What is the advantage of this engine in the C8. It makes exotic noises, but I really can't understand any other reason for developing this engine. Chevy has proved for years it can make its typical pushrod V8 engines work. Why move to a more complicated engine, that will also be used in production versions.
I've heard that dohc engines get better balance of performance in imsa,wec,lemans etc than the pushrod engine. I'm sure there are many more reasons then just bop but I'm sure racing played a big role in it.
Smaller, lighter & rev higher.
Gunning after Ferrari and Lambo, etc.
Shadeux said:Smaller, lighter & rev higher.
Gunning after Ferrari and Lambo, etc.
in what world is a similar displacement DOHC engine smaller and lighter?
In reply to Shadeux :
Honest question: I thought one of the advantages of staying pushrod in the LS motors was size and weight. How is DOHC smaller and lighter? For instance the Coyote engine supposedly takes up a lot of space by comparison.
Yeah there's a lot of good reasons for overhead cam...but size and weight aren't on that list.
I imagine part of the reason is that being mid engine now there's less packaging constraints, particularly height.
To a certain extent, it may be that since they are trying to compete with the ultra exotics, the buyers they're going after simply expect the engine to have those features.
Years ago I remember reading somewhere that GM stuck with the pushrods in the Corvette for packaging reasons. As in the more compact size allowed for a lower hood line. Obviously that's no longer a consideration.
My personal reservation for this application in this car is that there's a good possibility that the timing chains are going to be a super expensive long term maintenance consideration.
Separate intake and exhaust cams allows for better variable valve timing, which is really useful for emissions. That may mean less restrictive cat packaging, which means more power. Also, high rpm is easier on the valvetrain.
The old ZR1 had DOHC heads, no?
The flat plane is to make a fun noise and give a street car some racecar cred and because both Ford and Ferrari sell them. I can see the advantage on a race car but I have my doubts about street car suitability or about how the C8 market will react to a car that doesn't go rump rump rump.
dps214 said:Yeah there's a lot of good reasons for overhead cam...but size and weight aren't on that list.
I imagine part of the reason is that being mid engine now there's less packaging constraints, particularly height.
height is my guess.
Unfortunately, the rest of the world seems to be over low hood heights, which is a shame, so this engine may make the rounds beneath other things,
Think of it, when we start decreasing the number of Gen III/IV engines and pine for the good ole' days
In reply to Keith Tanner :
The TiVCT is also better for power, especially vs. dual equal- which is all a single cam can do.
The funny thing for the C8 is the same for the GT- the racing version will probably be de-rated due to the rules. Which is good for durability and fuel economy while racing.
MrFancypants said:My personal reservation for this application in this car is that there's a good possibility that the timing chains are going to be a super expensive long term maintenance consideration.
Audi V8 anyone?
bobzilla said:Shadeux said:Smaller, lighter & rev higher.
Gunning after Ferrari and Lambo, etc.
in what world is a similar displacement DOHC engine smaller and lighter?
Those are the pro's for a flat plane crank from what I've read. I've never been near one.
There may be more valve train but there's less block is what I thought.
Because the C8Z is a Motorsports oriented car, thus a Motorsports oriented engine is fitting. Modern head tech, and a flat plane crank allow the engine to rev higher. Higher revs = more horsepower because hp = (torque x rpm)/5252.
While a flat plane crank has many advantages, one disadvantage is that it's an NVH nightmare. Luckily, in a sporty application, some nvh can be seen as a positive factor. Also worth noting that dual mass flywheels and crank damper tech has come a long way and can do a much better job of damping crankshaft torsional vibrations than in the past.
Why flat-plane crank? Probably because Ford had one in the GT350, so the Chevy marketing department decided they have to have one too.
Why DOHC? Probably because flat-plane crank only makes sense if you're going to bump the revs up, and DOHC does that better than OHV. Alternately, maybe the rules at Le Mans have been tweaked and the OHC motor is required for that.
