Forged pistons on standard rods?

So my engine failed a compression test and I'm 99% sure it's the piston rings and a scabby cylinder that is the cause.

Full story here:

Trying to turn failure into a silver lining im leaning more towards a rebore and oversized pistons (I also then have some more aggressive cams gathering dust).

All the overbore options as forged so, and with the cams and headwork I can take the power higher but don't really want to splash out on forged rods as well.

Is that a terrible idea? How are the standard rods in these engines?

In for a penny.

PS you can get oversized non forged pistons.


But it will take some searching.

Flob said:

In for a penny.

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That phrase will be the end of me!

Flob said:

PS you can get oversized non forged pistons.

PISTONEs MAHLE FR4 CLIO 172/182

gtt-store.es

But it will take some searching.

Click to expand...

Ooo plot twist, the question then will be is the power gain worth the difference in price...

You can get those Mahle O/S pistons on autodoc for £100 each delivered, they're also advertised on eBay for £79 each

The part number is 021 PI 00117 002 for the +0.5mm set.

So you're going to be into it for circa £400 for a set of OEM spec pistons, and depending on where you go, around £250+vat to get four cylinders bored, honed and the deck refaced.

That's a lot of money when you can get a good 172/182 bottom end that just needs a deglaze and set of rings for a couple of hundred quid.

Not sure if this is helpful info or not 🤷

I've got forged high comp pistons in mine -standard bore size - standard cams & rods with ARP bolts making 191bhp 168ft/lb

I'm used to dealing with mk1's but the F4 rods are a bit beefier in comparison and are basically an upgrade. So they're well up to the job on their own
Adding a set of ARP rod bolts is all I'd suggest for extra peace of mind, no need for forged rods unless you want to go mental with cams & itb's etc

Just for added context, I got my pistons pretty much for free (complicated man-maths was involved) and got a load of other expensive bits & bobs for the rebuild at ridiculously cheap bargain prices and even with the bargains I'm still well over £3k deep into it and that was before the mapping.
I dread to think how much your build is going to cost if you're buying oversized pistons plus the machine work 😳
As mentioned above, compared to a used replacement bottom end it does seem a bit mad to go down that route

I agree, it could be done as cheaply as possible, and don't get me wrong I am not completely decided on which path to take. However in my head it will be very disheartening to spend the time pulling the engine to change the block and getting a new one honed and some new rings only to be exactly back where I started. I would sooner spend a bit more to see some gain in the work being done. Perhaps that doesn't make much sense financially but this is also meant to be a hobby that I enjoy doing.

So I feel like I am looking at two options:

Option 1
New block, honed with 197 pistons and new rings - I think this should end up around £500 and a mild gain over what it would have been

Option 2
Current block rebored and forged pistons - £1000 - would also mean I can sell the 421 cams I have (basically new) to recoup some of the loss and use the 422 that I have never been able to sell, that will bring the difference down a lot, also I will then be left with a stronger engine that has more value if/when I come to breaking the car up, also more power compared to the above and current.

I probably am being a fool here but none of us get into tracking these cars to be fiscally responsible! 🤠