, too. How much? To keep the end rail gap constant (the same as before machining the port surfaces), multiply the amount taken off the port surface by the square root of "2" (1.414). This assumes that the intake and head mating surfaces are machiuned at 45 degrees, which is about right. Because my manifold did not sit level, I had it angle milled .040" on the high side and .070" on the low side. It now sits level with about .020" end rail gap and the intake ports are just below the head's ports.
Now I have to decide if I will massage the manifold's port shape to better match the heads. I'll probably widen the intake's ports a bit and try and find a way to lower the floor. The porblem is that you don't want the port volume going large-small-large, etc. You want uniform volume, or a taper from the plenum to the valve pocket. A taper is preferred by yours truly. I'm not sure that I can achieve much enlargement of the ports and still maintain a taper, or even uniform volume. A single plane manifold would be easier, but .... that's not what I got. I may just have to live with the port shapes, or just do minimal reshaping.
One take-away message from this is that you must not assume that a bolt-on part is truly bolt-on. I would have lost some real horsepower had I just bolted things up and assumed the match was okay.
I got the wrong water pump and am waiting for a replacement before I can completre the mock-up. Talk to ya later.
The first thing I found was that the manifold's ports were too high - the top of the RPM's ports were above the top of the head's ports, so an edge would be "seen" sticking into the port roof by the intake charge. That's bad news. I also noted that the end rails of the block and manifold did not sit parallel to each other - one side sat higher than the other by about .030" and the low side was bottoming out on the end rail. Also, bad news.
For those not famliar with how to go about checking port match "out-of-the-box", I'll explain. You need three measurements:
1. the distance on the head from the top of the valve cover rail to the top of the port.
2. the distance (with a fully torqued-down intake manifold now in place) from the rail to the top of the manifold at each port
3. the distance on the intake manifold from the top of the port to the top of the manifold (i.e., the thickness of the port roof on the manifold)
Take these measurements for each port (because they may all be different).
If the resulting measurements "2" + "3" = "1", above, then the top of the ports (intake to head) will match perfectly. Since these parts are not precision made, you will likely find each port will be a little different. In practice, getting the intake port roof to sit about .030" below the top of the head's port is about optimum. That's where I start.
From there you can mark the port width on each part (use felt tip marker and rule), assemble the manifold to the heads (i.e., to the longblock) and see how the ports mate laterally. You can also make measurements of the ports' depth and determine how the floor of the ports meet. the key is to register the roof of the ports, first and then work to the floor. It's not too tough, but it takes time.
If you find that you need to have the manifold machined, as I did, in order to lower the ports, the amount to tell the machine shop to mill off is the same amount that the port roof is too high on the HIGHEST manifold port. Let's say that the highest port was .020" above the roof of the head's port. The rest were close, but all a bit lower than this one. Now, I want the intake's port roof about .030" below the head's port, so I would remove .050" from the manifold's machined surfaces. You can use your judgement, depending on the variation from port to port - meaning that if all the others are lower than this one port, you might just take .040" off in order to have the one port .020" below and the other ports closer to .030" below. Hopefully, you won't have one port way higher than all the others, which might require some port work to get a better match.
Pay attention to the end rail gap. If you don't have much end rail gap before machining, machining material from the manifold port surface will reduce the end rail gap further. In my case, I had to have the end rails of the manifold machined, too. How much? To keep the end rail gap constant (the same as before machining the port surfaces), multiply the amount taken off the port surface by the square root of "2" (1.414). This assumes that the intake and head mating surfaces are machiuned at 45 degrees, which is about right. Because my manifold did not sit level, I had it angle milled .040" on the high side and .070" on the low side. It now sits level with about .020" end rail gap and the intake ports are just below the head's ports.
Now I have to decide if I will massage the manifold's port shape to better match the heads. I'll probably widen the intake's ports a bit and try and find a way to lower the floor. The porblem is that you don't want the port volume going large-small-large, etc. You want uniform volume, or a taper from the plenum to the valve pocket. A taper is preferred by yours truly. I'm not sure that I can achieve much enlargement of the ports and still maintain a taper, or even uniform volume. A single plane manifold would be easier, but .... that's not what I got. I may just have to live with the port shapes, or just do minimal reshaping.
One take-away message from this is that you must not assume that a bolt-on part is truly bolt-on. I would have lost some real horsepower had I just bolted things up and assumed the match was okay.
I got the wrong water pump and am waiting for a replacement before I can completre the mock-up. Talk to ya later.
What is the best intake to run with this combo?
