The V8 Owners Forum -

Has anyone broken a 3.9 piston?

What did it take to kill it?

How high can they be revved before falling apart?

What are their reliable limits?

Its written in both the rover books and said by many an expert that they're a bit poo howver i don't know anyone thats pushed them beyond their limits via proper tuning and use rather than stupidity if ya know what i mean!

Don't know what revs they'll take, but I've heard that 6500rpm is about their limit.
What I can tell you is this:- John Eales has been known to chuck 3.9 std pistons up in a lathe and skim 0.120" from both the crown and base, for using with a stroker crank to create 4.3ltr engines Personally, I'd have thought this would leave the upper land above the top compression ring a bit weak, but when talking to him on the phone trying to source some pistons for an OLD (read:- very early) 4.3 stroker kit that I have, he told me himself that is what they do
He reckons they've never had one fail after this machining......

My 3500 was running the original 1975 pistons for two years at the Pod, eventually running a 150 shot of gas with no probs. The new build has the same type of pistons, but new ones. The old engine regularly went to 6500rpm and the new one has been dyno'd at 7400rpm on a power run.

I assume the 3500 pistons are probably a lower quality than the 3900 ?

I'll be taking it to the Pod in Jan to start running the 200hp gas system. I'll keep you posted if anything melts!!!

Top ringland is possibly 10mm thick so skimming 3 mm off is fairly safe. They break behind the oil slot, by the pin bosses because they are very weak. 10 psi of boost will kill them off fairly quickly

For a high performance engine you would bin them rather then install them. They aren't a performance piston.

Boosted.