What is the maximum safe bore diameter for the 20VT engine. The pistons I had fitted had a bore of 3.267" (83mm) and a clearance of 0.0030".

The bores are scratched and a hone might not be enough. Can they be made any larger?

Thanks

John

I think you can go 84mm absolute max but you need a custom headgasket as the standard one will protrude into the bore. If you already have 83mm pistons then I suggest you get another block, or worse case re-line the block you have.

I think Barbz went to 83.5mm, certainly is the max I have ever heard of on a 20vt.

Thanks. I checked with Barbz and you're right 83.5mm is the maximum. Requires a longer running in period with mineral oil.

John

so what cc will that take you to?

Have a read at what JohnS says:
http://www.fiatcoupeclub.org/forum/ubbthreads.php?ubb=showflat&Main=39984&Number=499824#Post499824

But if your block need boring and you already have pistons in 83mm what are your options?

Maybe I missed it, but what was the damage to the pistons? If they’re re-usable isn’t it a better bet to ship out a replacement block from the UK and bore it out to match the pistons you already have? No idea on prices but I’d *guess* that might be cheaper than getting replacement pistons when the block is going to require some work anyway?

Piston's are FUBAR'd, check coupe chat for pics of the pistons

Seen it now. At least they'll make some interesting paperweights......

WOW just saw that thread. That’s some serious det. Do you know what/how that happened? I know how you feel as my pistons also got messed due to incorrect clearance and incorrect DTA ECU timing. Looking at the damage I would say you better start ordering another block, I wouldn’t gamble an 83.5-84mm overbore.

The timing was okay. The first thing Lightspeed did was check the ECU signal with the timing mark on the timing pulley.

I agree, I don't think I want to risk an 83.5mm overbore. If the honing doesn't remove the scores then I'll talk to the builders about sleeving. Otherwise I might be able to get a friend who's moving here to put a spare block in his container!

John

Better make it two to be safe

The place i use for rebores has the abilty to check the thickness of the walls on each bore before they are bored out

The main resaon for this is they do off-set boring as cast blocks all suffer from some sort of core shift, and this gives you the benifit of putting the bore dead in the middle of the bore casting.

Normally its not worth worrying about but if you are going to the outer limits of the bores then this can be quite helpfull as you will always get an equal thickness wall around the bore.

Also it will tell you before you have payed out for rebore if the block will go to that bore or not.

Not to mention finding out once the engine is fitted and running


Ricky

Last time I asked, CarlT was selling standard 20VT blocks for £125. So, if you can get it shipped to you cheaply, that would be your best option.

83.5mm is fine IMO but anything more is not. I would run 83.5mm all day long and it would probably be my preference of size. The Stilo oversize is 83.4mm btw and the 83.5mm CP pistons require a bore slightly under 83.5mm.

I would not sleeve the block as the process takes a lot of the strength out of the block. If you have to sleeve it then make sure you use a strong liner designed for high power cars, like some of the nikasil liners. I'm sure it would work out cheaper to ship a block over than to line it as well...