Why Did Ford Decide to do a Flat-Plane Crank Differently?
Why Did Ford Decide to do a Flat-Plane Crank Differently?
(OP)
Most V8 engine layouts are Cross-Plane (sometimes called Cruciform) due to the 4 common crank pins being positioned in two planes, 90 degrees apart. Usually the two end pins are in one plane, 180 degrees apart and the two inner pins are on a plane perpendicular to the outer’s. Figure 1 shows a typical V8 cross-plane crankshaft.

## Figure 1 - V8 Crossplane Crankshaft ##
Flat-Plane V8s are commonly only used in high-performance engines, such as the likes of Ferrari. As its name suggests, a Flat plane V8 crankshaft has all its crank pins in a single plane. It looks very similar to an Inline-4 crankshaft, albeit with longer crank pins to accommodate two big ends. Figure 2 shows a typical Flat Plane V8 crankshaft.

## Figure 2 - V8 Flat-Plane Crankshaft ##
There are two main benefits of a Flat-Plane:
So the question I am puzzling over, why did Ford decide to make use of a flat-plane crank layout in the new 2016 Mustang GT350R but (seemingly) throw away all the benefits gained by doing it differently?

## Figure 3 - Ford GT350R V8 Flat-Plane Crankshaft ##
I’ll explain “differently”. The GT350R crankshaft is shown above in figure 3. The very first thing I noticed was that is had an “up - down - up - down” configuration of the crank pins instead of the usual “up - down - down - up” layout as illustrated in Figure 2. Straight away I wondered why they had done that as I suspected (before I had a chance to do any calcs) that it was going to introduce some imbalance. This suspicion was further strengthened by the obvious larger counterweights, opposing each other at either end of the crankshaft, giving away that there was some inherent unbalanced (primary) couple.
So I did some calcs and confirmed that the unusual layout of this flat-plane V8 crankshaft did indeed have some unbalance.
The typical U - D - D - U layout leaves only an unbalance secondary, horizontal shaking force and a relatively small secondary couple in the vertical plane, all due to the reciprocating components.
The U - D - U - D layout however, even just looking at the rotating masses alone, has a primary rotating couple. So before even considering the reciprocating masses you have to add 2 large, opposing counterweights at either end of the crank to just make the crank balance. Then when you consider the reciprocating masses, you get the same secondary imbalances as the U - D - D - U but also more primary couple imbalance.
Then end result is a flat-plane crankshaft with the mass/inertia penalty of the cross-plane crankshaft. So why did they do it?
That is actually my unanswered question...unless I haven’t considered some other great benefit, I can’t see why they did it...apart from perhaps, marketing? Maybe being able to say the GT350R is different from all the rest because it has an exotic “5.2l V8 with flat-plane crank” (quoted from the Ford website).
I would really like to know more behind the decision.
Regards,
Jon Reynolds

## Figure 1 - V8 Crossplane Crankshaft ##
Flat-Plane V8s are commonly only used in high-performance engines, such as the likes of Ferrari. As its name suggests, a Flat plane V8 crankshaft has all its crank pins in a single plane. It looks very similar to an Inline-4 crankshaft, albeit with longer crank pins to accommodate two big ends. Figure 2 shows a typical Flat Plane V8 crankshaft.

## Figure 2 - V8 Flat-Plane Crankshaft ##
There are two main benefits of a Flat-Plane:
- Due to good inherent primary (1st order) balance (no primary shaking forces or couples) there is no requirement for large counterweights (a cross-plane has a rotating primary couple that must be balanced out with counterweights - hence the typical shape of the large end counterweights on cross-plane V8 cranks). This means reduced weight, reduced inertia, reduced package volume, which all equal increased engine acceleration and lower CoG possible.
- Exhaust Pulse Tuning - due to the layout, firing order is alternating from bank to bank, so each bank sees equally spaced pulses of exhaust gas pressure. This means exhaust tuning can be utilised to make the engine perform better. The cross-plane layout means each bank has unequal pulse distribution.
So the question I am puzzling over, why did Ford decide to make use of a flat-plane crank layout in the new 2016 Mustang GT350R but (seemingly) throw away all the benefits gained by doing it differently?

