Flat plane and roller crankshafts

[Pasquale]

Question 1
Does a flat plane V8 crank offer any performance advantages over a 90deg? Or for a better question, how do the characteristics of the 180* differ from the 90*. eg more top end/high rpm. I know many Ferrari V8's have flat cranks, are there other manufacturers that have used/use them? What about in racing? eg F1? I know in drag racing there have been only a couple of unsuccessful attempts.

Question 2
Basically same as above but for roller/ball bearing crankshafts. Any manu's using them other than motorcycle? Racing? How much of an advantage would it be?

Just curious.
Pat.

 

[EngJW]

#1-

The flat plane crank has a different firing order. The cylinders alternate by firing across banks. With the 2 plane crank, there is one pair of cylinders that fire one after the other. It is easier to design an exhaust system for the flat crank with 180 degrees between pulses, so a single header can be used for each bank. To get this same interval with a 2 plane, the headers have to cross over between banks (the Ford Indy engine of the 1960s and some Grand Prix engines around that time.)

The problem with the flat plane crank is the second order unbalance is larger than on a 4 cylinder, so it is hardly ever used for passenger cars.

#2- not aware of any roller bearing crankshafts other than for 2 stroke engines which do not have pressurized lubrication. On second thought, there is a 4 stroke industrial engine that uses them because they will accept higher belt loading than a sleeve bearing. It has splash lubrication.

John Woodward

 

[patprimmer]

A company called Okraza (spelling?) used to make a roller bearing (big end only) crank for air cooled VW's.

It gave advantages with the stock VW oil system which was inadequate for high performance.

Once aftermarket high performance oil systems became avaliable, the roller crank fell by the wayside, as it's only advantage of surviving in poor oiling situations was no longer a benifit.

Slipper bearings are actually more ductile, and have much larger effective bearing areas than rollers, and therefore can withstand higher shock loadings without fracture

Regards
pat

 

[tbuelna]

pasquale:

The only advantage to a flat crank (180 degree pins) vs. a cruciform crank (90 degree pins), in a V8 engine, is that you can obtain evenly spaced exhaust pulses on each cylinder bank. This makes a very effective 4-into-1 exhaust
header. The downside is a very nasty secondary force unbalance, that increases somewhat exponentially with stroke length. The cruciform crankshaft also does not produce perfect balance, but still can produce very smooth running with proper counterweighting.

With regards to roller bearing cranks, the only benefit to be gained is reduced frictional losses. In reality, a well designed journal bearing is very competetive,friction-wise, to a rolling element bearing. Most engine manufacturers went through the roller-bearing-versus-journal-bearing trade studies many years ago. The drawback to roller bearings, is that with the load reversals experienced by the reciprocating components in four stroke engines, roller rod and wrist pin bearings literally get beat to death.

good luck.
terry

 

[Pasquale]

It makes sense that a journal bearing has much more load bearing area than a handfull of small rollers or balls. I just thought the friction benefits might exceed the structual issues.

Is that really the only benefit in a flat crank (the exhaust)?

 

[patprimmer]

There can also be inlet tract advantages if a single plane manifold is used, but not so for individual runners from a big plenum, or dual plane manifold.

There is also reduced risk of crossfire, but carefull routing of leads eliminates crossfires without need for a flat plane crank.

Otherwise, each cylinder displaces the same volume, and each port still flows the same, and etc etc

Regards
pat

 

[Pancholin]

I built a ball bearing rod once for a Triumph 200cc single. I used a double row ball bearing and at first it seemed to work ok. Sooo I took it out to give it a shakedown run. Shakedown is putting it mildly! Centrifugal force took over at high RPM and the retainers and all the balls went to the far side. So much for the Triumph Cub. RIP! However the smaller and more positively retained needle bearings in other engines seem to work fine in both ends of the rod.
Pancholin