Looking for an engine builder who’s a fan of the factory design*

[IamFODI]

Spoke with someone at Mahle Motorsport today about the POWERPAK pistons for the S65. Really cool convo.

As I understand it, these pistons were designed around a 750 hp target and no emissions targets. With that in mind, one goal was to keep the top ring as far below the crown as possible. They expect this to extend the life of the top ring (I may have missed other benefits in the convo). The main downside is that there's a bigger zone above the top ring where byproducts can accumulate; theoretically, this might worsen the emissions profile (I get the impression they didn't bother to find out).

That increased distance between the crown and the ring is the reason for the slight CR increase. They figured the distance would be big enough to help and the CR bump wouldn't be big enough to hurt.

I'm not concerned about a slight increase in this car's emissions, but one thing I would care about is if the cats degraded more quickly. The rep didn't think that'd be a significant concern, though he was careful to say that wasn't his area.

Another thing I'd care about is if those byproducts, combined with greater blowby, degraded my engine oil more quickly. To this, the rep responded by expressing great confidence in the rings they developed and how well they work with Alusil bores.

Writing this, I'm now also wondering if that top ring might have a greater tendency to develop carbon buildup vs. the stock design. I'd care about that, too – though there's at least a potential solution out there (combustion chamber cleaning fuel additives).

Overall, I'd still prefer a good cast piston, but I'm really seeing why Partee likes these pistons for some applications. If I had to pull the trigger right now, I think I'd be sold on these.

[omgzirra_exe]

just WPC the rings.

[IamFODI]

Originally Posted by omgzirra_exe

just WPC the rings.

Do you think that'd reduce carbon buildup?

[THEROK]

I bought a 10K mile 2011 M3 from EAG and have piled on 1.8K miles of my own. For all I know given its observed state of condition, it's been very well kept.

Yet I wouldn't mind that 5% added engine alacrity, that 5% additional power without sacrificing the no nonsense quality of a healthy stock S65. As they say a bird in hand is better than two in the bush. But I can't help but wonder if I can have my S65 cake and eat it too.

Great thread!

[IamFODI]

Originally Posted by THEROK

I bought a 10K mile 2011 M3 from EAG and have piled on 1.8K miles of my own. For all I know given its observed state of condition, it's been very well kept.

Yet I wouldn't mind that 5% added engine alacrity, that 5% additional power without sacrificing the no nonsense quality of a healthy stock S65. As they say a bird in hand is better than two in the bush. But I can't help but wonder if I can have my S65 cake and eat it too.

Great thread!

...Small but nonzero chance I could help defray the cost of a rebuilt engine by buying your factory one. LMK...

[omgzirra_exe]

Originally Posted by IamFODI

Do you think that'd reduce carbon buildup?

it would probably prevent carbon build up from sticking.

[IamFODI]

Here’s a minor wrinkle: Increasing the distance between the piston crown and the first ring can reduce power as well. This is because it increases the volume of the zone around the piston where the air-fuel mixture can't burn efficiently and usefully.

https://www.enginelabs.com/engine-te...le-motorsport/
https://www.enginebuildermag.com/201...r-of-a-piston/

I don't get the impression that the stock piston has a super high top ring, and I feel like I remember hearing from the guy at Mahle Motorsport that their POWERPAK pistons for this engine only lower the top ring very slightly. So, this effect is probably insignificant in this case.

It is, however, yet another illustration of the fact that every design decision by a competent OEM has at least some good reasons.

Don't think this moves the needle on any decisions I'd make – i.e., if I had to pull the trigger right now, 99% chance I'd still go with a Partee build with POWERPAKs. But I might dig into this aspect further, if only to learn more.

[omgzirra_exe]

Originally Posted by IamFODI

Here’s a minor wrinkle: Increasing the distance between the piston crown and the first ring can reduce power as well. This is because it increases the volume of the zone around the piston where the air-fuel mixture can't burn efficiently and usefully.

https://www.enginelabs.com/engine-te...le-motorsport/
https://www.enginebuildermag.com/201...r-of-a-piston/

I don't get the impression that the stock piston has a super high top ring, and I feel like I remember hearing from the guy at Mahle Motorsport that their POWERPAK pistons for this engine only lower the top ring very slightly. So, this effect is probably insignificant in this case.

It is, however, yet another illustration of the fact that every design decision by a competent OEM has at least some good reasons.

Don't think this moves the needle on any decisions I'd make – i.e., if I had to pull the trigger right now, 99% chance I'd still go with a Partee build with POWERPAKs. But I might dig into this aspect further, if only to learn more.

i would probably say it is negligible, just like how oversized Rod Bearings / Main caps do the same thing, you probably wouldn't want to run a combination of both as oversized either. if it was me, i'd probably do oversized mains and std rod bearings.

[THEROK]

Originally Posted by IamFODI

...Small but nonzero chance I could help defray the cost of a rebuilt engine by buying your factory one. LMK...

What's the going rate for a 12K mile S65 these days?