6.2L Pistons... Anodized?

[More Power]

Does anyone know with certainty whether or not the 6.2L pistons were ever or are now anodized?

Way back when, Banks indicated in their Sidewinder turbo kit instructions that we should limit the 6.2L EGT to 1100 degrees F because the 6.2L pistons were not anodized, like the later 6.5L pistons. The 6.5 can handle 1250 (when measured before turbo) for the time it takes to pull the longest grade with any rated load.

I suppose another question for the engineers out there, is whether anodizing actually helps reduce heat absorption or makes the pistons more durable? And to follow on, which is better - ceramic (the ceramics we've read about being used on the 6.2/6.5 pistons) or anodizing?

There is a significant power difference between 1100 degrees and 1250.

Jim

[Robyn]

Jim
I have looked high and low for 6.2 pistons that have the coated crowns and have yet to find any.
I know that the specialty houses will do the ceramic coatings for a price.

I have a grizzly reminder of what the excess heat can do to the pistons though.
A 6.2 piston sitting here with a neat little hole burnt right through just north of the exit on the precup.

Yup right on through.

I have seen a few stock 6.5 pistons melted in the same fashion too.
I dont know what the black finish is on the stockers but it resists marking by a scraper when cleaning the crowns off during a rebuild.

I think the ceramic coatings that are done aftermarket are most likely of a higher heat resistance though.

I called all the major piston makers and inquired about coated 6.2 pistons and none had any offerings.

I am of the opinion after seeing several turbo'd 6.2's melted in this way that keeping the injectors in top shape with a good spray pattern and proper POP is absolutely necessary to keep from "torching" a piston.

The last toasted 6.2 I tore down had this and I took the squirt from the bad hole and tested it.
Very low pop with all sorts of dribbles and it peeeed more of a stream than spray.

My personal take is that many 6.2's got fitted with an aftermarket turbo and the overall health of the engine may have been of dubious quality which results in poor perfornance and ultimately a "crispy critter".

Even with a coated piston the above scenario could play out easily due to a poor burn.

Just my thoughts

Robyn

[More Power]

Thanks Robyn....

I recall talking to a member several years ago who did an informal test of his own using a blowtorch and one-each of a used 6.2 & 6.5 piston to see what their heat tolerance was. He mentioned the 6.2 piston melted through much-much faster... So, this informal test of his would indicate a coating of some sort that really did work.... :)

Jim

[Robyn]

Yes indeed
The black coating GM used sure does help.

I am suprised that the piston manfactures have not hopped on the bandwagon with coated pistons for the 6.2.

Probably not worth the $$$ to tool up for it considering the fact that the 6.2 is fast becoming a dynasour.

Robyn

[MaxPF]

The black coating is a hard anodized finish. Anodizing is nothing but aluminum oxide (Al2O3). It actually conducts heat quite well as far as ceramics go, but it is still a poor conductor of heat compared to aluminum (aluminum = 237 W/m*K, Al2O3 = 35 W/m*K). So, it does act as a thermal barrier. It also puts compressive stress into the aluminum which, much like nitriding steel, helps prevent cracking.

I got a quote from a place here in Phoenix to hard anodize the crowns of my Mahle pistons: $300 for the set of 8.

[ThePIGSmith]

I've been studying this topic and am seeking an answer.
Should an enthusiast with a '93 model 6.2L motor install a turbo kit, either from Gale Banks or OE 6.5L parts
without first considering replacing the pistons with this Anodization?
Would pistons without this protective coating limit the amount boost and thus power?

[MaxPF]

Mahle's catalog doesn't show any 6.2 pistons with anodized crowns. If your 93 block is a 599 casting you can overbore it to 6.5 std size and use 6.5 turbo pistons, which ARE hard anodized. Another option, albeit pricey, is to anodize the croens of the 6.2 pistons. This is tricky since the pistons must be masked off with parrafin to avoid anodizing unwanted areas, as well as having the acid bath attack the niresist ring land insert. The anodize should cover the crown out to approx. 3/16" from the edge.

Personally, I would simply run it as is. Lack of anodize doesn't limit how much boost you can use - that is limited by compression and how much firing pressure the engine can withstand. The hard anodize on the crown helps the pistons tolerate high EGT excursions. As long as you keep your EGT's within reason there shouldn't be a problem. A charge air cooler or water injection will definitely help keep EGT's to reasonable levels. People have said that the 6.5 piston has a thicker crown, but I have seen no evidence to support this. The only difference, besides size, appears to be the hard anodize on the crown.