Bltzkrg

What procedures and or precautions need to be taken when getting block work done on the turbo motors? I have heard that there is a special way of boring that needs to be used for these motor... ? What can you all tell me about that? Thanks for the help

m42racer

Nothing special if done correctly, but if not can be disastrous. All these blocks are machined the same way. The Piston bores are honed then lapped and brushed with pads and a special polish.

Best to get someone who knows this work to do it.

Bltzkrg

Sounds good, we have done many blocks before I was just curious if this one gets any special treatement. Ill give him a call. Thanks, Matt

RKD in OKC

The Alusil bores do require special treatment. I don't know the specifics, but do know it requires both a special polish and hones.

333pg333

It will totally affect what pistons/coatings you can use depending on how it's done.

Bltzkrg

Well here's what I'm doing and if you could shead some insight on it, stock block as of now, I'm wanting to just go .020 to get rid of the light scoring on the cylander walls. I will be using CP pistons. From what you all say, I will need to get in contact with some one about the correct rings and correct polish on the block right?

Jeremy Himsel

You need to send it to someone who has the proper equipment to bore, hone & lap alusil bores (stones, felt pads, compound). Typically Sunnen equipment and materials are used.

SeaCay

The factory service manuals spell out the procedure in detail, including stone, pad and paste part numbers.

2bridges

Hey SeaCay - what section?

SeaCay

Volume 1, section 13, pages 53-57.

2bridges

exactly where you stated - Thanks!

APKhaos

There's some very specific technique and very specific tools and materials required for re-boring and honing the Alusil cylinders used in many Porsche and BMW models.

All the information you need is HERE .

The honing processed and materials are discussed in detail from page 57 on. You need a machine shop with a Sunnen honing mill, the correct Alusil stones, pads, & pastes, and some real experience with using them. Its fairly easy to destroy a block using Chevy honing procedures.

SeaCay

Anything to help!

Richgreenster

After reading everything on this link I am still wondering what Alusil really is. Is it a coating that must be applied to a block after it is bored out? Or is the silicon already in the block and is exposed with lapping paste. What is the truth???

I have heard that after a 951 is bored out, the cylinder walls are too soft and wear out fast.

By people who really know for a fact and have or rebuilt a 951 personally!

What is the longevity of a 951 engine after a rebuild? OR is it better to just sleeve the block?

lejams

Alusil is not a coating. Alusil is an aluminum/silicon matrix, (ALU-minum SIL-icon). The honing process removes the aluminum exposing the harder silicon. Relatively speaking, if the engine is built or tuned wrong, Alusil can be more vulnerable. But a bad build or mis-tuned engine, etc., you will have catastrophic consequences with any type of block or sleeve - period. Alusil blocks will perform x hundreds of thousands of miles. The longevity of any engine depends on how & what you build it for, and how you maintain it, and how you drive it. Thus to say, a properly maintained 951 engine in stock form as Porsche designed it with the Alusil bores is good for 300k ++. The turbo and other parts will wear out long before the block will. Sleeving is another option with different benefits then the stock Alusil cylinder walls, i.e. many more pistons available, more forgiving then Alusil, in that individual sleeves can be replaced making the next re-build perhaps easier. Regardless of Alusil or sleeving, whoever does the work better know what the hell they are doing, otherwise the pain is just from a different unadvantageous point.