Flat plane C6 Z06. Dreams do come true

[12,000 RPM]

https://jalopnik.com/some-mad-genius-gave-a-corvette-z06-a-flat-plane-crank-1829362964

https://www.youtube.com/watch?v=Hgi7gW_QyOA

Man I would love a flat plane 302 or something in a Miata. HP/TQ/NVH wouldn't even matter. If my brain serves me right all that's needed to do this is a new crank, cam and changing the distributor connections

[GoCougs]

Why wouldn't HP/TQ/NVH matter?

Here the owner spent a fortune on it and ended up with a less powerful, less useful (power band) motor than the LS7 the car originally came with. The GT350/R has some of the same issues - too much complexity for too little power and usefulness.

In this day and age, to make this work, you need VVT and VVL, a la Ferrari.

[12,000 RPM]

Why wouldn't HP/TQ/NVH matter?

Here the owner spent a fortune on it and ended up with a less powerful, less useful (power band) motor than the LS7 the car originally came with. The GT350/R has some of the same issues - too much complexity for too little power and usefulness.

In this day and age, to make this work, you need VVT and VVL, a la Ferrari.

There is more than enough HP/TQ here to do damage in real life (as opposed to winning a bench race) and NVH in the Z06 was compromised to begin with.

Again the only 3 parts necessary for this project were the crankshaft, camshaft and ECU tune to fix the ignition/fuel order. No complexity at all, with a much better sound. I would take the GT350/R over any Camaro, ZL1s included, just for that engine. Both cars are deep into the realm of diminishing returns with regards to performance in the context of 99% of drivers' skills and driving environments (track included), so you may as well go with the one that's more enjoyable.

[MrH]

No complexity at all? Then you go on to talk about diminishing returns?  And you think this is a good idea?    This is some next level Tarvish-esque trolling.

[FoMoJo]

Why's he selling it?

[Soup DeVille]

This was a complete engine teardown and rebuild. Not only would it be a very expensive custom crankshaft and cam, that would also mean replacement of all main and lower con-rod bearings, and numerous seals.

the parts list on Jalopnik makes this a 40,000 project if its a dime.

[Payman]

This was a complete engine teardown and rebuild. Not only would it be a very expensive custom crankshaft and cam, that would also mean replacement of all main and lower con-rod bearings, and numerous seals.

the parts list on Jalopnik makes this a 40,000 project if its a dime.

I could build a FFR Cobra with a crate Voodoo for that scratch.

[CaminoRacer]

I could build a FFR Cobra with a crate Voodoo for that scratch.

Not quite. Isn't a Voodoo $20k? You could buy the FFR kit and the engine, but you'd be short the transmission, rear end, and wheels. And the cost of little things during assembly.

[GoCougs]

There is more than enough HP/TQ here to do damage in real life (as opposed to winning a bench race) and NVH in the Z06 was compromised to begin with.

Again the only 3 parts necessary for this project were the crankshaft, camshaft and ECU tune to fix the ignition/fuel order. No complexity at all, with a much better sound. I would take the GT350/R over any Camaro, ZL1s included, just for that engine. Both cars are deep into the realm of diminishing returns with regards to performance in the context of 99% of drivers' skills and driving environments (track included), so you may as well go with the one that's more enjoyable.

It is decent power, but that's probably ~10% less power than an LS7 for what is probably $50k+ in custom engine work (and surely bet that engine won't have the reliability/durability of the LS7). Legitimately accommodating ~8,500 rpm is a lot of work in valve train and reciprocating component design.

Is the GT350 worth $20k over the lowly Camaro SS despite it not being any quicker (at least 0-60 and through the 1/4 mile)? Some say yes - the GT350 was a big hit, but then again, paying a lot for the pleasure. It's just too much, esp. considering Ford knew that was the likely result.

[Payman]

Not quite. Isn't a Voodoo $20k? You could buy the FFR kit and the engine, but you'd be short the transmission, rear end, and wheels. And the cost of little things during assembly.