## Figure 3 - Ford GT350R V8 Flat-Plane Crankshaft ##
I’ll explain “differently”. The GT350R crankshaft is shown above in figure 3. The very first thing I noticed was that is had an “up - down - up - down” configuration of the crank pins instead of the usual “up - down - down - up” layout as illustrated in Figure 2. Straight away I wondered why they had done that as I suspected (before I had a chance to do any calcs) that it was going to introduce some imbalance. This suspicion was further strengthened by the obvious larger counterweights, opposing each other at either end of the crankshaft, giving away that there was some inherent unbalanced (primary) couple.
So I did some calcs and confirmed that the unusual layout of this flat-plane V8 crankshaft did indeed have some unbalance.
The typical U - D - D - U layout leaves only an unbalance secondary, horizontal shaking force and a relatively small secondary couple in the vertical plane, all due to the reciprocating components.
The U - D - U - D layout however, even just looking at the rotating masses alone, has a primary rotating couple. So before even considering the reciprocating masses you have to add 2 large, opposing counterweights at either end of the crank to just make the crank balance. Then when you consider the reciprocating masses, you get the same secondary imbalances as the U - D - D - U but also more primary couple imbalance.
Then end result is a flat-plane crankshaft with the mass/inertia penalty of the cross-plane crankshaft. So why did they do it?
That is actually my unanswered question...unless I haven’t considered some other great benefit, I can’t see why they did it...apart from perhaps, marketing? Maybe being able to say the GT350R is different from all the rest because it has an exotic “5.2l V8 with flat-plane crank” (quoted from the Ford website).
I would really like to know more behind the decision.
Regards,
Jon Reynolds





RE: Why Did Ford Decide to do a Flat-Plane Crank Differently?
edit: Sorted now.
Regards,
Jon Reynolds
RE: Why Did Ford Decide to do a Flat-Plane Crank Differently?
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RE: Why Did Ford Decide to do a Flat-Plane Crank Differently?
Regards,
Jon Reynolds
RE: Why Did Ford Decide to do a Flat-Plane Crank Differently?
TTFN
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RE: Why Did Ford Decide to do a Flat-Plane Crank Differently?
In each bank, it could be 1-2-3-4 or it could have 1 and 3 swapped (3-2-1-4 i.e. 1-4-3-2 which is the exact same scenario flipped end to end) or it could have 2 and 4 swapped (1-4-3-2 which is equivalent) or it could have both swapped (3-4-1-2 which is 1-2-3-4). Interesting. Either way, each bank fires each cylinder in sequence from one end of the engine to the other evenly spaced, it's only a matter of whether that sequence goes front-to-back or back-to-front. (I know that's not the actual way the cylinders are numbered, we're just looking at each bank - bear with me.)
The other bank - let's suppose this is the one that trails by 90 degrees - either has its own firing order inserted 90 degrees after, which would put both power strokes on the same crank pin at the same time, or 450 degrees after, which completely separates the firings on each crankpin. I'd say that's more likely.
The first cylinder of the second bank in the firing sequence fires 90 degrees following the third cylinder in the first bank in the firing sequence in a nice progression from either back-to-front or front-to-back. The firings are nicely spaced between the front half of the engine and the back half of the engine and so are the intake suction strokes and there's never an overlapping power stroke on the same crank pin. (I don't think it is possible to achieve this with a cruciform crossplane-crank V8) Heck, the compression stroke on the second cylinder in the bank doesn't start until the first cylinder's power stroke is mostly finished.
I think Ford knew what they were doing.
RE: Why Did Ford Decide to do a Flat-Plane Crank Differently?
WAG1: Maybe their crank grinder automation deals with UDUD better than UDDU.
WAG2: Maybe it's used in a vehicle where you have to rotate the crank in increments in order to remove the oil pan axially, and two throws in a row wouldn't clear the rear seal face of the pan.
Example: The penultimate E-series van, where you had to remove the top half of the intake manifold and jack up the engine before you could begin to get the oil pan out, and you still had to rotate the crank to clear the oil pan, because the engine was installed in a tight fitting porthole in an otherwise very solid front crossmember.
Mike Halloran
Pembroke Pines, FL, USA
RE: Why Did Ford Decide to do a Flat-Plane Crank Differently?
FP UDDU (typical) is statically and dynamically balanced, hence no additional CWs required either end like on a cross plane V8.
Ford's UDUD FP reintroduces the dynamic imbalance similar to the cross plane hence the need for thicker, opposed CWs. So why go FP but loose the mass/inertia savings by going UDUD ?
Regards,
Jon Reynolds
RE: Why Did Ford Decide to do a Flat-Plane Crank Differently?
