Which Fiat Twin-Cam to use: 1756 or 1995?

[mack124]

Hi,

I¢ž¢m currently doing up a Fiat 124 CC and I have been offered a 2.0 ltr Supermirafiori engine at a good price. The question is. Do I stay with the 1.8 with more power and less torque or do I go for the 2.0 with less power and more torque? I am running a 3.9 differential which may suit the 2.0 better?

The other thing is I have a set of twin downdraft webers and manifold off a 124 BC and was going to put then on my motor. Without any other modifications what sort of power increase would I be looking at from either of these engines? Would the 1.8 benefit more than the 2.0 or the other way round?

Any information you can give me would be greatly appreciated.

Thank you in advance for your time.
Kindest Regards
Gill

[Guy Croft]

Hello Gill

sorry for the delay but I am computer-less at my facory unit due to being hit by lightning. All in all it's not my week.

The Fiat TC 2liter is strangled by the OE twin-choke carburettor and struggles to produce anywhere it's full power potential much over, dunno, 5700 or so, whereas with twin DCOE or IDF Weber it will fly past that and peak at 6000 and still pull strongly way past that.

Sure the 1800 has a shorter stroke, 79.2 compared with 90mm on the 2 liter TC - which means that, yes it will tend to produce peak power higher up the rpm band (in like-for-like spec) but for sheer pulling power, it's no contest in my view. If you drove a 2 liter and then an 1800 in the same spec you'd really feel the loss of torque on the 1800.

Remember you get a very finite maximum torque value from a normally aspirated 8v engine, it's related to atmospheric pressure and engine size, 125lbf ft on a 1600, 141lbf ft on an 1800 and 156lbf ft on a 2 liter, give or take a bit for actual swept volume, so if you spend the same money on carbs and head work etc on the 2 liter, you're going to get alot more acceleration for your money.

I like the 1800, did a lot of them in the late 80s for my own 124 CSA as a test-bed, but after years more experience I'd go 2 liter given the chance. People said to me in the late 80s, early 90's, 'oh, you'll never get the 2 liter TC to rev..' Not so, my NHRA 2 liter 8v raced to 9500 every event, and getting them to pull comfortably to 7000 and over is easy - gasflowed, good billet cams, twin carbs.

The power gain from twin 40 Weber IDF is in the order of, say (GC guess, never just dynoed that) 10-12bhp on its own. 44IDF give much more torque than 40s even on the 1800. It's not exactly true that one size engine will benefit more than the other from a swap to twin carbs, except to say that the bigger the engine the bigger the carb and choke can sometimes be. In other worsd, fitting 40s on an 1800 may yield a greater gain proportionately (bhp gained per cc of engine size), than when you fit them on the 2 liter. But I'm not saying rush out and buy 48s, it's not that simple!

I hope this makes sense and is helpful.