QUIOTE:..."""'ll try to keep this simple, but in general, a 3 cyl engine is a very poor idea. """

And yet I read recently that BMW are developing a 3-cylinder petrol and diesel engines for the next generation 3 Series, while Mercedes are doing the same for the next C Class. I think I read that Ford are doing a 3-cylinder for the next Focus too.

These cars I mention are not even models at the bottom of the respective makers' ranges, so there must be something going for 3 pots.

Meanwhile, for those who think that 3 cylinders are too many, Fiat have brought out a 2-cylinder 'Multi-air' petrol engine for the 500. VW too have a 0.8 TDI 2-cylinder diesel engine design which has been used in a few prototypes, including versions of the Up!, I think.

Edited by Sofa Spud on 19/08/2010 at 23:08

. Am I alone in still thinking that there's something in the saying of old-fashioned engineers - 'There's no substitute for cubic inches' ?

Its all about fuel consumption, though, Avant, and the big engines weren't exactly renound for it when used in typical UK driving conditions!

I wouldnt be suprised if the engine has massive problems

That's not debate - just prejudice!

Ford reliability has been pretty good over the last 15-20 years. Co-developing engines is the standard practise these days - it costs too much to go it alone, even BMW shared development of their small capacity petrol turbos with PSA.

The car you drive is (at least) 85% Ford, tweaked by Mazda. Engineering wise Ford are as good as anybody.

So in actual fact the Mondeo is actually around 25-30% Mazda. This may be the reason for the increased reliability between a mark 2 and mark 3 mondeo

The MZR is the best part of my Mk3 mondeo. The engine is strong and reliable. The rest of the car has disintegrated once already (needed new suspension, and I mean all of it) before 70k, clutch died due to leaky slave cylinder, it's had one electrical fire and quite a few things don't work, the driver's seat is busted, the power steering whines and whistles...

My only experience with turbo-charging triples is with modified Triumph motorcycles, the same turbos spool up much faster on the Triumphs than they do when fitted to similar capacity four pots, the dyno charts don't lie, the torque comes in much earlier and they are easier to fuel, you often have to do wacky things at low revs to get the four pots to fuel properly, not so with the triples, the build up of boost is smoother and more linear - they just work better. To get past the lumpy nature of a triple at low speeds as a designer, you make the crank or flywheel a bit heavier and the problem disappears, as four pots often need counter-balance shafts and crank dampers the weight increase is negligable, again Triumphs pull hard from tickover - not a problem. Let's see how well the Ford fairs before passing judgement - the road tests I've read so far are very positive. If I was going to design a small capacity turbo-charged lump I would end up with the Ford design, which was the inspiration behind the original thread.

Throttle response is also hampered by balance shafts and harmonic dampers required on most four pots plus the mechanical loss of another cylinder and assiciaed valve-train - it's all swings and roundabouts. Gasoline isn't ever going to be as efficient as diesel it contains less energy per cc – however it could be close thanks to emissions gear reducing the efficiency of diesels - petrol does have other advantages like burn rates so higher rev ceilings and lower gearing can make up for lack of torque.
The big win if we should switch to small petrols will be the lack of a horrible cacophony of diesel clatter within a 50 yards of a traffic jam! I find the noise of a line of diesel cars almost unbearable.

Whether you can see a reason for it or not, I have witnessed a big difference in turbo response comparing like for like three and four pots. The weird holes in fuelling caused by wieid acoustics creating "stand-off" (reducing kinetic inlet charging) at low revs doesn't seem to happen with three pots either. I've spent hours of dyno time trying to clean up (full)throttle pick up at low revs with four pots – never had an issue with a triple.

I should imagine piston speed determines the rev ceiling of any petrol engine regardless of configuration.

Thread brought back from the dead again for an update.

Manufacturers who have jumped on the small three pot petrol turbo bandwagon since the last update:

BMW, Renault, PSA, Vauxhall - wasn't such silly idea after all! ;-)