16K, plus 14K for the kit, leaves 10K for a donor with tranny and everything else.

[CaminoRacer]

16K, plus 14K for the kit, leaves 10K for a donor with tranny and everything else.

Oh, I usually look at their complete kits. I'm a snob.

[MX793]

Why wouldn't HP/TQ/NVH matter?

Here the owner spent a fortune on it and ended up with a less powerful, less useful (power band) motor than the LS7 the car originally came with. The GT350/R has some of the same issues - too much complexity for too little power and usefulness.

In this day and age, to make this work, you need VVT and VVL, a la Ferrari.

Any very high specific output engine (100+ hp/L) sans VVT/VVL is going to have a narrow/peaky powerband regardless of the crank configuration (or cylinder configuration/count).  A FPC is not inherently peakier than a CPC.  The peakiness stems from the head, intake, and exhaust design.

Why FPC?  For one, it's lighter than a CPC since it doesn't need the heavy counterweights.  This leads to a snappier, more responsive engine (similar to light-weighting the flywheel) and in a high performance vehicle (like a race car), less weight and less rotating mass are always more desirable.  Less mass also means less stress at higher RPMs.  Another benefit is that since the power pulses are now evenly spaced, it's easier to design exhaust headers and intake runners that are harmonically tuned to permit better scavenging and improved volumetric efficiency (more power).  You can do the same with a CPC, but the headers end up much longer (and heavier).  Sans VVT/L, a harmonically tuned setup like this means that the engine only runs optimally over a much narrower RPM band and off of that band its efficiency is reduced (this is true of any N/A engine with any crankshaft configuration).  Newer tech like VVT/L essentially allows us to have our cake and eat it too, as it allows optimized breathing over much wider ranges, so you're no longer compromising power at low RPMs for maximum performance somewhere else.

The downside to FPC?  The main one is NVH.  They suffer the same momentum imbalance that makes traditional inline-4 cylinder engines buzzy.  The amplitude of this imbalance only increases as the displacement, and reciprocating mass, goes up.  CPCs offer far better balance and smoothness, which is desirable in a road car.  As with a larger I4, the only way to quell this vibration in an FPC engine is to use balance shafts, which adds weight and complexity back into the engine.  At which point, you may as well have just used a CPC.

If you're not going for balls-out performance (with or without VVT/L), the NVH compromise isn't worth it in a street car, which is why practically all street-use V8s are CPC.  You just end up with a buzzy motor that performs exactly like a much smoother one.  Most people will take the smoother one that doesn't result in a car with more rattles than an infant daycare center after 30,000 miles.

[12,000 RPM]

I can't hear you guys over that engine note. FPC LS7? OK I can understand the beef. FPC junkard 302 or old SBC in basically anything old, light and foreign (Miata, E36, 240SX, hell even a 350Z)? You guys are talking like this car is being built to commute 100 miles a day in or something. I get that Cougs is doing it because his only racing experience is on spreadsheets but I'm surprised at the rest of you. I'd maybe destroke and bore it out to control vibrations but come on man. Poor man's FPC V8? How can you hate on that.

[Soup DeVille]

I can't hear you guys over that engine note. FPC LS7? OK I can understand the beef. FPC junkard 302 or old SBC in basically anything old, light and foreign (Miata, E36, 240SX, hell even a 350Z)? You guys are talking like this car is being built to commute 100 miles a day in or something. I get that Cougs is doing it because his only racing experience is on spreadsheets but I'm surprised at the rest of you. I'd maybe destroke and bore it out to control vibrations but come on man. Poor man's FPC V8? How can you hate on that.

I like the engine; but think its wasted in a basically stock Vette, and it certainly is more complicated than "just three parts." Should be in something that's basically race prepped.

[MexicoCityM3]

If someone wants flat plane crank sounds for not that much money the way to go is a used Ferrari. I mean props for trying but I'd never do it or buy it done from this guy.

