Australian 2V Closed Chamber Heads

[hazmat1620]

Does anyone have these on their truck or Bronco?

What type of benefits do you get with these heads?

[Johnny]

Bill is running a set, and I believe OX is too.... I'm not really sure what the benefit is, I believe it is low rpm torque.... but I could be wrong...

[OX1]

Main benefit is small comb chamber, making the ability to up compression to a normal (say 9-9.3:1ish) or slightly higher than normal level do-able on pump gas with decent timing. Issue with stock M-block 2bbl heads is too much volume between deck surface on block and top of piston face @ TDC. Makes stock engine prone to knock, even @ stockish 8:1ish compresison ratios.

I got a set of alum CHI aussie heads (based more or less on 2bbl aussie clevelands), but they are not on any engine yet.

[Johnny]

duh.... I wasn't even thinking about bumping the compression..... Hell I knew that...

[OX1]

duh.... I wasn't even thinking about bumping the compression..... Hell I knew that...

I kinda mixed two things there. One fix is with Tim's pistons, to minimize "squish" (the piston to deck height area @ TDC), which I'm told is the main culprit with knock tendencies. The other is the smaller chamber heads which ups compression (and also helps knock tendancies a bit just by it's chamber shape).

[hazmat1620]

Thanks Johnny and OX for your advice and help!

[jopes]

I got them to. Had EFI on the engine as well. but currently it is parked in a storage with out a body to put it in. :(

[jigmister]

how do they reduce knock? Higher compression = more knock right?

[1TONAMERA]

how do they reduce knock?

Like they said, they run a different shaped chamber that changes the "squish" or quench area (among other things probably) that changes the whole dynamic inside there during the combustion process.


Higher compression = more knock right?

Not always.
Some newer engines are running way higher comps (over 11 to 1 on some Vettes) without knocking. You can even run low-test gas without too much trouble. But if you want the full benefit, you'd have to run Premium most likely.

It's all about the shape and layout of the combustion chamber.
Yes, just raising the compression on a given engine not originally meant to have high-compression could easily make it more sensitive to spark knock, but in these later model engines, along with the overall shape of things, they've changed a LOT of the basic layout. Including the location and angle of the valves and the location and angle of the spark plugs. Add to that things like valve shrouding/unshrouding, fuel-injection, intake and exhaust port shapes and whatever other characteristics are important, and you can get some whopping high numbers now, that wouldn't even have been conceivablee on pump gas back in the seventies.
Except maybe for a modified Hemi or something.

Paul