Aluminum heads or cast heads?

[joetiii]

I spoke with a supposed Porsche mechanic on an early car for sale. He lead me to believe that in 1970 & '71 that the 2.2 911T had cast heads while the E & S had aluminum heads. From what I read, Porsche put aluminum on all the 2.2's.

any thoughts?

I'm checking out a T that has aluminum heads and he claims that it must be E or S cam & pistons. The engine number says its a T and Zeniths sit on top.

[jluetjen]

Somebody's a touched confused.

1) All 911's have heads which are both Cast and Aluminum. Specifically they are cast aluminum. Porsche has never used anything else on the 911.

2) One of the differences between the early 911's is that the T's had Cast Iron cylinders, while the E's and S's had Byrol which is an iron sleeve cast into aluminum cylinders. So from the outside the cylinders will look like aluminum, but the pistons see an iron surface.

3) Starting with the 2.7's, Porsche started to used cylinders which were entirely aluminum, but which either had a silicon layer deposited on the inside surface instead of an iron sleeve (Nickosil), or used silicon in the aluminum alloy for a similar affect (Alusil).

If confusion with the heads is what the supposed "Porsche Mechanic" told you, I'd look for another mechanic.

As far as which form is better? The answer is that it depends. Each has it's strengths.
* The cast iron cylinders keep their dimensions better which allows the rings to seal better. They are also relatively cheap and can be rebored without too much hassle.
* Byrol cylinders are lighter then the cast iron, conduct heat away from the heads better, and can be rebored to a degree.
* Both of the types of aluminum cylinders are lighter still, and do a better job of conducting heat out of the engine. They do expand more when heated which makes ring sealing and piston clearances somewhat more challenging, but Porsche obviously got those issued figured out. In some cases they can be rebored, but then the surface finish must be reapplied to provide the correct surface for the rings and pistons. As far as I know it's not done that much. Others can fill you in on the trade-offs between Alusil and Nickosil cylinders.

[joetiii]

So in this particular case, when engine work was done, the rebuilder may have used the Byrol heads. This does not mean there is any performance difference tween the two heads, except that the byrol will diddipate heat better. Correct?

The question still begging to be answered is what else has been done to the engine while the cylinders were upgraded? and why?

[Wil Ferch]

listen closely.... Birol ( sp?)...aka "iron-sleeve".. is not a type of "head"...it's a type of cylinder.

Re-read the answer from John, above,again... this time, with all due respect..... a little more slowly....

- Wil

[randywebb]

Biral

[jluetjen]

I stand corrected!

[randywebb]

"Nickosil"

Nickasil !

[joetiii]

I read fast and think slow and type poor.

sorry

[Wil Ferch]

no... "Nikasil"

No "C"....gotcha !

Wil ( all a bit goofy today...eh?)

[jluetjen]

Today??? I can't spell well on any day of the week! Why should today be different?

[randywebb]

I sit corrected!

Now I see there is no C.

[Grady Clay]

Guys,

What is the phase of the moon?
I spent all morning correcting my spelling and typos.

Joe, in the absence of an invoice there probably isn’t any way to tell without looking. Who built the engine?

You could hope the Biral cylinders have 911E or 911S pistons in them. HeHe. That would raise the compression ratio; how much would depend on their being 2.2 or 2.4, E or S. You need a knowledgeable eye to look for you. It is possible to modify the engine to accept 90 to 92 mm pistons & cylinders of the Nikasil or Alusil type. A practiced eye can tell the differences.

It is possible to measure the cam timing and tell if they are set to T specs or some other.

You should look at the bottom inboard side of the heads (lower part facing the crankcase) and look at the casting dates. They should be close to the same dates and period correct for the year of the engine.

What are the engine serial number and Type number? The S/N should be of the form *610xxxx* and the Type 911/03 or similar. That will give you clues as to the original configuration.

Best,
Grady