Flat-plane crank V8's are back, Ford AND Chevy!

I find the coming Chevy flat-plane ZO6 engine more interesting than some mechanic forgetting to turn off the tattle-tale in a car he is test driving.

Now Ford and Chevy will both have flat-plane crank engines.
What are the strokes of those engines?
Flat-plane cranks usually have short strokes or they get more vibration than modern "Princess and the Pea" sensitivity level drivers will tolerate.
Of course if the block is a clean sheet design they can always lean on the Balance Shaft crutch.
Which adds complexity, weight, and expense.

Will this herald the return of flat-plane cranks and matching cams to the aftermarket?
Really wanted an FP crank for my 327 build.

The C8 Corvette Z06 will be powered by a 5.5-liter V-8 engine derived from the unit that powers the Corvette Racing C8.R. Known internally as the LT6, this V-8 features dual overhead camshafts and a flat-plane crankshaft. Thanks to that Ferrari-esque layout, the Corvette Z06 is expected to rev up to around 9000 rpm and produce a reported 617 hp in the process. 

*scans quickly, nothing about V8s in the 2.5l range, dismisses news*

Zero interest in big truck engines.

The sound though...

Let's hope they don't eat themselves alive ala GT350.

Ford's flat plane is already dead isn't it? They ditched the flat plane for the GT500, and the GT350 is no more.

Pete. (l33t FS) said:

*scans quickly, nothing about V8s in the 2.5l range, dismisses news*

 

Zero interest in big truck engines.

Only 336", so smaller than the 350's of recent vintage.

STM317 said:

Ford's flat plane is already dead isn't it? They ditched the flat plane for the GT500, and the GT350 is no more.

Really? Already?
Too bad, the sound as they came up the grade at Virginia City wide open was pure music!
Never saw what their stroke was.
No inherent reason for FP cranks to fail any sooner than bent cranks.

I think crossplane v8s sound better at high rpms than flat plane ones. Generally though, the advantage of a flat plane is that they come on song when a crossplane hits the limiter.

I tried really, really, hard to get an aluminum block and flat-plane crank for my 327.
Neither got to happen, both are technically available but just too many $$$.

In theory I could get the same sound from a "Bundle of snakes" header set but it's a lot of work just to confuse people. Still might be worth it. 

RichardSIA said:

STM317 said:

Ford's flat plane is already dead isn't it? They ditched the flat plane for the GT500, and the GT350 is no more.

Really? Already?
Too bad, the sound as they came up the grade at Virginia City wide open was pure music!
Never saw what their stroke was.
No inherent reason for FP cranks to fail any sooner than bent cranks.

Ford's "Voodoo" flat plane v8 is 5.2L which is pretty large for a flat plane engine. It will turn 8250rpm. The info I'm seeing says 94mm bores and 93mm stroke. They run 12:1 compression. I believe they've had some oil consumption and NVH issues as they've acquired more miles.

 I believe they've had some oil consumption and NVH (?) issues as they've acquired more miles.

Seems unlikely that those are accounted for by the FP crank so would seem to be related to other design elements.
Oil issue could be related to the high RPM.
I wonder if the Chevy will have similar issues.

My acronymese is weak today, NVH = ?

Noise, Vibration and Harshness.

The problem with flat plane V8 cranks is fundamental. Due to the way the pistons move on that crank design, you end up with a secondary imbalance that can't be designed out. When displacement gets high enough, the inherent vibrations become a problem. Not in a "princess and a pea" way, more in a "stuff keeps breaking" way. That's what balance shafts are intended to address, and I've been told that the tendency for the Ford flat plane engine to take apart transmissions with vibration is why it was never offered as a crate engine. They sound like twin four cylinders which some people like, but it's hard to come up with more justifications for the design than that.

Cross-plane V8 cranks are perfectly balanced from a physics viewpoint. There's a good reason it's been a dominant engine configuration for well over a half century.

I am aware of the vibration issue, it is why FP engines need to keep the stroke down to around three inches or less.
Note the reduced displacement of the ZO6.
True Ferrari's* kept the FP stroke short and added four more cylinders.

If a 3.25" stroke FP SBC crank were to appear at my doorstep I would still run it.

There  is a company selling complete FP SBC's, they will not sell cranks or cams separately.
As I recall they are selling 327's not 350's.

*"A Ferrari is a twelve cylinder automobile".
Enzo Ferrari.

I don't believe Ferrari used flat plane cranks in their V12. The Colombos certainly weren't. The "boxer" (not really, it was a 180* V12) might have been. The different bank angle would have affected the physics.

