FPC worry? Should I?

[JimmyTwoTimes]

And Ferrari's V12s do not have flat plane cranks either whoever said that before.

Um... you're incorrect on that.

http://www.nytimes.com/2012/06/03/automobiles/autoreviews/family-travel-at-the-300000-price-point.html?pagewanted=all&_r=0

"Conventional V-12 engines are renowned for soothing, buttery power, but the FF’s flat-plane crankshaft imbues the exhaust note with a hard-edge malevolent bark. If the FF’s 12 pistons were a jury, they’d never reach a verdict."

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[Jimdohc]

XPC, FPC, I3, I4, V8, V12 are all balanced and imbalanced. There is more than one force related to mass that need to be balanced. It's a compromise.

XPC V8(90degree V), rotational imbalance- whole engine wants to wiggle/twist
FPC V8(90degree V), secondary reciprocating imbalance- engine shake

Rotational imbalance is easier to fix. Just requires large counter weights. Large counter weights limit rpm & rob horsepower.

To fix a secondary reciprocating imbalance requires balance shafts that spin twice the speed of crank. Or just live with the shake. Size of secondary imbalance is relatively small under high load conditions. Most noticeable at idle and other low load situations. Depending on engine mounts, it's possible the whole GT350 will shake at idle and 65mph cruise but feel silky smooth at full throttle.

 

[Todd15Fastback]

I love this new car and have seriously thought about putting an order in for this and leave my '15 GTPP that will be built next Monday.

But....Due to this new FPC, I am really leery at this point. I also had a custom 2000 Cobra on order and we all know those were never made due to the '99 horsepower issue on that Cobra. This is a pretty drastic change, at least in my mind it is from an engine standpoint. I am going to wait and keep my '15 GTPP and then see how these materialize over the coming months and then decide. I am all about NA power and this just fits me perfectly, not to mention the suspension setup, etc. It will be hard to resist this car but hopefully no major issues and all the new owners will enjoy this fine specimen of a hotrod that Ford is about to build.

 

[DHG1078]

Ford's 3 cylinder is not a FPC. The 1.0-L crankshaft's throws are offset at 120°.

http://articles.sae.org/10714/

oops, your right. not sure why i thought it was 180°

 

[wproctor411]

Ford will be fine with this and their racing development people have been tinkering with this for a long time. The aftermarket did for a while too, I'm getting old, does anyone remember Bruce Crower converting some modular and SBF ford engines to FPC? Crower did a few chevy engines too.

It's been 20+ years. From what I recall they ran terrible at idle but had the siren song of the high rpm V8 at WOT.

 

[flaps]

Um... you're incorrect on that.

http://www.nytimes.com/2012/06/03/a...e-300000-price-point.html?pagewanted=all&_r=0

"Conventional V-12 engines are renowned for soothing, buttery power, but the FF’s flat-plane crankshaft imbues the exhaust note with a hard-edge malevolent bark. If the FF’s 12 pistons were a jury, they’d never reach a verdict."

That isn't right. V12s are similar to flat plane V8s in that they have groups of 4 cylinders at different angles from each other, but instead of two groups at 180°, they have 3 groups at 120°. Like in this video:
[ame]

This video shows them assembling an older Ferrari V12, but it is still the same V angle and crank design. It is just like the first video.
[ame]

Here is the crankshaft from the Ferrari FF. It is zoomed in so you can't see the whole thing, but you can tell the crank pins are not 180° from each other.
[ame]

And from Wikipedia: http://en.wikipedia.org/wiki/V12_engine

Since each cylinder bank is essentially a straight-6, this configuration has perfect primary and secondary balance no matter which V angle is used and therefore needs no balance shafts.

Which means it would make no sense to use a flat plane crank in a V12 since the 120° design already works perfectly.

 

[66coupe]

Which means it would make no sense to use a flat plane crank in a V12 since the 120° design already works perfectly.

It does make sense, depending on what you want to accomplish. A 120° V12 is a great choice for a smooth, powerful engine, such as in a luxury car. A FPC offers better exhaust characteristics and, I believe, has a lower crank mass allowing it to rev quicker and with a higher red line. A FPC makes a better race engine but it runs rougher and is not as well suited for a street car (except in limited cases like this).

This is the trade off Ford made with the V8 in the GT 350.

 

[nametoshowothers]

it is clear the contributors (most) to the posts are not mechanical engineers with experience in designing engines. So take most feedback with a grain of salt and for the entertainment value. I frankly will be happy to trust ford on this engine and take it to 8000 rpm every morning on the way to work. My neighbors will come to love the new alarm clock next fall

 

[91z28350]

Lol

 

[Flipflopp]

I remember reading that Ford was having trouble developing this engine and having catastrophic failures during testing. (link to article below) This was in June, just a few short months ago. I'm also wondering what the longevity of the engine is and how it will handle aftermarket mods. Because lets face it, some people are always looking to add more power over stock.

http://wot.motortrend.com/1406_2017_ford_mustang_svt_gt500_successor_spied.html

 

[flaps]

It does make sense, depending on what you want to accomplish. A 120° V12 is a great choice for a smooth, powerful engine, such as in a luxury car. A FPC offers better exhaust characteristics and, I believe, has a lower crank mass allowing it to rev quicker and with a higher red line. A FPC makes a better race engine but it runs rougher and is not as well suited for a street car (except in limited cases like this).

