36 replies to this topic

[merlyn6]

Could someone please explain the "flat plane crank"as used in some V8's. Benifits, drawbacks, ect. Thanks

[MacFan]

"Flat-plane" means that the crank throws are all in a single plane - i.e. if you laid the crank on a desk it would be flat. The engine effectively becomes 2x 4 cylinders rather than one 8 cylinder engine (the firing order is that of a 4 cylinder engine), so it makes more of a 4cyl noise than a smooth V8 "warble". The main advantage of the flat plane crank as I understand it is improved exhaust gas extraction due to to pulse tuning effects - basically the exhaust can be tuned, much like that of a 2 stroke engine, to improve breathing over a range of rpms.

[DangerMouse]

If you wanna know just how sweet a flat plane cranked V8 can sound listen to a TVR Cerbera - Hmmmmmmmmmm.

(The TVR has a 75 degree V angle by the way.)

[Wolf]

DM, or Ferrarri. And I don't think they'd put performances at stake (if costs were the only gain).

[marion5drsn]

The 180-degree crankshaft for V-8s was developed by De Dion-Bouton in 1909 and is considered by many to be the first successful V-8 engine made. Both Cadillac and Hispano-Suiza copied it in its various forms in 1914. The problem with this crankshaft is its grave tendency to SHAKE in both the Primary and Secondary. All 180-degree crankshafts V-8s have a short life. Just why anyone would put them in a regular road car just flabbergasts me. After using the 180-degree crank for about 9 years Cadillac developed the 90-degree crank to rid its engines of the Primary and Secondary Shake.
Since engines at that time (1923) were slow turning they only used four counterweights as the 90-degree crankshaft has the Primary balanced by having a lower conrod and crank arm coming up (Or down) on the opposite bank at the same time as one is coming up (or down) or the other side. The counterweights ridding the engine of the fore to aft Shake (Moment) due to the antisymmetrical crank. Since the pistons in a 180-degree crank do not arrive at the top at the same time the engine has the secondary Shake but does not have the fore to aft shake due to the crank being symmetrical end for end.
Wolseley (Hispano-Suiza 180-degree) in 1918 built an engine with eight counterweights that counteracted the primary Shake but did nothing to rid the engine of the Horizontal Shake which occurs twice each revolution. This is the reason that some believe the engine still broke its propeller gearboxes.
To properly balance a 180-degree crank in the Horizontal Secondary Shake it is believed that a shaft running at twice engine speed and with suitable counterweights is needed. To my knowledge no one has done it, as it seems it would be very heavy.
If you have questions about this phenomenon please go to Volume 2 of Charles Fayette Taylors book on, “The Internal Combustion Engine”, pages 240 to 305.
Yours M. L. Anderson

[DangerMouse]

Well TVRs flat plane V8s are bullet proof mechanically even at high mileages, yup the electrics stink but mechanically they are solid as a rock and can knock up huge mileages without major work despite the quite high specific power outputs.

[marion5drsn]

Mr. Dangermouse

It may be that you and I have inadvertently found the problem with the TVRs electrics! Since the TVRs have problems could it not be possible the problem with the electrics is with the crank and not in the electrical system. Altho the shake may be of high enough frequency that the driver does not feel it, the question may be, “Does the electrical system feel it?”
Since I know not the bore/stroke, rpm, the conrod length or the weight of the upper portion of the conrod/piston I can’t say how bad the shake is!
Has the factory made any statement about why they choose the 75–degree bank angle as this might aggravate the shake also. Just because the driver doesn’t feel the shake doesn’t mean the rest of the car isn’t affected. Shake can affect many things, such as parts falling off along with,” Mysterious happenings” I, for one feel this car is, unbeknownst to the driver a “bone shaker”. It would take an engineer of ability and with plenty of instrumentation to really analyze the shaking of this car or with any other car with a 180-degree crank.
I do not mean to demean you or these cars with these cranks only to bring to light the problems with these cranks. Yours, M. L. Anderson

[merlyn6]

What I am wondering is what are the performance advantages of a flat plane crank, as used in some high performance street cars, and some indy V8's? Is it more torque? How? Why did Ferrari, and TVR go to a flat plane crank in the 355/360, and the Cebera?

