Fiat/Lancia TC 8V and 16V block strength question

[Guy Croft]

I have a question.

I hear from time to time that Block X is stronger than Block Y. In this case I am referring to 2 liter 16v Fiat Coupe Turbo and Fiat Tipo and Evo 2 Integrale.

I have surveyed both blocks with measuring gear in the regions where I might expect some extra strength and found no difference in any region between any of them other than minor +/-0.5mm to 1mm variation that one might reasonably anticipate from sand casting an SG iron block.

So am I looking in the wrong places? Comments welcome and I will look again. For interest what I can tell you is that in some areas the 131 block is actually thicker than either of those two! I doubt if there is any design difference between any of them in this context but I could be wrong.

Thanks,

GC

[ICI]

...

[Evodelta]

Hello Guy,

It's a subject I've pondered over for some time, I'm glad you've brought it up!

Don't all the block types you tested have balancer shafts fitted? I think they do, I wouldn't be surprised to find very little between them.

As you will know some people use the Croma block as the basis for a performance engine build, the theory is that because it comes without balancer shafts, but takes a 16v head they will be at an advantage because of not having to mess around removing the shafts, blanking off oilways and mainly it will be lighter. My thoughts are that it won't be as strong as a balancer shaft equipped block, simply because (the balancer shaft block looks) a whole lot stronger, it has a shaft retaining casting linking the tops of the bores at one side and one linking the bores at the base on the other side, it just looks so strong, almost as if someone designed it this way when they knew they were going to do battle in the World Rally Championships........

Could you measure the strength difference between these blocks? I assume not very easily and only (probably head gasket?) failures due to block bow under large amounts of boost would point to any inherent weaknesses in the Croma block as compared to the balancer block when used in extreme cases.
Your thoughts?

Martin.

[Walezy]

As far as I know the blocks used in works Integrale had no balancing shafts(the same blocks as Croma). But I may be wrong, this is just something I have heard from a person that had a workshop full of Integrales in London.

[Guy Croft]

Yes, I imagine that balance shafts would add some longitudinal stiffness here and there but not down where it's needed along and perpendicular to the crank axis. It's crank torsionals and their relative effect to engine mountings that fracture blocks. As for block/head interface yes, weakness there could certainly cause problems but there is no problem in that department with any Fiat/Lancia TC (or any other engine I can thinkn of come to that..)

The things you have written are interesting but in order to keep_on_topic (!) I am actually only looking for keynote info regarding metal thickness that springs from a design criterion, thanks.

GC

[SteveNZ]

As for block/head interface yes, weakness there could certainly cause problems but there is no problem in that department with any Fiat/Lancia TC (or any other engine I can thinkn of come to that..)

GC

The redesigned Fiat SOHC blocks of 1988-1993, 1372cc and 1582cc are weak in that area. I had a Fiat Uno turbo Mk2 develop a crack accross the deck, which of course blew the head gasket.

[Guy Croft]

Steve, hi

these things can become the stuff of legend so I want to concentrate on traceable failure mode.
You have had one Uno Turbo block crack, yes? This failure was traced to what fundamental cause?

Massive overtightening of head bolts with head and block out-of-true and of course very severe overheating from cooling system malfunction/detonation/high back pressure can crack a block, I have seen it once on a TC 131 unit but that is not what I'd class as a design weakness.

The Vauxhall 16v XE block is very weak compared with the TC Fiat eg. I mean nowhere near as strong. Flimsy, even, by comparison. But I have no report of a failure in any one I've been involved with even at very high levels of tune (265bhp plus and over 8500 rpm) in very arduous duty.

GC

[SteveNZ]

Steve, hi

these things can become the stuff of legend so I want to concentrate on traceable failure mode.
You have had one Uno Turbo block crack, yes? This failure was traced to what fundamental cause?

GC

Yes I had 1 block fail. To be honest, I did not investigate the cause as I just accepted it to be one of those things. I knew cracked blocks were a problem on these engines. I saw another 2 do the same and have read about many other occurrences on the web. This problem is far from rare.

For the record, the rest of my engine was in very good order. With a basic visual inspection I could not find any problem. I have a complete history and the only mechanical issue with the engine at all was a leaking frost plug that was replaced when the car was about 6 years old.

I was interested to find out why these engines do this. I have heard many theories but none are plausible in my opinion. I believe the blocks have a design problem. Fiat redesigned the blocks again for the Punto. 1.4 and 1.6 blocks now had a honeycomb rib cast into the rear of the block. They also had smaller frost plugs. Maybe they made the block thicker too. I have never checked that. Whatever they did worked, cracked Punto blocks seem to be very rare. The earlier blocks are also very reliable, I have never heard of a similar failure.