[CaminoRacer]

Just get a destroked LS7 from Lingenfelter and call it good

[MX793]

I can't hear you guys over that engine note. FPC LS7? OK I can understand the beef. FPC junkard 302 or old SBC in basically anything old, light and foreign (Miata, E36, 240SX, hell even a 350Z)? You guys are talking like this car is being built to commute 100 miles a day in or something. I get that Cougs is doing it because his only racing experience is on spreadsheets but I'm surprised at the rest of you. I'd maybe destroke and bore it out to control vibrations but come on man. Poor man's FPC V8? How can you hate on that.

FPC on a pushrod is a waste.  The valvetrain can't keep up with revs the FPC supports.  It'll sound cool, but it's not going to rev any higher or perform any better than a regular 302 unless you dump a bunch of money into the heads and valvetrain and headers (and much of this, like the crank and cam, will be totally custom work), and it'll be worse than the buzziest 4-banger you've ever experienced.  You're just going to end up with all of the downsides of an FPC and none of the upsides that actually make it alluring.  And it would honestly be cheaper to just buy a Ferrari 308 or 328.

[12,000 RPM]

FPC on a pushrod is a waste.  The valvetrain can't keep up with revs the FPC supports.  It'll sound cool, but it's not going to rev any higher or perform any better than a regular 302 unless you dump a bunch of money into the heads and valvetrain and headers (and much of this, like the crank and cam, will be totally custom work), and it'll be worse than the buzziest 4-banger you've ever experienced.  You're just going to end up with all of the downsides of an FPC and none of the upsides that actually make it alluring.  And it would honestly be cheaper to just buy a Ferrari 308 or 328.

Of course there is upside. The sound! Can't see why the heads/valvetrain or even the headers would be "custom"... there is plenty of off the shelf stuff to support ~7K which is enough. Heads and valvesprings don't care what order events happen. Cross plane headers are inherently compromised as they can't fully take advantage of scavenging so that's prob no big deal. Compared to a 4 banger of half the displacement, vibrations only increase by 41% rather than 100%. The Voodoo doesn't run a balance shaft and I'm pretty sure none of Ferrari's V8s do either. And Ferrari V8s are fine vibe wise in my experience. Plus I've driven 4 bangers with balance shafts deleted and they were fine as well.

People are acting like this would be some kind of road trip pick up my mom from the airport car. Hell no. Come on guys. It would be a track day ripper. An Italian soul trapped in a JApanese tin can with the heart of an American horse. That is way cooler to me than a glacial engine-out-every-6-months 308 Can't a man dream

[GoCougs]

Any very high specific output engine (100+ hp/L) sans VVT/VVL is going to have a narrow/peaky powerband regardless of the crank configuration (or cylinder configuration/count).  A FPC is not inherently peakier than a CPC.  The peakiness stems from the head, intake, and exhaust design.

Why FPC?  For one, it's lighter than a CPC since it doesn't need the heavy counterweights.  This leads to a snappier, more responsive engine (similar to light-weighting the flywheel) and in a high performance vehicle (like a race car), less weight and less rotating mass are always more desirable.  Less mass also means less stress at higher RPMs.  Another benefit is that since the power pulses are now evenly spaced, it's easier to design exhaust headers and intake runners that are harmonically tuned to permit better scavenging and improved volumetric efficiency (more power).  You can do the same with a CPC, but the headers end up much longer (and heavier).  Sans VVT/L, a harmonically tuned setup like this means that the engine only runs optimally over a much narrower RPM band and off of that band its efficiency is reduced (this is true of any N/A engine with any crankshaft configuration).  Newer tech like VVT/L essentially allows us to have our cake and eat it too, as it allows optimized breathing over much wider ranges, so you're no longer compromising power at low RPMs for maximum performance somewhere else.

The downside to FPC?  The main one is NVH.  They suffer the same momentum imbalance that makes traditional inline-4 cylinder engines buzzy.  The amplitude of this imbalance only increases as the displacement, and reciprocating mass, goes up.  CPCs offer far better balance and smoothness, which is desirable in a road car.  As with a larger I4, the only way to quell this vibration in an FPC engine is to use balance shafts, which adds weight and complexity back into the engine.  At which point, you may as well have just used a CPC.