I do suggest you re-read your OP, since you wrote: "There are two main benefits of a Flat-Plane:"
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RE: Why Did Ford Decide to do a Flat-Plane Crank Differently?
However, I do see an advantage in avoiding firing impulses on adjacent cylinders along the crankshaft (if that is in fact an advantage and one worth pursuing), which I don't see a way to do with a conventional flat crank.
The rotating inertia disadvantage remains.
"Schiefgehen wird, was schiefgehen kann" - das Murphygesetz
RE: Why Did Ford Decide to do a Flat-Plane Crank Differently?
RE: Why Did Ford Decide to do a Flat-Plane Crank Differently?
Remember the TDM 850 parallel twin, with its unusual 270° firing interval? Some said that was all about making it sound like a V-Twin, not about performance - the extra hassle of balancing it was the price to be paid.
Steve
RE: Why Did Ford Decide to do a Flat-Plane Crank Differently?
Contrariwise, I vaguely remember pictures of exotic cylinder heads and exhaust system applied to the 351 Cleveland V8 as installed in the Ford Pantera that brought all the exhaust ports to the inside of the "Vee" and knitted them together into bundle of snakes for an even firing header system. I might have this wrong as it may have been a Ford smallblock applied to the original GT40, or a Pantera Cleveland with conventional cylinder heads where the individual exhaust pipes were extended rearward as needed to join them into even firing pairs and quartettes. But you get the idea, i.e. going to a lot of effort to get an even firing exhaust system from a "cross-plane" V8.
"Schiefgehen wird, was schiefgehen kann" - das Murphygesetz
RE: Why Did Ford Decide to do a Flat-Plane Crank Differently?
Regards,
Jon Reynolds
RE: Why Did Ford Decide to do a Flat-Plane Crank Differently?
There's a link in http://forums.corner-carvers.com/showpost.php?p=10... to the "revised" sound. Pretty sure I've heard a stock GT350, and it's nothing like this.
Norm
RE: Why Did Ford Decide to do a Flat-Plane Crank Differently?
At last, some light shed on the exact issue I have been trying to explain/get to the bottom of:
http://www.edmunds.com/ford/mustang/2015/long-term-road-test/2015-ford-mustang-gt-coyote-voodoo-cross-plane-flat-plane.html
So...if I am reading into it right...its all about MARKETING! The sound it makes seems to have driven the decision making on the odd layout.
Annoyed I didn't find that in my searchings.
Regards,
Jon Reynolds
RE: Why Did Ford Decide to do a Flat-Plane Crank Differently?
"Schiefgehen wird, was schiefgehen kann" - das Murphygesetz
RE: Why Did Ford Decide to do a Flat-Plane Crank Differently?
[img]http://www.mustang6g.com/forums/attachment.php?att...[/img]
[img]http://www.mustang6g.com/forums/attachment.php?att...[/img]
Link to the discussion and more pictures: http://www.mustang6g.com/forums/showthread.php?t=1...
Norm
RE: Why Did Ford Decide to do a Flat-Plane Crank Differently?
----------------------------------------
The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.
RE: Why Did Ford Decide to do a Flat-Plane Crank Differently?
Having more rotating inertia makes the power delivery more gentile. That pays off on race tracks: It delivers smoother power impulses to the drivetrain, and the engine has more inertial torque when you need to drop the clutch.
When I was racing motocross and XC, it was common to add flywheel weights to the engines to make them more ride-able.
"Formal education is a weapon, whose effect depends on who holds it in his hands and at whom it is aimed." ~ Joseph Stalin
RE: Why Did Ford Decide to do a Flat-Plane Crank Differently?
I can understand why you might want to take some of the suddenness out of a wheelstand (I used to ride a 350cc 2-stroke triple that had light-switch behavior between being off the pipe and on it), but I doubt that to be a concern with the GT350. Nor will drag racing be all that important, though there will be those who will at least try it out there.
Norm
RE: Why Did Ford Decide to do a Flat-Plane Crank Differently?
"Schiefgehen wird, was schiefgehen kann" - das Murphygesetz
RE: Why Did Ford Decide to do a Flat-Plane Crank Differently?
RE: Why Did Ford Decide to do a Flat-Plane Crank Differently?
je suis charlie
RE: Why Did Ford Decide to do a Flat-Plane Crank Differently?
"Schiefgehen wird, was schiefgehen kann" - das Murphygesetz
RE: Why Did Ford Decide to do a Flat-Plane Crank Differently?
