Bob asked a question on Friday. The question is why the Fiat 130 V6 motor was not used in the Lancia Thema instead of the 90 degree PRV6.
I will quote the comment in full: “What were the limitations of the 60-degree Fiat 130 V6 that prevented it from being mounted in FWD applications like the Thema / Croma (and Gamma) compared to the 90-degree PRV V6, let alone from receiving further development like later versions of the related Fiat 128 SOHC 4-cylinder engines?”
Let us take as our text the wise word of Wikipedia as a starting point. The Fiat 130 engine had its roots in the what is called the “128 type A” motor, which seems to have been designed at about the same time.
That 128 engine was an in-line four with an iron block and aluminium cylinder hear with an SOHC; the camshaft was belt driven. (So – is that assertion true, that in in-line four can be used as the basis of a V6? I don’t know enough about this but I feel the answer is no. Let’s move on.)
The Fiat V6 was a cross-flow V6 with a 60° vee angle, twin-overhead camshafts and a toothed belt like the L4 128 engine. The engine underwent development and increased in capacity to 3.2 litres. That’s the engine which Lancia might have used. The 2.8 litre engine achieved 140 bhp which the press considered insufficient.
Off the top of my head the 1969 car managed about 22 mpg. The enlarged engine managed 165 bhp and at least similar fuel economy. The Fiat V6 also drove the rear wheels and had its exhaust pipes mounted on either side of the centre line, leading me to imagine longitudinal mounting.
So, that’s the Fiat V6.
Let’s turn to the PRV as used in the earlier Lancias. Like the Fiat engine it was originally deployed in rear-wheel drive cars so that maybe means it doesn’t matter for an engine which wheels are to be driven. Plus: The 90 degree engine could be shorter and lower (says Wikipedia) so it takes up less space. Negative: the uneven firing order of 90 degree engines has to be addressed by “split crankshaft journals to create evenly spaced ignition events.
Wikipedia alleges the initial version of the Lancia PRV6 has these characteristics: It produced 148 bhp, less than the Fiat’s later iteration. The torque produced was 181 lb ft, nearly the same as the Fiat. The Lancia produces its max torque at 2700 rpm versus the Fiat’s 3400 rpm. Something tells me that the PRV thus produces at least as much power as the Fiat engine but earlier – that means it gets through the gears faster, if my engineering knowledge is not all rubbish.
The Thema weighed 1300 kg. The end result is still a miserable 22 mpg average fuel consumption, even with the lardy 1600 kg Fiat 130 saloon. The PRV weighed about 150 kg; I could not find a figure for the Fiat engine.
The Thema V6 had a nought to 60 speed of 8.2 seconds, one second faster than the Fiat.
All in all, the case for the PRV is not outstandingly clear: marginally more torque lower down, acceptable fuel economy, acceptable performance and a compact size. Perhaps the main argument going for it was that it was in production whereas the Fiat 130 wasn’t. The tooling was probably scrap by 1984. So, Lancia was able to benefit from economies of scale. That, more than anything else, I feel was the deciding factor along with the details that it was a marginally better engine.
(Author’s note: Be aware, gentle readers, that I wrote this late on the night of Friday the 25th of January without having the chance to read answers to Bob’s question. Then I went off for the weekend having scheduled this for today. Maybe in the interim better answers will have been proposed – I have not been able to accomodate them at present. This is my bid, for what it is worth).