One reason to keep the stroke down in a flat plane V8 (it's important to remember that different engine configurations require different ideal crank designs, so you cannot generalize to all flat planes) is to let it rev, because that's when it's going to make power. 

RichardSIA said:

I am aware of the vibration issue, it is why FP engines need to keep the stroke down to around three inches or less.
Note the reduced displacement of the ZO6.

Some data points:

The Ford Voodoo is loosely based on the 5.0 Coyote with a cross plane crank. They actually increased displacement and stroke length when implementing the flat plane crank.

GM's flat plane engine is 5.5L primarily because that's the maximum displacement now allowed in their primary racing class for the C8R. Reducing the displacement may also be beneficial for the flat plane crank design (5.5L is still a pretty large flat plane v8), but it's not the only reason they're now running a smaller engine than in the past.  GM went clean sheet with an all new 5.5L engine with DOHC and a flat plane crank specifically for the race car that is very likely to end up in some high performance street cars too.

STM317 said:

RichardSIA said:

STM317 said:

Ford's flat plane is already dead isn't it? They ditched the flat plane for the GT500, and the GT350 is no more.

Really? Already?
Too bad, the sound as they came up the grade at Virginia City wide open was pure music!
Never saw what their stroke was.
No inherent reason for FP cranks to fail any sooner than bent cranks.

Ford's "Voodoo" flat plane v8 is 5.2L which is pretty large for a flat plane engine. It will turn 8250rpm. The info I'm seeing says 94mm bores and 93mm stroke. They run 12:1 compression. I believe they've had some oil consumption and NVH issues as they've acquired more miles.

I think it's on the order of "add a quart of oil every time you get gas" type of oil consumption.

I haven't looked at prices for them during this pandemic, but before this hit, the used values of GT350s had really taken a beating because of the engine issues. It was not a problem to find sub-10k mile cars in the low 40s. 

In reply to STM317 :

IIRC, the racing version of the Corvette has used a smaller displacement engine for some time due to the rule set.

Keith Tanner said:

In reply to STM317 :

IIRC, the racing version of the Corvette has used a smaller displacement engine for some time due to the rule set.

Yeah, you're correct. I'll edit the post above to avoid misinformation.

Yeah the previous race engine was a 5.5 ls7 based engine.

Keith Tanner said:

I don't believe Ferrari used flat plane cranks in their V12. The Colombos certainly weren't. The "boxer" (not really, it was a 180* V12) might have been. The different bank angle would have affected the physics

I am pretty sure that all V12s are "flat plane", in the sense that a flat plane V8 is different from a crossplane because the firing order is evenly spaced on each bank.   Given that an inline six has extremely good balance, and a V12 is more of the same when used with inline sixes' firing order on each bank, I can't see why someone would intentionally make an uneven firing V12.

From what I can see, the definition of flat plane is geometric: all the crank pins are in line. Firing order is a side effect.

Here's the Colombo crankshaft - clearly not a flat plane. Looks like it has the pins spaced out with 120* between them, which makes sense. A cross plane V8 has them at 90*.

If you want to get a certain type of person excited, call a 180* V (like the flat 12 Ferrari) a "boxer" (despite what Ferrari called the car). This is the sort of person who complains that the flat six in the big LEGO 911 GT3 kit is a 180* V6 and not the boxer it should be due to the crankshaft design. I am friends with this kind of person :)

In reply to Keith Tanner :

I always assumed that "flat plane" just described the crankshaft necessary to get an even firing per bank V8, so the term went with "even firing" rather than the actual shape of the crankshaft.

Keith Tanner said:

From what I can see, the definition of flat plane is geometric: all the crank pins are in line. Firing order is a side effect.

Here's the Colombo crankshaft - clearly not a flat plane. Looks like it has the pins spaced out with 120* between them, which makes sense. A cross plane V8 has them at 90*.

If you want to get a certain type of person excited, call a 180* V (like the flat 12 Ferrari) a "boxer" (despite what Ferrari called the car). This is the sort of person who complains that the flat six in the big LEGO 911 GT3 kit is a 180* V6 and not the boxer it should be due to the crankshaft design. I am friends with this kind of person :)

If you want more excitement point out that a 917 engine is actually a 180 degree v12 aswell but with air cooling.

We need a pic of the Lampredi crank.
If only for the eye candy.

Never claimed the FP cranks are superior, just interesting that they have made a come back.
Weather it endures only time will tell.

And I still want one for an SBC.
I know where there is a raw forging for an FP Buick/Rover crank.
High dollars and much more to be spent to make an actual part.