Accessible Flat Plane Crank V8s

Anyone dropped a flat plane crank V8 into anything else?

RX7 motors from Mazda just went through a massive price increase. We will see if it sticks, but the new list price is $13k for a keg, up from ~$6k. Vendors are already adjusting prices to $9k+, and with a decent sized turbo they just don't last that long, ymmv. You see where this is going.

The noise and power delivery of a flat plane crank V8 is enticing.

I know there's the Voodoo, don't know much else about it.

The new C8 Z06 LT6 is now out in the wild, this would be great, but isn't offered as a crate engine yet and might not be. Not many crashed ones either. I can also imagine this being sold at a crazy premium just because. Not sure how much it actually shares with other Chevy V8s, I'm guessing not much. Electronics might be tricky

Ferrai has their 458 V8, that would be the dream soundtrack. But the "cheaper" version that came in the Maseratis is a cross plane crank. The only swap I've found using a 458 engine was running Motec, and with Motecs micro-transaction style software, that's just not a road I want to cross. This would easily approach the cost a billet 3 rotor..

Ford's  GT350 had one. But they didn't have a reputation for longevity. Another option might be 180 deg. headers if sound is what you are persuading. In fact, that's exactly the answer.

Lol you're technically correct, but not emotionally correct. If I'm replacing the rotary, a normal LS with headers just ain't special enough.

I really hope the LT6 is offered as a crate

A couple groups have made cranks and cams to turn a regular ls into flat plane cranks.

A while ago I though I remember there being a kit for LS based blocks that made it flat plane.   Could be wrong on this.  I would assume all you need is a custom crank and cam. The rest could be off the shelf LS stuff. 

For this kind of cash outlay, the Ferrari engine might be

a viable option.

Plenty of flat-plane conversion cranks out there.  The real issue is why OEMs haven't embraced them.  They don't last long.  The harmonics created by a flat plane crank are pretty deadly, hence whey Ford (even with its 8-figure R&D budget) couldn't get the GT to last longer than from here to the end of the warranty period.

The real reason flat-plane cranks make power is that they demand equal air both in and out of the cylinders, which is also why they make the sound they do.  Flat plane cranks are also inherently easier to balance, making them lighter.  The real place for a flat plane crank is for max-effort, high-revving race applications where parts are disposable.  Reverse-engineering it into a street/track engine is a bit folly if you ask me... especially when you can get the same sound with 180 headers, and honestly, below 6000 rpms, the same power and potentially more torque from a cross-plane.  Even NASCAR and those multi-thousand-hp top fuel dragsters use cross-plane cranks.

Having said that... I'm all for it.  Do it.  But if you're looking for bragging rights, I would sooner use 180 headers and have something that will last longer than one season.

Video is a must.  You must post videos.  That is my only rule.  Can we agree on that, folks?

I've kinda wondered what machining it might take to get a VW 4 cylinder crank into a 3.6 V8.  The 4.2 has different bore spacing, but the 3.6 is the same 88mm bore spacing and the right head is the same as a 16v.  You'd use two sets of 16v cams.

I'm thinking that the crank might not have enough extra room to make the rod throws wider, but it might work with a combination of widened throws, heavily narrowed rods, and running the rods offset in the pistons.  One of the hurdles to overcome would be that I've never seen a VW four crank, but the Audi fives (same lineage) have rolled fillets on the rod and main journals.  They basically use rollers to locally peen/forge the journals at their sides, making them stronger at the weakest point in the crank.  So, widening the journal would make the crank weaker than just the material removal, and the journals would have two deep grooves in them.

This is probably the easiest way to go, as I do not think there are any other V8s that share architecture with inline fours.  Yes, Mercruiser four based on the 385-series Ford, but when talking flat plane V8, smaller is better.   3.6l is probably as large as you'd want to go, maybe too large.  They have the same vertical shaking forces as inline fours, except twice as much.

When all is said and done, it's probably cheaper/more reliable (more reliable is cheaper) to get a Ferrari 3-8 engine.  I am pretty sure ALL Ferrari V8s are flat plane, as is the V8 engined Lotus Esprit.   You can always tell by the intake manifold shape, flat plane engines are either independent throttle or they group the cylinders as left and right banks. 

