Hey guys and gals

Sitting here thinking a bit, as I have read a lot around the forum but still would like some definite answers..

What would be the best way to port a A12 head?
How high can you go/how thick is the walls?

Its for a street engine that will be raced once a while, but have just read so many different things..

I'm thinking a little about just raising the top a bit, and letting the bottom be as is.
Maybe doing something like what D suggests here, http://datsun1200.com/modules/myalbum/photo.php?lid=1777 , with makeing a D?

Or is it better just to get a A14 head and call it?

The motor is going to have a SC12/14 I'm thinking. Might go turbo if I can get i approved by the DOT in Denmark

Chears
Toby

I'm sitting here and designing a set of intake-manifold plates and would like to just make it a part of the design from the start.

Something like this... ( Or will I hit the water jacket? )

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Yes, better to get an A14 head and call it good

I agree, u can ask PJZ for one that is not heavily shaven
but has some decent work done

I've ported 3 GX heads over the years and simply used a dremel; nothing fancy clean up the casting marks, matched the manifolds and gaskets to the head. The one sport I removed a bit of metal was around the valve guide bowl area to smooth it out. The other area was the valve seat; where the seat meets the heat it protrudes into the head by as much as 1mm meaning it's cutting the diameter by 2mm, simply getting the seat flush with the port wall where they meet makes a big difference.

Yes an H89 oval port head or GX head would be a better way to go but since it's only your time nothing wrong with cleaning up the head you have. If,your budget is tight I would install larger valves and clean up the ports in the head you have. A good head may be anywhere from $500-750 so working with what you have isn't always a bad idea.

If your budget as room in it as the others have said just buy a better head.

Tom

Okay then.. Still some things to sort out;

1. A A14 head will lower compression. How will this hurt performance? Or does it counter for it by the bigger valves?
2. If I choose to stay with what I got, can my original question get answered, regarding how much and how i should port the head?

Rallytwit, installing larger valves require the head getting the seats maken bigger by a shop, and when it's there anyway, I might as well get it ported by them, right?

All aside I would also be keen to know what I can expect from doing this power wise ? :)

But have sent a PM to PJZ and is hearing him what he want for a head ^^

D shaped ports can work very well as long as they're not upside down.

A14 head won't lower compression. Most A14 heads are the same CCs as A12, although some later A12 & A14 heads (certain 1982 and newer) have a slightly larger chamber. See Chamber Size. In A12 engines, there are many piston dish sizes, which is primarily what determines compression ratio

All A14 heads come with the larger valves. All A12 heads have the smaller valves. By the time you add cost of new valves, and machine shop costs, it's usually better to obtain a good used A14 head. It's factory ported for larger flow already (80 HP vs 69 hp). Porting the A12 head makes sense when racing class rules don't allow head swaps, or when you are doing all the labor yourself

Of course there are two types of porting:

* Porting for maximum HP. If your goal is maximum HP, better to get the best head to start with. The downside is that power shifts to high RPM (power at low RPM is reduced)

* Porting to maximum the head efficiency. By doing 1) Port Matching and 2) Bowl Cleanup you ensure the head is working well (and there is no downside, all RPM is improved)

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this is how much





See Head Porting