^ what he said. All double valve springs will do is put extra pressure on the pushrods and cam.

If you really want to rev past 6K then valve float will be one of the least of your worries :D

regular valve springs are good for 6400 RPM. GX double-valve springs are good for 7000 RPM.

If you like the rev-happy engine, all you need to do is stick a GX camshaft in your A15. You don't even need double valve springs. Rev it to 6000 RPM all day.

well.... many thanks for your answers guys.

i think i will use an oval port head a14/a15 cause gx ones are rare and expensive (wish i had one).

i want to know if using the falt-tops would have any problems with the valve train.. i guess not.

10:1 CR is good, it really doesnt matter for me to not have hp's i just want to build a good a12 to have it laying there with a 4 speed gearbox i have till a get a nice sedan someday :P for now im just collecting parts.

and the reason that i choose the a12 is because i had one the changed to a15 and really didnt like so much, i just prefer the tiny original rev-happy a12.

i understand now the oil pump thing and have another question

what do you thing about doble valve springs on the stock a12???

Nissan Competition oil pump for A-series engine

* 15010-25720 COMPETITION OIL PUMP Generates an oil pressure of over 100psi and does not self prime

Changing to flat top pistons won't gain you that much. Te biggest bang you'll get for your money should be in head mods, ie; a good port job, an increase in intake valve size, along with larger inside diamiter seats. Then, maybe consider changing to a hotter cam, increased carburation, and headers (extracters). Unless there is a reason to keep an A12, why not just install an A14 with the same mods? You get a whole lot more in the same size package.
Basicly put, make it possable for the engine to breathe, 40 DCOE's work much better when the engine can get air/fuel in and out and a stock head isn't capable of handling that much more than the factory provided. Open up the ports and the valve area and things start to work the way you want them to. Why else do you think that GX heads have big oval intake ports instead of the small round ones?
As far as compitition oil pumps go, pressure doesn't help without volume. All of the factory compition oil pumps that I've seen are high pressure with the same rotor set as the standard pumps. If you really want to increase pressure, increase the volume and the pressure will also increase at the same time due to putting more oil through the same area. It is possable to adapt L series rotors to an A series pump with some machine work and a spacer, there have been posts about this in the past.

Compression ratio stock is 9.0:1

With flat-top pistons and special thin Datsun head gasket, it is 10.0:1

(dished pistons are stock)

Doing the full 10:1 compression will give you an extra 3% hp -- from 69 hp to 71 hp.

The competition oil pump is high-volume. But the stock oil pump supplies all the oil needed for 7000 RPM usage. No advantage to the competition pump until you are turning very high RPMs.

That all depends on what you mean by "flat top" pistons. A12 pistons are pretty flat from stock (I dont think domed pistons work very well in a closed chamber head..)

The best way to raise compression would be to get the head faced, and use a standard head gasket (a thinner head gasket with bumped CR will not end well)

I doubt you would squeeze 100hp from an A12 with just CR, carb and exhaust. You would need a decent grind cam at the very least, and all you will end up with, is a grumpy #OOPS# of an engine that doesnt go as hard as an A15 anyway.

As for the lightened flywheel - that wont do a damn thing without getting the bottom end properly balanced with it fitted, and IMO the "competition" oil pump wont be worth it either, unless you are running "competition" spec clearances in the bottom end of the engine, and a similarly prepped rocker train.

IMO just take baby steps. Get the exhaust sorted first, then maybe a carb swap. Once you have got your head around tuning and making the most of that, THEN start thinking about an engine rebuild for compression etc.

been thinking on a stock rebuilded a12 just with a set of flat top pistons

Q's

1-what is the a12 stock compression ratio?
2-what will be the compression ratio with the flat tops
3-will it have issues????
4-can this be done? stock a12 just with a set of flat top pistons?
5-what is the size of the stock head gasket?
6-can i put a tinner one with this setup for a little more compression?


would love doing this, to latter add a competition oil pump i have, custom made extractors, 40dcoe webers, lighther flywheel and less accesories the better

what do you guys think? will it make at least 100whp?

all of this running stock head and bottom end (just flat tops and maybe tinner head gasket)