Hi all.

I am planning to do some work to my A12 engine later on. I am doing research now first before I do anything.

I have started to do some research here where I live with regard to cylinder head and also talked to a guy at our local cylinder head shop who loves playing with datsuns. He is about to turbo his A15 motor.
Anyway, he is talking about BMW valves and valvesprings on the GX head. 8500rpm ability if engine is balanced and right cam is used.

Anybody done something like this?
I am thinking of A15 and double valve springs to keep it Datsun/Nissan original.
Is the BMW valve not a better option if it works, meaning they are stronger and of better quality?

Use what ever works no reason not to use BMW parts if they fit the job.

Just watch the valve weight.

I am actually curious why they use the BMW valves. I will phone him and ask him about it.
I asked him about distance between exhaust and intake valve and he said that there is space allowed between them to be save.

It is actually strange because why then not using A15 valves with double valve springs. A15 valves are Nissan and will be less effort to fit. What is so special about using BMW valves and springs. I wonder if it is not to do with the type of metal compound that is used to make BMW valves that makes them stronger and more reliable for high revs.

it comes down to the shaft dia of the valve. nissan will have certain valve head diameters while other cars will have different ones, but still the same shaft dia. these can fall in between the nissan spec'd ones and give you a greater range to choose from. all that will need to be done with some is they may need to be cut to length and re colleted to match the A series lengths.
hope that makes sense ??

I have a little idea what you mean, but what is the benefit of it.

you can go for bigger valve diameters which will help in getting fuel into the engine and exhaust out. best one to start is to go a little bigger in your exhaust valves.

The benefit would be that the BMW valve might have a different seat angle as well, which is better for higher flow. I also know that BMW valves are a good deal lighter then the Datsun ones, so that's less weight to stop with your valve springs, hence higher RPM's.

Also the way BMW valves are manufactured, they use a different material for the actual head of the valve than for the stem. The two are friction fused together. I've never seen any of them break. The reason for the different materials are, that different heat dissipation abilities are needed for the head and stem, and the wear characteristics for both are different. Thus using two different materials more suited to the jobs at hand, gives you a better valve all round.

If he can do the job properly, and it sounds like he can, I would say go for the BMW valves, you wouldn't be disappointed.

kulula.
You gave me the answers I was looking for.
I knew that there must be something special about the BMW valves but did'nt know what. Now I know.

Now to phone and find out what the job will cost. As we all know, budget before the job.

What do you want to do with the engine? For street use you can use the A15 valve sizes & still have very good performance, but puting a full race head on a street 1200 will give you a really good top end, & if you normally drive at 6,000 rpm in urban areas, then you will really love the difference.

If, however, you only occasionally see the stock redline of 6,500 rpm, then perhaps the mods can be kept in the more 'affordable' range. My own GX head is fitted with 37mm inlets from the A15 [lightened & polished] along with some stainless exhaust valves at 32mm dia. Ports are basicly stock & this will provide all the performance I want, particularly in the all important mid range, which is where my engines spend the bulk of their life.

The car is only a weekend driven car and gets flogged as it is currently.
I am looking to improve it a little.

I do not know if anyone here where I live knows how to lighten valves. But according to the cylinder head guy, he has done plenty of BMW valve conversions. Even for one guy that supercharged his A15 fitted with a GX cylinder head.No-one complained yet.
I am as I am typing waiting for his quote to do the job as it entitles the following:
Valves.
valve guides.
valve stem seals.
valve seats.
light skim to get a fresh deck.
cleanup of cylinder head.
I am actually worried about the quote as he said it is not a quick job.
I will then let the intakes be swirl flowed and the exhaust gasflowed.
The combustion chamber equal cc'ed and polished.
Basically it will come out the same as boofhead's engine.

276 cam and later removal of the Hitachi SU's and fitment of sidedrafts.