[marion5drsn]

The big advantage of the 180 degree crank is the ability of the designer to tune the exhaust on the 360 degree principle.
The 180 degree crank fires as two four cylinders side by side arranged in a Vee. That is the left fires 1-2-4-3 The right fires 3-4-2-1. This is from the front. This in a book 1918 INSTRUCTIONS For the CARE and OPERATION Of MODEL A-I-E Hispano-Suiza AERONAUTICAL ENGINES. Wright-Martin Aircraft Corportion, New Brunswick. New Jersey, U.S.A.
To the best of my knowledge this is the only advantage of the 180 degree crank! As I have stated before why anyone would put one in a road car baffles me. At this point I am working on the TVR engine and since I have only a little information on this particular V-8, I am forced to work on the firing order first. It doesn't look good at this point.
The firing order being off by the same amount as the bank angle or 18 degrees. A problem here is the lack of books on the TVR. Yours, M. L. Anderson
[p][Edited by marion5drsn on 11-17-2000]

[Yelnats]

MacFan; I know what you mean when you say that a flat plane crank can be tuned "just like a two stroke" but must question the words "just like".

A two stroke uses a megaphone expansion chamber to produce a backwards echo pulse in the exhaust that drives the next fuel charge (which tends to follow the exhaust gases) back into the still open exhast port before the port closes. So the pressure wave at the port is positive on a 2 stroke. Whereas a flat plane crank engine uses the exhaust pulse of the adjacent cylinder to extract exhaust gases from the still open exhaust port so the pressure wave there is negative.

Same principlal but polarly different applications I beleive.

[Ray Bell]

Flat plane cranks became popular in stock block V8s during the F5000 era, and the cars sounded a lot better for it.
Another time I know of a flat plane crank being used was when an engineer from Repco built up a V8 engine for his Peugeot 403. He made a crankcase and spigotted two blocks and standard heads on it, using a normal crank and rods with the big ends reduced to half normal width. Using 203 pistons, the capacity was 2580cc, and it is said to have gone quite well. There was no lattitude for changing counterweights significantly.

[DangerMouse]

marion5drsn, I'm sure engine vibration could make a significant difference to overall vehicle reliability. However, with modern computer modelling techniques and the advent of fluid filled engine mounts design to damp at certain frequencies I cannot see why it should have an impact anymore! Also inherent balance can be machined into cracks that are naturally out of balance for the same reasons, computers and CNC machining tools mean that the natural balance of an engine isn't as important as it used to be.

I think F1 and (particularly) 4 stoke GP bike engines will see some very strange fire orders and crank angles optimised at maximising traction rather than power.

I believe the Current Mac engine has a weird firing order and the strange sound of it has nothing to do with the exhaust as commented in the press. I bet it fires at weird intervals to give a large 'freewheeling' period (a big bang engine) to gain traction like some GP500 two strokes.

[MacFan]

Yelnats, you are correct, but I said "much like". What I meant was, just as in a 2 stroke engine, careful exhaust design can achieve much more than simple extraction of burnt gases, and can increase power measurably if done correctly.

[desmo]

Interestingly, as far as I can ascertain F1 cranks use only five throws with a pair of con rods sharing each one.

[Yelnats]

Sorry Mac Fan, my reading comprehension skills sometimes leave a bit to be desired.

[karlcars]

We experienced a severe shake problem with the 3.9-liter DFL version of the flat-crank Cosworth V-8 in 1981-82 for Group C racing. Finally admitting culpability, Cosworth set to work on a system of rotating counterbalances for the 1983 season. The stresses involved were indeed high. An engineer recently told me that some of the test units tore themselves out of the crankcase.

Since the engine was planned to be turbocharged for 1983, our best solution would have been to go to a 90-degree crank. I know that exhaust tuning is still important with turbos but I would say that it is less important. For example, the successful Mercedes Group C V-8 engines of 1988-90 raced with 90-degree cranks.

[MacFan]

Karl, can you utilise pulse tuning effects with a turbo engine? I would have thought the turbo would have interfered with that.

