Hello, I have taken a couple months off from my 78 bronco project and the forum but I want to get back into the swing of things...

I have a set of aussie 302c heads I got off ebay for cheap I am wanting to fix up and put on my 351M (later to be upped to 400). The heads are stock untouched and bare. I have never done anyhting with heads b4 so I would like some advice. I was gonna take it into a shop to have it tanked and 3 angle valve job. But before I did that I figured I should do the port work and stuff. Is there any site I can go to that has good details on how to port? And what inparticular to the aussie head? I heard that its mostly the exhaust side that needs opening up more? I can handle cleaning up the chambers I think just not sure about the porting. I have a couple of die grinders (electric and pneumatic). Or does porting not really need to be done?

My plans for the motor are to eventually up it to 400c.i. and add fuel injection along with a good cam and matching pistons to make a reall good torquey 400 that will move bigger tires around as a dialy driver ok and get decent milleage and drivability. I have another 400 motor too I want to build all - out, but one I want to keep more streetable and in the 350HP range or so. Because I have 2 motors though I can swap parts back and forth if I find that one part isnt as streetable for example.

 

The Aussie heads will probably up your compression to far for pump gas unless you get a custom reverse dome piston.

AFAIK the aussie head exhaust port is free of the thermactor air bump and flows well. Do not gasket match the intake or exhaust ports. Unless you know all the little "secrets" of how the ports line up in the completed assembly. All that is required is a little blending around the valve pockets and remove any casting flash and rough spots. You will be using a Weiand or Edelbrock intake and these manifolds are designed to work with the intake ports as manufactured. Watch out for intakes on ebay that have been "ported", they don't work as well as unmodified units.

 

Torque 1st
Not to start anything but my heads have much larger ports than the intake. In case your wondering the casting number is D5TE.

 

That is as it should be. If the head intake ports are not bigger than the intake manifold ports there will be a disruption of the air flow. The moving gas must always go from a smaller port into a larger one or a standing wave pressure disturbance will result, a "shelf" if you can visualize it, that blocks flow. There is some "slop" in the way the parts fit together due to production and assy tolerances. The port sizes and the gasket "hole" are all designed to avoid the "shelf effect" that will absolutely destroy airflow. Hence with all of the production tolerances involved the intake manifold ports are smaller than the gasket and the head intake ports.

People that "gasket match" their heads are forgetting that the slight movement of the gasket and intake during assy will destroy all of their work, making their carefully contrived parts perform worse than the "as manufactured" units. Sometimes it is possible to enlarge the ports slightly by carefully controlling the brand and lot of gaskets used (they vary too, even in the same lot) as well as using pins and other methods to hold the alignment between the heads and the intake. In practice it is just not practical.

 

my understanding is that if you go from a larger intake to a smaller port, you would increase velocity by the venturi effect.

 

Ahhh, yes and no. With a nice smooth transition you will get an increase in velocity inside the venturi but the venturi itself acts as a restriction to flow. Port mismatch will not give you a smooth transition either.

The racers (NASCAR et al) use carefully blueprinted motors, jigs, and fixtures, etc so alignment mismatch is reduced. They can get away with a lot more than we can with off the shelf parts. They also have TV cameras that can be snaked down intakes to check for "errors".

 

Thanks Torque1st... I was hoping I could get away without doing to much porting. Is there anyone else with porting suggestions for aussie heads. I think I know just what you mean about "blending around the valve pockets and remove any casting flash and rough spots". There is roughness below (when the chambers are facing up) the valves from when they cut the valve holes straight and doesnt perfectly match the ports feeding them. That shouldnt be too much a problem to grind smooth.

As for too high a compression... That appears to be an endless argument. And there wont ever be a clear answer because pinging depends on so many variables. Even the brand of gas because octane rating arent the same (R+M)/2 obviously averages R and M (RON and MON) and so on and so forth. And I do eventually plan on putting the correct reverse domed pistons when I up it to 400. But on the 351M it will have less compression (slightly) than most people figure because everyone figures it for a 400. Plus I will try everything to make it more ping proof like polishing the chambers, adding electronic FI, getting higher octane gas (i can go to ultra 94 around here), not going to agressive on timing, etc. etc, possibly going slightly rich if EFI will let me. There are lots of things to do to make it more ping proof.

Truth is I dont know if it will work out for a street motor. But I figure I ill try and see. And if it doesnt, thats why I got 2 motors. One for street and one not for street. I'll just throw the old heads back on my daily driver truck, and save the aussies for my 'built-to-the-hilt' truck. I am just dieing to try em because they been sitting around for a year now. And if everything works out I dont see why everyone says its so expensive to use. I paid less than $300 for the heads shipped on ebay, and valves and springs dont cost anymore than they would on any other head. I am gonna do all the porting and polishing myself but still all the machine work done is gonna cost the same wether you got an aussie or 4V cleveland or stock 400 head? It appears to be cheaper even, because the exhaust restriciton isnt there (less porting). Thats the way I look at it anyhow.

 

Keep your compression below 9.5:1 with polished chambers and you should be OK. If you can get the quench to work properly then 10.0:1 should be OK. If you drive at 2500ft then you may be able to go higher just watch it if you drive to a lower altitude. EFI may allow anothe 0.1 compression but when it comes to de-tuning the engine to reduce ping you will get decreased fuel mileage and power output. It is best to build the engine properly in the first place. I am shooting for 9.2 or 9.3:1 for my engine. A few extra compression points aren't worth the hassle and decreased economy and power that will result if you get it wrong.

All gas is rated with (R+M)/2 and has been for ~25 years, but the octane posted may not be equal to the gas coming out of the pump.

Some of the allowable compression confusion comes from improperly figured compression ratios that are posted and more confusion comes from the altitude and gas grade factor.

 

Yeah Torque1st, its all good. But keep in mind modern stock engines can run over 10:1 stock on 87 not 94. Not saying that an M-Block can, but it can be done and is common practice. Like i said b4, there are lots of variables (emphesis on lots).

Oh and about gas, yes (R+M)/2 has been used for ~25 years but what I am saying is that 87 octane from one place might not be the same as 87 octane from another place, even if they both are Exactly 87 octane as determined from (R+M)/2. Most people dont realize that (most dont really care lol). If you substitue imaginary numbers for R and M:

Gas station #1: R=100, M=50... (100+50)/2 = 75 octane

Gas station #2: R=50, M=100... (50+100)/2 = 75 octane

So both gasolines are rated at 75 octane but one has double the value of R as the other, And the other has double the value of M. Obviously they will react much differently to pinging.

This is just a heads up. The bottom line is that if your border-line pinging try different gas (from a different supplier) and you might find one pings less for the way you drive. But the truth is it is sometimes difficult to figure out who is actually supplying the gas (different company gas stations can all use the same supllier).

 

One of those big variables when you get into those numbers is combustion chamber design etc etc in order to get the right swirl & flame propagation.

I will stick to the numbers above for an M-Block which is what I thought we were discussing in this forum, not some newfangled computer optimized engine.

Those published octane numbers are why I made the statement about whatever is coming "out of the pump". I think most everybody uses the research method nowadays, it is too complicated to run the motor method. Most of the gas isn't even tested, it is just a blend of feedstocks tapped off at different points in the refining process with known properties.

You are correct about the same supplier for different brands. The same supplier can deliver different grades to several stations out of the same truck since there are multiple internal tanks. You never know what you are going to get. A big supplier may have multiple tanks for product storage and may do a little "blending" on their own. I use Phillips/Conoco gas in my vehicles and I avoid gasohol if at all possible.