If you're not going for balls-out performance (with or without VVT/L), the NVH compromise isn't worth it in a street car, which is why practically all street-use V8s are CPC.  You just end up with a buzzy motor that performs exactly like a much smoother one.  Most people will take the smoother one that doesn't result in a car with more rattles than an infant daycare center after 30,000 miles.

Flat-plane crank engines exist for (much) higher RPM. Ergo, to make them fully usable per their specs they need VVT and VVL.

[GoCougs]

FPC on a pushrod is a waste.  The valvetrain can't keep up with revs the FPC supports.  It'll sound cool, but it's not going to rev any higher or perform any better than a regular 302 unless you dump a bunch of money into the heads and valvetrain and headers (and much of this, like the crank and cam, will be totally custom work), and it'll be worse than the buzziest 4-banger you've ever experienced.  You're just going to end up with all of the downsides of an FPC and none of the upsides that actually make it alluring.  And it would honestly be cheaper to just buy a Ferrari 308 or 328.

The motor in this Z06 is a reworked GM pooprod LS 5.3L.

[MX793]

Of course there is upside. The sound! Can't see why the heads/valvetrain or even the headers would be "custom"... there is plenty of off the shelf stuff to support ~7K which is enough. Heads and valvesprings don't care what order events happen. Cross plane headers are inherently compromised as they can't fully take advantage of scavenging so that's prob no big deal. Compared to a 4 banger of half the displacement, vibrations only increase by 41% rather than 100%. The Voodoo doesn't run a balance shaft and I'm pretty sure none of Ferrari's V8s do either. And Ferrari V8s are fine vibe wise in my experience. Plus I've driven 4 bangers with balance shafts deleted and they were fine as well.

People are acting like this would be some kind of road trip pick up my mom from the airport car. Hell no. Come on guys. It would be a track day ripper. An Italian soul trapped in a JApanese tin can with the heart of an American horse. That is way cooler to me than a glacial engine-out-every-6-months 308 Can't a man dream

Where do you get 41% from?  With the variables involved, two different 4-bangers with the same displacement may not exhibit the same levels of vibration.  The asymmetry of the piston velocity curve is a function of rod length relative to the stroke.  Mass of the reciprocating parts obviously plays a role as well.  With a V8, not only do you have essentially the vibrations of a second 4-banger, you have them at 90 degree angles so you've got both vertical and lateral elements, vs only vertical in a 4-banger. 

"Need" for balance shafts is a relative term.  A big 4 doesn't "need" balance shafts, but without them the vibes transmitted into chassis are both uncomfortable and potentially damaging.  Ferrari has gotten away with it in their 8s because they are generally smaller displacement.  They also run relatively high rod to stroke ratios (the 458's was 1.77:1, 360M was 1.74) and ultralight rods and pistons (488 uses titanium rods) to keep the mass down.  A 302 Ford has a lower rod to stroke ratio, it's going to exhibit greater asymmetry in the velocity curve.  And having a larger bore as well, pistons will be heavier than a Ferrari 458 or 488 (which, interestingly, have longer strokes than the Ford).

I think it was EveryDay Driver who tested a GT350 that had some miles on it and the one guy noted (and you could hear it through the mic) that after whatever relatively few miles (presumably hard) it had on it, practically every panel inside the car was buzzing and rattling.

You've driven a 2.5L+ 4-banger sans balance shafts?  Do tell...

[MX793]

Flat-plane crank engines exist for (much) higher RPM. Ergo, to make them fully usable per their specs they need VVT and VVL.

Define "fully usable"?  Racing V8s have been using FPCs for well longer than VVT/L has existed.  And, of course, high performance motorcycle engines run at high RPMs and high specific outputs to this day without VVT/L.  Ford used it on the Voodoo partly as a gimmick, but also because extracting 100 hp/L out of a motor that size without VVL (which is a technology Ford doesn't have in its box of tricks) required going to older-school methods of extracting high VE at higher RPMs.  Came at the expense of low-end power (a 5.0 Coyote has more low and midrange grunt).

