14nz bottom end 12st head?

[turbojolt]

Anyone ever done this? I know it will all bolt together Im only worried about comp ratios and potential valve contact...

Im sick of spending money on a crappy spi when I have all the bits to potentially convert it to a carb engine in the garage.. which will also help eliminate all of the shocking wiring done to make the spi engine fit and run


any help would be great. if not I will just risk it and spend 30 quid on a new top end gasket set and bolts ;)

[Peredur]

Should be fine, decent comp ratio and improved flow. Shouldn't have valve contact issues with a standard or fairly mild cam.

[turbojolt]

would just be the std 1200 cam for the time being...can you see any other issues im over looking?

[Stuart]

It'll be fine, and worse case you lose £30 finding out :)

[boffer8]

Will be fine, been done before and with good results, if going to be using a lairy cam in the future then pistons would need pocketing.

[turbojolt]

boffer8 you have any links to other builds or contacts you know of people that have done this?

[jimbob-mcgrew]

i had an idea to do this to mine in future.

that combo's roughly a 10.68:1 compression ratio.

i was thinking of skimming the 1.4 pistons down a touch, to provide a little more breathing space for the valves, and to bring the CR down a tad, to roughly 10.2, so it would run on regular unleaded without any issues.

i guestimated roughly 85 ish horse with a 1.3s camshaft (6.0 & 6.0 mm lift, compared to the 12st's 5.1 & 5.5 mm)
the main jet on the 1b carb might need opening up a tad also, to keep up with the extra fuel demand.

elmose on here has done it.
he has a high lift cam in his too, and hasnt had any issues.

[jimbob-mcgrew]

it seems a pretty nice match to mate together too, as the bore/chamber sizes between the two are only 0.2mm apart, practically nothing.

[mowgli]

It should work fine, even if you use the 12st carb and manifold. You might need super unleaded petrol though.

[turbojolt]

Ive got a carb and inlet from a 1300sr

[Stuart]

Valve clearence is fine on std pockets upto about 12mm of lift (check though)

[scott.parker]

Do it! Just do the bloody thing and stop moaning! lol

[turbojolt]

its already half done ;)

[jimbob-mcgrew]

Ive got a carb and inlet from a 1300sr

even better, that'll prob run half decent, straight out the box, just a twiddle on the mixture screw.

quicker flowing manifold too

[turbojolt]

that's why I got it mate was ment to be going on my 1200 but this seems a lot better home for it now. going to be interesting to see how this goes might have to chuck it on a rolling road (not that anyone ever believes the figures anyway lol)

[therealnovaboy]

Anything is better than an 14nz.

[mowgli]

i dunno.... but tj might just make a nice little motor this time..

the 1200st cam is really low lift, so valves hitting are really unlikely

[Southie]

What's the advantage on doing this compared to a 1.4sr with a decent cam then?

[Peredur]

More compression and flow due to the different port size

[turbojolt]

And its cheaper