Is the Maserati V8  in things like a quattroportte a flat plane? Ferrari engine with a different sticker.

Fast web searching says the Maserati V8 in the Quattroportte from the 2000's on is basically a Ferrari V8 with a cross-plane crank instead of flat plane.  This is the same thing they did on the Lancia Thema 8.32.

Pete. (l33t FS) said:

This is probably the easiest way to go, as I do not think there are any other V8s that share architecture with inline fours.  Yes, Mercruiser four based on the 385-series Ford, but when talking flat plane V8, smaller is better.   3.6l is probably as large as you'd want to go, maybe too large.  They have the same vertical shaking forces as inline fours, except twice as much.

Does the Audi 4.0T V8 share the bore spacing with the 2.0T?  The other specs are the same, IIRC.

Seems like Scat is making flat plane crankshaft for LS engines:

https://www.lsxmag.com/features/sema-coverage/sema-2021-scat-cranking-out-power-with-flat-plane-crankshafts/

I can't find them on Scat's website though...

codrus (Forum Supporter) said:

Pete. (l33t FS) said:

This is probably the easiest way to go, as I do not think there are any other V8s that share architecture with inline fours.  Yes, Mercruiser four based on the 385-series Ford, but when talking flat plane V8, smaller is better.   3.6l is probably as large as you'd want to go, maybe too large.  They have the same vertical shaking forces as inline fours, except twice as much.

Does the Audi 4.0T V8 share the bore spacing with the 2.0T?  The other specs are the same, IIRC.

Possibly.  I know the 4.2 V8 had 92mm bore spacing in the block (and 88mm bore spacing in the head.... srsly weird engines) but not sure about the 4 liter.

For sure, you can't pick them up cheap to free like you can with the 3.6.  And it won't have timing belts, which potentially makes things difficult, because it may have different cams on each bank so they can use the same cam phasers, instead of timing belt strategy of having the same cams but different depth cam sprockets.  All conjecture.

In reply to Appleseed :

It doesn't share the crank. There are a few other differences as well. It's a shame because the Maserati version is less than an LS3 crate, while the Ferrari version would get you 1000hp+ with an NRE build.


So pretty much, true flat plane cranks are unreliable, or unreliable and expensive.

Now I'm understanding BMWs philosphy. Too bad the I6's are as long as they are, not to mention the weight.

In reply to mr2peak :

Flat plane cranks are not inherently unreliable.  They just shake like a four cylinder, except they do it in two planes not one, and those two planes do not cancel each other out.

In an even firing four cylinder, or each bank of a flat plane V8, two cylinders are at BDC and two at TDC at the same time.  The center of mass of the reciprocating mass is thus a point halfway down the stroke.  All four pistons are at 90 between DC at the same time, but because the crankpins are a half stroke offset to the side and the connecting rods are not infinitely long, the pistons, and therefore the reciprocating bits' center of mass, is a fair bit BELOW half stroke.  So in effect there is a shaking force as the reciprocating center of mass moves up and down twice per revolution.

Which is why 99.999% of V8s are crossplane, they don't suffer from this shaking force.  And why four cylinder engines much larger than 2 liters have a pair of balance shafts that counter rotate, so they cancel each other out except for the up and down direction.

I suppose an OE who wanted to prove a point could make a flat plane V8 with four balance shafts, or possibly just three.

What's it going to cost to spin an LS 8k+? Probably a good bit less than a VooDoo or ZO6 LT

Note that one does not NEED a flat plane to spin fast, and for larger engines it is counter productive because the shaking wrecks everything.  (I vividly recall a story about trying a flat plane in a Pro Stock car, the shaking was so bad that "the tach looked the size of a dinner plate"!)

They do sound nice.  And if you make the exhaust quiet and run one of these guys, you get the aural benefits without the pain in the ass:

Or maybe

Costs less than a crank, too, and you can run any cam that you want!

If Ford's experience with the Voodoo is any consideration, you may HAVE to run one with a flat plane, apparently the up/down/down/up configuration plays hell in a 8 cylinder plenum manifold.  The Voodoo has a fairly unusual up/down/up/down layout specifically to make it work with a standard type intake manifold.

(ITB all the things!)

