Alright here it is im 19 and in the Military this is my first rebuild of an engine and in need of some advice.

1. I just picked up some 302/351 clevor Aussie closed chamber heads on ebay the guy who sold them advertised a 58.4 cc chamber. But i noticed on all the forums and tech sites that the 302 clevor heads are advetised as 62 cc were there two different aussie heads??


2. I also would like to know about my CR because on a forum talking about a 351m it was a concern and they have shorter stroke. At www.projectbronco.com they have a CR calculator
and depending on the results from the first question just bolting on the heads will give me 9.4 to 9.7 : 1 CR and the pistons already have 13.75 cc dish thats before I mill the deck and heads to square them up if im lucky it will only be the deck at .005.

3. Finally what is the quench effect I notice this comes up a lot with closed chamber heads

 

Yes there are 2 different Aussie Cleveland heads. The 302C heads are closed chamber heads with small valves. They are unique to Australia and were never sold in the US. Aussie 351C heads are open chambered also with small valves. They are basically the same as 2V 351C/M/400 US heads.

The 351M and 351C have the same stroke while the 400 stroke is .5" longer.

Quench effect is the turbulence created when the piston comes very close (.040") to the flat surface of the head. It helps cool the A/F mixture and prevent detonation of the mixture. It basically minimizes the risk of detonation at higher C.R.

 

Bill,

If you convert a 351m to a 400,crank and 400 stock pistons can you use the aussie heads. Thanks Art

 

OK so the 62cc heads are the aussie 351c heads and the 58.4 cc heads are the 302 closed chamber and im looking at closer to 9.7 : 1 CR

Would the quench effect at this CR and if so when does the quench effect become usless on 91 and 93 octane fuel

 

dsc - You can use the Aussie heads on any 351C/M or 400. Depending on what type of pistons you use will determine what your final static C.R. will be.

dsmith- No, the Aussie 2V 351C heads have chamber volumes over 70cc just like the open chamber US 351C heads. Variances of a few cc's here & there are fairly common so if you have Ausse 302C heads then you're in the ballpark of 58cc - 62cc. Any type of "clean up" work in the comb. chamber such as unshrouding the valves, etc. will also increase the final volume. Now if you throw into the mix Aussie 4V 351C heads which are closed chamber with large valves and have chamber sizes of 64cc - 67cc then it can get pretty confusing.

Quench effect depends on how close the top of the piston comes to the flat surface of the head. In general most engine builders will tell you that the maximum distance for quench is .040" - .045". Anything larger than that and there isn't any quench. (In open chamber heads it's virtually impossible to get any quench effect at all.) Now if you keep in mind that most head gaskets are somewhere between .035" and .040" then you can see that inorder to get any decent quench effect you need to run the piston pretty close to "zero deck" IOW the top of the piston is virtually even with the top of the block. Increasing the octane rating of the fuel has no effect on quench altho' it might allow you to run a slightly higher static compression ratio.

Keep in mind that cam selection will also play a critical part in how the engines performs. IVC (int. valve closing) timing will determine what your "dynamic" compression ratio ends up being which is basically what the engine "sees" when it's running. Different cams allow different static ratios because the intake closing is what determines how much real world compression actually builds in the cylinder. Confused yet?

 

Bill I was told by the experts on this site I could not use Aussie heads with a stock 351m piston. I put the eng together and it pinged like crazy. Shazam gave me a lot of support. So i am ready to do it again 351 m converted to 400, crank/400 (stock pistons) no heads yet. Still have the aussies if they will work I will use them if not I need stock heads. What should I do? Thanks Art

 

The CR I got was with stock pistons with a 13.75 cc dish and a 58.4 cc chamber. How could i find out the volume of my heads and once i've done that would machine shop be able to open them up to somewhere between 62 to 64 cc or is there a piston
a slightly bigger dish for the 400?

What is the absolute max CR I could run 93 octane on

 

The problem with the 400 is that the piston sits too far down in the cylinder like +/- .050" depending on what the comp. height of the pistons you use. Add the .040" of the head gasket and you'll play hell trying to get any quench out of it at all. What you really need is pistons which come all the way up to the top of the deck which have a large enough dish shaped to match the comb. chamber shape of the heads and provide you with a static C.R. of 9.5:1 or less. You also need a cam which gives you a decent dynamic C.R.

 

I was planning on running a Comp Cams Xtreme Energy with


in ex

256 268

212 218 @.050

.487 .493 lift

and 110 Lobe seperation

 

Where would i be able to find pistons like that i sure there hard to find?

 

I'm 'bout in the same boat with my 400 project. I have the Aussie 2V heads with stainless Manley valves. Volume checks at 60 cc's with .010 milled off the surface. I think the only thing left that I can do is call JE and order a set of custom pistons. The project has been stalled now for 2 months, but I don't see any other way. Thank God for this site- it has helped me enormously.

 

If you use 58.4cc heads on a 351M with 13.75 dish and 0.016 deck clearance and a cam with an IVC of 59 degrees ABDC the Dynamic Stroke Length is 2.82". The Dynamic Compression Ratio is 7.92:1. That should be good for 91 Octane or better.

If you use the same cam and heads on a 400 with 13cc dish and 0.0565 deck clearance you get a Dynamic Stroke Length of 3.26". The Dynamic Compression Ratio is 8.32:1. That is higher than I would feel safe with on 93 Octane unless I had a quench effect. I suggest a longer duration cam.

Remember that as you increase duration low end torque decreases as well as vacuum. You might need a high stall converter, if you have an automatic.

You can get custom pistons made that will give you zero deck clearance and a suitable dish to keep the compression reasonable, but they are expensive.

 

I have now a 351m converted to a 400, different crank, stock pistons and a crane 272h cam. If I just put the aussie heads on with this configuration I don't think it will work. Would just changing to a different cam work,what type? Or should I just dump these heads for the stock one's . I am leaning towards dumping them. Art

351 modified to 400
crane 272 H
Crane roller rockers
Headers
edelbrock 1406
edelbrock performer 400
Msd dist
MSD 6A
C6
3:55 rear
30 inch tires

 

dsc im runnig almost the same config on my motor but im thinking about running a compcams XE256H or XE262H with comp magnum roller rockers at 1.72

daoes anyone know the degrees of ether cam at ABDC

 

Art,
The Crane H272-2 has an IVC of 67 degrees. This will give you a Dynamic Stroke Length of 3.04" in a 400. With 58cc heads, 0.0565" deck clearance, 0.040" gasket, and 13cc dish, the Dynamic Compression ratio is 7.87:1. That should be OK for 89 or higher Octane.

I have now a 351m converted to a 400, different crank, stock pistons and a crane 272h cam. If I just put the aussie heads on with this configuration I don't think it will work. Would just changing to a different cam work,what type? Or should I just dump these heads for the stock one's . I am leaning towards dumping them. Art