[merlyn6]

Thanks all who have replied. I own a Ferrari 355 F1, and have driven the 360 Modina F1, I was wondering why Ferrari went to a flat plane crank. The engines are smooth as can be in both cars, the exhaust sound is awesome, the power is great, but did all that come from a flat plane crank? Is exhaust tuning the only benifit? Are there no torque benifits? I know it works, but am wondering why?

[marion5drsn]

Desmo; Have recieved the copy of Race Tech and the picture of the computer is very much as I believed. Crank has six main bearing and 10 counterweigths. The crank is antisymmetrical end for end and this is one of the reasons for the ten weights.It is my belief that the counterweights also prevent a lot of torsional vibation. My sketches of this were correct. Now I must put in some time and see if the crankarms are arranged as I sketched, as I was using the Dodge firing order. If they are then I will have a better understanding of the whole crank.
Also in this article the statement of the separation of the crankarms from one another is curious as this would mean that the bottom side of the pan might be made into a girdle and the main bearings are supported like the old Allison.
Yours , M. L. Anderson[p][Edited by marion5drsn on 12-22-2000]

[desmo]

Marion,

If you figure out the firing order from the image let us know. The crank throw spacings seem odd to me. I assume a concensus has been arrived at up and down the paddock through trial and error by now on the best crank geometry/firing order by now, although I wonder if Ilmor mightn't be going a different route than the others there.

Thanks,
Kurt

[Martin]

DM,
do I inderstand correctly from this thread that engines might have cranks with more than two planes? I'd never thought of it before. I suppose you could have all the cylinders firing within a few degrees of each other. But what would be the point? I'm curious.
Cheers
Martin

[DangerMouse]

The point would be to enable the tyres to recover from the violence of the engine firing aiding traction.

It's well known in both Superbikes and GP500s that if you get all the combustion strokes out of the way and allow 270+ degrees of crank rotation to be purely freewheeling, tyre wear is decreased and traction is greatly increased - and the riders feel for rear end grip is greatly increased to as the power delivery strangely is much less aggressive.

You’d lose a small amount of horsepower in F1 engines as you’d have to drop the rev ceiling slightly unless you run the engine as 5 sets of 90o twins which would balance perfectly, but the traction and tyre wear benefits are immense.

[Martin]

Surely you'd need a big flywheel to push all the compression strokes at the same (or similar) time?

[Halfwitt]

Originally posted by marion5drsn
Also in this article the statement of the seperation of the crankarms from one another is curious as this would mean that the bottom side of the pan might be made into a girdle and the main bearings are supported like the old Allison.
Yours , M. L. Anderson

Girdle? Allison? Please explain.......

Mr. Dangermouse,

As far as I understand from old bike books, it isn't quite so simple as changing cranks etc. The bearing loads go up massively, and so other crankcase materials need to be used (stiffer / stronger) or the castings redesigned. Suzuki were the first to try it years ago on the old sqaure-four factory RG's (XR70?? not sure). It barely lasted long enough on the dyno or the track before the engine exploded. I know RG 500 crank cases aren't the best in the world, but Suzuki gave up on it. When Honda did it they did it properly, i.e. from a clean sheet of paper, and reaped the benefits in terms of reliability

[DangerMouse]

Halfwitt - quite right, but that was before the days where we can routinely machine balance into intrinsically out of balance designs by nature of computer modelling and CNC lathes!

Martin, there would be nothing to stop you firing your 5 pairs of 90o Twins 3-4 degrees apart once the first one fires it drives the next etc.
For the above reasons the cams could easily be ground given a simple programme, and the ignition system again isn't constrained by any mechanical reasons now ignition systems are computer driven.

