Hi fellas, well my quad throttle injection is coming along nicely and should be running in a month or so and i'm now looking at building a bit more of a performance motor than the stock a14 i currently have.

My questions are regarding the bottom end, i have all but organised my head with larger valves and port job from bige (ernie at ATE race engines) and am wondering how to put together a good and cheap (as if they go together) bottom end.

I have sourced some 78mm pistons from a really old datsun with 19mm pins but they have a higher crown than an a15 piston by 8mm.

my thoughts were run a shorter rod and an a14 crank but not sure on the losses associated with a shorter rod to stroke ratio.

thoughts?...

does anyone know the difference in length between the a12 rods and a14/a15 rods, i've searched but cannot find.

a12 rod 121.5mm/17.45 pin & a14/15 rod 133mm/19mm pin {11.5mm different in length]u would need to bore out little end to 19mm but then piston to short.

wow that is heaps shorter! so not worth the effort? What length rod would i need to get the piston to sit at deck height with an a14 or a15 crank and what rod/stroke ratio would that give me?

which one a14 or a15 different in stroke

my A14 in the wag was bored 60 thou,this made the bore and stroke the same and was using the standard 1400 rods also balanced bottom end and a 30/70 cam grind,it was good strong and reliable.

OK here's my workings out, not sure if i'm on the right track...

standard
A14 stroke 77mm rod 133mm ratio 1.727
A15 stroke 82mm rod 133mm ratio 1.622

i would need a rod 8mm shorter for the a15 crank and 3mm shorter for the a14 crank...?
A14 stroke 77mm new rod 130mm ratio 1.688
A15 stroke 82mm rew rod 125mm ratio 1.727

or do i have to double the 8mm? i'm starting to confuse myself!

thats none as a square bore set up bore & stroke the same good combo works well. bigger bore with shorter stroke tend to rev harder .rod ratios std a12 1.66 / a14 1.72 /a12rod with a14 stroke 1.57 longer the rod the better.
a14 piston comp height 32.5mm a15 are 30mm so are u using a a14 crank or a15 different strokes different pistons.

I would say the best setup that I have heard in the past is the square option whereby the bore and stroke are the same.

Keep us updated on the throttle setup as I am tempted to go that route as well in the future. Through my PM's I think you knew that.

can use either crank, weighing up how it would all work.

1200gx man, i'll be posting pics of the welded up manifold soon :)

so if i use an a14 crank do i need a rod 127.5mm? and an a15 needs 125mm?...

the a14 and 127.5mm rod combo would give me 1.65 ratio i think?