Pete. (l33t FS) said:

Flat plane cranks are not inherently unreliable.  They just shake like a four cylinder, except they do it in two planes not one, and those two planes do not cancel each other out.

What happens if it's a flat plane crank V8 with a 180 degree V?  So a flat, flat-plane crank V8 (not boxer)? :)

In reply to codrus (Forum Supporter) :

That might actually work out.

Now I am curious what the layout on the Porsche aircooled eights was.

Some Googling:

According to Bill Oursler, the P908 firing orders were:

1--1,8,2,6,4,5,3,7; bad vibrations with 135 or 225 degrees between opposite pistons
2--1,5,2,7,4,8,3,6; better, but still had vibrations
3--1,7,2,8,5,3,6,4; final version that eliminated vibrations; a true boxer with 180 degrees between opposite pistons

With numbering like that, I deduce that cylinder numbering was Ford style, 1-4 on one bank and 5-8 on the other, if a boxer arrangement had 1 and 5, 7 and 3, 2 and 6, 8 and 4.  And it is a CROSS PLANE CRANK!

Likewise, the first arrangement would be a "flat plane" given that the firing order went 1-2-4-3 on one bank and 8-6-5-7 on the other.  (Basically a standard inline four, but drumming inwards instead of outwards on bank 1)  The second is the same as the first but with bank 2 rotated 360 degrees in the firing order.  (5-7-8-6 instead of 8-6-5-7)

Hmm.  Well, Porsche engineers were very good, and if they came to this decision with empirical data... they're the ones who did the R&D, I'm just some guy with an opinion.

I wonder why they didn't try the other iteration on bank 1, now.

(edited because I made a derp regarding the flat planes' bank 2 firing orders.  It's fixed now)

I fully support ITB'ing the world.

Spinning an LS to 8k is fun, but it's still an LS, and that's just not enough to justify ditching the rotary. I looked at doing a high rpm 3uz build, but cams alone are near $3k and that's just the start. Base engine is cheap, all the aftermarket stuff is made of gold. Also not as light as I was lead to believe.

I have my doubts the LT6 will even be offered as a crate. It's the Corvettes last N/A hurrah, they might actually want to keep it as something special just for that car. It's a shame though.

What about the delightful sound of a 5 or a 10?

So wait, a Ducati 90 degree twin has perfect primary balance. Would this not work on a 90 degree cross plane V8? Like it's just 4 V-twins linked together.

The Ferrari mill is 90, or close to it. 

In reply to wheelsmithy (Joe-with-an-L) :

Not a perfect secondary balance, though.  And when you stack the twins to make a V8, that gets amplified unless you null it out by going to a cross plane crank.  (isn't this where we came in? )

I am strongly in favor of fives, not so much tens, but any port in a storm  I am sitting in a turbo five powered car right now, have a turbo five powered Audi keeping jackstands safely held down, and my future plans for one of my RX-7s is either a Volvo five with a 5-1 header, or a high revving 4.8.  And I am leaning toward the Volvo because I prefer the five cylinder sound, and V8s have a kind of leaden feel.  Like let off the throttle on the highway at only 4000rpm and the car just slows because of all of the engine drag. Bleh.

5's are great in a Volvo or Audi, but they won't make V8 power without boost. I'm after no less than 450whp n/a, otherwise again, it's just not interesting or fun enough to replace the rotary. I have no issues with LS swaps other people do, but I do think you should choose an LS that makes at least what a reasonable effort build on the stock engine would have made.

The only V10 I know much about is the S85. It's big, and at 529lbs isn't especially light, about 100lbs more than an alloy block LS. I'm open to a V10 if there's a way to cut the weight

The flat plane V8s out there are true performance engines. High power density, low internal mass, reasonably light, high redlines and a supercar sound track. The cars they come in are special cars in their own right; supercars or halo cars. It's really hard to come up with all that in a different package, and all of those cars are $300k+ where I live.
 

So the reasonable ways to get a flat plane crank V8 is to convert an LS, find a crashed C8 Z06, swap the Ferrari V8, or swap a Voodoo and hope for the best (they don't seem to last long). I'm not up to converting a VW V8, but I do hope someone tries that!

Build your own boxer flat 8 or better yet flat 12 out of two vertically stacked Subarus connected together with chain drives.