Flat plane crank?

[si b.]

Gentlemen,

It's Tuesday 3.55 and here is your starter for ten!

Bit of a teccie question and maybe I'm being a bit thick (I know a fair ammount about engines) but what the hell is a flat plane crank?????? and how does it help the TVR engines performance.

You don't have to be too gentle on me I know what a crank is!!!!!

Answers on a postcard please..........

Cheers,

Si

[Bob C]

I think!

A flat plane crank is one where all the big end journals are in one plane i.e. half the pistons would be at TDC and the other half at BDC. And I think the reason for this is that it makes the crank much stronger.

or maybe its all b*ll*cks

[MikeyT]

I remember reading a great description of the AJP Cerbie engine (flat plane crank) somewhere on the net but can't remember where. Think it said it sounds more like two V4 engines running together than a traditional V8 (ie the Rover lump)

No doubt the more technical members will be able to put all this in English

TVR owner one day

[bertie]

Yep, A flat plane crank has all it's journals at 180 degrees and would hence lie flat rather than the traditional crusifix crank of the woofley Rover V8 with journals at 90 degree intervals.

This gives less low down torque as you get two large bangs per rev rather than 4 smaller bangs per rev if you get me, but does make better top end power as you can tune the exhaust scavenge better. However they are less refined at low revs.

The other advantage to TVR is that you can use a standard 4 cylinder engine management unit.
Also you are effectively only working on a 4 cylinder unit, albeit 2 fitted onto 1 crank.

Developing and calibrating a true V8 ECU is much harder.

This also applies to the speed six which runs as 2 3 cylinder engines end to end hence it's rather different character to your normal straight 6.

[Alistair H.]

So does that mean that two plugs are sparking at once?

[bertie]

Yes, wasted spark as it's called.

[tvrmark]

If you had a wasted spark system on the AJP wouldn't you have 4 plugs sparking at the same time. 2 at the firing stroke 2 at the begining of the induction stroke. While the others are on the upwards strokes 2 on compression and 2 on exhaust

Mark

[si b.]

Thanks guys, the penny's dropped now, pretty logical when you think about it!

Never been in a TVR powered TVR (Griff 500 owner see), sounds like they must run like a bag o'nails at low revs but with plenty of character!!

I can now sleep at night, thank you!

Cheers,

Si

[Greenv8s]

quote:
Thanks guys, the penny's dropped now, pretty logical when you think about it!

Never been in a TVR powered TVR (Griff 500 owner see), sounds like they must run like a bag o'nails at low revs but with plenty of character!!

I can now sleep at night, thank you!

Cheers,

Si

If you want to hear what a flat plane crank V8 sounds like at 8000 rpm, listen to the video of my V8S going up Loton Park ( www.roop.ik.com -> Index -> Videos ).

Cheers,
Peter Humphries (and a green V8S)

[tvrmark]

Pete,

You haven't got a flat plane crank; have you?

Mark

[bertie]

Not unless he's fitted an AJP engine into his S.
The Rover is a crusifix crank.
Also it's a pushrod engine so it's unlikely, though not impossible, to rev to 8000rpm.

[ewl]

. in the motorcycle world this subject was introduced by phil irving, the designer of the vincent motorcycle engine.it waS IN regards tothe british vertical twin, its vibration and necessity for a large flywheel to overcome inertia forces at top and bottom dead centre. he proposed a 76 deg crank interval as with a rod of twice the stroke this gives one piston at maximum speed while the other one is stopped. in practice 90 deg has been found to be at least as good, enabling lighter cranks and the quicker revving drivers swear by.the rule then seems to be crossplane cranks in straight engines and flatplane in v engines to balance inertia forces of pistons, .yours, ewl.

[clive f]

here you go............

http://www.projectm71.com/Cross_FlatPlane.htm

[pacman1]

Holy thread resurrection Batman!

eta, welcome aboard ewl!

Edited by pacman1 on Saturday 26th November 06:30

[scotty_d]

si b. said:

Thanks guys, the penny's dropped now, pretty logical when you think about it!

Never been in a TVR powered TVR (Griff 500 owner see), sounds like they must run like a bag o'nails at low revs but with plenty of character!!

I can now sleep at night, thank you!

Cheers,

Si

They are not to bad low down to be fair i found my chim 400 worse around town than the Cerb. But it does not like speeds below 50 mph TBH it just wants to rev and rev hard!!!!

[cjj799]

As you probably all know, Ferrari V8's are flat plane crank engines. That is why for example a 430 or a 458 sounds completely different to say a Merc AMG or a McLaren MP4 12c which have cross plane cranks.

[Bassfiend]

Basically ...

Flat plane = screamer

Cross plane =



Phil

[Mark.]

scotty_d said:

They are not to bad low down to be fair i found my chim 400 worse around town than the Cerb. But it does not like speeds below 50 mph TBH it just wants to rev and rev hard!!!!

This.

My Cerbera is far better around town than the Chimaera, pootles around in 4th at 30/40 mph, where as the Chimaera seems to be 'between gears' at that.
But it's further round the right of the speedo the AJP comes to life, it just never, ever seems to run out of steam!

[miniman]

What a waste.

3 more days and that would have been a DECADE thread resurrection.

[ewl]

thanks for the link, i've been trying to work out why if a 90 deg v twin has perfect balance and a flatplane v8 is 4 90 deg twins together, then why did early flatplane v8 s vibrate. this looks like it will help my mental processes,.ewl