RE: New Ford Fiesta ST - official!
Discussion
Interesting article on "Rev hang" here: https://www.carthrottle.com/post/rev-hang-explaine...
Seems to be an emissions thing. Perhaps the new sport mode(s) will enable drivers to selectively disable this annoying "feature".
Seems to be an emissions thing. Perhaps the new sport mode(s) will enable drivers to selectively disable this annoying "feature".
gweaver said:
RumbleOfThunder said:
I noticed the flywheel thing on the BMW video further up the page. Takes an age for revs to drop down again.
The Ford 1.0l triple has a counter-weighted crankshaft pulley and flywheel to balance the engine. Somebody posted above that one of the engineers stated the lack of internal friction is what causes the revs to drop slowly, so not the flywheel.The BMW 1.5l triple has a balance shaft, so presumably doesn't need a counterweighted flywheel or pulley.
No idea what Ford have done to balance their 1.5l triple, but unless they've deliberately engineered it so the revs decay fast, I guess it'll have the same issue as the other two.
blade7 said:
Onehp said:
0,5l displacement has long been cobsidered ideal,
Say what...Edited by Onehp on Tuesday 28th February 03:28
VeeFource said:
This doesn't make sense to me as engine braking is primarily a function of swept capacity vs the inertia of the the moving parts (especially the flywheel) with the frictional losses of the engine being relatively marginal. Parallel twin motorcycles are very free-revving because they don't have much in the way of a flywheel despite even fewer frictonal losses per capacity compared with a triple.
Inertia of moving engine parts has little to do with engine braking, when the whole car is the moving mass. Flywheel does play in of course, but you can't fake the very low engine braking with a heavy flywheel without making the engine extremely lazy to rev up, which the 1.0 certainly isn't. Swept area is of course and you prove the point nicely, since friction is of course related to swept area. But modern engines also have much lower friction with special oils, bearings and most notably, low friction piston rings. All for a low mpg and emissions. As is rev hang by calibration apparently. But can't say I was hindered by it when whipping a 1.0 around a track. Light on the nose and with the already famed chassis calibration of Ford, it was actually good fun despite a massive power deficit and the esp always on. But these were never a sporting proposal really, Ford has another year before sales start (!) to nail the Fiesta ST 3-pot calibration. Edited by Onehp on Tuesday 28th February 03:49
Onehp said:
Inertia of moving engine parts has little to do with engine braking, when the whole car is the moving mass. Flywheel does play in of course, but you can't fake the very low engine braking with a heavy flywheel without making the engine extremely lazy to rev up, which the 1.0 certainly isn't. Swept area is of course and you prove the point nicely, since friction is of course related to swept area. But modern engines also have much lower friction with special oils, bearings and most notably, low friction piston rings. All for a low mpg and emissions. As is rev hang by calibration apparently. But can't say I was hindered by it when whipping a 1.0 around a track. Light on the nose and with the already famed chassis calibration of Ford, it was actually good fun despite a massive power deficit and the esp always on. But these were never a sporting proposal really, Ford has another year before sales start (!) to nail the Fiesta ST 3-pot calibration.
Sorry I should have made it clearer, I was talking about the effect of engine braking as in the rate the engine slows itself when taking off the throttle with the clutch disengaged as we were talking about rev hang. Maybe there is a specific term for that I'm unaware of but as such the mass of the car then doesn't come into it, only the inertia of the moving parts of the engine.Edited by Onehp on Tuesday 28th February 03:49
RumbleOfThunder said:
TameRacingDriver said:
People are going on about the 3 cylinder sounding better (potentially) but what about when its running on 2 cylinders as the article says it will when just driving gently? What will it sound like then? A lawn mower?
You won't hear it. s m said:
RumbleOfThunder said:
TameRacingDriver said:
People are going on about the 3 cylinder sounding better (potentially) but what about when its running on 2 cylinders as the article says it will when just driving gently? What will it sound like then? A lawn mower?
You won't hear it. VeeFource said:
Sorry I should have made it clearer, I was talking about the effect of engine braking as in the rate the engine slows itself when taking off the throttle with the clutch disengaged as we were talking about rev hang. Maybe there is a specific term for that I'm unaware of but as such the mass of the car then doesn't come into it, only the inertia of the moving parts of the engine.
Thought so. When I brought up engine braking as illustrative, I basically mean lifting off. The 1.0 would then just continue to roll as if one had put the box in neutral, so little resistance there is in the engine. This is a sign of very little friction in the engine, which would also, apart from sw calibration for emissions, explain why revs don't drop as quickly as in, say, an old school 7L V12 
Onehp said:
Thought so. When I brought up engine braking as illustrative, I basically mean lifting off. The 1.0 would then just continue to roll as if one had put the box in neutral, so little resistance there is in the engine. This is a sign of very little friction in the engine, which would also, apart from sw calibration for emissions, explain why revs don't drop as quickly as in, say, an old school 7L V12
The friction of the engine even in the normal sense of engine braking (as in when in gear) still shouldn't really come into it as it's so negligeable. The swept volume, engine rpm and as you put it before, mass of the car are what will ultimately determine engine braking in the regular sense.VeeFource said:
s m said:
RumbleOfThunder said:
TameRacingDriver said:
People are going on about the 3 cylinder sounding better (potentially) but what about when its running on 2 cylinders as the article says it will when just driving gently? What will it sound like then? A lawn mower?
You won't hear it. I think the new ST will run on two cylinders most of the time, with the exhaust in the quiet mode so that the switch from three to two isn't obvious. It'll go to three cylinders with the active exhaust coming in at wider throttle openings, higher rpm and in sport mode.
s m said:
RumbleOfThunder said:
TameRacingDriver said:
People are going on about the 3 cylinder sounding better (potentially) but what about when its running on 2 cylinders as the article says it will when just driving gently? What will it sound like then? A lawn mower?
You won't hear it. 
t. VeeFource said:
The friction of the engine even in the normal sense of engine braking (as in when in gear) still shouldn't really come into it as it's so negligeable. The swept volume, engine rpm and as you put it before, mass of the car are what will ultimately determine engine braking in the regular sense.
Engines with similar swept volume have large differences in engine braking. With swept volume I presume you refer to the compression and expansion of air without detonation? But the throttle body is closed on a gasoline. But friction is directly related to swept volume also. So perhaps we mean similar things but state it differently. Gassing Station | General Gassing | Top of Page | What's New | My Stuff