This is the trade off Ford made with the V8 in the GT 350.

That only applies to a V8. A V12 doesn't require heavy counterweights like a crossplane V8. Putting a flat plane crank in a V12 would just put it out of balance and give it a weird firing order. A V12 is basically just two I6s put together, which are already naturally perfectly balanced when their crank pins are 120° apart.

 

[nametoshowothers]

I remember reading that Ford was having trouble developing this engine and having catastrophic failures during testing. (link to article below) This was in June, just a few short months ago. I'm also wondering what the longevity of the engine is and how it will handle aftermarket mods. Because lets face it, some people are always looking to add more power over stock.

http://wot.motortrend.com/1406_2017_ford_mustang_svt_gt500_successor_spied.html

every engine program breaks engines - that is called testing and finding the limit, back in the day when developing engines for experimental cars, broke 4 engines in one day - engine end up setting world fuel economy record back in 1988. So got to find the limits one way or another

 

[Mazda]

it is clear the contributors (most) to the posts are not mechanical engineers with experience in designing engines. So take most feedback with a grain of salt and for the entertainment value. I frankly will be happy to trust ford on this engine and take it to 8000 rpm every morning on the way to work. My neighbors will come to love the new alarm clock next fall

Didn't you know that everyone on the internet are engineers and scientists?

 

[Red]

I'm quite ambivalent about making this post. One the one hand, I'd like to expand/correct a general idea promulgated several posts up. On the other hand, correcting is generally very bad form in venues such as this. Based on the poster's other posts, which are generally spot on (in my opinion), he/she seems to be a decent person and will hopefully not be offended. I'm not getting into a pissing match, period. Does no good and time (for me anyway) is limited...

So, with all that out of the way, this post concerns the secondary imbalance. I will keep it as non-technical as possible, but there will be a tiny bit of 'math'. I will even simplify to the point of being technically incorrect, to get a general point across. If anyone wants to point that out and correct me, no offense taken.

First, a more 'real life' instance of rotational imbalance (this would be a primary imbalance): a washing machine where the load has gotten all fubar'ed and is plastered to one side of the drum. I think we've all seen this (or perhaps this is more an indictment of my laundry skills ). During the wash cycle, the entire machine can/will gradually walk across the floor due to the imbalance. But during the spin cycle, where the drum spools up to a higher rpm to fling water out of the clothes, the machine smooths out. But, the laundry is still in the same position on the drum. What happened? Why did the imbalance appear to lessen?

The imbalance appeared to disappear due to the fact that the force of the imbalance is applied in any one given direction for a shorter and shorter period of time as the rpm increases.

To keep things simple (and brief!) accept the following as a given:

x(t) = a*t*t/2

meaning that the displacement due to a constant acceleration equals half the acceleration multiplied by the time squared (and here's where I'm taking liberties w/ correctness -- I'm using translational dynamics yet taking about rotational dynamics). We also know:

a = F/m (Newton's second law for constant mass).

So let's look at how the displacement (of our washing machine) varies with time. Just picking force and mass values out of thin air, let's say the washing machine mass is 30 kg (approx. 66 pounds) and the force of the laundry imbalance is 10 Newtons (about 2.25 pounds). If we were to apply this force to the washing machine for one second, it would move 0.15 meters -- or about six inches. Now, assume the force of the imbalance acts for 0.1 seconds (I'm making a rough analogy to 600 rpm here). Now the washing machine will move only 0.0015 meters, or roughly 0.06 inches. Not much...

To finish up this little analogy (and before making another post, I guess, with some specific numbers for the 5.2), recall that the force of the imbalance (due to the laundry being on one side of the drum) changes direction. At one instance, the imbalance force might be pointing out the front of the washing machine. At some later time (determined by the rpm of the drum) the force will be pointing directly out the rear of the machine (for a top-loaded washing machine). So the machine is actually getting pushed and pulled by this force. Hence we have something called a harmonically excited oscillator.

The equation(s) for harmonically driven oscillation give the displacement (the motion) as a function of, time, mass, spring constant, and damping constant. And it would be asinine to go into them. Suffice to say, that as the frequency of the oscillation begins to significantly exceed something called the undamped natural frequency of the oscillator, the displacement of the oscillator becomes relatively very small depending on the characteristics of the oscillator and the driving force. And, in this case, the force is being applied in one direction for such a short period of time that the mass (the washing machine) just doesn't move much.

So, this is why an engine w/ an imbalance will appear to smooth out at higher revs -- not because the imbalance itself either disappeared or is very small.

More to come regarding the 5.2 -- a computer run finished up a bit ago so I have to do some work before submitting yet another.

 

[Backorder]

Wow Red...I spend enough time in my Geophysics classes with math...:-D you did explain it and dumb it down well though :-D

Not arguing with you at all, just saying that was detailed and u even mentioned an equation! This is he weekend dangit! Lol


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