Flat plane crank V8 vs LT2 V8 reliability
Safety Car
Joined: Dec 2009
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From: Alberta
2022 C2 of the Year Finalist - Modified
C2 of the Year Finalist - Modified 2020
Different engines rev quicker than others. Building quicker revs allows for different gearing etc. Power to the ground is drivetrain loss, and certainly different engines will build RPM faster than others even through the wheels.
Safety Car
Joined: Dec 2009
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From: Alberta
2022 C2 of the Year Finalist - Modified
C2 of the Year Finalist - Modified 2020
Completely disagree - which is why so many engine builders and race teams spent countless hours and 100s of thousands of dollars or more into R&D to lighten engine internals.
Cruising
Joined: May 2019
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There's no reason a flat plane crank V8 has to be unreliable. Heck, every 4 cylinder engine has a flat plane crank. Yes, a FPC V8 will vibrate more than a CPC V8, but that doesn't necessarily mean it won't last.
I don't really understand why GM is doing a FPC V8 in the C8. I do believe that GM needs a better naturally aspirated engine, though. The pushrod engines are just too dead at higher RPM. In my opinion it's the worst thing about the Corvette - it needs a better engine. But GM can just use a dual overhead camshaft V8 like many others do in order to get better power delivery from a naturally aspirated engine. They don't need to go to a flat plane crank. IMO just the optics of it are annoying. Ford does a FPC, then 6 or so years later GM does one? And in their flagship product? Too much fodder for trolls there.
I don't really understand why GM is doing a FPC V8 in the C8. I do believe that GM needs a better naturally aspirated engine, though. The pushrod engines are just too dead at higher RPM. In my opinion it's the worst thing about the Corvette - it needs a better engine. But GM can just use a dual overhead camshaft V8 like many others do in order to get better power delivery from a naturally aspirated engine. They don't need to go to a flat plane crank. IMO just the optics of it are annoying. Ford does a FPC, then 6 or so years later GM does one? And in their flagship product? Too much fodder for trolls there.
Safety Car
Joined: Nov 2002
Posts: 4,168
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From: FLL Florida
There's no reason a flat plane crank V8 has to be unreliable. Heck, every 4 cylinder engine has a flat plane crank. Yes, a FPC V8 will vibrate more than a CPC V8, but that doesn't necessarily mean it won't last.
I don't really understand why GM is doing a FPC V8 in the C8. I do believe that GM needs a better naturally aspirated engine, though. The pushrod engines are just too dead at higher RPM. In my opinion it's the worst thing about the Corvette - it needs a better engine. But GM can just use a dual overhead camshaft V8 like many others do in order to get better power delivery from a naturally aspirated engine. They don't need to go to a flat plane crank. IMO just the optics of it are annoying. Ford does a FPC, then 6 or so years later GM does one? And in their flagship product? Too much fodder for trolls there.
I don't really understand why GM is doing a FPC V8 in the C8. I do believe that GM needs a better naturally aspirated engine, though. The pushrod engines are just too dead at higher RPM. In my opinion it's the worst thing about the Corvette - it needs a better engine. But GM can just use a dual overhead camshaft V8 like many others do in order to get better power delivery from a naturally aspirated engine. They don't need to go to a flat plane crank. IMO just the optics of it are annoying. Ford does a FPC, then 6 or so years later GM does one? And in their flagship product? Too much fodder for trolls there.
Why do you want to rev an engine? Revving is to get more power out of small displacements at the cost of poor gas miliage and high opiston speeds. The worst thing is that it raises CG which upsets roll couples in your suspension design and costs $900 more to manufacture and weighs more. True, you can't protect the machine with an ******* performing botched manual shifts.
Last edited by Shaka; Nov 29, 2019 at 02:40 PM.
Cruising
Joined: May 2019
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The V banks in V8s cause complex torque couples and pulsations that require < square bore and stroke ratios. The secondry shakes in a L4 is one thing. Let 2 of these engines be joined together at the hips in a V, and it will create a whole new set of problems.
