Zero10

I see, So the SKF really doesn't indicate Mahle... I hope the guy is mistaken.

I'm still a bit lost on the coatings, as in, what I should do with the coating on these if I get them. The skirts are pretty scratched up.

I was looking at the factory manuals a while ago, and I thought 100mm pistons were 99.98 - 100.00, matching cylinder bores of 100.00 to 100.02
and the first oversize range was 100.48 - 100.50, with bores of 100.50-100.52, but I could be mistaken.

The piston crowns are dirty, but if I find a tolerance group number up there, I will presume they are indeed mahle pistons. Hopefully this is the case.

pk951

I don't know if this is of any help or not but there is a guy on the list who is using NA pistons in his turbo. So far by all accounts his engine is still running with NA pistons he made 351 RWHP.This could be a cheaper route to take?

evil 944t

There is a guy selling a short block in Panorama for $1k. Cheaper than pistons.

hosrom_951

Zero: Ski probably has the best price yet on new Mahle 100.5mm pistons (is the tolerance group the one you are after?) Too bad my supplier only has 100mm Kolbenschmit for Turbo and Mahle for NA/S2/968 models.

What i am afraid of is that with all you're thinking on tolerance groups, pistons and so on, i have this gut feeling that you are missing out on something. Double and tripple check the play, measurments and clearances on the block, crank, torque spec etc.....

And btw, the prices for Mahle pistons are going up. As a matter of fact, there are some "rare" pistons (for the 2.8 stroker?) that are starting at $1,600+ or so. You would be saving on purchasing pistons soon, rather than later when prices are really high.

Zero10

What brand would factory pistons be?

I have considered N/A pistons, then turning the boost down, but I like it better this way.

I'm not sure what I could be missing out on?
I'm not picky on the tolerance group, as long as I have them in my hands, so the machine shop can bore the cylinders to match the pistons.
Right now, I have to bore out to 100.46mm to make the cylinders clean again. This means I can take any 100.5mm pistons (I think)

A short block for $1000 sounds pretty damn good. Can he guarantee that it is within factory tolerance for a new block? If so, I hope it's the same tolerance group as my pistons (0). If it is, I'm 100% interested.

evil 944t

I don't know the guy . Its an ad in Panorama (PCA mag). Check it out. If you need the info, I can look it up.

Zero10

Definately interested. I'm about 20% sure I have a line on some used 100.5mm pistons, but they're overseas, and will cost a lot to ship here, so a local(ish) short block may be just as feasible, OR, if I save enough cash on the block and these pistons, I could buy them both... muhahaha, put the second engine in the back, make twice the power, bwahahahahaha....
Sorry, I'm at school right now, in a very boring class

evil 944t

you got PM

evil 944t

2 - pm's

hosrom_951

Zero: The factory manuals indicate that Kolbenschmit were the "factory" pistons, but Mahle was also used (maybe USA models???).



I hope you don't already have bored out to 100.46mm since the minimum is 100.50 as shown!

Zero10

No boring work done yet (haha, 2 meanings! )
I plan to take it out to piston diameter + 0.01mm, this is near the bottom end of new piston-wall clearances. The manual (IIRC, I don't have it infront of me) specifies new pistoin-wall clearance as 0.008 to 0.02mm, I feel 0.008 is a touch on the tight side, but I want this thing sealed up tight as a drum when I'm done, so I would like to keep the clearance to a minimum.
I was just saying, that to take every last scratch out, it would have to go to 100.46, so I absolutely must use at least 100.5mm pistons.
I'm toying with so many options right now my head hurts. Why couldn't this have been on my NA, and then the turbo would have an excellent engine, and I could buy your 100.5mm pistons, lol.

Is it possible to dish the hell out of N/A pistons to make the compression ratio right? Or would that make the crown too thin?

Dishing pistons is relatively cheap, or so I am told. I could then thermal barrier coat the crowns, and still come out at around $1000?...

hosrom_951

daniel951 is running NA pistons on his car, boosting 16.5psi (or so) without problems (have NO idea what his CR is).

But i wouldn't dish any pistons myself, unless a good vendors does this kind of service/product (testing the strength, stresses, CR etc....it would be more "reliable" that way).

Did you try looking for used oversized pistons? (you may get lucky LOL).

Zero10

I am about 40% sure I have secured a set of used 100.5mm pistons for a really good price.
If not them, then I am 100% interested in your N/A 100.5mm pistons Hosrom. That would give me what, 9.6:1 or 9:1?...
Would give me a bit more low end grunt, and make some more power under boost. I never planned to top 15psi of boost anyways, since I don't want to change injectors, intake, fuel pump, etc, so the max boost limitations wouldn't matter, and it should make more power from my K26/6.....

Hosrom, do you have the pistons sitting there, ready to ship? And if so, are they properly coated for use in alusil bores?

hosrom_951

BTW: there is a gentleman selling a full 951 engine with turbo and stuff for $1K........search the threads.

Zero10

Yep, there is, and I wrote him, but I'm a little cautious to buy another used engine, at this point, the miles are unknown, but for $1k, I expect higher miles. I already have 99% of the rebuild parts in my room, so I'm rather committed to a rebuild at this point.

I have heard some very encouraging things about using the N/A pistons.
The fellow selling the used 100.5mm turbo pistons has got to have the world's worst communication skills. I will e-mail him 5 or 10 times over a 2 week period, then I still have to call him for 2 or 3 days before I get a response. I'm getting very tired of waiting. Every day I go without pistons, is another day I have to break in my new engine before racing. Not cool.

Hosrom, are the pistons you're selling already coated with iron graphite (or iron ferrite or whatever)?
If so, can I use the stock wrist pins and clips with them?
If I were to buy them from you, how soon could we get the pistons shipping? I'm getting a little antsy staring at a motor in pieces every day

Using N/A pistons has really gotten me thinking. Gives me N/A like power until the turbo spools up, then it should go like hell Seems like that's the best of both worlds. I don't plan to make huge power, or run really high boost with this car, as it's first job is daily driver, and it's second job is toy for the track, and I don't want to get into aftermarket engine management, turbos, intakes, etc. Keeping the boost low, and cranking up the compression ratio sounds like a great idea, gives me a minor edge on the other guys running 12psi on a stock 951