DOHC gives you better power-to-displacement, but OHV (with a bit more displacement) generally gives you better power-to-engine-weight or power-to-engine-size. So when race series rules (or tax policy) limits you to a certain displacement, you want OHC. If there's no displacement limit then OHV may be a better choice for a race car.
In reply to Shadeux :
Not enough to offset 3 more cams, 16 valves and springs and followers, longer chains etc.
codrus said:Why flat-plane crank? Probably because Ford had one in the GT350, so the Chevy marketing department decided they have to have one too.
Why DOHC? Probably because flat-plane crank only makes sense if you're going to bump the revs up, and DOHC does that better than OHV. Alternately, maybe the rules at Le Mans have been tweaked and the OHC motor is required for that.
DOHC gives you better power-to-displacement, but OHV (with a bit more displacement) generally gives you better power-to-engine-weight or power-to-engine-size. So when race series rules (or tax policy) limits you to a certain displacement, you want OHC. If there's no displacement limit then OHV may be a better choice for a race car.
Since the ACO does very much focus on fuel consumption, I would bet that they will give the smaller of two engines that have the same power output the advantage, as it should get better fuel economy. But realistically, fuel economy is one of the most important things in the GTLM class. The fast lap speed is totally dictated by how fast the P1 (and and thus P2) cars go- and everyone has the same kind of timing restriction. So the winner is the one that spends the least time in the pits and can maintain that relative speed for the longest time on the track. Which means if you can be fast, then fuel economy over 24 hours is the most important thing that can make you win.
Shadeux said:There may be more valve train but there's less block is what I thought.
Why? The cylinder the crank spins inside would still be the same size.
ProDarwin said:Shadeux said:There may be more valve train but there's less block is what I thought.
Why? The cylinder the crank spins inside would still be the same size.
It is a slightly smaller engine in the C8R- 5.5 instead of 6.2l. So smaller bock and smaller crank. The flat plane also means cylinders can share throws, which also makes the engine shorter- so there's another weight reduction.
The heads, on the other hand....
In reply to ProDarwin :
In-block cam packaging would be gone at a minimum
Maybe it's just a push the envelope design wise? The C8's going mid-engine for the first time, why not look at a total clean sheet for the engine package too?
-Rob
rob_lewis said:Maybe it's just a push the envelope design wise? The C8's going mid-engine for the first time, why not look at a total clean sheet for the engine package too?
-Rob
It would have been funnier if they'd jumped straight to DOHC so we could swap an LS in...
alfadriver said:ProDarwin said:Why? The cylinder the crank spins inside would still be the same size.
It is a slightly smaller engine in the C8R- 5.5 instead of 6.2l. So smaller bock and smaller crank. The flat plane also means cylinders can share throws, which also makes the engine shorter- so there's another weight reduction.
The heads, on the other hand....
Lets ignore size, I was only disputing the claim that Flat Plane crank = smaller block than Cross Plane.
What do you mean by share throws? In what direction would this make the engine shorter? (length or height)
Mr_Asa said:In reply to ProDarwin :
In-block cam packaging would be gone at a minimum
Ah, smaller block from OHC. That makes more sense. I thought the claim was Flat Plane = smaller block.
In reply to ProDarwin :
Share throw = two rods on one crank pin.
But now that I think about it, even 90deg v8's share pins- so that becomes a wash.
IF it did become an advantage- the engine length would be shorter.
Height is mostly stroke, some how much connecting rod angle you can deal with.
Sorry about the mix up.
D2W said:What is the advantage of this engine in the C8. It makes exotic noises, but I really can't understand any other reason for developing this engine. Chevy has proved for years it can make its typical pushrod V8 engines work. Why move to a more complicated engine, that will also be used in production versions.
The time is rapidly coming when it no longer can work. Things have progressed markedly in the past 24 or so years since the LS1 was designed.
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