Chris White

Here is my alusil vs sleeved philosophy –
Positive points for Alusil –
• Very good ring wear characteristics
• Thermal expansion similar to pistons
• Its stock – you already have it!
Negative points for Alusil
• Easily damaged / scored
• Requires special coatings
• Small choice of stock type pistons
• Damage cannot be repaired
Positive points for sleeving
• Very tough surface – damage resistant
• Wide range of pistons designs (custom) available
• Easy to rehone/ rebore
• MID design strengthens block
• Major damage (dropped valve) can be repaired with new sleeve
• Replacement pistons are ½ price of Alusil pistons
Negative points for sleeving
• Initial expense
• MUST be done correctly
• Excessive clearance can cause noise when cold
The biggest plus for sleeving is for race / track engines. If you want seriously high output for a race use engine you have to accept the fact that the engine will need ‘refreshing’ on a regular basis. The higher the output (for race use) the faster the wear and the less you can accept less than maximum performance. For example a 911 GT3 RSR engine has to be sent back to Germany for a rebuild after 40 hours of use – and that engine is putting out less than 100hp per cylinder.
With a sleeved engine you can rehone the cylinder back to round and order some custom sized pistons and you are back on track again. Sure – this is the on the extreme end of engine performance but some of the output levels that are being realized for street /DE engines are pretty high. You want that kind of output you will pay the price in wear (it doesn’t matter if it is alusil or sleeved – it will wear faster).
So, what about street engines? I don’t recommend sleeving for all projects, it’s a great answer if you have a worn or damaged block, if you want a custom spec piston or very high output - but if your alusil bores are good, then I would keep them on a mild mod job.
As for the question about the longest mileage on an MID set up, they have only been around for 2 years so don’t look for a high miler out there. Besides – high mileage doesn’t mean much, I could set up an NA with MID sleeves and I don’t think it would ever wear out! Now how may track hours @600hp, that would be an interesting question. I’ll let you know when I get to take one apart…

m42racer

To answer the first question, I agree, if the block doesn't need sleeving don't do it. Blocks that are sleeved should only be done if a larger bore is required or the repair requires a sleeve. As for Pistons, there are many out there that can be now used in the stock bores. Some of these are better than others. These can be made in any size. The Ring selection is critical and the sizes available dictate the final repair size.

I agree with the comment about the Deck Plate. Fit this before sleeeving. If you reaaly want to make the block stronger the Deck Plate is the stronest way to achieve this. Blocks with MID sleeves are not as strong. If fact they are less than stock. So much material is removed to fit these and ther block upper rails move all over the place. I was involved in the development of the Deck Plate for the 944 engines and saw first hand just how much these things twist. I don't want to knock the use of these sleevs, but if you want a better solution, the dry liner when installed correctly is far better. No sleeve is even better.

Hone the block, fit the correct Pstons and if you reaaly want a solid block fit the Deck Plate system. Also I would recommend the Girdle dowelling as this really ties the whole lot together.
Ask around and get the whole story.

333pg333

Well I'm the owner of the 3.1 in question, only it's 3.0, but that's semantics. The issues we have had have no relation to Chris' engine building expertise as he didn't build it. He just sold us the parts so there is no criticism from us towards Chris on this. We have put it together with the spec's that were provided and have had problems. This is not a slight on the Mid Darton system or Chris White, nevertheless there are issues and they suggest piston to wall clearance. Now this could have been exacerbated by the JE's propensity to expand more than some other pistons out there and we would also like to hear from other users of this combination but they don't appear on Rennlist often. We can only surmise that it is incorrect installation combined possibly with climate differences (pretty warm in Sydney) or a freakish blend of alloys used in our batch of JE's. If we had installed them way too close then perhaps it should have occurred before 880 km's were racked up on the new engine and on all 4 pistons. On his car my mechanic used the spec supplied which called for 0.004" and so we went 0.00680 on average on mine. There is also a lot of speculation on clearances. If a n/a road car is asked to use 0.004" then wouldn't it be acceptable to use 0.006 or even more on a turbo race oriented car?
Anyway back to the topic. I can see that there are some great points for both wet, and dry sleeving or not at all. The more this is discussed and by those that have the products then the better educated decision making the next prospective customer can be.

Geneqco

Hi Patrick,

I really hope you get to the bottom of this soon.

Do you really think climatic differences would have played a part in this? The US has greater temperature extremes than we do in Sydney and it's not even summer here.

