I currently have a A15 in my 1200 sedan. I have recently bought a spare 1500 head and taken all the valves out and rocker gear and valve stems out and then went buzurk with the die grinder. Haven't finished yet but exhaust ports are almost as big as inlet and did a fair bit of work to the short bend radiuses to improve flow. I have still to do combustion chamber work yet.

The real reason for all the head work is that i want to put that head and a14 conrods and pistons in the a15.
I know some people have done this mod so i am directing this at you mainly as you can notify me of any other things to look out for or be wary of and how much power,and harder does it go.

I realise you have to take off 40 thou off the top off the piston.
As my engine was a low km import i think 60,000 km out of a nissan Vanette, i think it would be good to use.
Will i be likely to have to make valve reliefs in the pistons for this mod, i know how to find out if i do but i would like to hear it from someone who has done it.
i think the head i'm using has plenty of meat in it(ie. not had to have it faced many times)
I am going to polish and shot peen the conrods, balance everything so it should be all good there.

What likely compression ratio am i looking at for this sort of work and what hp roughly, i'm only running a weber 32/36 at the moment and a very mild cam 25/65 grind. this is going to be street driven every day and some motor sports so any other suggestions would be greatly appreciated.
cheers

I'm pretty sure A14 and A15 rods are the same.
Its just the piston thats different.
Be careful taking meat off the crown of the piston as you might run out of compression height and blow holes in the tops of the pistons.
You may need to cut reliefs in the top of the block for valve clearance if you go with bigger ones......I did. This might limit where your top ring also sits on your piston depending on the depth of them.
This and the valve relief cuts will depend on the size of the camshaft you use.
Measure the size of the chambers after the valves are fitted to calculate comp ratio.
Mine runs essentially flat top pistons....24cc chambers. I calculate it at approx 12.9:1 but my slide rule might be off.
1mm overbore A15 crank (stroke)

Neil

Yeah the A14 and A15 conrodsare the same just deak height is differant in the piston so thats why to take off that 40 thou, i asked baz the owner of Datsport here in South Australia, he said taking that much off the top is like stuff all and should be fine (approx 1mm)

I'm using standard valves but does anyone suggest any good valve springs for higher rpm (brands, part no. $$$)

The A14 stroke, at 77mm, is 5mm less than the A15. That means that the A15 pistons rise 2.5mm higher [& fall the same amount lower] than the A14.
If you use A14 pistons in the A15 engine, the top of the piston, now rising 2.5mm higher than before, will protrude by this amount from your block. This is fixed by machining this amount from the crown. If you take 1mm from it, then you will still have some piston sticking up past the top of the block.

If you take 2.5mm from it, you had better have a real good look at the distance between the top of the piston, & the top ring. By now it's geting pretty thin & the strength here is becoming marginal, particularly if you are pushing noticeably more compression.
I think you will find that this land is only about 5mm thick in stock trim, & that's not a real lot to play with.

Think twice, then act once. [Measure it twice]

I understand this, this is the differance between the two cranks, A15 longer than A14 giving the A15 more torque. The A15 block is also slightly taller than the A14 block as well from memory so that also accomodates for the extra stroke in the crank.

This is not the problem, it is the pistons. As i believe or can last remember the piston in the A15 does not quite reach level to top of block. So what i need to find out is the pin to top of piston measurement to work out how much the A14 piston will be higher than the A15 piston. Does this make sense.

A15 block, A14 or A15 conrods(same length) and A14 pistons in comparison to all A15 parts ie. standard A15.

A15 compression height 30.0mm
A14 compression height I can't seem to find a listing on.

This is centre of pin to top of crown

Quote:Giving more of everything. The point of the crank is larger displacment. This results, all else being equal, in more low-speed power (torque), more mid-speed power, and potentially more peak horsepower.

Why do you want to use the A14 pistons? Simply to increase the compression ratio?

The A15 block is not taller than the A14 block.

Yes, the reason i wanted to use the A14 pistons is for compression rather than just being cheap and shaving the fark out of the head.
Sorry my mistake, yes the A14 and A15 block is the same height.
I have done some more research on this site and the go is 60 thou not 40thou.
I have been looking at something else as well which may be worth doing if i'm going to do this as well is bore it out and put bigger pistons.
This is what i have found:

pin to crown piston dia. pin dia.
RB20E 32.5mm 78mm 21mm
VG20E 30.5mm 78mm 21mm
A14 32.5 mm 76mm 19mm
A15 30mm 76mm 19mm

I know 20mm is the biggest someone has bored out the pin hole in the conrod, is 1mm more just a little too much to ask for, i think it may become too fragile and will make it not reliable and may brake.

I'm using Mazda pistons with 20mm pins.
They are dished but have 30.58mm pin height.
When milled flat they fit the deck just fine.
This doesn't compromise the strength of the piston either as the original crown is still in place in the centre.
I'm using STD mazda bore (77mm) as my block is 1mm over the stock A14 size (76mm)

Ah cool, i thought is was you who had the 20mm pins. So after enlarging the pin hole in the A14 conrods how much meat was left, do you think it will go another 1mm on top of that without loosing strength or too much strength?

If i can then the RB20E pistons look very inviting being 78mm diameter, 32.5mm pin to deck height and 21mm pins.

Has anyone tried puting these in their A series?

By the way, what would it roughly cost me to bore it out to 78mm?