ironbrew

OK. Still digging (thanks Mike) but... will be doing an engine shortly. Want to choose pistons so I can confirm 10 thou over is good enough or do I need 20 thou.

What is the difference between the Mahle 480 marines and the cummins qsb 480 marines? Is it enough to choose one over the other? I'm looking for durability long haul, not stupid power...

Do the injectors for these need to be the 03/04 nozzles (this is for an 04.5 engine)? How much gap in the oil rings?

Thanks

dvst8r

-20 thou over is the first size up in pistons.

-I'm not sure anyone could give you quantitative proof either way. That being said I typically use the cummins stuff, but probably just for ease of access then anything.

-Yes 03/04 spray pattern in the nozzles.

-I have never changed the gap that comes out of the box on the oil control ring or the second ring.

morkable

Mahle actually makes the cummins pistons. The QSB pistons get an additional heat treatment that the Mahles do not get.. other than that they are the same.

dvst8r

Which according to Cummins makes them ~20% stronger. Not sure if it marketing hype, or truth, or if it is even quantifiable over a pistons life. If you are not going all out in power, even stock pistons do fine. I have seen a number of million mile pistons, just depends on your goals.

ironbrew

Well, initially it is going to be relatively mild, balanced and smarty being the main things initially. If I have it open though... I might as well look at what I should be doing. Are you saying just stick with stock pistons (or Mahle equivalent) if I'm never going to be going huge power?

Mike Holmen

Remember that the QSB 480 marine is based on the 03/04 CR bowl. Use the 03/04 nozzles.

I prefer monotherms myself. Those things are a piece of art. I want a set for my 6.7L build. There have been a few papers on steel piston strenght vs. cast aluminum vs. forged pistons. Steel pistons are about twice as strong.

Steel pistons can take nearly twice the amount abuse (cylinder pressure/shoke loading) vs. a cast piston. Good idea for guys that typically break stock pistons in half using lots of timing/NOS.

I'm with Brett, I prefer cummins 480 marines, not saying buying directly from mahle is wrong. Hard to beat buying from cummins. We did a few engine builds buying pistons from cummins vs/ mahle.

We had the pins tight on a set of 24VP pistons mahle. Cummins has been perfect and has work flawlessly each and everytime.

I personally would also run 12V rings vs. CR rings.

dvst8r

That is a hard one to answer. It depends on your cheque book, is the best answer I can give.

I have seen 06 pistons look brand new after almost 500K when the top ring finally seized, and I have seen melted ones with 20K on them after someone tried to stack boxes, and run big injectors without knowing what they were doing.

My feeling is the Cummins QSB pistons are the strongest, best piston you can buy, without going to a forged or steel piston. Problem with forged is they do not last for high mileage they are meant for big horsepower race vehicles. As they do not have the steel keystone top ring land.

IMHO the order of strength for a CR piston goes like this:
-Monotherm


-Forged
-Cummins QSB
-Mahle / all stock truck CR pistons.

Yes I left that gap there purposefully, it is to show how much better they are.

Mike Holmen

I was reading a interesting article on pistons. Kolbenschmidt have piston designs that use a steel composite bowl/crown and a steel skirt piston. Suppose to be able to endure peak firing cylinder pressures of 210-250bar. Aluminum cast pistons are around 130-190bar. Also had some interesting graphs showing oil flow vs. cylinder power (steel have more oil flow requirements, than aluminum). Ring gaps vs. cylinder pressure, ring stress(strain) vs. cylinder/piston clearnace.

I was quite impressed with the amount of research that has been done on piston design and the amount of R&D that goes into the design.

The highest stress point in the bowl is the middle of the bowl (high point), followed by the round crown outside area of the bowl. Some neat piston temperature breakdown graphs.