[CaminoRacer]

A well-built & purpose-built 302 from either Ford or Chevy can rev over 8k without a flat plane

[GoCougs]

Define "fully usable"?  Racing V8s have been using FPCs for well longer than VVT/L has existed.  And, of course, high performance motorcycle engines run at high RPMs and high specific outputs to this day without VVT/L.  Ford used it on the Voodoo partly as a gimmick, but also because extracting 100 hp/L out of a motor that size without VVL (which is a technology Ford doesn't have in its box of tricks) required going to older-school methods of extracting high VE at higher RPMs.  Came at the expense of low-end power (a 5.0 Coyote has more low and midrange grunt).

"Fully usable" is a 529 hp $57k GT350 that walks a $37k 455 hp Camaro SS.

Motor bikes get away with it because of hp/weight ratio - an upper end sport bike will easily have 5 lb/hp - which equates to a ~3,800 lb GT350 w/760 (flat crank) hp.

[MX793]

"Fully usable" is a 529 hp $57k GT350 that walks a $37k 455 hp Camaro SS.

Motor bikes get away with it because of hp/weight ratio - an upper end sport bike will easily have 5 lb/hp - which equates to a ~3,800 lb GT350 w/760 (flat crank) hp.

You're falling into the trap of judging an engine by peak power alone.  And judging a performance car exclusively by it's 0-60/1/4-mile time.  In the element it was designed to shine in, a GT350 will walk away from a Camaro SS.  That element is not a drag race from a dead dig.

I'd also point out that a 505 hp, $75K 5th gen Z/28, powered by your beloved LS7, is also unable to walk a $37K, 455 hp 6th gen SS in a 0-60 or 1/4 mile Sprint.

[12,000 RPM]

Where do you get 41% from?  With the variables involved, two different 4-bangers with the same displacement may not exhibit the same levels of vibration.  The asymmetry of the piston velocity curve is a function of rod length relative to the stroke.  Mass of the reciprocating parts obviously plays a role as well.  With a V8, not only do you have essentially the vibrations of a second 4-banger, you have them at 90 degree angles so you've got both vertical and lateral elements, vs only vertical in a 4-banger.

This guy http://autozine.org/technical_school/engine/Smoothness2.html#V8

"As both banks run like an inline-4 engine, there is second-order vibration. For a 90° flat-plane V8, the sum of second-order force generated in the 2 banks is - by simple vector analysis - 1.41 times (root-2) of the force generated by each of the inline-4 it consists of. And the direction of vibration is left-right instead of top-down. In other words, while displacement increases 100% compare with the inline-4, the second-order vibration increases just 41%. That makes the flat-plane V8 more refined than an inline-4 although it is not as smooth and quiet as cross-plane V8.

To exotic sports cars, less refinement is not a big problem. Especially they usually employ shorter stroke and lightweight pistons and con-rods, the second-order vibration is greatly reduced." 

"Need" for balance shafts is a relative term.  A big 4 doesn't "need" balance shafts, but without them the vibes transmitted into chassis are both uncomfortable and potentially damaging.  Ferrari has gotten away with it in their 8s because they are generally smaller displacement.  They also run relatively high rod to stroke ratios (the 458's was 1.77:1, 360M was 1.74) and ultralight rods and pistons (488 uses titanium rods) to keep the mass down.  A 302 Ford has a lower rod to stroke ratio, it's going to exhibit greater asymmetry in the velocity curve.  And having a larger bore as well, pistons will be heavier than a Ferrari 458 or 488 (which, interestingly, have longer strokes than the Ford).

I think it was EveryDay Driver who tested a GT350 that had some miles on it and the one guy noted (and you could hear it through the mic) that after whatever relatively few miles (presumably hard) it had on it, practically every panel inside the car was buzzing and rattling.

You've driven a 2.5L+ 4-banger sans balance shafts?  Do tell...

