Ski

For all that inquired:

We should have two sets of test mules ordered, 100.5mm. There was a small change for keep the CR the same as stock, cc volume. We have run into a weight issue, these pistons are lighter than stock. These will not be produced or sold until the test mules have put some serious miles on them and I know one will be a dedicated track car - our track car will be one. So maybe by the end of the summer or early fall, we will have some more info.

Ski

new arrivals....100.420mm

TRP951

those look nice what are they going to be looking for after they get tested?

hosrom_951

Bret:

100.420mm?

smallest size (tolerance group 0) shown in the manual is 100.480mm, would this make a difference?

Ski

It's the forging that they had. 100.420 measurement above the bottom skirt, clearance each side suggested by Mahle of .040 (.0015") would equal 100.5. This is suggested by Mahle, based on the 2.8L pistons and the reproduction 968T pistons they do. The first cars that used these, sold by Heritage and set for 16V heads, at tolerance less than .0.025, actually made less power. When they opened the bore a bit, rings still in tolerance, they actually gained HP/torque and they have the sheets to prove it - thus Mahle recommendation for .040/.0015" clearance on each side of the skirt. My test block will either be that or .030/.0011"

You cannot reproduce the original forging. If you want OEM, probably a dozen sets left around the world at $1600 + ship, well according to Sunset a few weeks ago.

I'll double check the weight when they get here but should be 460 grams, 70 grams lighter than my OEM 100.5. The coating is Ferrostan iron coating. After the first engine is built, testing for any balance issues, clay the top for valve clearance, $1150 shipped in the US. The first engine should be up and running within 2-3 months if all goes well.

The dish of the dome is .7mm taller than stock due to lesser amount of material underneath. But to offset that, the dish is now symmetrical, so you really don't have to worry about making sure one side is down, follow the arrow, etc when installing the pistons. We just want to find out if the stock gasket thickness will give enough clearance or use Cometic(most will anyway) at an increased thickness.

pk951

Sounds like very good news, and at a price that wont break the bank. It would be to early to compare those pistons to the Tom C pistons which seem to work well also.

reno808

What type of rod's are you useing ski???? becuase combonations also will play its roll.. i know you know that. What would you reccomend using those pistons??

Ski

We're going to do one engine(JAB Racing) with stock rods and put it in the track car after Hallett. I think one other test mule is using Carillo rods but I will check with him and see, not sure of the third. We do have a small, small concern about balance, reciprocating mass, since these are lighter than stock but we all( 3 test mules) agree it should be minimal if it arrises at all. Pistons should all come in balanced, we will all balance the rods...and I want to thank the other two test people who came onboard for this. If they want to speak up I'll let them chime in. If these work, they may be better suited for race is there is a minimal balance issue; if not then they will be suitable for all intended uses.

Yes, Tom C pistons, for what we have done, are working well indeed and cpt_koolbenz now has his up and running as well, 101mm.

RajDatta

Ski, not sure if you ever noticed but why is the dome on a 968 turbo piston different than the one on a 944 turbo. Any chance you could ask Mahle to shed some light on that. The 2.7 NA head is similarly designed to the turbo head, so why should the piston be different?
Thanks in advance.
Raj

Ski

The Heritage Motorcar piston is designed for the 16V head, not sure of the other but I can ask them next week.

Tom Carson

I believe this is what Raj is asking...why the 104mm 8v turbo Mahle is not symmetrical?
Also...are you saying the piston orientation does not matter? (I thought the wrist pins were offset for a reason)

Ski

that was just a guess on the orientation. The dish is now symmetrical to get the same cc amount, to maintain the proper compression ratio as the OEM 100.5, which I sent to Mahle. This forging is not as deep as the OEM piston, therefore Mahle needed to open up the area to maintain the proper cc amount or the CR would have been 9.1:1. I'll let you know if there is an arrow on it, I'm at work, but I don't think there will be.

http://www.heritagemotorcar.com/index.htm got to engine components then to 968 turbo pistons to view these, which are done for the 16V head.

RajDatta

Ski, I was talking about the 8 valve Mahle 968 turbo pistons, not the Hetitage 16 valve turbo pistons. After all, Mahle made those as a special case and not as reproductions because there was no such thing as a 16 valve 968 turbo. The original 968 turbo S pistons were copied for Andial to run with alusil block instead of the originals for nikasil blocks.
Sorry if I wasn't clear.
Raj

Ski

Raj, they are going to check on that and hope to find an answer. Also, what forging, if any, they have.

Well, these are off to the test mules today, three of them, all track cars with one of them getting some street use. I'll report back after the initial findings and reports. As you can see, new rings, wrist pins, circlips, and sheet with diameter and gram weight. couple of pics: