What's the maximum valve sizes for the A15 cylinder head? Has anyone used valves from alternative makes and altered them to suit? Can BMW valves with 7mm stems etc be used?

When using the thinner stemmed valves, can anyone recommend a supplier for lash caps, bronze valve guides etc?

On the chamber volume, what's the max volume that is achievable after adequate deshrouding of valves? I measured the standard chambers are 29cc.

Which A15 head do you have? The combustion chamber varies with the three main castings.

Early A15s use:
* 37 mm intake valves
* 30 mm exhaust valves

Some late A15s use:
* 35 mm intake valves
* 30 mm exhaust valves

inlet valve sizes 40/41mm, ex 33/32mm depending on bore size,if bore size is 77mm or less, 41/32 valve are best so the exhaust doesnt hit side of bore. u may need to relief the bore if u go bigger exhaust.cheers

I had a play around and think you could fit up to a 44mm intake if you can be bothered playing around with offset valve guides and run valves with 7mm stems. Thats with a 79mm bore.

I used 38 inlet and 33 exhaust out of an L series (8mm shafts)
I still had to notch the 77mm bore for exhaust valve clearance
I didn't see the point of going any bigger
Heavy valves float more at higher rpm

I have an H89 head with 42mm inlets. I've bolted it to bare block (with a 77mm bore) and looked down to the chamber with a torch. People harp on endlessly about "shrouding the valves" whenever someone mentions sticking big valves in. But I can say that mine has a decent amount of clearance to the bore wall. Plus since then i've had it bored out another 40 thou. I don't know if mine were offset or not. But the zhorst valve is fair close to the bore on the other side of the cylinder.

I'm far from an expert on datsun heads, but I can tell you from experience with other engines that if the valve gets shrouded enough, even if you get everything to mechanically 'clear' each other, it can still negatively affect flow, and you can get more flow with slightly smaller valves (assuming you do the throat/bowl/short turn re-working to suit each properly) If you can't get the throat and short turn right for a bigger valve, you'll actually start to lose flow.

All I can say is this - if you are going to aim for the biggest valves that can physically fit, you'd better go to someone with massive experience with that head who knows just how to make it work harmoniously, It's very easy to lose flow and velocity at the same time.

Very true. a skilled head machinist will work to chase flow without losing velocity. The bloke from hemi performance swaers and declares that bigger valves on a 265 don't really improve performance, except in the very high rev range. (Higher than is considered safe for those engines) Unless however the engine has forced induction. When the charge is getting forced in, it is desirable to have as little restriction as possible. Which Is why I can't wait to see how my new engine goes with the 42mm inlets!

I don't want to go off on too much of a tangent, but you might want to ask (when it comes to hemi heads) a few people on moparmarket.com about the various vendors, and especially where headwork is concerned. There is one place that sells a 'full race head' which is nothing more than a 245 head with 265 valves and poor throat/bowl work, which basically are rubbish. They magically don't have any flow charts for the heads, but they 'know' they are better than the competition. If you are going to spend money on a hemi head, the chi alloy one is very hard to beat, it's got a much better chamber, with swirl and quench and is of course alloy, so even if it only flowed the same (and it flows more than most) it would be able to run more compression and make more power and get better economy.

IF you are going with a factory hemi head, to get a really good result (and this is technically illegal for historic racers in Aus) you need to weld up part of the chamber, and often the bowl, to be able to grind the right shapes in there.

Still off topic (sorry) I do vist mopar market daily, and I'm well aware of people's extremely low optinion of hemi performace on the whole. (many guys also say the CHI heads dont offer value for money.) When the old hemi performance website had a forum as part of it, the bloke who owned it was adament that going larger than stock in the valves didn't improve performance unless revving over (can't remeber the figure, but it was high) RPM's.
He also claimed that he'd seen this first hand through years of dyno testing. Whether or not thats true I don't know. (Or care)
I was merely using that as an analogy to compliment my comment regarding the goal being intake velocity increases with porting.