Difference in the head

[Schultz]

I am just wondering if anyone could tell me what the little nipple is with the valves as the head I am taking of has not got them. I am referring to them little things next to the spark plug holes. They look like little welsh plugs turned upside down.

Old head that I am taking off.


New head I am putting on.

[ProZac]

The new head your putting on has Jet-valves. They're meant to introduce combustion chamber swirl for a more efficient burn or something.... But they're really famous for making the heads weaker, which leads to them cracking more easily.

Probably fine if it's not cracked though :-).

[Schultz]

Thank you Prozac

I really appreciate that.
Now I know what them little things are. The reason I am using that head is because it is the head that was set up with the block I am using and it has double valve springs on it.

[ProZac]

If your original head isn't cracked, I'l swap the double springs across into it. There are schools of thought that reckon the jet valves promote detonation too. I've personally never seen any evidence of it, bit I have read it somewhere.

The jet valves are also buggers for getting clogged up, plus it's a whole 'nother set of valves that have to be lapped in, heh. They don't take long to do though!

[Schultz]

G'day Prozac,

Sometimes I wonder about my own sanity ~ I am sure that I am going crazy in the head, maybe a bit of dementia.

I have fitted the older head already and I can't really change it now, well not till I blow the head gasket next time, but I am wondering if I should not have used the newer head because.....

I should have mentioned this earlier but forgot: The new head is ported and polished with no damage to the water journals where my old head has quite a bit of water damage from not using any green stuff in the engine.
The other thing was that there is a very obvious difference of about two millimetres in the head. That one with the Jet-valves has been machined a lot.

Thank you again for your help.