12 replies to this topic

[Peter]

There has been quite a lot of talk by the teams of problems with vibrations from the new 2.4 V8s.

I would have thought that this would have been less than the V10s with their inherrent "oddness" of crank angles.

So what is the problem?
Did Cosworth have this issue with the DFV engines? If so, how did they overcome it?
Is it because the engines rev much higher these days? Is it something to do with the vee angle?

(Obviously a straight 6 has good dynamic ballance and a boxer 12 will presumably be the same but what is giving the "new" problems?)

[Rainer Nyberg]

This answer comes from Luca Marmorini of Toyota from the Toyota F1 website.

Quote

From http://www.toyota-f1...20050715-2.html

Why does a V8 engine vibrate more?
A 12-cylinder engine is fully balanced and you can have some 10-cylinder engine configurations that are well balanced. For example, the current Toyota V10 has very few vibrations. But if you use a 90-degree block and a flat crank typical for a V8, it’s impossible to balance the second order vibrations. With a road car engine you might do it with a counter-rotating shaft, but on a racing engine, you don’t. That is one of the main reasons why we wanted to run the engine so early. It is not so much for direct engine purposes but to monitor the components around the engine and the effects of the extra vibration.

[Paolo]

Quote

Originally posted by Rainer Nyberg
But if you use a 90-degree block and a flat crank typical for a V8, it’s impossible to balance the second order vibrations

And what happens if I use a non-flat crank ?
I'm no engine expert, but seem to recall that there is an "ideal" angle to minimize vibrations for each configuration.
That angle is given by 360/(number of cylinders per bank)
It amounts to 60° for V12, 72° for V10, 90° for V8, 120° for V6.
So how comes that the "ideal" V8 vibrates so much ?
Maybe these configurations are intended for a different type of crank ?

[GeorgeTheCar]

Peter,

Most of the issues are covered in the V-8 90 degree crank thread and you should read that and if you have questions, pose them then

[TDIMeister]

Quote

Originally posted by Paolo


And what happens if I use a non-flat crank ?
I'm no engine expert, but seem to recall that there is an "ideal" angle to minimize vibrations for each configuration.
That angle is given by 360/(number of cylinders per bank)
It amounts to 60° for V12, 72° for V10, 90° for V8, 120° for V6.
So how comes that the "ideal" V8 vibrates so much ?
Maybe these configurations are intended for a different type of crank ?

This formula applies to ensure that the engine has equally spaced firing events, but does nothing to address reciprocating- and rotational imbalances, the former referring to the complement of pistons going up and down their respective bores and the latter dealing with non-sinusoidal articulation of the connecting rods.

There are certain combinations of cylinder count, vee-angles and crankpin angles that result in perfect balance, most of which are already well known. Others "deal" with imbalance by balancer-shafts, crank counterweighting, engine mount design or nothing at all...

To address your question in the first line of your post, a 90-degree crank in a 90-degree V-8 can be made to balance provided the reciprocating assembly are suitably counterweighted at the crank. However, this adds a lot of added weight to the crank, both for an extra plane of crankthrows and for counterweights, plus the inherently reduced crank stiffness. Also, as has been discussed before, exhaust scavenging becomes more complicated because there are instances of two cylinders on the same bank having their exhaust strokes in rapid 90-degree CA succession followed by long dead periods.

All these factors tend toward 180-degree cranks being the de facto preference for V8 F1 engines, although it might not be out of the question for a renegade team to field an engine with a 90-degree crank...

[phantom II]

Intersting aticle in this months Hot Rod about a 4/7 swap on firing order in a small block 2 plane Chevy. Someone posted an article on the Maserati and Ferrari V8. The 360 has a flat crank with a highly specialized intake that accounts for the extra power at a cost of additional engine and valve train stresses due to vibrations.

