Should the ZO6 really go Flat Plane Crank?
 

Hello everyone, new guy here. I've been following the news on the upcoming ZO6 with much excitement and also some concerns. They say the C8 ZO6 is going to be FPC, so it can rev considerably higher than pushrod engines. That is all cool and all, but the more I research about these engines, the less convinced I get about it actually being the better engine. And considering that they want the ZO6 to be NA, it gets very hard for an engine like this to produce 650 hp. I see many disadvantages (much higher vibrations, wich bring more disconfort to the cabin and considerably lowers the long-term reliability of the engine, considerably reduces the displacement the engine can safely have, tend to be more expensive to maintain, less torque on lower rpms, and lower torque in general, etc). All of that so that "the engine sounds better". The tradeof doesn't seem to be worth it in my eyes.

I get why they want the ZO6 to be NA, and that is great, but the displacement of 5.5L that is being rumored is quite high for this kind of engine (the mustang gt350 owners have been complaining quite a bit). I wonder: wouldn't it have been better for GM to dust off the LS7 from the C6 ZO6 and modernize it? A much bigger displacement would help a lot, plus these engines are more reliable and used to rev decently for pushrod engines (7.000 RPM). Besides, I think the development of such engine would have been waay cheaper. What do you guys think?

I trust the Corvette engineers and quite frankly I don't think they care what we think. We can discuss it but in the end it won't matter. Everyone doubted that GM could pull off a proper mid engine sports car and look at what they achieved with the C8. I think they'll get it right.

It makes more power--and comes with most of the disadvantages you list above--we can only tell longevity after it has been released.

But if these tradeoffs are not worth it to you, you are free to buy a LT2 C8.

5.5 L is very big for a FPC--but there are a couple of considerations--transmissions break due to TQ, clutches slip due to TQ, so lowering TQ and adding power up top means the transmission does not need as much work as it would have needed if GM dropped a 7 L pushrod motor in C8--a motor that would not be legal in the series GM wants to run the C8.

You don't have to get one.

I don't doubt the capabilities of GM engineers nor do I think the ZO6 will be a bad car at all. In fact, I'm very excited about it. I see why they want to make it naturally aspirated, with which I totally agree. I was just wondering if they weren't taking the hard way to make it happen. Developping a new engine costs hundreds of millions, and many things can go wrong in these projects. Besides, making 650 hp out of this engine will be difficult (but not impossible, of course), so I was thinking maybe a bigger displacement would help. If the car makes less power than the previous generation, I think it would become tougher to sell (even though I personally don't care so much as long as pwr/wgt stays the same).

Thanks for the insight! I didn't think about the transmission. But Porsche and Ferrari also use similar transmissions, and they still prefer to use smaller displacement, right?

About the racing series of the Corvette: How long do they have to start mass producing the engine they are using in the races? Couldn't they have waited to use it only with a TT ZR1? (Just a theoretical question since it would probably be too expensive to develop this engine for such low sales numbers)

And all that power and torque is useless if you cant put it to the ground. Huge torque down low makes a street car loose and dangerous in the lower gears.

Ferrari got 570 HP out of 4.5 L 10 years ago. Direct scaling would give 696 HP, a bit less stratospheric red line brings this down to 650 HP.

I, personally, this the motor is targeted at 600 HP which will be a "piece of cake" for a FPC 5.5 L.

IMHO the majority of the rev increase is due to the DOHC design we believe is in the C8R 5.5L engine. FPC improves high rpm efficiency (scavenging, pumping losses, etc.), but the revs are cam and layout based. Again, IMHO.

Have a good one,
Mike

Who says it's not going to have push rods? I've not heard anything about it having OHC's

We're all guessing, but the DOHC rumor is based on the knowledge that the C8R engine is DOHC, and IMSA rules state that the number and placement of camshafts have to be the same as the production vehicle.

Have a good one,
Mike

Completely agree if you add "in year 3" to the end of your statement! :D

No point in doing FPC and not having DOHC. Couldn't get the revs with OHV. Can't get the high-end power and have it streetable without DOHC and VVT.

I Hope if it is TT FPC that the redline is decent. With a higher redline they can play some games with gearing that will make the car feel even stronger in lower gears. I would rather just have NA. Lighter all around.

Mercury Racing did this DOHC LS7 without VVT that makes 750HP prior to its 8,000RPM redline. If you scale that to displacement you get 589HP in a 5.5L. Put in VVT, FPC, and a few other tricks it seems like 600HP would be very do-able.