I saw a video on the GT350 over the weekend that mentions packaging constraints being a main driver for the crankshaft configuration. One constraint mentioned was not being able to use separate plenums for the cylinder banks. I'll see if I can find a link to the video and post it.
Kyle
RE: Why Did Ford Decide to do a Flat-Plane Crank Differently?
For road racing, the theory is that less engine inertia allows the engine rpm to change quicker, which means quicker changes and faster acceleration/deceleration of the car.
The physics of acceleration don't change between the drag and road tracs, so one of the theories is wrong. I've run across a few people who reduced rotating engine inertia via a much lighter clutch/flywheel and then went down the 1/4 mile faster. So the reality is that having more engine inertia just makes it easier to consistently launch a clutched car.
RE: Why Did Ford Decide to do a Flat-Plane Crank Differently?
A closed-course racer, either road course or "oval" doesn't need to care nearly as much about 1st gear launch traction, either because the starts are rolling starts or because the wheels are allowed to freely spin (sacrificing a small amount there in exchange for better through-the-gears acceleration everywhere else). The classic illustration here would be the big NASCAR "sedans" leaving their pit space following a stop for fuel and fresh tires. The only "surface preparation" for closed course events is whatever tire rubber has been left on the pavement during practice, qualifying, and from what any supporting series leaves. Some of which may not even be on the line you need to be on to prevent being passed.
Norm
RE: Why Did Ford Decide to do a Flat-Plane Crank Differently?
Hemi - more engine inertia would help the launches using the same launch rpm, but in reality you would launch at a higher rpm with less inertia.
This engine has to be kept above 3500rpm to stay in the powerband. The engine torque increases by over 100 ft-lbs going from 3000 to 3400 rpm.
RE: Why Did Ford Decide to do a Flat-Plane Crank Differently?
Hence, I remain skeptical.
Of course, one can conceive of a high tech, ultra light, ultra high speed flywheel connected via a high ratio reduction gear to the drivetrain proper, that is spun up to the moon prior to the start of the race, and totally eclipses the engine in power delivery during the race; but that is not the configuration of a drag race vehicle as we know them today.
I guess the reduction gear needed for the task wouldn't be exactly lightweight, but maybe an electrical coupling could provide the needed speed reduction at a lighter weight.
"Schiefgehen wird, was schiefgehen kann" - das Murphygesetz
RE: Why Did Ford Decide to do a Flat-Plane Crank Differently?
je suis charlie
RE: Why Did Ford Decide to do a Flat-Plane Crank Differently?
As long as the crank is lighter than a cross plane crank, it is smart for them to do this.
I have also heard that balancing flat plane V8s with displacement over about 4.5L is harder to do. I do not understand exactly why that is said. Does anybody have ideas as to why that is said?
"Formal education is a weapon, whose effect depends on who holds it in his hands and at whom it is aimed." ~ Joseph Stalin
RE: Why Did Ford Decide to do a Flat-Plane Crank Differently?
RE: Why Did Ford Decide to do a Flat-Plane Crank Differently?
If you can't keep the revs up high enough on the launch - IOW, the engine bogs before adequate road speed is reached - it won't matter how much more advantageous the light-MOI setup is everywhere else. The race has already been lost. It at least used to be common for 40-lb flywheels to be fitted to small-block Chevy engines, and the numerically high axle gear ratios also frequently fitted would perhaps "cover for" the lower vehicle accelerations once the engine is operating in its best powerband and the tires fully "hooked up". It's really just a matter of optimizing the entire combination for a clearly and very narrowly defined performance measurement.
On a small time step level, rotational momentum converts to additional torque as the rpms drop, and how much this amounts to also depends on the rate of rotational deceleration. You might for a very brief period of time "gain" 100 ft-lbs this way, which might just be enough. Consider that clutch engagement isn't necessarily instantaneous from no grip to no slip, and that there likely is some torsional "wind-up" in driveshafts, axles/half shafts, and tires that provide some delay and (slightly later) energy returns of their own.
Norm
RE: Why Did Ford Decide to do a Flat-Plane Crank Differently?
Guessing the magnitudes of the forces and moments and the phase relationships among those components between banks that are still separated by 90° has something to do with it. Dividing the con-rods into two masses with no MOI of their own is at best an approximation.
Norm
RE: Why Did Ford Decide to do a Flat-Plane Crank Differently?