Thinking logically, you were running zero/low boost and I would have thought if they were properly designed and had the proper clearance to handle the difference in expansion rates between piston and sleeve for a high boost 700 hp application that any difference in ambient temperature anywhere on the globe would not come close to the extra thermal load they should be able to handle.

What do you think? Have I missed something?

333pg333

Hi Scott,

I should have explained that comment better. With the climate or temp differences I was alluding to the fact that we didn't seem to hear any piston slap on cold start. This possibly could be that they warm up and expand more rapidly and reduce or remove the slap very quickly. Hey I'm grasping at straws here too. lol.

Diver944

I have JE pistons in my Nikasil sleeved 3.2 built here in the UK by Jon Mitchell and SPS engines, I'm no engineer but I can relay my own experiences as an owner.

I now have 5000 miles on the motor running at 18psi boost including three track events. There is a minimal clattering sound at first startup that disappears within a minute which has been explained to me as a result of the different expansion trates of sleeves, block and pistons. Almost immediately you cannot hear it as it is masked by the normal running sound of injectors, exhaust etc.

We went for a sleeved design because it is inherently much, much stronger than the original block and if the worst should happen to one cylinder then it is a simple case to replace the liner in that cylinder. Jon was confident enough to say we could go to a 3.4 engine on a street car and it would not need to be opened up again until a normal lifespan had passed. This would obviously be less with a full on race engine. I erred on the side of caution and chose the smaller 3.2 option

When the liners were machined, Jon stressed that the whole block was mounted in an assembly with a dummy sump in place so that conditions were perfect and the liners would be 100% perpindicular to the plane of the deck. When they assembled the pistons inside the block I know that even the rings had to be machined some tiny amount until they were happy with the fit.

Olli Snellman

S2 block with 104mm Wössner pistons. Wössner use Mahle raw material and coats pistons excately the same way as Mahle did with original pistons. Wössner set is about 1200€ including rings & wrist pins. Iam building a 3liter with this way

pk951

I don't want to sound negative towards the midsleeves from darton. From what I have heard one of the top engine builders for these cars does not use the midsleeve system. True or is it just a lot of talk?

evil 944t

I know Scott Gomes said, he stopped years ago because of leaks( to many heat cycles on a street car) but that could have been an older design. I know JME dry sleeves too.

m42racer

I know that PD does not rtecommend the MID sleeves for thess engines either. To be fair, they do install MID sleeves into other blocks(Honda, Ford etc) but these are for drag racing. I was told that leaks were the main concern. The drag engines use no water, no leaks.

I was told it al comes down to the application. Some (blocks) are better suited to this kind of design. Others like the 944 block are better suited to dry sleeving. You make your choice who you wish to listen to. Thats 3 respected engine builders who it appears have chossen not to use them.

lejams

Regarding the factory 3.0 block with Siamese cylinders and Alusil bores, I think that any sleeving process should be considered secondary, not the other way around. Alusil cylinder walls being softer and more vulnerable doesn't negate strength in a block that has good engineering & design like the 3.0. I am one to believe that the open deck design of the 2.5 combined with detonation is a primary cause of the failures many of us have experienced, but not the Alusil bores in themselves. Even though it could be negligible, I think that the integrated design of the Siamese cylinders on the 3.0 S2 & 968 block, is stronger than any secondary sleeve and deck application on a 2.5. Of course If you're in serious trouble with a 2.5 block and it's what you're working with, it's your only option.

For MID sleeves on a damaged 2.5 or 3.0, I can see advantages for race applications where the engine would be apart frequently and you can change sleeves & O-rings as needed. Whereas with MID on a street car, after some time and mileage I would be concerned about the O-ring being a potential weak link going unchecked and maybe leaking. Negating the O-ring concern on a street car, overall I like the wet sleeve. Needless to say dry sleeving has been around forever... JMO

Weston Dillard

I have 6 years on a non-sleeved 3.0 block 8 valve turbo motor doing 10+ track weekends/year with 2 drivers. It makes about 350 WHP. It has been pulled down once for rings and bearings, and is about due for that again. We know the factory stuff is durable. If you have a solid block with good bores, I recommend you use it. If your bores are shot, the decision gets a lot harder.

West

Olli Snellman

West,
what pistons do you use ?

333pg333

Olli, have you been using the Wossners? What sort of clearance did you set for them?

lejams

West, This may be somewhat off topic but still might be helpful to the cause. What mods are you running and what boost to run those numbers with such reliability?