[marion5drsn]

Mr. Dangermouse; There is an old article in Race Tech magazine dated August/September 1998 page 18, column three, paragraph three, line 3.
The line states; Losses in respect of pumping air more than oil or water. Contemporary Formula One engines made an important step not long ago when the concept of partitioning the crankcase was introduced. With each pair of cylinders separated from the others,
air is no longer pumped the length of the crankcase. A lot of unnecessary work is saved. End of paragraph.
The article fails to state just how this was achieved!
In World War II there were five Vee type engines used in aircraft. In the U.S.A. the only V-12 was the Allison V-1750, England the V-1650 R-R, Germany the Jumo-211 ((2,136 cubic in.), Mercedes 603 (2714 cubic in.), U.S.S.R. used a Hispano-Suiza of which I have very little knowledge.
Only the Allison used the girdle to my knowledge,altho the others may have used it. This was a piece of aluminum, probably forged, that made up a part of the main bearing. In the pictures that I have it may have been the lower part of the mains themselves. This seems to have run from the front to the back of the engine, which is thought of as the oil pan on most engines.
Puzzle, is the bottom part of the “oil pan” a reinforcement of the mainbearings or is the partitioning just a flimsy piece of material
to prevent the air from loosely going from one area to another?
Yours, M. L. Anderson

[DangerMouse]

Reducing pumping losses through this method have been used on Motorcycle race engines for at least 15 years.

The same methods are being used on road bike engines now.

[marion5drsn]

Mr.Dangermouse; You missed the point,that is; Does the partion become a part of the main bearing web and does the it add to the block support? Since we can't get into the internels of the lower end just how much web support does add, if any? Do you know where have you seen any pictures or text stating whether or not the partions are heavy enough to do this job. If you know of such information please tell me where, as I am always looking for new sources. Yours, M. L. Anderson[p][Edited by marion5drsn on 11-12-2000]

[marion5drsn]

. Desmo; I’ve been working on the sketch in Race Tech magazine. It is the same as the Dodge V-10. Therefore the Firing Order is the same as the Dodge if Judd numbered the cylinders the same (doubtful). The Dodge firing order is # 1-10-9-4-3-6-5-8-7-2. This is front to back with # 1 on the left front viewed from the driver seat. An oddity of this crank is the number one throw has a drilled hole pattern for some reason. Possibly for a pendulum vibration damper.
Pratt & Whiney and others used these on radial engines since the early 1930s, invented by a Frenchman I don’t know just how long ago.
The crank has the usual 5 throws, six mainbearings and ten counterweights. This amount of counterweights is not unusual for an antisymetrical crankshaft. This would be to counteract the fore to aft shake (Moment), which would shake the crank in a 360-degree rotation somewhat like a wobble. All in all it is not much different from what I though it would be. This after doing the Dodge crank.
One of the beautiful things of the 10 counterweights is the reduction of fore to aft torsional vibration in conjunction with the Longitudinal Moment. They also act as a flywheel which these small engines need as they likely have no additional flywheel. Also using counterweights as a flywheel allows the engine to be slightly shorter and smoother in action than a single flywheel in the back of the crank.
Yours With Appreciation, M. L. Anderson

[desmo]

The angles between the throws on the Viper engine are, if memory serves 52 and 90 degrees giving an uneven firing order. The geometry of the crank in the magazine appears nothing like that to me. Aso note that Judd mentions in the article that at the RPMs they run now, they are running into a nasty second-order torsional vibration in the cranks.

[Yelnats]

An interesting concept that a pulsed power output will allow recovery of traction between pulses. One would have thought that the turbine like power delivery of a multi cylinder engine would lower the peak tourque pulses resulting in LESS loss of traction, not more. This is intuitive only but in the history of F1, there has been more than one accepted theory discarded after proving ineffective in practice.

I would be interested to see if there's a theoretical basis to the traction recovery or if it has been extrapolated from the tractable performance inherent to the broad-band tourque delivery of twin cylinder motorbikes.

[Jaxs]

The partition of cranshaft bearings and journals is now quite popular, the current 1400 Peugeot diesel using this configuration within an ally block to achieve the necessary stiffness. The lower half of the main bearings form the lower section of the crankcase and all the bearings caps are removed in one piece and as an integral section. This is apparent in photographs of F1 engine and the bolted section at the crankshaft centre line.