Quote

Originally posted by TDIMeister


This formula applies to ensure that the engine has equally spaced firing events, but does nothing to address reciprocating- and rotational imbalances, the former referring to the complement of pistons going up and down their respective bores and the latter dealing with non-sinusoidal articulation of the connecting rods.

There are certain combinations of cylinder count, vee-angles and crankpin angles that result in perfect balance, most of which are already well known. Others "deal" with imbalance by balancer-shafts, crank counterweighting, engine mount design or nothing at all...

To address your question in the first line of your post, a 90-degree crank in a 90-degree V-8 can be made to balance provided the reciprocating assembly are suitably counterweighted at the crank. However, this adds a lot of added weight to the crank, both for an extra plane of crankthrows and for counterweights, plus the inherently reduced crank stiffness. Also, as has been discussed before, exhaust scavenging becomes more complicated because there are instances of two cylinders on the same bank having their exhaust strokes in rapid 90-degree CA succession followed by long dead periods.

All these factors tend toward 180-degree cranks being the de facto preference for V8 F1 engines, although it might not be out of the question for a renegade team to field an engine with a 90-degree crank...

[Wuzak]

Quote

Originally posted by TDIMeister

All these factors tend toward 180-degree cranks being the de facto preference for V8 F1 engines, although it might not be out of the question for a renegade team to field an engine with a 90-degree crank...

I wonder....

Do you think it is possible that someone might see a benefit in the 90° crank, and place the exhaust in the vee so as to be able to get the exhaust scavenging effect?

There were a few F1 and Indy cars that had the exhaust in the vee during the '60s.

[Halfwitt]

I'm not sure there is that much to be had from this exhaust scavenging effect. All of the pictures I've seen so far show a 4-into-1 collector, not the 4-2-1 you would expect if this effect was being taken advantage of fully.

[12.9:1]

It's difficult to get the pipes short enough for tuning at high speed, so no room for, 4-2-1

[TDIMeister]

Not only that, but routing the header runners under the engine for a cross-flow exhaust implies having to raise the engine, raising the CoG. That is a bad word in F1.

[vvillium3]

weren't there engines that ran in reverse where the exhaust and intake were in their opposite position???? If this were done, scavaging could be done with a 90 deg crank... Obviously this isn't done now, why is that?????

[GSX-R]

The answer is less. At least for crossplane V8.

[TDIMeister]

Quote

Originally posted by vvillium3
weren't there engines that ran in reverse where the exhaust and intake were in their opposite position???? If this were done, scavaging could be done with a 90 deg crank... Obviously this isn't done now, why is that?????

I think this could be a big, big reason as well, a trait that plagues any DOHC cross-plane V8, and much more so an engine that would rev in the F1 realm:

Quote

Production V8 engines almost always use a two plane crankshaft (four crank throws disposed at 90 degree intervals) which provides good balance but an uneven firing order along each bank. Because of this a four cam production V8 inevitably has the cams asymmetrically phased around the axis of each camshaft as shown in the diagram. This gives rise to irregular loads on the drive between the crankshaft and the cams and between the two camshafts on each head.

It is perhaps then not surprising that on the Jaguar V8 the tensioners on the secondary camshaft chains in particular have developed a reputation for being troublesome. In fact it may not be that there is any weakness in the tensioners themselves, rather that at certain critical speeds heavy torque reversals on the chain can produce higher than expected stab loads, a condition which can probably be exacerbated by some usage patterns. It is perhaps interesting that the later 4.2 V8 uses more rugged morse internal tooth primary chains and that when BMW introduced a similar V8 (four valve, twin OHC, Nikasil bores, sintered fracture split con-rods) in 1992 they used duplex chains throughout. Whilst Jaguar's design team, in choosing a single link chain drive, did specify that it should be rated for heavy duty, one wonders if there have been any regrets that space wasn't made to use a duplex chain rather than relying on the lightweight valve gear to let them get away with the narrower option?

(source: http://www.jagweb.co...erformance.html )