Rover owners: Creating VVC inlet port models for measuring and planning head modifications

When you want to modify a head for improved flow or improved flow characteristics you usually use a mixture of calculation, bench testing, CFD and, with experience, looks-about-right - no one on it's own will normally give you a good answer.

Traditional head porting work on the inlet side was (is) based around

1. Removing notches and bumps in the port.

2. Getting as straight a shot at the back of the valve as possible.

3. Tapering the port to start big and progressively taper down.

There are other issues but i'm not showing port work here so i'll save it for later.

The one piece of information that you must start with is port measurements, and measuring inside of a port, especially on relatively small ports in sub-2.0 engines is awkward and when they bifrucate from a single inlet to two valves (4 valves per cylinder engines, or more) it becomes more tricky unless you have tiny hands and unnaturally jointed fingers.

A long standing method to overcome this is to make a mould of the port, and this is how I do it:

First, clean up the head with some nice high-VOC thinners, and wipe some mould release agent, silicone grease or similar all over the ports.

Then get some two pack RTV - a normal tube silicone sealer type wont set at the thickness of the core of the port - which has good self-releasing properties and a low hardness. I got this from an ebay seller and it's the best i've ever used:

You'll need to mix it properly, by mass, and although i'm showing 122g (111g of base and 11g of activator) i'd recommend about 100g in total for VVC inlet port.

It needs to mix properly to make sure that it will all set, or else you get a goo spot:

Tape over either the inlet or the combustion chamber side holes to keep the RTV in.

Note: You'll notice I am actually working between two moulds - 1 of the full port and 1 with the valves in place, so if you make a mould with the valves (also wiped with anti-stick media) you'll need to tape then in place.

Pour it in slowly, giving it a mix and a prod with something to prevent air bubbles becoming pockets.

Now level up the head and fill the port all the way up (or fill from the inlet side if you have valves in place)

The RTV will set in a few hours, but I usually just leave it for at least a day if not two. The you need to get it out. I have mangled a few in the past and had to restick them together, but this RTV is quite strong and could be hooked and pulled - consider putting something in the rubber to allow you to grab it and that will embed over a large area. I use LEGO trees when i remember to buy them,and you can buy them separately from LEGO shops.

You'll need to push it in as you pull it

...but it gives up

This is what you get:

You can see this one was done with the valves in place. If it's your first go i'd do it that way, as when you knock the valves out the hollows allow the RTV to deform and it makes it easier to get out.

And this is what we are looking at; the air.

With this done you are ready to measure the sections and learn where any pinch points are, and in conjunction with a cutaway head you can learn where you can and cannot cut metal from the port to improve the flow path.