Aluminum heads 289

gtonavy said:

Did you think about having your current heads ported?

That is what I did to mine and am very happy with it.

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Helmantel said:

Porting stock heads to a level where it makes a noticable difference is not very difficult (like 22GT more or less said). They can also be ported to be on par with entry level aluminum heads, but then you need to know what you're doing (although it's still no rocket science, just a lot of work).

For your mild power goals, porting the stock heads would probably be sufficient. Of course, they won't look like aluminum heads.

The pistons you have, have very large valve reliefs (like 8 cc), which lowers the compression quite a bit, so aluminum heads would probably need to have their combustion chambers reduced to around 55 cc in order to keep compression ratio reasonable.

A .030" over 289 has a displacement of 4805 cc or 600 cc/cylinder. Required volume at TDC for a certain compression ratio is displacement/(CR-1).

To achieve a 9:0 compression ratio: 600/(9-1)=600/8= 75 cc
The valve reliefs are 8 cc, the gasket around 9 cc, so the combustion chambers in the heads need to be around 75-8-9= 58 cc. Maybe a few cc's less, depending on how far your pistons are down in the bore. With everything per stock nominal dimensions, that would account for ~2cc.

To achieve a 10:0 compression ratio: 600/(10-1)=600/9= 67 cc
The valve reliefs are 8 cc, the gasket around 9 cc, so the combustion chambers in the heads need to be around 67-8-9= 50 cc. Again, maybe a few cc's less, depending on how far your pistons are down in the bore. Such small combustion chambers would of course require milling, possibly pushing the save milling limits of the heads.

Of course, you could go for 9.5 which would require less milling.

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kenash said:

Hey 66FSTBCK,
Calculating CR is not that complicated, once you understand the principals involved. Think of it this way. You have a stock engine, all parts being considered, the factory lists the CR (compression ratio as "X" value. To calculate CR, the formula model needs:
bore dia.
stroke
head gasket bore dia.
compressed gasket (after torquing heads)
Chamber CCs (mfg will offer)
Piston:
valve reliefs CCs (if piston has valve reliefs cut-in) (this number is a negative number for calculation)
Dish CCs (if piston has a concave relief)(this number is a negative number for calculation)
Domed CCs (if piston has a raised surface, or opposite of dish)(this number is a positive number for calculation)
Area between the piston and wall and between the top ring (compression) and surface. (In a number of cases, this is known to be about 2 CCs./ hole.
The known depth (in the hole) when the piston is at true TDC. The number can be listed as either a "-" minus number, a positive "+" (piston protrudes out of the hole slightly), or "Zero", piston is "dead" even with the block surface. As an example, my piston is "out of the hole -.005", for calculation purposes.)

Once these "knowns" are entered into a CR calculator, and the CR is revealed. Any deviation to the entries will change the CR. For example, if you decide after the fact to "clean up" the combustion chamber, by bowl blending etc. (this removes metal). This, in affect, increases the CCs of the combustion chamber. This increase will reduce the CR. because you "opened up" or increased the total volume of the equation. So, simply stated, if you remove metal or increase the bore, increase the "compressed" gasket to, let's say .041, from .039, this will reduce CR.
These basic calculations provide you, what is typically known as "static" CR. This is what we all typically discuss and hype.
However, I won't go into it as it may add a layer of confusion, but the actual CR that occurs with an engine in operation can, actually, be lower by as much as a point! This CR is referred to as "dynamic".
I hope you gain something from this. For others, if I've miss-stepped somewhere, let me know. I'm old, it's getting late, and I want a beer!
Happy Trails!

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kenash said:

Hi,
Those heads with the right hardware and the following pistons "can" make excellent power. with the right cam and supporting systems. That is, if you do not exceed a specified gross lift. Someone here mentioned a total "lift" that, if "not exceeded", would work with your stock style pistons. Re-read for this.
I can tell you, I'm running these heads, my gross lift is .570/.562, and I needed them.
Hope this helps.

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