Cast Iron vs Biral

[67R69S]

Hello Folks, chasing down some leaks on a '71 911T engine and I noticed that the cylinders are close to the wear limit. I have a set of biral cylinders kicking around and was wondering if there is any advantage to using them. Car is never raced and is rarely driven to its limits. Engine is completely stock and I'm not looking for any more power than it has. The car is very original, this will be the first major engine work on it. I wonder if changing the cylinders will devalue it at all. I've searched the archives and online but could not find much information. Thanks for any insight you might want to share.

Regards, Gunther

ps: Dave in Ottawa, if you are reading this I have lost your contact info. How is the new 911 working out?

[Eagledriver]

They are lighter and not worn out

I doubt that anyone would consider this a devaluing upgrade.

-Andy

[wkbergman]

If I recall - I'm a novice at rebuilding - the 911T has iron cylinders. I'm sure my '70 911E has biral. The biral cylinders can be honed with that criss-cross pattern that helps a good break in. Like Andy says, this would be considered an upgrade. You're still with OEM parts. See Wayne's "911 Engines..." p. 54.
Cheers
WB

[304065]

Gunther,

If your car is a Concours-winning 911T then changing from cast-iron cylinders to biral (aluminum fins cast around iron sleeve) WILL devalue it insofar as it's not original, and the amount of the devaluation is the cost of a teardown and replacement of the non-original parts with original.

That said, there are probably only a handful of concours Ts around so the likelihood of yours being one isn't that great-- you are probably more interested in performance.

To which my answer is, the Biral cylinders are fine, but they have their own limitations, the first of which is heat rejection-- better than the cast-iron but not as good as Mahle Nikasil. They are also subject to wear just like the cast-iron cylinders. If you search in my engine teardown thread you can see some nice pictures of wear and gouging on the inside of my 80mm Birals.

To correct that, I had them honed to 81mm and a set of custom JE pistons made up.

My answer would be, if your iron cylinders are worn, your pistons are probably worn too. The skirts probably have wear and I would be surprised if the ring grooves are in spec. In that case, consider getting in-spec pistons along with the cylinders.

Another alternative is to have the cylidiners bored out 1mm to clean up the dimensions and go with custom pistons, this is around $1000.

Still another alternative is to go with the Mahle Nikasils. An all-aluminum cylinder is the best technology Porsche used, best heat rejection, wear charcteristics. It's not uncommon to find later Nikasil cylinders with very little wear after hundreds of thousands of miles. Also, there are aftermarket cylinders by QSC and then special things like LN Engineering's Nickies, search here for more info on these.

If I were you I would bore the iron cylinders and have new pistons made up.

Good luck!

[Eagledriver]

I would stay with the cast iron or biral. If you go to all aluminum you open yourself up to all the pitfalls of pulled studs, timecerts, and/or Dilivar stud breakage.

-Andy

[67R69S]

Gentlemen, thanks so much for your replies. This forum is great! I have decided that, since the cast iron cylinders served me so well, I will have them bored to first over and re-use them. Planning for the inevitable, we picked up a set of genuine Porsche first over pistons from Stoddard about 25 years ago for the princely sum of $99, including rings and pins. I realize the birals are probably a better cylinder but I don't know the history of them so I will go with what I know. We've owned this car for 34 years and it is super original down to all the factory paperwork, but its probably not concours condition as it is driven occassionaly. John, nice engine teardown write-up!

Thanks again guys! Gunther