MA10/12 information?

[Mark]

couple of questions I wanted to ask regarding the MA10 and 12 engines,

what are the actual differences? are they exactly the same apart from the bore and stroke? I know the two camshafts are slightly differant but thats about it,

the standard max torque figures are quite low standard, 3200 and 3600, is there any reason for this? could this be down to the inlet manifold? or even the camshaft? I have read somewhere that the standard camshaft is only 235 duration, which i thought was quite low, I am replacing my cam for a 270 duration cam any ideas if the peak torque figures are likely to be higher up within the rev range?

 

[Andrew]

They are very similar engines. The MA12 has a slightly taller block due to the longer stroke.

Engine torque is primarily affected by displacement. In an ideal engine, the torque curve would be flat. Most tuned engines have the torque tail off at the redline due to friction and other parasitic losses in the engine.

However, it tails off really early in the MA series. In this case, it is due to the fact that the engine simply cannot breathe well enough above this RPM to operate at the optimum point. This could be due to either cams, manifold, or head.

The camshafts on it are about average in duration for a normal engine of that period. I haven't got figures for lift of both cams, so can't say which one has higher lift.

I have tried an MA10 head on an MA12 block. There wasn't any appreciable difference, but then we didn't put it on a dyno. Take note that there are two different cam belt pulleys. I think one is for the MA12 and the other the MA10, to account for the decreased block height and the length of the cambelt. Make sure you use the right one, or you will rapidly say bye to the engine.

There also appear to be different designs of head, but I don't think anyone had ever bothered really recording it.

 

[Mark]

thanks andrew.

the camshafts are:

MA10
Outer diameter of journal 39.95 to 39.97 mm
camshaft bearing inner diameter 40.00 to 40.03 mm
journal to bearing clearance 0.03 to 0.07mm
endfloat 0.03 to 0.31mm

cam lobe height:
inlet 33.77 to 34.02mm
exhaust 33.73 to 33.98mm

MA12

cam lobe height:
inlet 33.98 to 34.23mm
exhaust 33.94 to 34.19mm


the ma12 cam appears to be the better one as far as valve lift but duration is unknown for them both,

as far as restrictive parts go i think i have them all covered, I've a selection of parts for my micra,

4-2-1 exhaust manifold
custom inlet manifold
fast road cam

andrew do you think the peak level of torque will be higher up in the rev range? I've been doing some reasearch into engine tuning etc but dont yet fully understand it all. I was told that the ECC MA12s had better cylinder head ports? dont know how considering they produce far less power.

but at the end of this all I'm hopeing for about 80-85bhp, I mean the AX GT engine is only 1360cc and produce 85bhp and 85ft/lb of torque and there 8 valve engines, and there only 135cc bigger!

I hope the restriction is in the Inlet manifold