Carpokes Porsche Forum

Holy cow, 0.006 seems massive!

And yeah, this block is staying Alusil. Very much a street car, though I'd love to use it for some DE in the future - hardly enough to go crazy over, but I guess the point is I'm perfectly happy letting it come up to temp...

Does all that help or just make it more confusing?!

A little of both
Seems like it will be difficult to go wrong on the 2.0-2.5 side of things, given that's squarely within Mahles own specifications. Unless I misunderstood everything!

I won't dare to comment on the right gap for this combo, but as a longtime follower of various 944 engine builds (including my own), I can remember quite a few motors that self-destructed/seized on start-up or shortly thereafter because of piston to wall contact. I can't think of any that self-destructed because the clearance was too big. My totally unscientific sense it that people err on the side of going too small. They are shooting for those high-precision German specs, but without the same level of measuring or machining precision the factory can muster (and, ultimately, putting a lot more heat in them than the factory anticipated with more boost).

chris white wrote: Thu Oct 27, 2022 2:30 pm you will get piston noise on cold start with about .006" or more clearance

Ah, reminds me of my 1976 Capri II V-6, which was bored and stroked from 2.8 to 3.0. It ran a long-duration solid lifter cam and forged pistons, along with Hooker headers. It was music to my ears, and plenty of it when cold!

OK, so I went and did a few things:

- I found some clearance info for 4032 pistons, and along with a lengthy paper from Mahle (mostly just to corroborate assumptions, it's primarily about piston design...), and material info for both 4032 and 2618. Porsche's clearance info isn't useful, 'cause I've no idea what the original pistons are made of.

Set equal the hot clearance (I don't know the number, because I don't know the CTE of the block, but I do know the CTE of both alloys: 21 and 24.1). To achieve the same hot clearance as 4032 (Wossner, in this case) pistons, you need around 0.09mm less diameter on a 100mm piston. This ends up at around 3.3 thou radial clearance, all told.

- I called Mahle
They were surprisingly easy to access, and willing to walk thru drawings with me. They stuck by their recommendation of 2.0-2.8, mentioning that there was a revision tightening that from 4 thou clearance some 5 years ago.

I've managed to convince and un-convince myself of various decisions along the way, but I'm planning to request 2.4-2.5. I trust Mahle's figures more than my own napkin math, but I'm letting the math decide where on their range I place things. Or something like that...

Still alive! Been futzing with other non-engine things, and other projects, and life

Block's done (whew), just need to take the time to shoot down to Portland and pick it up. Will be dragging along and getting balanced the rest of the rotating assembly, 'cause why not.


Does anyone with more experience (so...anyone!) have thoughts on the aftermarket crank scrapers and baffles available? I obviously have the late oil pan with a scraper kinda cast in, and was planning on dropping in a new Porsche baffle (likewise with the integrated scraper), but figured I'd ask before pulling the trigger.

Similarly, and I think I'd answer this myself if I had the block sitting here: Is it generally safe to clean up the internal oil pump housing face? Mine's a bit marred, and I'm tempted to get a machinist to take it down 10-20 thou to clean things up. Most of the pictures I've seen online of disassembled pumps show some similar damage. It's my intuition that the ring cast in the outer rotor (block side) mates deeply enough with the block that were the rotor assembly to move a small amount forward there wouldn't be any problems, but..still curious.

Finally, picked up some KW V3 coilovers that I'm rather excited about.

IJ crank scrapers in Florida - knowledgeable guy and nice products....can take a while sometimes!
if you use one of those the pan scraper is not important.
the oil pump surface is not an issue - it gets coated with the anaerobic sealer and that can fill any irregularities.

chris white wrote: Wed Jan 18, 2023 12:02 am IJ crank scrapers in Florida - knowledgeable guy and nice products....can take a while sometimes!
if you use one of those the pan scraper is not important.

That's unsurprisingly who I was looking at. Sounds like I should order one asap then! Are you saying forgo the factory plastic baffle if I drop in one of his scrapers? Or would this also require the windage tray he makes?

the oil pump surface is not an issue - it gets coated with the anaerobic sealer and that can fill any irregularities.

I mean the internal surface that mates to the rotor (& apologies for the cruddy picture):


Note the mar that runs the arc between the two geroter mounting holes.

Have you considered oil shedding coatings?

Doing it with my engines as it’s cheap and easy to do myself.

I'm no expert (at all) on oil pumps. When I built my motor, the pump looked like that so I just bought a new one from Porsche. I think it was like $500 back then, but no idea if they are even available any more. I'd be worried about adding too much clearance by machining it, and having it pump less than it should...??

p.s., you'll love the KW's -- they transformed my car....

gruhsy wrote: Wed Jan 18, 2023 12:55 pm Have you considered oil shedding coatings?

Doing it with my engines as it’s cheap and easy to do myself.

I had not really even known it was an option. Do you have any resources? The stuff I found on a cursory search was mostly just services offered.

I'm no expert (at all) on oil pumps. When I built my motor, the pump looked like that so I just bought a new one from Porsche. I think it was like $500 back then, but no idea if they are even available any more. I'd be worried about adding too much clearance by machining it, and having it pump less than it should...??

Yeah, they're about the same price from dealers. Closing in on 2x from other vendors