I have gone through my 351C combo several times before so won't do it again (see under thread 'Need Power'. Basically, assuming my motor is cranking out say 300hp at the flywheel, with stock 2v heads (9:1 comp), if I were to bolt on some stock Aussie heads (~10.6:1 comp), (ie only difference being the size of the combustion chamber), what sort of hp gain could I expect? or would the increase be more noticible in the midrange? (I am happy to have to use 98 RON gas so don't worry about that aspect). I am curious because I am very tempted to bolt on the set of AUssie heads I have out in the garage, but hesitate as to wether it they will make any real difference?

 

you have 98 octane pump gas??? i hate you!!!




just kidding - must be NICE!

 

98 RON, yes. I think the US uses a different rating... ie our 98 octane = your 95 or something like that.

 

that's still 2 higher than we have - looks like our "premium" would be about equal to your "regular" - see my post under "comp & pistons"...

 

>I have gone through my 351C combo several times before so
>won't do it again (see under thread 'Need Power'.
>Basically, assuming my motor is cranking out say 300hp at
>the flywheel, with stock 2v heads (9:1 comp), if I were to
>bolt on some stock Aussie heads (~10.6:1 comp), (ie only
>difference being the size of the combustion chamber), what
>sort of hp gain could I expect? or would the increase be
>more noticible in the midrange? (I am happy to have to use
>98 RON gas so don't worry about that aspect). I am curious
>because I am very tempted to bolt on the set of AUssie heads
>I have out in the garage, but hesitate as to wether it they
>will make any real difference?


yes there will be a difference. with the compression increase and since the aussie heads flow better then the 2v heads i'm gonna say 50-75 horsepower. i'm going out on a limb here and taking a guess so don't hold me to it. it could be more but i really don't think it would be less than 50 horse.

later........:P

 

Actually, the 98 RON is only our 93. You can find the octane calculation formula on the web. One cheap and easy way to boost octane is to use "paint thinner" aka toulene or xylene(sp?--not sure I spelled those right, I'm not on my computer to post all the blending info I have).

--J

 

I really like this info site. It's like an online encyclopedia.
http://www.howstuffworks.com/gasoline.htm

 

"yes there will be a difference. with the compression increase and since the aussie heads flow better then the 2v heads i'm gonna say 50-75 horsepower. i'm going out on a limb here and taking a guess so don't hold me to it. it could be more but i really don't think it would be less than 50 horse."

I won't hold you to it 50-75 HP is way too high of an estimate. Also, the Aussie closed chamber heads do not flow any better than the US 2V head, only the chamber shape is different. The best "rule-of-thumb" that I've ever seen on compression ratios is you can expect ABOUT 4% increase in HP for each 1 full point of increase in compression. Taking that into consideration and you bolton the Aussie heads, you should see an increase in compression to 10.6-11.5 or so, this is a wag. You really need to measure everything to find your true comp. ratio. HOWEVER, since we are working with guesstimates, let's assume he increases his compression to 10.6 as he said. If he optimizes his carb and ignition tuning, he may see an increase between 12-20 hp....and that is being optimistic. Anytime you raise the compression on an engine, you should build the complete engine package to take advantage of that higher ratio.

--J

 

when i cran a "generic" setup in my dd2k, thats about what i saw, a 4% change. it was about 20hp gain. had i known the full setup, i would have gotten a more accurate response.

 

Yes, maybe a 20 hp more, but if you install roller rockers, polish the combustion chambers, mill the block to get 0 deck clearance to get the quench effect to work, Gasket match, and a little porting, then we are more in the 40-50 hp ball park.

thats my opinion anyways.

Werk


GMC = Generally Misconstructed Crap

 

yet another thought:

if aussie heads gives only 12 to 20 hp more,
then why everyone keep saying that they are the hot ticket and the way to go for bolt on horse power? they all say crap or?
why aussie heads are so costly?


Werk

GMC = Generally Misconstructed Crap

 

If someone had "destop dyno" they could plug the change in and see what it said.

 

I've mentioned before that I thought the quench head benefits have been overstated on street engines.

Quench heads with dished pistons are worth up to 20 HP over the open chamber with flat tops. If the pistons are not very close to the top of the block, the quench effect won't work. I haven't found replacement pistons for the 400 that work well with quench heads and keep a streetable compression ratio.

The Aussie heads are not expensive in Australia. They should be about $25-50 a set. It's the locating, cleaning, magging, packaging, shipping and making it worth someone's trouble that adds to the costs.

 

with dd2k i would need to know a lot of silly info. but it was 20hp a cr point. i thought it was low so i checked it twice. we usedto figure @35hp in the old days, but then we would drive the the refinery and get 132 octane super high test.

yes im that old

 

Well i think people usually go with some kb-silvolite pistons with that setup, and make the quench effect work. don't know which piston it is but... looks like there is an answer to this problem. they get 0 deck clearance also. There Must have a piston which works good on the 400 with aussie heads... if not then why would we buy aussie heads? i myself have a pair that i want to rebuild, install 4V valves, gasket matching, polish combustion chambers, install Roller rockers, have some port work done to them, good blending of the bowls with the new valves size ... don't you think that after doing all this i wouldn't get more than 20 HP from them? even considering no change of the pistons since there is none that will work efficiently with aussie heads,as you suggest. Lets say that i dont stroke my 351M to 400 and just bolt on these... ok so the quench effect won't work right, but isn't the quench effect only supposed to allow to run more compression with less chance of pigning? well then what is the upper compression limit to run pump gas? i will have to have the heads milled anyways... they are supposed to be 58.4 cc right now, the guy that sold me these told me so. my stock heads are at 78.4 cc so that's a nice -20 cc at least. Should help some. Can we once and for all have the thruth about those aussie heads? are they worth it at all then?? is it true that they flow better than the US 2V stock since the stock have a bump in the exhaust ports? of so, then this is another thing to consider. Can someone post all the pros and cons about aussie heads so we can make a clever choice in the rebuild process.

thank you for taking the time to read all this.

werk



GMC = Generally Misconstructed Crap