I'm trying to decide how i want to rebuild my 400 and i keep hearing everyone talk about aussie heads. I have found a pair that i can get that have been hot tanked and magnafluxed. I have a couple of questions; what is magnafluxed, what kind of changes will i have to make in order for them to work with everything else?

 

Magnafluxed means checked for cracks.

Use the search function for info on these heads. They have been discussed many times.

IMO they will raise your compression to high if used with flat tops and it is difficult to get the proper quench with available FT pistons for a 400. You can do it with Cleveland pistons and re bush for the smaller pins, but your compression will still be to high for pump gas. To get a proper compression ratio custom reverse dome pistons are required although if you check you may find a part number that will work somewhere here.

 

I have a set of Aussie's for my clvd mustang. I got them from powerheads.com. The guys there are helpful and can build a set of heads. If you give them a ring they could probably answer more questions than I can.
The reason it will raise your comp ratio is that Aussie's have the quenched chamber of the old clvd 4 barrel heads. A smaller or "quenched" chamber means less area above the piston which translates into more compression. All 351M-400's had open chamber heads for emission reasons and some detination problems with the newer unleaded fuels of today. I don't know how hard it would be to find pistons for this application. I'm sure other people have done this combo before you. Look for the pistons used for either 4bbl or the boss heads. These should be the same as the ones for the Aussie's.

You'll get alot more flow from a set of Aussie's than stock 351M-400 heads. I personally have them stuffed with 2.19 & 1.71 ss valves and hand ported.
Good luck!

 

351C 2V and pre '75 400 heads have virtually identical ports as the Aussie heads. You won't get any more flow from a set of Aussie's than stock 351M-400 heads. Before buying anything from Powerheads, look at an independant flow test of their heads vs the stock 2V.
http://home.isoa.net/%7Emharrisj/fordhead.html

 

I thought the aussie heads were a bolt on to a 400. Now everybody is saying that it will be too much compression. Let's try to clarify this a little. What are the cc's on the stock 400 heads (1979) and the cc's on the aussie heads? What exactly is the compression going to be on a stock 1979 400 with aussie heads? I was just about to buy a new set of aussies, but I'm not in a position to tear the engine down to replace pistons. Thanks for the help.

 

http://www.projectbronco.com/

then click on technical, then how to build 351M/400. you will find a chart that has a estimate of the cr change. its about 10.75:1

 

Joe,

Just because they bolt on doesn't mean you should do it.

Chambers on stock '75-up 400 heads are 75.6 - 78.4cc. Chambers on Aussie 302C heads are 58 - 62cc.

With stock bore and '77-up truck pistons (13cc dish), Aussie heads will give 9.5-9.9:1 CR.

With the 400's stock 0.067" deck clearance, that is way too high for premium pump gas.

 

Hey, thanks guys, I thought for some reason that I would end up with about 9-9.25 to 1. I figured with a little more cam it would work with 93 octane, but that's way too high. I think I have a crack in one of my heads so I was going to go for a little more power and mileage. So I guess I'l pull it apart and have the stockers checked, maybe take a little out of the exhaust port, true up the deck, and add the cam. We'll see how it goes.

 

Brain... I was looking on your link to Ford head Flow Data and I didnt see any aussie or stock 351M 400 heads on the comparison?

 

351C 2bbl is the same as pre '75 400
351C PwrHead is Aussie 302C heads with 4V valves 2.19, 1.71

 

Ok that makes a little more sense... and can I assume that the post-'75 351M/400 heads have more restrictions than the ones listed?

 

Just slightly.

I can't remember the exact numbers right now, but I had some late-model (D5AE) stock M-block heads flow benched a few years ago, and those numbers were very close to the numbers published for stock Aussie 302C heads, which are slightly less than the early US-made 351C 2V heads.

When you consider that the Aussie heads don't have a Thermactor bump in the exhaust port, and they don't have a water jacket around the valve guide boss in the bowl like the late-model M-block heads, you could say they flow worse than US-made heads.

 

Velly Intelesting...

 

Australia made another head for the 351 engine. They feature semi quench chambers measuring 72-75cc. It may be a better compromise to get the desired compression ratio.

 

Looking at that table comparing flow rates, I was floored by the huge advantage that the 351C/2v heads had over all other cylinder heads up to the .400 mark. Even the Powerheads 351C/2v heads don't flow as well.

Having just gotten my hands on a pair of Oz heads I can see why they do so well; the ports have smooth, gradual bends - no strange kinks anywhere.

To me the 351C/2v heads are no-brainer, especially for a truck 400.