Daemos

Hello from down under. I am contemplating building a new motor, however, I'd like to use Mahle 4032 low-expansion stoker pistons for low noise, long life and no oil consumption compared to high expansion pistons. This will be mostly a daily driver, so lots of cold starts, and stop and go traffic. The part number I am looking at is: SUB193642I16

I am aiming for around 420-430 bhp on 98 octane and 500-520 bhp on E85 (which burns much cooler than 98 octane)

Not too many shops in Australia have actual experience with these pistons, and the shop I'd like to build my motor, is willing to try.The information I am trying to find out is:
1) bore size as the pistons are 92.5mm, do I need to bore them out larger to compensate for thermal expansion? and
2) Piston to wall clearance for my desired power range.

If anyone could step in and help me out it would be greatly appreciated.

gazney101

iTrader: (5)

Does the clearance info not come in the box with the pistons?
I may have miss read but I remember an engine builder saying that the clearance is in the piston..
Example: a 92.5 mm piston will be something like 92.2 or there about.
I could be way off but that's how I took it

MOTORS S GT

iTrader: (2)

If I was specking an engine to run 520 it would not be 4032 material, I would go with 2618 & run 0.0762mm initial clearance.


You measure the piston skirt & add the clearance you want to run with, & measure all 4 as Mahle are not always the same size.

Daemos

I'm pretty sure that 4032 will be okay. We run factory EJ207 short blocks with ARP 625/RCM Extreme 11mm head studs to 305KW at the wheels (not sure at the crank) on E85 reliability without issue. I'm unsure if the UK gets e85 at the pump (which is 85% ethanol and 15% 98 octane) E85 makes a massive difference, as that would be around 250kw at the wheels on 98 octane.

In comparison, with the 4032 material I'm looking to run a maximum of 320 kw at the wheels on e85 and maybe 260 kw at the wheels on 98 octane.

Would cosworth be better? I know they use a similar material, but i'd hope for the price premium they would be very consistent with their sizing.

JGlanzaV

iTrader: (3)

Cosworth have had multiple failures recently. Wouldnt want it anywhere near my engine.

And for what its worth Motors GT, has built more of these engines than you can shake a stick at. Paul is a subaru guru so heed his advice!

Daemos

For what it's worth I wasn't disagreeing with him. If I was running pure 98 octane aiming for that type of power, 100% 4032s wouldn't be enough. If I was running a pure track car I wouldn't use 4032s either.

On E85 along with flex fuel sensors it's a whole new ball game (again stock block EJ207s + big port heads + ARP 625 11mm head studs) do 305kw atw on E85 no issues for long term reliability. I'm only looking to make a maximum of 320kw atw on E85.

Again is E85 available in the UK? When it first arrived in Australia (at the petrol stations) it allows for cars to be pushed much harder. E85 is 85 percent ethanol and 15 percent petrol. For example, same car, 98 octane allows this car to go to around 250KW atw safely for long term road use reliability...E85 allows extra timing and boost to go upto 305KW atw safely for long term road use reliability. That's 20% more power from running an E85 tune on e85. E85 burns much cooler, doesn't knock, depending on the station is much cheaper/L than 98, it smells better, and it's better for the environment!

E85 does have downsides, you need larger injectors, e85 compatible fuel pumps and fuel lines. And it uses about 30% more volume per kw than 98 octane.

Thanks for letting me know about cosworth failures...the pistons are quite expensive...for $500AUD more than the cost of the cosworth pistons you can get a brand new v7 EJ207 short block!

boosted

I run 100mm mahle high expansion pistons at .003" clearance. They are quite noisy.
I believe the low expansion ones run .00015-.002" clearance.

merlin24

iTrader: (1)

Mahle recommend 0.0025 ~ 0.0033' P/W clearance for the 4032 grade piston but that is only a recommendation and not neccasarily correct for your individual build

Daemos

I have their catalogue from their North American site they state the recommended piston to wall clearance to be between 0.0016-0.0024" for their 4032 grade and 0.0031-0.0039" for their 2618 grade. Wonder if they recommend different values in the UK than they do in North America.



Mahle North American catalogue