Reshaping Combustion Chamber to lower CR (Fiat 1368cc 16v)

[kritip]

Hello,

I have a 16v 1368cc Fiat superFIRE based engine. (Found in most modern (>~2003) 1.4L petrol Fiat's)

83mm stroke
72mm bore
CR of 11:1

It is not an easy engine to modify, hydraulic lifters that would be a big problem to change, inability to easily change the cam timing, etc.

I am looking at possibly turbo charging this engine in the future. It's my own personal car, and I'm just a hobbyist.

To lower the CR, the only real option in my budget is a copper decompression plate, or removing material from the combustion chamber. I have not measured the true CR yet, but assume it's very close to the manufacturers specification.

I have a spare head, that is of little use due to a different intake stud pattern, so with a dremel, I would like to see how much I can reshape and remove from the chamber.Do you have any tips or advice on this matter? Or is it a big no-no?!

The pistons are already dished , cast aluminium. Can material typically be taken from these as well?

Here is a photo of the combustion chamber:

Fiat 1368cc combustion chamber

P1000161.JPG (77.38 KiB) Viewed 4584 times

Thank you for any help, ideas and advice.

Kristian

[Guy Croft]

OK.

You'll never get the CR low enough by modifying the chamber, and as for fitting one of thes so-called decompression plates you'll lost all the squish - which is worth keeping esp on a blown unit because it inhibits detonation and improves burn. Moreover never run n/a pistons in turbo applications. Turbocharged pistons MUST have thicker crown and heavier ring lands on top and second ring. Decompression plates are for users who won't buy the right pistons for their application and no more than that. And, there is no shortage of forged piston manufacturers who can make the right configuration for you if you are prepared to pay them to do it.

Most - incl you Kristian - I am sure, are keen to learn and that's where I come in. So I will just say - but for the general edification of all readers - I try to coach professional methods here - even if it takes me hours (and how it does..) and brings me nothing in return. Attempts to build any engine without due care and attention to professional methods - in my long exp - always leads to disaster - on turbocharged gasoline engines more so than_any_other_kind.


GC

[Walezy]

My friend has made such conversion in his Fiat Palio 1,2 16v engine and what happened after few months of road use was that the crankshaft was bent. I can imagine that this is hard to belive but the timing marks on the flywheel and on the crankshaft pulley did not match at all. After replacing the crankshaft it was fine for some time, later the car was sold so I do not know how long it lasted. It had something about 0,7bar pressure. As far as i remember he had some decompression plate but I am not sure right now as it was about 5 years ago.