Making a Silicon Port mould

[brad_m]

This has come about as part of the porting thread in the 6cyl section on Fordmods.com
http://www.fordmods.com/ford-4l-and-6-c ... 86312.html
At first we were asking for people to donate cracked, corroded and other wise junk heads to give us the ability to create a bit of a head library.
For the most part this is to sort the fact from the fiction regarding all the stories about which head is better ect. Getting heads also gives us the ability to modify flow test many individual changes with out needing to ruin good heads.
It's proven difficult to obtain heads even though a number of people have said they had junk heads and would donate them.
Taking moulds in the end works out cheaper, PLUS the chance is there to mould already ported heads to compare with out damage or down time.



Port moulding

What you will need.
500g fast set silicon. In this case I am using Pinkysil Bought online from http://www.amcsupplies.com.au
Small amount of dish liquid (free mould release)
A kitchen scale
A mixing cup
and a mixing spoon.




First step is clean the port and valve you are going to mould. Leave the valve stem seal in place as it will help to hold the valve in place.
Place the head on a plastic covered table with the exhaust ports facing down, You want the head reasonably level.





Put a small drop of dish liquid on your finger and coat the back of the valve and about 2cm of the stem.
Also coat as much of the port and valve guide as you can.
In doing this you do not want to wet the port with dish liquid, you only want a 'dry' coating.
Sorry no pic of this process.

Once done install the valve making sure it is seated firmly.



Place the cup on the scale.



and then zero the scale



Slowly pour in 80 grams of PART A


Then aero the scale again.
Slowly pour in 80 grams of PART B

Mix thoroughly to get an even, consistent coulor. At this point as we are using a fast set silicon you only have at most ONE minute to get the mixing done other wise the silicon will start to set and you will be rushing to pour the now thick lumpy silicon before it's wasted. TRUST ME

Once mixed pour the silicon slowly into the port until full


Depending on the head you are moulding, you'll have a little left over

If you have a lead sinker moulds, now would be a good time for making some bright pink slingshot ammo


De-moulding

After 20 mins the mould is ready to come out.
Give the valve a tap to knock it loose and remove it.




Insert a flat screw driver to gently pry the mould away from the port walls, do this right around the mould at both ends.



Mix a small amount of water and dish liquid and with the screw driver still inserted tip some into the gap, again all around and at both ends working the mould to get all of it soaked.



Now push from the manifold end with handle of the screw driver and push the mould out.
This may take a fair amount of force.




The finished mould

[holmsy]

whats the use of this?

[misk]

i'd say to help with porting, to see the shape of the port better.

[SL33PNcoons]

He's fabricating marital aids But nice. I will do this with my ported head while its off the car if you like? EF tickford stage III port job by hoppers express. see what you think.

[brad_m]

He's fabricating marital aids But nice. I will do this with my ported head while its off the car if you like? EF tickford stage III port job by hoppers express. see what you think.

That would awsome, thanks.

[TUFED6]

Wow pretty cool shit. What have been your findings so far?

[brad_m]

That particular port (AU1 VCT) narrows at the short turn and has the valve guide protruding at the same point creating a choke point.
The choke point is what limits flow at high lifts, below roughly .350" lift the shape of the valve, seat ect is what controls flow.

Until the choke is fixed puting grinding burr or paper roll anywhere between the port entry and the start of the short turn is waste of time.

For the DIYer the time and money best spent is removing the guides and shortening them by 3mm (using the shortest one as a guide to modifying the others) then tappering them down. 30 degree back cut on the valves, taking the seat width down to 80thou and then having the the seat in the head cut to make the contact area right the in the centre of the seat on the valve. A good machine shop will know what you are talking about.

If you must grind something, widen the port around the guide and the blend all of the rough maching in the bowl of the port.
For beginners the blending is best done with a flap wheel as it's hard to make big mistakes with them, then take the pollish off with a 60 grit cartridge roll.


That's about all I would recomend a beginner does on any of the I6 heads.

[XR_Lightning]

cool idea, defintely interesting

[brad_m]

whats the use of this?

Here is the reason I moulded that port.



Autospeed flow a STOCK AU head at 117cfm at .500" lift. They tested it at 10" H2O
To convert from 10" to 28" we mutiply by 1.67.
That puts the AU head 195.39cmf@.500" lift tested at 28" H20.

Now if we work back to the MCSA of the port at the choke point in the turn(MCSA = min cross-sectional area) .
The MCSA is 864mmsq.
Through some math we can use that to show us what flow the MCSA will support with an air speed of 350fps. When I do this I get 195.494CFM @ 28" H2O. (those findings prove the formula)

IF we then work our way through the port,
The port proper can support 230cfm
The seat area can support 281cfm
Curves, shape change, and other things will effect the flow. Meaning if you didn't touch the seat area at all and brought the rest of the port to a point that it could flow 280cfm you probably will not get 280 through the seat.

[mad_keen]

Wouldnt porting everywhere until you cant port no more be the best?

[SNR]

Until you can port no more? I.e. when you hit a water or oil jacket? Ideally you want a port that promotes flow. Just opening up "everywhere" means you have areas that the port drops in pressure, which would slow down or distort the flow

[brad_m]

Wouldnt porting everywhere until you cant port no more be the best?

No because you would end up with a bad shape and to much variation in CSA and also to much CSA resulting in low air speed.

[mad_keen]

Thanx for clearing that up