K10 head info please

[BiAS]

I've spent the last couple of evenings reading threads on here but can't find what I'm looking for..............................

Are the MA10 and MA12 heads interchangeable?
What are the differences?
Are the valve sizes different?
I keep seeing references to '91 + '92 K10s having ECUs, is this just on the cat equipped cars?

Hi BTW (Y)

 

[curtis]

The heads on the MA10 and MA12 are the same
Valve size is the same

There are a couple of differences with the ma10 heads as one is the 55bhp and other is 50bhp type iirc

Also if you get the head from a super s, ECU car then they have sightly bigger ports and valves iirc

They are interchangeable!

 

[Speedle]

i have a big port MA12s head in my garage that i have for sale.

IIRC i dont think the heads are the same? im sure the ports on the MA12 are different. i'm sure Ed said something about this in the past but its been such a long time i could be completly wrong. but either way they are completly interchangeable.

there are 2 versions of the MA10 block however the MA10 50bhp (usually the 4 speeds have this engine) and the MA10s which is 55bhp i believe 5 extra bhp comes from a different compression ration but i cannot remeber what it is of the top of my head.
(usually the 5 speeds) and

then the MA12 60bhp and the MA12s (IIRC) also 60bhp which is used on the later k10's and has all the cat and emision crap on it. obvisouly removing this would mean the MA12s would have more power over the standard MA12 as it has the bigger port head on it.

hope that makes sense not sure it does lol

BiAS=Bodge it and scarper perhaps?

 

[curtis]

I used the valves out of a ma10 head and fitted them into the ma12, fitted perfect

 

[Speedle]

i have no doubt the valves are identical mate but im sure there is a "slight" height difference between the the MA10 and MA12 heads i remeber Ed mentioning this in the past although he may have been comparing the MA09 and MA10 heads like i said memeories a bit rusty these days like most of my old k10's no doubt

 

[BiAS]

Thanks for the prompt replies folks,
Yes speedle, Bodge it And Scarper (Y)

So, are the 'ecu' cars single point injection or are they still carb?
Are the cams the same? The Haynes book of lies only shows the lift as being the same but has no details on the duration.
I ask this as currently I have a '91 facelift 998 K10 with serious mileage, rust and no 3rd gear..................
.........and a '91 facelift 1235 K10 with 86,000 miles, no rust and 2 bent valves.
My choices are to put the complete MA10 head on the MA12 block but with the MA12 inlet................or take the valves out of the MA10 head and put the MA12 head back on the MA12 block.
What sayeth the combined wisdom of Micra Sports Club??

 

[richj]

the head will go on without any problems, as long as you know how to change a cam belt.

 

[boyracergt]

the ecu cars still have a carb just a more complex one. not sure about the cams but if the ma10 and ma12 heads are interchangeable and the valves etc are the same size id use the ma10 head on the ma12 block as the ma10 has a higher comp ratio than the ma12 (9.5:1 vs 9:1) i might be wrong though... also im 99.99% sure the inlets are the same id also use ma10 carb on the 1.2 as slightly bigger jets. but im still a bit of a k10 noob so you might want to check

 

[BiAS]

Now with pics!

Right then, the valves are the same size on both the heads(Y)
The combustion chamber in the head is the same depth on both the heads but the dish is smaller in diameter by 1.7 mm, this suggests to me that the MA10 (4 speed) head is fractionally higher compression.....................................
However, whereas the MA12 head has inlet ports that look like this:

The theoretically higher compression MA10 head has inlet ports that look like this:

What's the swirl achieve?
The outer port size is the same but the area round the valve head is smaller.
My heart says biggest most direct route into the cylinder (ie MA12 head) but is there something really obvious I'm missing?

 

[Ed]

The swirl does just that, swirl the intake charge to promote better atomisation, and therefore better economy/emissions, I would suspect at the loss of a bit of top end power. Also, the 1.2 has a bigger diameter head as it has a bigger bore! So, gains lost in putting a theoretically better head on a 1.0 are lost by the drop in compression.

FYI the March ST head is like the 1.2 head but as the 1.0 size but lower compression...

 

[Baz]

Great information to know!

 

[natemicra!]

The swirl does just that, swirl the intake charge to promote better atomisation, and therefore better economy/emissions, I would suspect at the loss of a bit of top end power. Also, the 1.2 has a bigger diameter head as it has a bigger bore! So, gains lost in putting a theoretically better head on a 1.0 are lost by the drop in compression.

FYI the March ST head is like the 1.2 head but as the 1.0 size but lower compression...

So ed fitting a ma12 head on an ma10 head will give more power? I know the ma10 has more compression , but couldnt you skim the ma12 head and have a better flow and more compression?