704cc watercooled engine rebuild forged internals turbo injected etc.

[Craigp018]

Hi, I'm going to rebuild my 704cc watercooled Fiat 126 BIS by FSM 2cyl 4V OHV engine.  Can anyone help by suggesting or naming where I can find the forged internals from (pistons etc.)??  I'm thinking of reboring it as I want to make as much power as I possibly can.  I'll also resleeve so that I can get that 2mm out of that rebore (pictures included).  Also, can I run this Abarth crankshaft? (pic included)  I know it's a bit costly and the project is going to cost a lot of money and it's not easy but I'm quite determined and have the necessary time to proceed this project.  The injection is not that much of a problem I'll get it sorted out for sure my only problem right now is from where can I find the forged internals or order custom ones (pistons, conrods etc.)??  The main reason why I'm concerned about forged internals is becuase I'll turbocharge the engine later on, throw a pooload of boost at it, race it till I break it and after that I'll fit a motorcycle engine instead, however, I don't want to skip the step of modifying the 126 BIS's standard engine to the brim and giving it a go for what it's got.  Forged internals are my only problems right now as I have no idea from where I can find them, I'll appreciate and be more than glad if you can help me, I also live in Malta so ideally whoever has or does them could ship them to  me

[1973/126]

 I wouldn`t do it.
 The cranks on these cars is a real weak point with a two bearing design. There is a member on here - Smallcox who has a turbo-ed air cooled 126 and he has broken two cranks including a brand new one.
 You could probably run it with some sensible boost, but anything radical would destroy the engine.

 I don`t think you can use that crank in the picture in a bis. Looks like a higher stroke crank.
 They do forged con rods for air cooled cars which would be the same as the bis.
 Pistons would be difficult as they are shorter than the a/c ones and I haven`t seen any aftermarket pistons for the bis.

[Gadge]

I may be able to help you with some info. Last year I built up a BIS engine with a view of doing some fast road modifications using aircooled tuning parts. I did this partly because the opportunity presented itself and partly because I was curious to see how and what parts could be carried over.

I first looked into re-boring the liners as I found some forged 500 Pistons that would've increased the capacity to 750cc (800 was also an option). The problem with re-boring BIS liners is that they are actually quite thin - around 3.5mm - and something like 2.5mm needed to be bored out at least to gain the capacity needed to fit the Pistons. So the only way to do it would be to buy/have made liners to suit. Now that's no big deal as an engineering shop could do this BUT the block that the liners bond to will also have to be machined out too and there's not a lot of metal down there to remove. Basically Fiat seem to have reached the maximum capacity already so I looked at the crank.........

Another way to increase capacity is to have a longer stroke and sure enough a forged long throw crank from an aircooled is available (around €1000) however even this idea isn't easy either. If you remove the crank case of a BIS you'll see that space is VERY tight! The crank weight - that's the big part in the centre of the crank - passes very close to the camshaft, the oil pump drive and the crankcase. You'll notice that the crank weight has a thin ridge on it that goes around the bottom of it. That's there because the crank weight passes so close between the bottom of the cylinder linings. Now that's not to say it won't pass but for €1000s I wasn't gonna take the chance. In the end I fitted just lightened rods (maxspeed) and a lightened flywheel. A forged crank to standard spec is avalable so in my opinion if money isn't a problem then perhaps all the internals (rods,crank,pistons and flywheel) can be changed for lightened items but capacity increase I'm afraid would be realisticly impossible.

I know absolutely nothing about turbocharging a 126 but again in my opinion wouldn't be worth the effort unless your really bored. Thses engines don't rev up particularly quick so I imagine the turbo lag would be so great that it'll all come at the top end of the Rev range just as your changing gear so pretty useless. People forget just how big turbos are so you also have to consider where the turbo will go. You need to find the space next to or below the head to fit them then route a suitable pipe to an exhaust box. Not an easy think to do I imagine.

If it were me i'ld just stick with mildly modifying what you have. Thses cars are not slow they will keep up with traffic and will do 90mph if in fine tune which has to be fast enough surely??