m42racer

Some time ago, there was a discussion about Turbo Pistons for the stock blocks. What size is wanted. Is it the 100.00 repair size or just 104.00 Turbo size. What is the current prices offered for these? I know these Pistons are special, so what size does everyone want? I think some one asked if there was a demand for these. If so, what size, what CR and how many would be interested. Cost is a factor, but first we need to tell them how many sets would be ordered, to get a price. I have been told these would be special ordered from the original manufacturer.

BoostGuy951

I think Mahle just started coming out with turbo pistons for the 104mm block. Read that in a post on the 928 board.

Tom M'Guinn

stock 2.5 pistons are 100mm

stock 3.0 pistons are 104mm

add .5mm for the "one over" size

Porsche does not sell 3 liter turbo pistons for Alusil blocks like ours. They only sell high compression pistons cut for a 4 valve head, like the 968.

Mahle recently made a special 104mm piston designed to run in a 3 liter block with an 8 valve head, like the 1989 2.7 liter head or the 951 head. They are already hard to get in stock size. Andial sold them.

BoostGuy951

I think there might be a market for a piston that will run in an enlarged alusil bore. These cylinders have ample wall thickness. They could be bored substantially and still maintain good wall thickness. It would be nice to have a piston that you could run without sleeves.

BoostGuy951

Here is how much metal would have to be removed to fit a 2.5 block with 104mm piston:








Here is for a 106mm piston:




Though I dont know what is acceptable as far as wall thickness for aluminum. I know you can go very low in steel.

Danno

Please note the wall thickness on the cylinders as well. The 100mm bore has a 9mm thickness while the 104mm bore has 8mm thickness. If you bore out a 100mm cylinder to 104mm, it's only 7mm thick or 1mm less than the 3.0L engine. Then going to 106mm on the 100mm cylinder reduces wall-thickness to only 6mm. That may be pushing it a bit since I know several people that have cracked the cylinders in their blocks (using stock bores even).

Tom M'Guinn

Interesting. You get even closer when you consider that Porsche's approved "one over" on the 3 liter is 104.5, which takes the walls down to 7.75. On the other hand, the cylinders on the 968 block are supported half way up with metal -- i.e., the water jackets are only half as deep. I wonder if that extra support allows for thinner walls?

BoostGuy951

The 104mm blocks are also siamesed for better rigidity.

seb928s

106mm looks really scary to me on these 2.5l blocks. 104 would be the safe bet.

DHC8FO

Hey guys, I'm looking at a scorched piston on my #3 and was thinking on going 100.5. New pistons ect. However I may have located someone who can replace the Alusil back to factory. I'm planning on a daily driver, so I'm thinking that if I could locate a used piston that was stock in good condition, I might try that. I thought about just buying a new one, but I'm leary about mixing old and new metal. I still need to disassemble mine to determine the group.

If anyone has a piston let me know?

Mark

DHC8FO

Hey guys, I'm looking at a scorched piston on my #3 and was thinking on going 100.5. New pistons ect. However I may have located someone who can replace the Alusil back to factory. I'm planning on a daily driver, so I'm thinking that if I could locate a used piston that was stock in good condition, I might try that. I thought about just buying a new one, but I'm leary about mixing old and new metal. I still need to disassemble mine to determine the group.

If anyone has a piston let me know?

Mark

hosrom_951

When you bore the cylinder wall(s) to 100.5 or more, does this include the sleeves? i mean the stock is 100mm with sleeves, if you over bore to 100.5 does the machine shop measure 100.5 and remove that 0.5 then add the sleeve or what exactly? the same goes for the 104mm, or does sleeving takes up no measurement (just curious).

Pauerman

I think the discussion revolved around the availabitlity 104mm Alusil Turbo pistons. Andial was the only vendor supplying these pistons and I believe they sold all their sets - 50 standard size sets and 50 1st oversize. Are you looking to contract Mahle out to make another batch? I paid $1200 for my set of 104mm Turbo pistons.

HTH

DHC8FO

Reference hoshrom_951

sleeve size of Alusil liner is 105.00mm-with 107.00mm top flange, so if you bore to 100.5mm you are still in the existing sleeve. This is the method referred to in the mant. manual. The option I thought I might try is to replace the sleeve and reuse the existing 3 pistons as they are in good shape. Providing I could find a 4th stock piston. From all of the discussions it appears that there should be a good supply as it appears everyone is increasing the bore. There may be some variation on the size of the stock pistons as there was a reference to 0,1,2 sizes, so I need to check the size of mine.

Anyone try this before?

86-944NA
87-951 Project

hosrom_951

DHC8FO:

So this means, when you over bore for 104.00mm for a 2.8L block. You do not have to re-sleeve it? because there would be 3.00mm of sleeve left correct?