6.9 Piston Weight

[Oversize]

Anyone know or able to measure the weight of a 6.9 piston? Faced with a rebuild, would one be well advised to souce custom hi compression pistons made from lighter high strength modern materials? Would such a mod allow a M100 to rev higher and more quickly?? I remember reading a while ago about max piston speed that MB engineers were faced with during 6.9 development. Obviously they were concerned about durability and the pistons not coming apart but with that comes increased weight. Was the weight the main factor in the rev limit?

I heard 6.9 pistons also have an iron band for a reason unknown to me. Has tech & materials come far enough now that there's a better alternative to standard pistons?

I'm thinking of changing pistons in the future on an Aussie engine, but retaining stock rods.

 

[motec 6.9]

Have it somewhere . Old pistons are sitting in my brothers garage in Perth. But they are attached to the rods. From memory they were close to 900grams where quiet heavy forged pistons rods are beefy as well. Only other person I know with them sitting around out off engine has a few in W.A

 

[Oversize]

900g is almost 1kg! That's almost 8kg of weight spinning back and forth at 5K RPM! It has also been suggested by a clever person we could ask a part supplier! To be continued....

 

[motec 6.9]

Give an idea my cast 292 Chevy pistons are 920 grams. Forged Ross 250 pistons are 488 grams . Forged 292 were around 580 something. That's why 250 pistons but need longer rods to use.

 

[Oversize]

Apparently 6.9 piston & rod complete is 2220g?? Does that sound about right?

 

[motec 6.9]

Yes picked mine up like that and they are quiet heavy . built like rods from a Hemi .

 

[Oversize]

That's nearly 18kg of rotating mass not including the crank & torque convertor! Yikes...

 

[motec 6.9]

Crank well at a guess its over 40kg probably closer to 50. As I said standard cast pistons for a 292 Chevy 6 are over 900 grams thats why I went with 250 forged at 488 grams.

 

[Oversize]

Here’s a newly arrived high compression piston for my mate Colin’s engine. Valve reliefs yet to be cut. The only difference between the standard low, medium & high compression pistons was the depth of the concave dish on the piston heads/crowns. So this engine will contain pistons that have a higher ratio than the standard Euro pistons. Estimated to be around 9.5:1 but will hopefully have a more accurate figure when assembly begins.

 

[Oversize]

Oh & I’ll try to get the weights of old vs new....

 

[c107]

Are you going custom rods too, or just Pistons?

 

[Oversize]

Just pistons & I heard today they’re a similar weight to standard but I find that hard to believe

 

[Styria]

Has anyone brought all of this to a satisfactory conclusion ? I recall an "unmolested and untouched" 6.3 engine. on a Ch.109 I was restoring. Now, this is original and gospel - No.2 and No. 5 (as viewed from the front) had four ring pistons, as opposed to the other six that had three ring pistons. The four ringers were heavier than the three ringers, but there was also considerable difference in the weights of the conrods they were fitted to. Yet, when all eight were weighed individually, there was no difference at all in weight between the types of assembly used. I swear to the best of my knowledge, that engine had never been touched. I purchased the car as a write off from the GIO auctions when they were conducted at Waterloo. I only went there to purchase a Motor Bike, but finished up with the 6.3 plus two Rover 3500s. Regards Styria