Steel sleeves in an alu block usually is no problem. Just look at several 120+ hp per litre motorcycle engines,that comes with them as stock...problem free. (yes,I know many of them have ceramic or NiCaSil cylinders nowadays.)

 

alright, guess that cast iron sleeves in aluminum blocks are the problems then?

 

Ok, here are the typical sleeving problems –
The steel/iron sleeves are set in place using an interference fit, the OD of the sleeve is greater than the ID of the hole. To get them to fit you need to heat the block and cool the sleeves. If you don’t have a fixture (specially made) to hold the sleeves in place as the block cools the sleeves will be forced out of the block just a tad. You won’t be able to see it so you won’t find it until you run the engine hard and the sleeves sink into the block and your head gasket starts leaking.

You also need to have a head plate made up to simulate a torqued in place head so that you can bore and hone a true cylinder. None available commercially – make your own!

There are a couple of other tricks to doing it right that have to do with the prep of the sleeves, either you can get Darton to do some finish machining or do it your self.

So the experience part means that the person has to have the right 944 specific tools – you can’t fake them and it doesn’t make a whole lot of financial sense to fabricate them for one job!

As for the aluminum sleeve question – this is possible, you can even get alusil sleeves. The problem is that you can’t use aluminum pistons in aluminum based cylinders with the proprietary Mahle/Porsche coating (available only on Mahle pistons at a pretty hefty price tag). There has been some work experimenting with other coatings but the results aren’t quite right, hopefully this will be worked out someday.

My personal opinion is that the alusil concept is great for long term piston wear but it is fairly weak when it comes to resisting damage from contamination (scoring from carbon deposits and such) The nodular iron sleeves are extremely hard and resist scuffing and scoring . I had a Cometic MLS head gasket let go and dump coolant into a cylinder at the track. The piston is trash but he cylinder walls cleaned up nicely and are back in action – an alusil block would have been trashed.

As far as the 106mm size – I am not wild about it, it can work for a street car that is not running big boost. Using the correct sleeve you will be left with .101” thickness for the sleeve and .100” for the remaining alusil. I like to see .120” sleeve wall thickness minimum.

The new MID sleeve may change this since you don’t have to worry about splitting the difference between the sleeve and the alusil cylinder.

Chris White

 

What do you feal the boost limit is for the 106 mm ? and I will stay under that.

The MID sleeve sound really nice, lets us know how it does.

 

Ok...so basically it's the same sleeving a 944 block as sleeving just about every sports motorcycle,then. Same problems often apply there,but we leave the sleeves under 20 tons of pressure until they are both cold. No probs then. Thanks,I wondered if it was something unusual with the 944 engine I didn't know of.

 

Thats why I didnt want 106mm bore, I wanted to run 20psi safely... maybe a little more 23-24 with water injection.

 

I hope 20 psi is not what Chris means when he says big boost.

 

Well hopefully he will chime in! I had talked to a "guy" on the list about this and thats why I am looking at a 2.7 over a 2.8. The figure may be higher than that, its just the one we (he) talked about.

 

Chris: Sorry for my questions but i really want to learn about sleeves since i have a completely damaged 944 NA block that could turn out for a project one day??? (the pistons are sized and the engines doesn't cranck at all, even by hand).

Going back to the aluminum issue, Mahle pistons are Alusil correct? Note: in Mahle's 2005 Catalog they stop manufacturing the 944 Turbo pistons, so expect prices to get even higher what they are.



Kolbenschmit has 944 turbo pistons, but they are Nikasil (which are compatable on the stock alusil blocks if i am not mistaken). How would Nikasil pistons on alusil sleeves work out (i do not quite understand how the alumium sleeves and piston coatings effect each other, please note that )

 

You got it a little back wards – the 944 bore material is Alusil and the pistons are aluminum with a proprietary coating so that the aluminum will not gall. Aluminum on aluminum does not work well, especially under heat and pressure! Nikasil is another coating/material that Porsche uses for the 911 cylinder barrels.

Alusil is just aluminum with silicon content (the silicon is a really hard material that is responsible for the long wear charities of Alusil). One of the nicest properties of Alusil is that it has the same thermal expansion rate at aluminum - so the cold clearance of the pistons in the cylinders can be very close.

Sorry – I can’t help you guys out too much on the 106mm deal – I have refused to do many of them because of the thickness issue. I have done 106mm NAs that haven’t had any problems. I am about to do a 106mm MID set up so I can give you guys some info later this spring.

One of the difficult areas when you talk about how much boost a 106mm can take (or any size for that matter) is how well the engine management is tuned. I am not just talking about air/fuel mixtures (that’s the easy part) it’s the ignition timing that gets very critical. AS somebody that supplies blocks, pistons and such to other people I want a good safety margin in there so when the customer ‘plays around’ with the tuning the whole thing doesn’t expire at the first sign of detonation. If you have the engine management dialed in then the 106mm thing wouldn’t bother me too much except for long term track use. Past experience has shown me that the whole engine/intercooler gradually heat soaks over the course of a ½ hour session and the intake temps keep going up and up. Sooner or later (sooner for a larger displacement / higher boost engine) the engine will hit that magic point and autoignition of the mixture will occur – this is a bad thing.

Chris White

 

By the way – one other theory on the 106mm thing –
I believe that the 104mm has the capability to run a higher boost level than the 106 – enough so that the .1 liter difference doesn’t’ matter. Better to build a stronger 104 and add a lab or two of boost. Especially for the track where you want the added durabilty

Chris White

 

Chris,

Thanks for all the explanations.
Is your sleeve kit steel, alusil or aluminum?

 

None of the above…!!
Nodular Iron

 

If you ever going down under for a holiday and can caryy the kit on as 'carry-on' luggage, let me know

 

I hear ya with that one HMD. How much does the kit weigh?