Last data point. The DOHC LS7 is listed as 498lb w/o accessory drive. The LT4 is listed at 529lb. Figuring 30lbs for accessory drive is probably right there. Take out a few lbs for FPC, maybe.

There are still many of us here who do not believe it will be an NA motor. More like modern supercars with a 4.XL displacement and Twin Turbo's. A 4.4L Twin Turbo FPC would make 700hp with ease and be competitive with the very top level of supercars which is traditionally what the Z06 benchmarks for performance.



Have you been living under a rock? DOHC is literally the ONLY possible rumored engine for the Z06. There is not one source out there saying it wont be a DOHC.

No, a FPC has few benefits, and many detriments for a street car. It is not necessary in a street car. The differential in the mass of the crank is inconsequential to the overall rotating mass of the driveline. It helps in faster shift in a manual, but with the DCT, I don't see the advantage. Better to spend your money on lighter wheel tire combos, where the rotating mass is further from the axis of rotation. The differential in available RPM versus a FPC is not there. High RPMs are detrimental to fuel efficiency, due to greater friction. The Corvette still has to be worried about fuel efficiency. It will be a Twin Turbo DOHC engine. GM has already planned for that almost 3 years ago. I have seen nothing since that has convinced me that the plan has changed. When it is multiple GM internal documents versus internet speculation, I am going with the GM documents.

This guy thinks the Z06 is the twin turbo with the center exhaust and separate wastegate pipes, but that might also be the ZR1.

Let's be honest here: none of us know what the next level C8 is going to be, other than probably a DOHC, and that's just an inference from the C8R engine and the IMSA rules. We don't know if there will even BE a Z06, ZR1, Zora, or whatever. We *think* there will be at least the Z06 and Grand Sport, and maybe the ZR1, but that's just based on the C6 and C7 product development.

I'll honestly be surprised and a bit disappointed if Chevy puts a FPC in a customer car. As RX mentioned above, a FPC offers little to no advantage on a street car, even one that is tracked. We can debate the merits of OHC vs. OHV, but that's a different thread.

Have a good one,
Mike

A 600hp N/A FPC would be a hoot in a 3000lb car. I think 600hp would be a reasonable, attainable target for a N/A FPC. The thought that I keep returning to is that, IMO, the Z06 will not be a de-contented lightweight model....it'll very likely be 3650# plus, after a few lightweight parts are added to offset the added weight in the engine, tires, and cooling. I don't think 600hp will be enough differentiation over the base model, at this weight. It would need to be sub-3300# just to match the power-to-weight of a C7Z.

They could easily meet the power goals with a TT cross plane or TT flat plane. The flat plane architecture carries vibrational baggage that begs for a solution, but has a tuning advantage. The vibration issue could be solved by either internal counterbalancing or external MR mounts, or by simply using a smaller displacement short stroke, assuming you wanted the tuning advantage of a flat plane. The existing mounts on the C8 chassis are mostly in the wrong direction for secondary absorption, not a big hurdle, but the counterbalancing would add a lot of parts and rotating mass. There's a reason you don't often see counterbalanced FPC V8s. CPC is much easier.

Don't see why they need an FPC. They've known how to get the advantages of an FPC without the disadvantages for 50 years:


https://cimg3.ibsrv.net/gimg/www.cor...37e92e0561.jpg

I think they need FPC simply to produce the right noises so that they can fully clear the mid-engine exotic hurdle. It will put Corvette fully into another buyer demographic.

Look how many people here in this forum keep mentioning that they hope the C8 Z06 sounds like a Ferrari: it’s the defacto driver experience benchmark.

Oh your wrong, someone on here that was saying that it would be all electric! :jester

IMO, the question is why did they go to the FP on the C8R? It takes a LOT of engineering to make that work on a 5,5 lt engine. If they can get it to work on the C8R and apparently they did, then they know what they can get in a street engine. On another thread I posted a bunch of remarks from MB AMG that they used a FP to get the tuning effects for their within V turbo charged engine. If GM wanted the same effects for a twin turbo street Vett(?), there's no need to mount the turbos within the V.
Here's how complicated it can get, the C8R race engine could be going for high rpm power capability of the FP while the street twin turbo could be using the tuning effect of the FP for better twin turbo performance and not using the high rpm potential.
I suspect that we simply won't know GM's reasoning until sufficient members of the engine family are in production that GM can present the entire engine family story. Even then all we'll get is the "official" version until some one retires and writes the "real" story, if ever.