The displacement doesn't matter much. It's more about the stroke. Ford 302 has a ~75mm stroke. I have driven several F22 (95mm stroke) and H22 (91mm stroke) Hondas with their balance shafts deleted with similar mounts. I wouldn't want to do a road trip in those cars but they were fine for ripping up, and those H22s revved to ~7.5K fine. An old Miata or E36 is going to have rattles and the like anyway. There were no rattles in either of the Ferraris I drove. The Voodoo engine is weird in that it has a flat plane engine with a weird firing order. So that's another subject.

Smarter play is probably a Honda K swap. Less weight and ~250WHP instead of 300WHP. But what's the fun in that?

[MX793]

This guy http://autozine.org/technical_school/engine/Smoothness2.html#V8

"As both banks run like an inline-4 engine, there is second-order vibration. For a 90° flat-plane V8, the sum of second-order force generated in the 2 banks is - by simple vector analysis - 1.41 times (root-2) of the force generated by each of the inline-4 it consists of. And the direction of vibration is left-right instead of top-down. In other words, while displacement increases 100% compare with the inline-4, the second-order vibration increases just 41%. That makes the flat-plane V8 more refined than an inline-4 although it is not as smooth and quiet as cross-plane V8.

The key phrase missing here is "of a 4 cylinder with the exact same stroke, bore, rod length, and reciprocating mass".  Also fails to acknowledge the lateral component which an I4 doesn't have.

To exotic sports cars, less refinement is not a big problem. Especially they usually employ shorter stroke and lightweight pistons and con-rods, the second-order vibration is greatly reduced." 
The displacement doesn't matter much. It's more about the stroke. Ford 302 has a ~75mm stroke. I have driven several F22 (95mm stroke) and H22 (91mm stroke) Hondas with their balance shafts deleted with similar mounts. I wouldn't want to do a road trip in those cars but they were fine for ripping up, and those H22s revved to ~7.5K fine. An old Miata or E36 is going to have rattles and the like anyway. There were no rattles in either of the Ferraris I drove. The Voodoo engine is weird in that it has a flat plane engine with a weird firing order. So that's another subject.

Smarter play is probably a Honda K swap. Less weight and ~250WHP instead of 300WHP. But what's the fun in that?

Stroke alone is not the determining factor.  Shorter stroke doesn't guarantee less buzz.  Longer stroke allows lighter pistons for the same displacement (smaller bore), which will reduce buzz.  The Ferrari 360M and 458 both have a longer stroke than a 302 Ford.  Assuming you fitted the Ford with lightweight rods and pistons to eliminate the reciprocating mass advantage of the Italians, the Ferraris will still have lower 2nd order vibration amplitudes.  Why?  Because it's the stroke relative to the rod length, and the 302 has not only a short stroke, but also relatively short rods.  Coyote is even worse in that regard, with Voodoo being only the tiniest bit worse than Coyote assuming the rod length shrunk by the same .3mm that the stroke went up vs Coyote.  The Voodoo certainly has a well lower rod/stroke ratio than the Ferraris.  Toss in the much larger bore, with heavier pistons and rods, and it's going to buzz a fair bit more than any FPC V8 Ferrari has put out.

As noted, displacement, or specifically bore, comes into play because a larger diameter piston is going to be heavier, which will in turn require heavier rods, and as the reciprocating mass goes up, the amplitude of the vibration goes up.

[Soup DeVille]

That's also specifically talking about second order vibrations. A 90 degree non-counterweighted flat crank V8 will also have substantially increased first order vibrations.

[MX793]

That's also specifically talking about second order vibrations. A 90 degree non-counterweighted flat crank V8 will also have substantially increased first order vibrations.

FPC has the same 1st order balance as an I4, which is actually better than a CPC.  The banks are longitudinally symmetrical (2 pistons at TDC when the other 2 are BDC).  CPC requires substantial counterweights to dial out the 1st order vibes.

[Soup DeVille]

on an inline engine, yes. Now add another set of pistons on the same journals at 90 degrees to the first set.