rod and crank bearings for 3.0

[dougallen]

building a street 3.0 litre. pmo 46, mod s cam, j and e 10.4, electro twin plug. have stock crank. question is do I boat tail crank and add groove to center and what brand of bearings should i use?

[KTL]

For the recent racecar engine build I went with GT3 rod bearings (996-103-121-94) and std. Glyco mains. A lot of the pros here say that the non-Porsche dealer main bearing sets from Glyco leave a bit to be desired in terms finish. They often have to buy multiple sets and piece together a nice set. So they've resorted to buying dealer direct instead.

I don't have the experience to visually ID a less than perfect main bearing. So I looked closely at my Glycos I got recently from Pelican and all seemed in nice shape. A few of them had a feeling of sharpness along the outer edge of the bearing. Otherwise they look good.

I recall Mike Bruns @ JB Racing saying that he's seen some that looked like they were cut with a jigsaw. Other posts from people showed bearing wear that looks washboarded and it was suggested that was a bearing quality issue, not a mechanical engine issue causing the washboarding. So the consensus was to go with bearings from Porsche directly because their quality selection results in a better set of bearings.

Boat tailing the crank (actually knife-edging) is good for reducing weight more than helping with windage losses. Since the Porsche crank is not basking in oil and thus the crank counterweights aren't passing thru a pool of oil, it's more lightness benefit than windage.

Are you thinking of grooving them all? Typically #4 is grooved and the supply hole enlarged when you cross-drill the crank. But just grooving them isn't going to hurt anything. For instance, Supertec grooves their own custom made GT3 cranks. They groove the crank surfaces because then you don't need to have bearings grooved every time they're replaced.