Howdy.....
I am curious about how much an improvement the Aussie 2v cleveland head is over the US version. I do know from personal experience that you can barely get away with 9:1 compression with the open chamber (the 4 barrel open and closed chamber heads are out of the discussion here because of their impracticality on almost everything that would be run by the gentlemen on this website, not trying to be rude....) US cleve heads, and I have seen 10:1 on 4v closed chamber heads.
Have any of you switched from US 2v's to Aussie 2v's, and was there any noticeable increase in power along with the compression increase? To dig up a set and have them built is cost prohibitive if there are minimal gains.... sorry if this question if muddled, I am up late with an ill child, and I just rememebered to type this out....

 

>Howdy.....
>I am curious about how much an improvement the Aussie 2v
>cleveland head is over the US version. I do know from
>personal experience that you can barely get away with 9:1
>compression with the open chamber (the 4 barrel open and
>closed chamber heads are out of the discussion here because
>of their impracticality on almost everything that would be
>run by the gentlemen on this website, not trying to be
>rude....) US cleve heads, and I have seen 10:1 on 4v closed
>chamber heads.
>Have any of you switched from US 2v's to Aussie 2v's, and
>was there any noticeable increase in power along with the
>compression increase? To dig up a set and have them built is
>cost prohibitive if there are minimal gains.... sorry if
>this question if muddled, I am up late with an ill child,
>and I just rememebered to type this out....

I bought a set of Aussies to go on my 1972 351 CJ (to replace open chamber 4V heads), but sold them when I realized I would have to use fuel additives, or back way off on compression to use them with fuel available here (South Dakota). Yes - there is gain whenever you increase compression, but the amount depends on what else you have done to the engine.

I checked my Dyno software, and going from 9:1 to 11:1 on my otherwise nearly stock engine (I have added a Performer intake and 750 CFM carb) I would only gain 30HP. If I were doing an all-out build, I would want to get every HP - but I can spend a bit more attention to the head work and the cam, and more than make that 30 HP up. Certainly the head work/cam plus the higher compression would be ideal - if I could find fuel to run it. Even with quench, I suspect you would need 93+ octane to run above 9.5:1. If you are in an area (like I am) where high octane fuels have 10% alcohol, don't count on it helping you run higher compression.

Personally, I will be replacing the 4V CJ heads with 2V heads, having some massaging done to the heads and installing larger valves...

 

thanks..... I knew the quench head was an improvement over the open chamber setup, I just have not had the chance to experiment as to how much a improvement, or if it was worth the extra cost. Of course, it is still early, and maybe others have had better luck.

Note: I live in beaverton, OR, and of course we have the dreaded alcohol blends, which come to find out, according to my info, actually makes your car pollute more on cold mornings, and since it does not have the same energy output as straight gas, you use more of it. Also, The booze-blend is cheaper to make, Getty fuel was busted for selling it out of season a few years back, turns out they were making a ton of money on it.....of course, this is just my info.

And thanks again for posting intelligent replies, I have read several of yours and others, and except for a few bad apples(or just maybe spell and grammar check should be installed on this site...and occasionally I am just as guilty....lol) this site in general has quite a few articulate individuals giving accurate information out..(alright moose, what do you want?!?...)
thanks

 

I'm not sure this will help you. I did a complete rebuild on my engine with the Aussie heads in mind. So everything was set up to work with those heads. The amount of HP I have now compared to the stock 2V motor is a lot. I haven't dynoed it. But estimates are around 350 HP compared to 250 before. I have about 10:1 compression and am getting a little detonation on hot days. So I will be working on a fix for that soon. I live at high altitude and can only get 91 octane.

 

Well, I'm going to chime in here, even though I may be one of the bad apples. ;-)

I have ran over 10-1 compression with open chambered US heads, both 2v and 4v heads, without detonation. The Aussie heads will give you more compression, but you sacrifice flow for that compression. The Aussie heads flow terrible in stock form, worse than the US head does. The reason being the intake valve is shrouded badly by the small chamber. With a stock form aussie head, what you gain in power from the compression, you lose by the loss of flow.

When I ran open chambered heads on my street car, I polished the chambers, and spent several hours doing it. With the proper camshaft (one with some good overlap to bleed off some low rpm compression), and careful attention to timing, I ran 10.4-1 compression with US 2v heads, on 93 octane without detonation.

Although this isnt entirely relavent to this topic, my open chambered 4v heads have gone faster than my closed chambered 4v heads did on my raccear. They both are ported and flow within 5 cfm of one another, both used the same camshaft/intake/carb/trans etc, and the open heads have 11.5-1 compression, the closed were 13.85-1 compression. The best I ever got with my closed heads was 6.27 in the 1/8. The best with my open heads has been 6.18. I feel it is all related to the intake valve not being as shrouded on the open heads (and my closed heads had some chamber work done to them so they werent as bad as if they were in stock form).

 

Thank you for joining our charming discussion, sir. Actually, I am leaning back toward the US heads the further I listen. I may have goofed up in my question concerning efficiency. I am curious if the closed combustion chamber shape is better for making more power than the open. What I now see is that the closed chamber head is not really much better than the open, and that the closed chamber design was an early attempt at trying to design a more efficient head, but needed more development, and then development was cut off by old Lee I. I never thought about valve shrouding on the closed chamber head, and went back to some old detailed pictures, and darn, you are right, they are really horrible with a 2.19 intake valve, much less a 2.06. But the debate rages on, and I just know that someone else will come out to defend the aussie head, and the $1000 or so it takes to get a set on a car...

 

 

[updated:LAST EDITED ON 03-Dec-02 AT 03:53 PM (EST)]Yes, the australian ports are smaller, this is restrictive to the top end power of which it seems those writing in are questing after. I myself do alot of off road and towing activites. I am interested in the aussie heads for low end torque because the port is tuned to favor velocity at low rpm. A company named Pavtek makes "3v" heads which combo the closed chamber with better porting. They claim to have better flow that 4v's with the compression advantages of the 2v's.

 

> When I ran open chambered heads on my street car, I
>polished the chambers, and spent several hours doing it.
>With the proper camshaft (one with some good overlap to
>bleed off some low rpm compression), and careful attention
>to timing, I ran 10.4-1 compression with US 2v heads, on 93
>octane without detonation.

I'd be interested to hear how much overlap is "good". Can you give us some idea of the cam specs?

 

G'day, my name is Dimmy, i live in australia, my cousin in the US asked me to send him a set of Aussie Heads that had been worked, if anybody wants any aussie heads, worked or not, contact me on dimitriost@mentonegs.vic.edu.au i'd be more than willing to help out.

 

bought a set of 302c aussies and looking to swap onto a 400 to seal the bird up and give a little til i get all my parts for a full build

i see one small repair so work has been done (before i got them and have the"origanal" valves i was told
couple split heads on them and gooves on 1+ keeper are gone what kind of damage should i look for. they seem fine
and need help setting them up on me engine

valve was thinking 2.19 1.71 so i have room later if needed
might as well leave stock, 400m rockers on for now
push rod is leeving the old ones going to make for a bad angle

now for more info
have a offy 360? intake >5000-5500 don't have an egr plate DARN
eldlebrock 650 manual

how much of a compression boost can i expect taking 20cc off the head with stck piston 78 truck

any help would be appreciated