Aussie heads, now what?
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Aussie heads, now what?
Hello, I just purchased a set of Aussie heads. Now the question. What do I do to them. I am building a 400 and want to get the most power on pump gas. Its going in a F150 4x4 and it is a daily driver. What do I do to the heads? Would the flat top pistons be to much with these heads? I plan to put a full roller cam in it. If you need more info, please ask.
Thanks Chad
Thanks Chad
Senior User
Joined: Jan 2002
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Aussie heads, now what?
On a C/M motor which has 9:1 compression with open chamber 2v heads, the closed chamber heads will bump it up to aroun 10.6/10.7:1 comp ratio. This is quite high for pump gas but I'm tol there are plenty of people who do it. The quench design of the chambers lets you run high comp. with lower octane gas.
Lead Driver
Joined: Nov 2000
Posts: 6,625
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From: Albuquerque
Aussie heads, now what?
Personally I'd stay with the 2v valves and do a "pocket port" and "port match". You don't need more than that for up to 5,500rpm. Piston selection is critical to not detonated/knocking. Stelite seat and stainless valves are nice but also probably not neccessary.
I'd go with a new set of roller rockers.
Bear Tracks
I'd go with a new set of roller rockers.
Bear Tracks
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Aussie heads, now what?
I was talked out of using a roller cam on my 351c. Scott at cam research said they don't work well in clevelands. He also said to just use the larger exhaust valve. I also ran into a problem with roller rockers not working because of the original machining, the studs on a couple of my valves were sticking up at a different angle than the valves. That left very little roller touching the top of the valve and would have worn out quickly. I ended up goin with a stock type rocker with a roller tip. Not as good but better than stock.
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From: Boise, Idaho
Aussie heads, now what?
[updated:LAST EDITED ON 19-May-02 AT 03:20 AM (EST)]Boy, I'm no expert here, but I thought I'd read somewhere on this board that you don't want the 4v intake valves, but something slightly larger than stock and with a 30^ seat instead of a 45^ seat. The second cut was 45^, and the third was 60^. I've forgotten what the valve size was so you'll have to surf around and find that citation, but the author of that post had racing experience and said that the 4v valve was shrouded.
To get maximum benefit from closed chamber heads like the Aussie heads, you must get the quench down to the minimum; .035". I've heard that Ford lowered the deck height of its 400 pistons to lower compression. Detonation City. You might want to search for specially dished pistons called reverse dome pistons. The dish is matched to the shape of the chamber to maximize quench while reducing compression.
[font color="red"]EDIT:[/font] Found the citation. I've copied it here;
Or, another option that has worked for me: Have the existing seats cut at 30-degrees. (from the standard 45-degree seats) You will need a set of 4v valves cut down accordingly to match the new 30-degree seat, but don't have the machinist open the seat any larger in diameter, just cut for 30-degree seat, with a 45-degree under the seat, then 60 degree blended into bowl. Your valve size, after cut down for new seat, should be approx 2.10 or so. Not much bigger than factory valve so shrouding is not dramatically increased, but I gaurantee low lift flow increases..........Just one of my little secrets...... - Don, New York
Good luck,
To get maximum benefit from closed chamber heads like the Aussie heads, you must get the quench down to the minimum; .035". I've heard that Ford lowered the deck height of its 400 pistons to lower compression. Detonation City. You might want to search for specially dished pistons called reverse dome pistons. The dish is matched to the shape of the chamber to maximize quench while reducing compression.
[font color="red"]EDIT:[/font] Found the citation. I've copied it here;
Or, another option that has worked for me: Have the existing seats cut at 30-degrees. (from the standard 45-degree seats) You will need a set of 4v valves cut down accordingly to match the new 30-degree seat, but don't have the machinist open the seat any larger in diameter, just cut for 30-degree seat, with a 45-degree under the seat, then 60 degree blended into bowl. Your valve size, after cut down for new seat, should be approx 2.10 or so. Not much bigger than factory valve so shrouding is not dramatically increased, but I gaurantee low lift flow increases..........Just one of my little secrets...... - Don, New York
Good luck,
Elder User
Joined: May 2002
Posts: 526
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From: Sin City, USA
Aussie heads, now what?
Powerheads charges $775 IF you supply the heads. They do use the 2.19 intake valve but they unshroud the valves and open up the chamber. They have flow bench numbers on the website. If you e-mail them, they are very quick to respond. I'll be using these guys for my next set of heads.
--J
--J
Elder User
Joined: Sep 2001
Posts: 887
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From: Jax FL
Aussie heads, now what?
the big debate was putting in the 4v valves and not porting them. once you unshroud the valves, the head chamber size increases from 58 to 62cc, the same size as the 4v head chambers. this is where the fun begins. I would never just put in the 4v valves with out the unshrouding.
Senior User
Joined: Mar 2001
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Aussie heads, now what?
Hi. Okay lets see if I am getting this right. If I put the 4v valves in and unshroud them it raises the chamber volume to 62cc and that would lower the compression down a little so I could run flat tops and be under the detonation line on pump gas? Also does polishing the combustion chamber help control detonation?
Thanks Chad
Thanks Chad
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