Easy match porting

[Adam]

If you play with geminis for long enough sooner or later you will want to have a go at porting a head, all I can say is go for it. You can purchase aluminium burrs from specialist trade tools shops such as the chain named (oddly enough) "Trade Tools" for around $52 each, I would suggest buying two, both cylindrical(rather than cone shaped), one with a short shank and the other with a slightly longer one.

Start off by ensuring that your head has the larger valves, casting number of 7, 14 or 21, check below where the mechanical fuel pump would be/is fitted on TF/TGs. IT would be a waste to port the smaller valved head when a big valve head only costs $85.

As a rough guide, fit a new gasket to the inlet studs and port the head smoothly out to the gasket line, ensuring you maintain a nice even diameter throughout the port with no rough edges.

Where the port curves downwards towards the valve, try to remove a fairly significant amount of metal. What you are trying to achieve is the straightest possible path for the gas flow into the cylinders.

The same is true of the exhaust ports, only don't remove too much metal at the bottom outside edge of the port as there is a water gallery running through there and even if you do remove metal it won't gain you much addition flow capacity, stick mostly to ensuring that the top outside edge and the bottom where the port curves down to the valve are both well ported.




If you are having the valves seats machined then also machine from the combustion chamber side of the ports smoothing out the areas around the valve seat and where the valve stem protrudes into the port. This is more complicated so it helps to have an expert around, that said, if you make a mistake, it only cost you $85 and you still have 3 more ports to practice on before you throw that head away, so while it is a set back, it isn't the end of the world.

If you are having the head's face machined (to ensure a flat surface for the gasket to seal on and/or to up compression) then I suggest smoothing out and polishing the combustion chambers, I would only suggest doing this if you are going to up the static comp because it probably adds an extra 0.5CC to the volume of the chamber and G161z compression ratios are too low already, aim for 9.5:1 as a barest minimum.

Once you have ported the head turn your attention to the manifolds, again placing the gaskets on them as a guide, if you port both the head and the manifolds to the line of the gasket you know that they will line up perfectly and you will have a beautifully match ported setup.

Port as far back into the inlet manifold as you can and also port the carby side of the manifold as follows. Remove the studs and the try and look diagonally down into the runners for cylinders 1 and 4, you'll notice your view is blocked by the bottom edge of the runner from the primary side of the carby, machine this section to allow a smoother flow around the corner and then do the same to the bottom edge of the secondary runner. While you are machining the secondary runner, grind the three little brass pipes so that they sit flush with the wall of the manifold, however ensure (using the blow on the end of a bit of pipe method) that they aren't blocked.

Port your exhaust manifold out the same way to align with the exhaust ports.

Then take all your metal shaving laden pieces away and have them sandblasted (I paid a local engine reconditioner $20 to do it all for me), when you get them back, meticulously clean them using high pressure air/toothbrushes/pipecleaners/soapy warm water, just get rid of ALL the sandblasting remnants, they will not do your engine any favours. Repolish the combustion chamber back to a mirror finish, take a few photos. Have your machining done (valves reseated, spark plug holes helicoiled, face machined) then decide whether or not you will fit a bigger cam and fit your nifty new head to the bottom end of your choice as per standard procedure.

[old forum]

Whenever you are grinding with an aluminium burr, or machining anything else for that matter, always use a light machining oil to lubricate the burr, I actually use an aerosol pack of castrol motorcycle chain oil, as it is thick and viscous enough to stay on a vertical surface and lubricates extremely well.

[old forum]

Great articles and pic's, keep up the good work. When I port a head I bolt down the gasket to the head and then spray paint (usually flourescent orange) the ports/gasket, then remove the gasket (it last's longer in case I slip) and grind only the painted metal. Hope this help's someone else.

Thanx, carl.

[old forum]

If you are looking at porting a head for your engine for the first time, you can always buy a small valve head for $20 and practice on 4 of each kind of port before you have a go at your more expensive ($85) big valve head.

[old forum]

this tip was passed onto my by an engine reconditioning friend, to allow youself full unblocked access to the ports, before you start assemble and bolt together manifold and new gaskets to the head, get a 1/8 drill and drill into the manifold and through the gasket going into the head itself, dont go too deep but deep enough to fit a 1/8 split pin, the intake side requires four on the gems(two piece gasket), and two on the exhaust if using the extractor gasket(one piece). this way you can remove the manifold and studs and leave the gasket on the pins while you do the match porting in the head and also the manifold, this actually "keys" in the gasket to both surfaces ensuring that there is no movement of the gasket on the studs when bolted together and holes are alligned perfectly with each other.
cheers.
neal.

[old forum]

posted by Fish on Sun Aug 26 01:29:35 2001 from 210.49.20.22

i was just reading the head porting article and would like to add this info regarding big valve heads.
When chasing a big valve head and the head is off the car or you have your head of your gemi look at the numbers on the valves.
If the inlet vavles have 00 infront of some numbers then you have a big valve head if you have 178 on the inlet valves then you have an late model head.

[Smokey]

here's a website that you may find useful
http://www.sa-motorsports.com/diyport.htm

[TXcoupe]

when u do get a small valve head and want to port go for it the small valve heads an flow just as much and more ( if done right) as the big vlave head. so dont go silly on the small valve head. do it right. then get some one to cut you new seats with big valves in it and she shall be alright jack.