Using 2.2S Pistons on a 2.4S engine...

[g3ngs]

Thanks Henry, I hadn't seem your reply come in and was replying to the message before when I was on my phone earlier this morning.

I'm very happy to take a definitive answer based on experience. Many, many of the threads suggested in the 9.8 and 10.3, though if that is the on paper number adjusted up for the 2.4 crank rather than the real world then I'll take the real world number.

If as you say it's more like 9.3 and then slightly more presumably for the 2.4 crank then it would make sense with arrivederci's experience.

Of the combination you mentioned of compression port size, exhaust, ignition and fuel

If heading down this path the 2.2S barrels and pistons would go in, ignition adapted with the tuneable 123ignition, >97 RON at the pump (in Europe 97 and up and in the UK 98 and up), an exhaust change is potentially on the cards too.

Increasing the intake port from 30 (or is it 29 in MFI as I've read in other places) may be unlikely as I'd rather not do anything that can't be (easily) reverted.

In the main and like you say, it is unknown what is in there at the moment and measurements and maths will be required to assess. When that point comes if suggests that the ports have been modified or things aren't "standard" then it would widen the scope for further change

[stownsen914]

I think Henry's post pretty much says this, but keep in mind that raising compression ratio or installing more aggressive cams won't increase power much if at all if you don't consider the whole package. For example, small ports with aggressive cams may not work well together. In fact you might just hurt low end and midrange performance, and not get much benefit on the top end either.

Re: compression ratio, I've heard that raising static compression with T cams yields high dynamic compression ratio, which can promote detonation (not sure if higher octane pump gas solves this). And by itself, may not offer much performance improvement.

[g3ngs]

Thanks stownsen914, yes this would be a combination approach rather than a throw it over the fence affair.

Despite changing the lines the thoughts on petrol quality is a constant bother and I generally put the highest rated available in. The tunability of the 123ignition might be some mitigation for timing and there are dual wideband lambdas in the heat exchangers with a DLG1 in the glovebox to keep an eye lean / rich.