Unusual Piston Set

[JohnHarrison]

Good morning guys, I have this unusual set of pistons and I need some help identifying them, nobody I asked till now have seen them before and yet they're pretty old.
They were in a early 2002 block I purchased from Germany, the seller told me the matching cylinder head is the 121 type but the crown design doesn't look like it to me.
Thanks in advance!

 

 

Edited February 2, 2023 by JohnHarrison

[Tommy]

They seem to be high compression race pistons for modified head with hemi chambers. Also looks like some polishing made for rods. Usually the old time race pistons were Mahle but I think these look different. 

[TobyB]

Yeah, I agree, that's for a single hemispherical head

(the 121 is 2, the E12 is 3)

 

I do wonder if they'd clear a 1.8i head...

 

Compared to modern single hemi profiles, they look rather... lumpy?

But the radiused edges make good sense.

 

t

 

[Preyupy]

The engine might have had a 121 head but the combustion chambers HAD to be modified.  Those are some old school pistons!  look at the rings and the distance from the top of the piston to the upper ring.  Going by the valve reliefs it had a big cam in it as well.  

[JohnHarrison]

Thanks for the answers!

Yeah they have a weird shape, it's difficult to notice it in the pictures but the flat top isn't centered and the intake pocket is slightly larger than the other one.

Sadly I don't have an use for them right now (I'm not even sure they're actually usable on a street car whatsoever) but nice to know they had their story, wish I could see the motor before it was parted out.

 

And funny how previously unseen parts for these cars still pop ups today.

[Preyupy]

12 minutes ago, JohnHarrison said:

" intake pocket is slightly larger than the other one"

Intake valves are usually 46mm and exhaust valves are usually 38mm.  You "can" use larger diameter valves but things start getting really close in there,  depending on the camshaft you can have vlave to valve contact!!!   

 

[uai]

21 minutes ago, JohnHarrison said:

I'm not even sure they're actually usable on a street car whatsoever

If they are within tolerance and you have the head for them - why not?
But they will need a pair of sidedrafts and I'd check the compression ratio.
Regarding tolerance they'll probably be ok with 8/100th mm up tp 12/100th mm above it's a bit too much and they'll start to be noisy and use oil

[gracer]

Could they possibly be BMW motorcycle pistons?

[AceAndrew]

John,  As mentioned it's for the 121 head that was bored in a hemi-shape.

 

Here's a visual reference I posted nearly ten years ago.  The NOS Motorsport Head as listed came from Vasek Polak's liquidation years prior.  

 

 

[JohnHarrison]

17 hours ago, Preyupy said:

 

Never tried an M10 with bigger valves, I guess one must have a compression above 10 to benefit from it? 

 

17 hours ago, uai said:

If they are within tolerance and you have the head for them - why not?
But they will need a pair of sidedrafts and I'd check the compression ratio.
Regarding tolerance they'll probably be ok with 8/100th mm up tp 12/100th mm above it's a bit too much and they'll start to be noisy and use oil

 

Sadly I don't have an hemi head, only a 118 and a 121TI (small valves variant), a machine shop owes me a favour so maybe I could get one done but I'm reluctant to sacrifice my own 121, it's in too great conditions; I bought this bottom end for the crankshaft to be honest and the seller didn't have the complete motor, it was just a bunch of stuff left over from his father if I remember correctly.

As carb I was using a DCNVH 38, I plan on daily drive the car so I'm slightly afraid of having a motor more difficult to tune.

 

17 hours ago, gracer said:

Could they possibly be BMW motorcycle pistons?

 

I know there is some BMW bike using 89mm pistons but my knowledge is basically zero on motorcycle haha 

[JohnHarrison]

17 hours ago, AceAndrew said:

John,  As mentioned it's for the 121 head that was bored in a hemi-shape.

 

Here's a visual reference I posted nearly ten years ago.  The NOS Motorsport Head as listed came from Vasek Polak's liquidation years prior.  

 

 

Great post! Interesting the differences in blocks too, maybe they are some early Alpina pistons then?

 

I found these CP Carillo pistons marketed for the 02, the base of the crown looks somewhat similar, I mean if we cut the top part of them it seems we'd get a similar section as mine set top, could they be related in design?

I didn't even try checking for interferences with my cyl head because they looked wrong already from a far but maybe I'll try to check by hand.

Edited February 3, 2023 by JohnHarrison

[kbmb02]

19 hours ago, Preyupy said:

The engine might have had a 121 head but the combustion chambers HAD to be modified.  Those are some old school pistons!  look at the rings and the distance from the top of the piston to the upper ring.  Going by the valve reliefs it had a big cam in it as well.  

 

And the skirts.

 

35 minutes ago, JohnHarrison said:

I found these CP Carillo pistons marketed for the 02

 

To the best of my knowledge, any/all pistons with the hemi-cut piston crown require(d) machining of the combustion chamber. If hemi pistons were available at the 'Alpina store' it wasn't a plug-and-play install. -KB

[markmac]

Digging through my pics I found something that looks pretty close to what you have.  I don't recall now where the image came from.  It might be an early piston design Alpina (and other used) and as Ken suggested you would need a full hemi head to do that.  Years ago I had Alpina make me up one, they used a new E-21 head to start, 46mm intakes and 39mm exhaust , port matched my Alpina manifold, 300 cam and matching hemi piston set.  E-21's are the easiest to convert to full hemispherical as most of the work is already done.  The other piston is the one they typically use.  I kept one of the original pistons so that I could get a new set made if I decided to ever go down that road again.  They (Alpina) do nice work, needless to say.

[mac]

+1 what Mark said. 

 

CP Carillo pistons for '02s look like the custom M&N IMSA-RS pistons "from back in the day". 

(Hemi head/high compression.)

 

Mac. 

[m-tuner]

the problem with full hemi heads is you are cutting the most important part of the head away,   the quench area, and you end up with a dome that restricts the flame front and huge valve relief  cuts  and a heavy piston,   basiclly a alfa  engine,  210-220 hp was it with  this set up now m10s are producing  250-260 hp as a 2 liter