The oval port single sidedraught manifolds are difficult to find, but are available.

In terms of running an A12 head on the A15, there isn't too much wrong with this, there are a slight difference between valve sizes in comparison to the A14 Round Port Head.

That manifold is special in the sense that it addresses cylinder feed/supply via the runner patterns/paths unlike the standard round port manifolds like the one that fandatstick put up (which just feed straight).

What do you mean by old bolt pattern and new bolt pattern?

Have faith in the round port head and that manifold, they can yield some pretty impressive power.

Sorry I replied again ^^^^^ before waiting for your reply.

If you believe the manifold has enough flesh to port out to an oval shape and you intend to match to an oval port head, your cheapest way around this would be to drill and tap a new stud between the two existing studs where the manifold mates up to the head.

You would need to mate the manifold up to the head and mark the hole this way, ensuring the ports are nicely aligned (perhaps remove the valves to get a clear view into seeing what is lining up where).

The A14 head would offer better flow (bigger ports bigger valves) and the performance would me much better at the higher end of the tachometer.

I reckon you get started and put the A12 head on the A15 and get everything nicely lined up. If you want help rebuilding the carb I can certainly help you out there.

When you get more cash you can either go oval port head with the introduced middle stud and some manifold port-work.

Personally I reckon you go bigger round ports and bigger valves on the A12 head, with a little de-shrouding work on the combustion chamber and some double valve springs.

ok thinking about this a little, you may be able to get an early a12 round port head and fit it to the a15 block.

you just have to do the reverse mods when fitting an a15 or late model head to the early block.

oil bolt and something else(cant remember) might not line up for lubing the head.

This would result in possibly higher CR but smaller inlet/exhaust valves may impede some flow.

I reckon get an early a12 head and see what needs to be modded.

At least it will work one day.
And higher CR would be fun! just not as high as Clyson went

Clyson (slyson?!) went way too high. 15:1.

You could do 13:1 seeing as you have e85 available in viccy-vic-vic.

Now Im confused about the different manifolds.
So round port a12 heads are the only one with this bolt pattern or are oval port heads available?
Did I read something about multi-bolt pattern heads or am I just imagining this?

I think it would be an awesome little setup, simple yet effective, looks great too!.
It would be easier to start with a round port and open both the head and the manifold up to suit rather than trying to open the manifold up to an oval port...something tells me putting an a12 head onto a a15 block is not going to be this simple, but what bettter way to learn eh?

oh wait, this isn't going to affect the exhaust manifold bolt up is it?
Initial view seem they are the same, just the intake that differs.

What about the approach of making a new round-to-oval flange for the manifold?

there is an "Oval" Cannon manifold available in the US, it's pretty rare though and sits really close to the head..
I've run singles on A12 in the past and had good results,
My A14 in the wags, I put a roundport head on it and single 40, but haven't done any tuning yet..

so what needs to be done to put the early round port a12 head onto the a15?

make sure the oil gallery to the rockers goes where it's supposed too..:)

anyone with mad welding skills be able to tell me how difficult it would be to weld a new flange on the manifold to bolt straight up to an oval head?

If it were thick enough, you could incorporate the round to oval porting within this flange, also might be giving it that extra bit of clearance for the extractors?

Just a commparo between the level of difficulty of swapping the head, then having to port it out, valve size ect... , you could do all this in one hit without having to remove the head maybe?