Hi guys im looking at the headgasket in the link below its a GX gasket 0.6mm, reason for needing it is to decrease piston to head clearence (increase quench) and increase compression abit along with the fly cut flat tops.

My question is that on the wiki it says its to suit a 79mm bore engine but on the Website it says will suit all a12 a14 and a15 engines.

So will it be find for a a12 with standard bore size of 73mm?

https://www.ebay.com/itm/GENUINE-DATSU ... c1123e:g:KJ8AAOSwwmlZgxsD

Thanks!

Hi D

Is that a round port with a raised roof and built up floor?

Looks like a nice port.

Are the valve guides cut down?

I have compared the a14 and a12 valve sizes a12 is 35mm a14 is 37mm dosnt sound like much but side by side theres quite a difference.

If the h92 being similar to a h89 made more power then the gx head then the valve size is definitely a limiting factor.

Not sure why datsun did this?

Gx head with a14 valves or even larger would make use of the larger ports

Very interesting i wonder what the reasoning is, the h89 inlet ports look quite well designed in comparison to round ports.

I honestly cannot figure out the theory behind large port whilst retaining smaller valves.

In my mind the h89 will have better flow charecteristics with the larger valves at all valve lifts until port size becomes a restriction at high rpm.

Even then i cant see the gx head outflowing it at higher rpm with the smaller valves if they both where utalize same lift cam.

I have always wondered how a gx head can flow more stock vs stock.

I realise the gx has bigger ports then the h89 but the have smaller valves in comparison to the h89.

Wouldnt it the gx head with bugger port but smaller valves tend to flow less or possibly be very similar to the h89?

Hope someone can give some insight on this or even share some flow figures.

Still looking.

I did come across those figures in the tech section.

From my research alot of the v8 guys run much more then 0.5mm closer to 0.85mm.

Has anyone successfully run 0.5mm in a small bore engine like ours?

Il definitely try find this tune up manual.

I did measure the piston height in relation to the deck and it sits about 0.24mm below the deck (maybe it was 0.34mm)

Which means even with a 0.6mm gasket we get 0.94mm of clerence which is why am getting the block decked.

But i will obviously have to remeasure with the new flat top pistons.

Just wondering what the smallest clearence people have run between the head and piston.

Im trying to get the quench as tight as i can engine will rev to 7500-8000rpm. I have not checked how much the piston rocks yet but will get to that.

Any idea how much a rod will stretch at those rpms?

Pm sent