38. The Offenhauser 360 inlet manifold

After finished the Holley carb I went to the inlet manifold.
It is an Offenhauser 360 - the lowest one you can get for the Rover v8.
The normal American cars did not have a leveled engine, so the manifold has to compensate this angel for the carb.
The Marcos instead has a leveled engine. On mine the carb was mounted in a bad angle.

You can buy a wedge plate to compensate this angle, but I do not want to come higher with the carb. A friend milled down the manifold until it has the same angle as the rest. The threads for the carb were gone as well...
Not to too bad as there was enough alu left over to set some Helicoils in metric M8.
With this I saved about 12mm in height, so I have space for a temerature isolation which saves the carb from being heated up by the manifold on longer runs. This is done with a 12mm Pertinax plate.

If the height will be still a issue, The aluminium adapter plate can be removed and a the carb can be mounted directly on a new shaped Pertinax plate. At the moment I will keep the alu plate and hope it will be OK.

Now the alignment of the ports has to be done.
The ports in the head were done by Rovercraft. All of them were ported in a - lets say good quality - it could be done in a better quality, but this was never a high performance engine and so it is OK.
A nice detail is the ramp before the valve guide. This ramp will help the air / gas to pass the guide with less resistance.
In modern race engines you cut off the valve guide in the port and use a better material, which will be durable long enough. Second step will be to use a valve with a smaller diameter in the shaft which passes the port.

I started to make a stencil from the head´s ports with carbon paper ( lucky, if you know where to buy it...). On the black marked ports of the inlet manifold I scribe the edges of the heads ports.

Done this a lot of times on 4 cylinder motors - easy.
Ups, but now there is another bank of ports which will be aligned on the manifold. And that V- form of the engine is not to make this alignment more easy. Depending on the gasket, the lower and upper edges will vary.
To make it short, it was a mess to get the correct position of the manifold to the heads for both sides and then to see, if the ports are really matching. I managed it with reference marks on the head, the stencil and the manifold and a endoscope lend from a friend.

Lets go one - the marked manifold ports.

Bad quality here, but in real you can see what you need...

To have another control about the matching of the angels of the ports, I use a small sheet of alu which has the same "diameter" as the ports in the head ( they all were the same ! ).
In the head, the ports will get narrow to the valve and in the manifold the port shall expand in the same angel. With the sheet you can check the ports in the manifold and when it can be easy pushed in, you know, the port is wide enough. Now you can concentrate on the inner part of the port.

 Here a picture of the roughly shapes ports. The corners are not finisched as well as the surface.

 Before the fine finish, I have to prepare the head. The ports in the head are more wide than in the manifold, but the hight of the ports in the manifold was higher than in the head.

Dammed. I have to port the mounted head.

So I pushed a lot of paper - the extra tearproof one - in the ports and "seal" them.

Scribe the upper edges of the ports - it was about 2mm ! - and mill them off. The gas lines at the top left were sealed before!

For all this milling jobs I used a straight grinder free hand and carbide cutters. The ones I like most are the pear form (the middle one). They gave a fine surface. For the smoothing I use fan grinders up to 240. 

I am not the polishing fan for ports - maybe on exaust ports to keep them longer clean. I think a surface which is smoothed by a 240 fan grinder is enough.

Maybe explain it with micro vortexes, on which the main airflow can slide or even with laziness.

Here the swept up aluminium from the manifold.

 I am really sorry, but I missed to take a photo from the finished ports. I finished them on another day and mounted the manifold at once.

The result looks good I think:

By the way, I closed the outlet of the heater with an aluminium sheet