A visual example of the 90 degree crank drawback.

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SchmidtMotorWorks
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Re: A visual example of the 90 degree crank drawback.

Post by SchmidtMotorWorks »

Tom68 wrote: Sun Oct 02, 2022 4:16 am Wow, I guess they had to try it, but anything over a pissant capacity that is being used in a weight sensitive environment is always going to be a disaster.
Weight isn't the problem with flat crank counterweighting.
The problem is that there is no counterweight design that will counter the piston vibrations which are at a different frequency.
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Re: A visual example of the 90 degree crank drawback.

Post by PackardV8 »

The general consensus on four cylinders is anything larger than 2.0 liters requires a balance shaft to have OEM levels of smoothness. What do you consider the upper displacement limit for a V8 flat crank in an OEM application? FWIW, both Ford and GM are now larger than I'd have thought.

OT random recollection - the V10 Ford truck engines are smaller displacement than the Mopar V10s, but the Fords have a balance shaft on the top of the left cylinder head; who'da thought to look there?
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Re: A visual example of the 90 degree crank drawback.

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PackardV8 wrote: Sun Oct 02, 2022 4:02 pm The general consensus on four cylinders is anything larger than 2.0 liters requires a balance shaft to have OEM levels of smoothness. What do you consider the upper displacement limit for a V8 flat crank in an OEM application? FWIW, both Ford and GM are now larger than I'd have thought.

OT random recollection - the V10 Ford truck engines are smaller displacement than the Mopar V10s, but the Fords have a balance shaft on the top of the left cylinder head; who'da thought to look there?
The vibrations mostly come from the reciprocating mass so the V8 in a flat plane crank config doesn't have any cancelling benefit. It just combines the vibrations of from two banks. It might be a little better to vibrate in two directions, but not much.

Given that the Yamaha does very well going intentionally away from a flat crank (and sound fantastic), I don't see any good reason to bother with them.
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Re: A visual example of the 90 degree crank drawback.

Post by skinny z »

The new Vette has a flat plane crank.
What's up with that?
5.5 litres. 4.104 x 3.150 stroke.
8400 RPM! (I had to read that twice).
Is it the short stroke that makes it workable?
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Re: A visual example of the 90 degree crank drawback.

Post by ptuomov »

I think that a flat plane V8 could be balanced with a single balance shaft if the shaft can be placed very close to the crankshaft. One idea would be to take an existing cam in block engine, use the camshaft tunnel to run a balance shaft at 2x engine speed, and install heads with overhead camshafts. Anyone done that?
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Re: A visual example of the 90 degree crank drawback.

Post by BLSTIC »

The falcon 6 (in the sohc iteration, not pushrod or barra dohc) ran an accessory drive drive shaft approximately where the camshaft used to be in the earlier engines. I think all it does is drive the distributor/tdc#1 sensor (depending on ignition system) and oil pump

It's not a balance shaft, but it's an example of a legacy hole being used in a ground up design
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Re: A visual example of the 90 degree crank drawback.

Post by Tom68 »

skinny z wrote: Sun Oct 02, 2022 4:38 pm The new Vette has a flat plane crank.
What's up with that?
5.5 litres. 4.104 x 3.150 stroke.
8400 RPM! (I had to read that twice).
Is it the short stroke that makes it workable?
It is stroke limited like all flat plane V8's they pushed the envelope with 3.15, even if you ignore the vibrations and go longer the motor and everything attached to it ends up too heavy in an effort to avoid failures.

Ford changed the orientation of the crank pins, arguably doesn't do much but it's a smallish capacity motor anyways.
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Re: A visual example of the 90 degree crank drawback.

Post by SchmidtMotorWorks »

ptuomov wrote: Sun Oct 02, 2022 5:37 pm I think that a flat plane V8 could be balanced with a single balance shaft if the shaft can be placed very close to the crankshaft. One idea would be to take an existing cam in block engine, use the camshaft tunnel to run a balance shaft at 2x engine speed, and install heads with overhead camshafts. Anyone done that?
I have modeled it in CAD, IIRC, it was possible to reduce it, but not eliminate it.
I suppose that it would be possible to make some rings that rotate on the crank axis, but why make a contraption like that?
For what application and what benefit?
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Re: A visual example of the 90 degree crank drawback.

Post by ptuomov »

SchmidtMotorWorks wrote: Sun Oct 02, 2022 11:16 pm
ptuomov wrote: Sun Oct 02, 2022 5:37 pm I think that a flat plane V8 could be balanced with a single balance shaft if the shaft can be placed very close to the crankshaft. One idea would be to take an existing cam in block engine, use the camshaft tunnel to run a balance shaft at 2x engine speed, and install heads with overhead camshafts. Anyone done that?
I have modeled it in CAD, IIRC, it was possible to reduce it, but not eliminate it.
For what application and what benefit?
Good question, I wouldn’t invest in a project like that. However, you might find some small series normally aspirated sports car application for it. The benefits would be marketing, ability to use an existing block design, and maybe some emission benefits from exhaust side of one needs the catalyst close to the exhaust ports. But one might as well just use the regular cross plane or flat plane Ford 4-valve engine (or copy it). So this was just technical speculation, the economics ignored.
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