[marion5drsn]

#-1--- 0 deg.--------0 DEG.
#-10- 54 deg.-----72 DEG.
#-9- 144 deg.-----144 DEG.
#-4- 198 deg.-----216 DEG.
#-3- 288 deg.-----288 DEG.
#-6- 342 deg.-----360 DEG.
#-5- 432 deg.-----432 DEG.
#-8- 486 deg.-----504 DEG.
#-7- 576 deg.-----576 DEG.
#-2- 630 deg.-----648 DEG.
90 deg -----------72 DEG.
BLOCK-------------BLOCK
ODD---------------EVEN
FIRE---------------FIRE




Desmo; I’ve been at it again and figuring out the actual degrees of the crankshaft angle on the Dodge and on an engine with a normal 72 degrees firing and bank angle. I’m going to see if I can get it on he net and making it look as it should.
Looking at the engine from the back (Drivers View)
The spacing on the crankshaft is 72 degrees and the bank angle is 90 degrees. This is the reason the firing spacing is 0 degrees and then 54 d instead of 72 degrees. One must remember that the Dodge block is made on the same machinery as the 90-degree V-8s!
A regular V-10 is 72 degrees on BOTH the firing angle and the bank angle All of this shows the reason the Dodge is an Odd fire engine and the Properly designed 72 degree is Even fire.

Yours, M. L. Anderson[p][Edited by marion5drsn on 11-18-2000]

[Hooster]

Flat plane cranck V8 engines don't sound very sweet. All you need is a Playstation Gran Turismo game to find that out. A normal V8 sounds much nicer.

[DangerMouse]

Flat plane cranck V8 engines don't sound very sweet

!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!?

I think you should stop driving a PS2 and try out the real thing! TVRs make an astonishing sound that makes the hairs on the back of your neck stand up, as do F355s I've driven both and to say they don't saound sweet is laughable - sorry!

The Rover/Buick TVRs don't sound anything like the TVR (AJP) engined varients which are stunning.

[marion5drsn]

H=4 x square root of 2 x (r/L) x C x (cos 2 angle)

H= Horizontal force that hammers the engine left to right twice each revolution.

The Horizontal force= (a) 4 times the square root of 2 (b) Times the (r/L) or the radius of the crankshaft arm (1/2 the stroke) divided by the length of the connecting rod centerline of lower bore to centerline of upper bore. © Times the centrifugal force of the upper part of the connecting rod and piston when fully assembled with rings, piston pin and any other miscellaneous parts. This part is easily found in MACHINERY'S HANDBOOK where all the appropriate constants are displayed.
(d) Times the cosine of two times the angle.

When you get through doing this little formula you will have the Secondary Shake. One must also remember that this applies only to the Horizontal and not to use the Vertical. Also this applies only if you have fixed the primary by using 8 counterweights opposite each crankshaft arm.

The Primary happens all the way through the revolution, 360 degrees and is the result of the crankshaft arm not being balanced by another arm at exactly the same point of the stroke on the opposite bank. This is the reason that all the arms need to be balanced opposite each crankshaft arm in any high-speed engine. The Primary should not be confused with the Horizontal Secondary, which happens only twice each revolution.
Primary Moment = 0 (Crank is symmetrical- no wobble end to end)
Secondary Vertical Shake = 0
Secondary Horizontal Shaking force = Above

This is from Kalbs formulas 1934 SAE Journal.
M.L. Anderson[p][Edited by marion5drsn on 11-30-2000]

[marion5drsn]

Flat Plane Crank 180 degree.
Karl Ludvigsen I have been thinking about your input in your post, 11-08-2000 17:28 about the counter rotating weights and their affect on the engine. It did not surprise me about the destruction of the engines in this test. The thing that did surprise me was your statement about how complete the destruction of the engines was. In my sketches of the shape of the force using Kalbs formula the force is narrow and resembles an ellipse slightly rounded on one end and very narrow on the end toward the middle, this on both ends left to right. One must remember that it is a Secondary force!
To duplicate this shape with any counter-rotating device would in my opinion require a mechanical device as a conrod, crankshaft other accoutrement. That is a crankshaft, conrod and piston in exact proportions as the original contained in the block. This would be an excessive burden on the engine just to achieve the counterbalancing forces. The Primary as counter balanced by Wolseley in 1918 is very simply achieved, but heavy in reality. Any other information you have on this test would be very interesting and important to me.
Yours, M. L. Anderson