It used to be said that inline 4s with displacement over about 2 liters had too much secondary vibration to be acceptable in passenger cars, without resorting to the complication and expense of a pair of counter-rotating secondary balance shafts. The pistons etc got too heavy for the final result to be ignored or "hidden" with squishy engine mounts
As a flat crank V8 is somewhat equivalent to two inline 4s, the 4.5 l limit you describe may have been referring to secondary vibration.
RE: Why Did Ford Decide to do a Flat-Plane Crank Differently?
"Formal education is a weapon, whose effect depends on who holds it in his hands and at whom it is aimed." ~ Joseph Stalin
RE: Why Did Ford Decide to do a Flat-Plane Crank Differently?
Stored energy is proportional to rpm^2 so after lowering the inertia of the engine, increase the launch rpm to get back to the same stored energy.
RE: Why Did Ford Decide to do a Flat-Plane Crank Differently?
Not only that, but you would have to launch the car when the engine is well past peak torque..
RE: Why Did Ford Decide to do a Flat-Plane Crank Differently?
I found the video. If you fast forward to around 7:30 in the video, there is an explanation as to why the GT350 flat plane crank is different than other flat plane cranks.
https://youtu.be/GbbNlkP-ZSM
Kyle
RE: Why Did Ford Decide to do a Flat-Plane Crank Differently?
RE: Why Did Ford Decide to do a Flat-Plane Crank Differently?
With a dual plane manifold on a cross-plane-crank V8, the intake strokes being drawn from each "plane" are evenly spaced 180 degrees apart. To do the same thing with a flat-plane-crank V8, it is simply the left bank kept separate from the right bank.
RE: Why Did Ford Decide to do a Flat-Plane Crank Differently?
"Schiefgehen wird, was schiefgehen kann" - das Murphygesetz
RE: Why Did Ford Decide to do a Flat-Plane Crank Differently?
I suspect that's the rule rather than the exception, at least for semi-serious and up dragstrip cars still equipped with a manual transmission. You might be able to find out what launch rpms people are actually using in the discussions found in the dragstrip sections of the various automotive-enthusiast message boards.
Norm
RE: Why Did Ford Decide to do a Flat-Plane Crank Differently?
That's OK unless clutch slip is being used to regulate torque to the wheels. Higher rpm means higher energy loss in the clutch - reducing the flywheel energy available to propel the car.
je suis charlie
RE: Why Did Ford Decide to do a Flat-Plane Crank Differently?
In F1 and other high-buck series in the early to mid 1960s many engines were designed with "downdraft" intake ports with the intake coming in between the wide-spaced cams. Despite the breathing advantage of unshrouding the long side this trend ended with the coming of the narrow valve angle Cosworth DFV.
A highly beneficial feature of downdraft engines was the ability to put the exhausts in the V, allowing more compact packaging and, critically for V8s, the ability to conveniently cross exhaust tubes to the opposite bank. This allowed bent cranks to be used with no power penalty from exhaust pulse timing effects in the headers. Some engines took advantage, getting rid of the vibration problems of flat cranks.
There still remained the disadvantages of a heavier bent crank vs a flat crank and, especially then, a weaker bent crank. So, you saw some of these downdraft V8s with flat cranks as well as some with bent cranks. I think the most iconic of the downdraft, bent crank engines was the Ford 4-cam Indy engine.
RE: Why Did Ford Decide to do a Flat-Plane Crank Differently?
The only way to actually implement your theory of using extremely high revs to get that inertial torque is to have an extremely low gear ratio for the gear that you are launching in, one which is impractical in real world racing.
And on the subject of engine torque backup: Given a specific amount of inertial torque, crossplane V8s attain that at an engine speed which is closer to their engine's peak torque. That means that their torque backup is used to maintain that rotational torque. Flatplane crank engines lose much higher amounts of rotational torque by the time the engine speed falls to peak torque RPM. That means that they then have to regain more that inertial torque, for which the speed was already poorly optimized to the physics of making wheels (with mass) spin and moving a car (with mass) forward to match the engines speed.
"Formal education is a weapon, whose effect depends on who holds it in his hands and at whom it is aimed." ~ Joseph Stalin
RE: Why Did Ford Decide to do a Flat-Plane Crank Differently?
The GT350 V8 engine in the video did sound very nice though.
RE: Why Did Ford Decide to do a Flat-Plane Crank Differently?
???
