9.8:1 pistons in stock 3.0

[carl74344]

I am looking for new piston and cylinders for my 1982 sc 3.0 w/cis. buget is important. need help. I looked at the qsc ones but no one has much good to say.someone said supertec has good sets of qsc. is that a way to go?


I find a lot of 9.8:1 mahle . I have 9.3:1 how big of difference is it?

I am having my heads re-built. not sure where to go from here.

[Eagledriver]

Mahle 9.8's are a bolt in replacement for your engine. New ones are expensive, but they are the best choice. Other options are used sets of 9.8 or 9.3 Mahle's. How bad are what you have now?

-Andy

[carl74344]

I have alusil p&c. # 3 has broken rings.

[Henry Schmidt]

We are no longer selling QSC cylinders.
The Euro 9.8:1 compression ratio can easily be reduced to comply with the inconsistent fuel quality available today.
I would tend to shoot for less than 9.5:1 by shimming the cylinder base. An increase in deck height from .040" to 060" should do the trick.

If you want to use JE pistons with reconditioned Mahle cylinders, call Don @ EBS.

[Eagledriver]

Originally Posted by Henry Schmidt

We are no longer selling QSC cylinders.
The Euro 9.8:1 compression ratio can easily be reduced to comply with the inconsistent fuel quality available today.
I would tend to shoot for less than 9.5:1 by shimming the cylinder base. An increase in deck height from .040" to 060" should do the trick.

If you want to use JE pistons with reconditioned Mahle cylinders, call Don @ EBS.

Henry,

Have you not found the Mahle 9.8 pistons to be much less than 9.8 measured at normal deck height? I've found that they measure about 9.4 with 1mm deck height. I'm sure they could be higher if the heads have been surfaced a few times but if not they are pretty low already.

-Andy

[Eagledriver]

Originally Posted by carl74344

I have alusil p&c. # 3 has broken rings.

I have reused Alusil several times. You could consider measuring and re-ringing your existing set.

-Andy

[dberman]

I have also had success reusing alusil cylinders following some of the other threads on Pelican.

[Walt Fricke]

I don't think 9.8s are available for Alusil use. I think these, which are/were a Euro only part (only the late Euro SCs had this, 81-83?).

I don't think 9.8 in an otherwise US 9.3 motor is going to do much good, as the late Euro SCs had the big intake ports and runners. The US engines (and the Euro engines) from '78-79 had these ports/runners.

If you have an '80-83 (aha - you have an 82), you can have the intake port bored out easily enough. But you have to have the larger runners, so you'd need to look for a set for sale.

The Euro spec 9.8 with track headers is a mighty motor indeed. The guys with 3.2s complain about them all the time. With something like SSIs for headers, you don't get quite all the power available, but should still be pretty close and streetable.

To Andy's point about what actual CR is, an engine builder friend of mine with a Whistler to check this has also commented that the stock build compression is lower than advertised. When I whistled mine, I found that to be so as well - rebuild was new Mahle Ps and Cs at 9.3 for a US motor SC, standard copper spacer/gasket, stock heads, bolt together. Several years later had use of the Whistler, and hmm. Can't find where I wrote down the actual numbers.

If you just want to rebuild, and your Ps and Cs measure out within tolerance, for sure the least expensive approach is to rering with the right rings and be done with it. Everything else is apt to be expensive. Used Nikasil 95s you might find. I suppose you could use J&E 9.8s? I don't know how well those work with CIS. Do they make a special one for Porsches with the swirl shape to the dome?

[willcall]

Try this Tech article.
He upgraded to JE 9.8 in his CIS as I recall but you need Nikasil's to do so.

Pelican Technical Article: Extracting Power from CIS 911s...

[Dan J]

I've seen many ring land failures on factory 9.8's (we used to race a car with them) so I'd avoid them
I think you should follow Henry's advice as to setting C/R

Jeff Gamroth has a very nice aftermarket forged (original are cast) version of this piston

[carl74344]

I am not sure if my pistons and cylinder are bad. # 3 spark plug was fouled black and oily. # 3 also was the broke head stud.
I can not find any markings at the base of the cylinders. I tried the magnet test.it did not stick. also I have 10 fins.I have read a lot post about Alusil but still do not understand if I can hone and re-ring them. it seems like most say no so I started looking at new P&Cs and the price is high. however mahle 9.8:1 seem to be cheaper then 9.3:1 is .5 cr really that much..

budget is important. having my car running and driving it is more important. not sure what to do. I will pull P&Cs tomorrow. I will pull them together as a unit. how do I check the to see if they can be re used. Wayne's book said to pull as unit and not separate . if I pull as unit you can not see the rings.i will not know if any are broken.

more HP is good if I get it ,but good running is what I am going for. I send my heads out Monday . full re-do. I am trying to do things right. thanks to everyone for the help.....carl

[Flat6pac]

If youre questioning the case bolts and not opening the bottom to see whats there after 32 years and other owners, why do you want to stress the bottom end with higher compression pistons, new rings and a valve job?
Bruce

[Walt Fricke]

I think when someone says you shouldn't separate alusil pistons from their cylinders, they mean to keep track of which is which. If things wear in together slightly differently, it makes sense to do it this way if you are going to, or hope to, just put them back in together.

This does not mean you shouldn't pull the piston out of the cylinder. Rings move around some, so it is not as if you need to retain the exact ring gap orientation when reusing old rings.

If you were doing something which required removal of the Ps and Cs, but weren't going to or check anything on them, it would make sense to leave the Ps in their Cs. Installing a P in a C is one of those slightly scary parts of engine assembly, because it is easy to break a ring, so if you don't have to, why? But where inspection is part of the program, just take them apart and stop worrying about that part of things.