An idle thought - engine design

[V Mad]

I was enjoying the lovely burble of my stag engine today as I was driving back from Brooklands Museum. My mind wandered to the question why did the designers choose a cross-plane V8 over a flat plane V8. I think the cross plane engines sound superb, so I am glad they went that way, but since many high performance cars have flat plane V8s, why was that not chosen for the stag? In fact American V8 engines, and other 'British' built V8 engines eg the Rover (Buick), Rolls Royce, and Turner designed Daimler V8 engines were also cross-plane.

I think the reasons for this choice were covered in one of the stag books. Maybe someone on here can recall it?

[Klaus Schlueter]

Some explanations are here:

http://en.wikipedia.org/wiki/Crossplane

The German wiki page explains that the "unevenly spaced firingwithin a bank of four cylinders" in combination with a seperate exhaust system for each cylinder bank causes the typical V8-burbel which we all like.

Klaus

[V Mad]

Yes Klaus, but my question was, what decided Triumph engineers to use the cross-plane? I bet is was a becuase of the cost!

(Flat plane or single plane is covered here http://en.wikipedia.org/wiki/V8_engine)

[Klaus Schlueter]

Interesting link Chris, very interesting infos. Concerning cost: why do you think the cost of the cross plane is lower than the cost of flat plane?
Klaus

[V Mad]

Off hand I dont know, perhaps someone here will know?

[Guest]

I was enjoying the lovely burble of my stag engine today as I was driving back from Brooklands Museum. My mind wandered to the question why did the designers choose a cross-plane V8 over a flat plane V8. I think the cross plane engines sound superb, so I am glad they went that way, but since many high performance cars have flat plane V8s, why was that not chosen for the stag? In fact American V8 engines, and other 'British' built V8 engines eg the Rover (Buick), Rolls Royce, and Turner designed Daimler V8 engines were also cross-plane.

I think the reasons for this choice were covered in one of the stag books. Maybe someone on here can recall it?

I think you have far too much time on your hands Chris

Jason

[KOY 23]

Nothing to do with cost and the Stag is hardly a high performance engine.

Cross plane cranks have large counterweights to give perfect balance, this gives a high inertia but smooth running. Flat plane cranks are nor perfectly balanced and balance cannot be solved by counterweights, so it is not smooth but has low inertia, allowing it to rev high and quickly. OK for racing engines where vibration is not a problem. Road going flat plane cars need balancer shafts.


edit. Just read the wiki article which confirms the above.

[V Mad]

I think you have far too much time on your hands Chris

Jason

I am 'retired' Jason. that's the plus side of getting old. Time to reflect and indulge I think.
Also I have my tax returns to finish and so I am easily distracted.

[73stagman]

http://youtu.be/2AzrOPPZFzs

This video will help explain the difference if anyone is still guessing!

[V Mad]

Nice one, it does help to see it animated.

[V Mad]

OK for racing engines where vibration is not a problem. Road going flat plane cars need balancer shafts..

I dont think they use balancer shafts on V8 roads cars do they? (Ferrari, Aston etc).

[Ian Durrant]

I am sure I read that triumph did experiment with a flat plane crank but the vibration was terrible so they abandoned the idea. I wish I could remember where I read that.

[KOY 23]

I dont think they use balancer shafts on V8 roads cars do they? (Ferrari, Aston etc).

Just Google it and argue with Google.

Are you sure the Aston is flat plane?? It is based on jag AJV8 which is cross plane.

[Staggard]

Just Google it and argue with Google.

Are you sure the Aston is flat plane?? It is based on jag AJV8 which is cross plane.

AAAAAAAH Google holds the mistery of life, who needs Monty Python

[Jeff]

Even wiki suggest the Stag engine is 2 Dolomite engines 'welded' together.

'In its simplest form, it is basically two straight-4 engines sharing a common crankshaft'.