Seems to me that a lower MOI crankshaft would lose less stored energy for a given rpm drop. That it has less at any given rpm to begin with is a separate question, but circuit racing is going to be more interested in reducing MOI effects while the clutch is completely engaged (this being most of the time) than in developing brief torque spikes via a (harsh and potentially risky) no-lift upshift technique.
Norm
RE: Why Did Ford Decide to do a Flat-Plane Crank Differently?
For launches, you want the inertial torque to be considerable around the speed where the engine makes peak torque. You also want that engine speed to be realistically close to what the car's speed can facilitate shortly after the launch is complete (when the engine is coupled to the drivetrain). Most guys don't let off much between shifts until going into 4th gear, and the gear ratio of that gear reduces how parasitic the MOI of the crank is to the car's overall acceleration.
RE: Why Did Ford Decide to do a Flat-Plane Crank Differently?
RE: Why Did Ford Decide to do a Flat-Plane Crank Differently?
Seems like Insistence on "hitting" the torque peak when shifting etc does not count for all that much.
Ed Iskenderian said it never did.
see attachment
==============
And then, specifically on the GT350 with flat crank, there are the on board confusers to be reckoned with, or do the reckoning.
"The performance software also includes launch control, which adjusts engine speed between 3000 and 4500 rpm and holds it there so you can simply drop the clutch and go."
http://www.caranddriver.com/flipbook/17-reasons-th...
It will be interesting to see who wins the 60 foot time competition. The launch control, or a keen driver au natural.
RE: Why Did Ford Decide to do a Flat-Plane Crank Differently?
If you go to a car show and talk to the older guys that can actually afford new cars, its common to hear them appreciating cars that "drive like a big block". I think the GT350 is a great car. If I were to sell my Cobra, it would be so that I could buy a GT350. But I won't sell my cobra :p They don't make cars that simple anymore. Nothing makes you appreciate simple cars quite like owning a complex one for long periods of time.
RE: Why Did Ford Decide to do a Flat-Plane Crank Differently?
"Formal education is a weapon, whose effect depends on who holds it in his hands and at whom it is aimed." ~ Joseph Stalin
RE: Why Did Ford Decide to do a Flat-Plane Crank Differently?
RE: Why Did Ford Decide to do a Flat-Plane Crank Differently?
RE: Why Did Ford Decide to do a Flat-Plane Crank Differently?
"Seems like Insistence on "hitting" the torque peak when shifting etc does not count for all that much.
Ed Iskenderian said it never did."
Ed was right. The torque peak is totally irrelevant to shifting. Shifting should be performed so that the average power output is maximised for the period spent in each gear. (assuming negligible engine rotational inertia etc etc)
je suis charlie
RE: Why Did Ford Decide to do a Flat-Plane Crank Differently?
As a road course kind of enthusiast for longer than I've held a driver's license, it's been a long wait for U.S. domestic sporty cars to truly be about more than just a powerful engine and a rumble-y exhaust note.
I know what you're saying here - I'm likely as old as many of those guys, and either driven or ridden in some of the same cars. And I feel much the same about my '08 as you do about your Cobra. Wish it was a bit simpler in some respects, developed a bit further in others, some of which I'm slowly doing on my own (with a modicum of success - 1.2+ lateral g's on true street tires, datalogged) A complete Voodoo engine and 3160 transmission would be a great swap, but that would probably end up costing nearly as much as I paid for the whole car even if I did all of the conversion work myself.
To the matter of inertial torque + engine torque, maximum acceleration in a given gear, maximum acceleration at any given speed, maximum acceleration spike on upshift, and optimum dragstrip ET and MPH results probably won't all happen during the same run. That doesn't make the logic behind any of them wrong, perhaps just not applicable to every situation.
Norm
RE: Why Did Ford Decide to do a Flat-Plane Crank Differently?
You can implement ideas into the car in the exact fashion that suits your needs, as long as you're capable and know what you want.
Back on subject! I think there were other issues (non performance related) that lead to fords counter-weighted flatplane crank. I do think the main problem was that balancing a flat-plane V8 that's bigger than 4.5L is not easy. This one is 5.2L. As somebody mentioned earlier, second order vibrations might start to get vicious.
http://articles.sae.org/13709/
"Flat-plane-crank engines have limitations. First, the lack of counterweight balancing typically limits cylinder displacement to about 4.5-4.6-L due to greater second-order vibration. Ford has solved that in the 5.2-L application with a new crankshaft-mounted damper system and extraordinary attention to NVH abatement during the design and prototype phases. According to Nair, the engine program (which was concurrent with GT350 vehicle development) nearly wasn’t approved for production.
“This [vibration] was our biggest engineering challenge even after we had the first prototype,” Nair noted. “Things were breaking and the technical guys were worried. Whether or not we continued down the flat-plane-crank path for GT350 came down to a critical prototype drive we had scheduled. After that drive, we all went into a meeting room for the debriefing. And we unanimously concluded that we simply had to have this motor! We were determined to solve the issues.” "
"Formal education is a weapon, whose effect depends on who holds it in his hands and at whom it is aimed." ~ Joseph Stalin
RE: Why Did Ford Decide to do a Flat-Plane Crank Differently?
This is precisely why the torque peak is crucial, or more precisely, the torgue and hp peak spread. You specify gear ratios to be able to run the engine in that range AND if you have more gears, you can narrow that band to give higher maximums.
RE: Why Did Ford Decide to do a Flat-Plane Crank Differently?
RE: Why Did Ford Decide to do a Flat-Plane Crank Differently?
The rpm for peak torque bears no relationship to the rpm for peak power. While I don't disagree with what you "invariably want to end up with" you can't assume that is what you have actually got so rules about operating between the torque and power peaks are by no means universal - ie not a rule at all.
je suis charlie
RE: Why Did Ford Decide to do a Flat-Plane Crank Differently?
An auto IC engine is a tuned system that makes NO torque at zero rpm. The torque must follow a curve from some low value at some low rpm to a peak at some higher rpm where it will begin to diminish as rpms increase. I can support a claim that torque does not disappear suddenly as rpm rises past the peak, but diminishes gradually at a generally increasing rate of decline.
Since power is a product of torque and rpm, power will increase from what it is at the torque peak as rpm rises until the rise in rpm is matched by the rate of fall in torque. That point is the power peak.
The simplest thing you can say about the relationship between the torque peak and power peak is that the power peak must occur at an rpm above the torque peak. That fact alone completely negates your statement that there is no relationship.
The rest of what I said assumes you are able to fully design your engine/gearing system so that you are able to put your power peak at the mechanical limit and your torque peak at the lowest range determined by gearing. If you are not fully able to design the system because of rules or some existing starting design or constraints, then other effects can occur. For a common example, if the engine can't breath well up to its mechanical limit (restrictor?) such that there is a safe margin above the power peak, then revving somewhat past the power peak could be an advantage. But, then re-camming to raise the torque peak rpm will usually also increase max power. You would ideally still have the torque peak at the lowest rpm accommodated by gearing.
RE: Why Did Ford Decide to do a Flat-Plane Crank Differently?
Same magnitude secondary horizontal shaking forces exist in both FP set ups. So I don't think this is purely connected to engine size as they didn't solve that problem.
Regards,
Jon Reynolds
RE: Why Did Ford Decide to do a Flat-Plane Crank Differently?
Norm
RE: Why Did Ford Decide to do a Flat-Plane Crank Differently?
In the future, that concept may be helpful as NWO emissions gestapo crack down on industry. Have the V-twins run and be balanced independently. The engine would basically be 4 separate V twins connected in line at their cranks. If you could do that, you could then connect them with clutches, instead of having them share a solid crank. The tricky part is adjusting phase appropriately so that the secondary forces don’t constructively interfere/overlap with each-other. That seems like a potentially beneficial platform for cylinder deactivation.
RE: Why Did Ford Decide to do a Flat-Plane Crank Differently?
The cost of a cross plane crankshaft is 2 times more than a flat plane crankshaft.
RE: Why Did Ford Decide to do a Flat-Plane Crank Differently?
"Schiefgehen wird, was schiefgehen kann" - das Murphygesetz
RE: Why Did Ford Decide to do a Flat-Plane Crank Differently?
I think they are early investors in the future market of where the Camaros and mustangs will be. T
"Formal education is a weapon, whose effect depends on who holds it in his hands and at whom it is aimed." ~ Joseph Stalin
RE: Why Did Ford Decide to do a Flat-Plane Crank Differently?
RE: Why Did Ford Decide to do a Flat-Plane Crank Differently?
Norm
RE: Why Did Ford Decide to do a Flat-Plane Crank Differently?
Cosworth stated that when they shifted from V10s to V8s in F1, despite their long experience with FP cranks, they were surprised at how destructive the vibrations were to the engine accessories.