Why do you want to rev an engine? Revving is to get more power out of small displacements at the cost of poor gas miliage and high opiston speeds. The worst thing is that it raises CG which upsets roll couples in your suspension design and costs $900 more to manufacture and weighs more. True, you can't protect the machine with an ******* performing botched manual shifts.
Why do you want to rev an engine? Revving is to get more power out of small displacements at the cost of poor gas miliage and high opiston speeds. The worst thing is that it raises CG which upsets roll couples in your suspension design and costs $900 more to manufacture and weighs more. True, you can't protect the machine with an ******* performing botched manual shifts.
To me driving on the road course is a lot of fun. I think a higher winding NA engine is great on the road course because it continues to deliver reliable repeatable power lap after lap. I do like big cubes as well, though. High winding + big cubes together, even better.
Safety Car
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From: FLL Florida
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Cruising
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So in your first statement you said that < (I assume you mean "under" by that) square bore and stroke ratio is required in a V8. Not true as there are plenty of over square b/s V8s out there.
Then you said that small displacement engines get poor gas miliage(SIC). I think you meant mileage. Typically smaller displacement engines get better fuel economy, just for your information.
And even your exact figure of $900 more to manufacture is laughable. Costs aren't that predictable and the cost difference will not be an exact number like that.
Upsetting roll couples? That's hilarious. My roll couples are downright angry, not just upset. And they will kick your roll couples' butt.
Then you said that small displacement engines get poor gas miliage(SIC). I think you meant mileage. Typically smaller displacement engines get better fuel economy, just for your information.
And even your exact figure of $900 more to manufacture is laughable. Costs aren't that predictable and the cost difference will not be an exact number like that.
Upsetting roll couples? That's hilarious. My roll couples are downright angry, not just upset. And they will kick your roll couples' butt.
Last edited by MAndretti; Nov 30, 2019 at 09:56 AM.
Safety Car
Joined: Nov 2002
Posts: 4,168
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From: FLL Florida
So in your first statement you said that < (I assume you mean "under" by that) square bore and stroke ratio is required in a V8. Not true as there are plenty of over square b/s V8s out there.
Then you said that small displacement engines get poor gas miliage(SIC). I think you meant mileage. Typically smaller displacement engines get better fuel economy, just for your information.
And even your exact figure of $900 more to manufacture is laughable. Costs aren't that predictable and the cost difference will not be an exact number like that.
Upsetting roll couples? That's hilarious. My roll couples are downright angry, not just upset. And they will kick your roll couples' butt.
Then you said that small displacement engines get poor gas miliage(SIC). I think you meant mileage. Typically smaller displacement engines get better fuel economy, just for your information.
And even your exact figure of $900 more to manufacture is laughable. Costs aren't that predictable and the cost difference will not be an exact number like that.
Upsetting roll couples? That's hilarious. My roll couples are downright angry, not just upset. And they will kick your roll couples' butt.
Le Mans Master
Joined: Jul 2000
Posts: 6,559
Likes: 4,501
From: North Dallas 40 TX
So in your first statement you said that < (I assume you mean "under" by that) square bore and stroke ratio is required in a V8. Not true as there are plenty of over square b/s V8s out there. That is not wha heid, he specifically addressed this in relation to flat plane crank engines in a V8 configuration.
Then you said that small displacement engines get poor gas miliage(SIC). I think you meant mileage. Typically smaller displacement engines get better fuel economy, just for your information. Again, not his point, pecifically higher RPM engines get worse mileage (read that as amount of fuel to produce a given horsepower), friction goes up with the square of the speed of the engine. A 50% crease international rpm increases friction by 225%. Given that it takes the same hp to push the car down the road at a given speed, higher rpm means worse mileage.
And even your exact figure of $900 more to manufacture is laughable. Costs aren't that predictable and the cost difference will not be an exact number like that. You are right it could be way more to produce a DOHC. Price a replacement 660 hp Ferrari engine versus a replacement 650 hp Z06 engine. You are purposefully avoiding correct point that DOHC engines are more expensive to produce. Higher RPM engines are more expensive to produce as they need stronger materials to withstand he addition stress of the higher RPM.
..........
Then you said that small displacement engines get poor gas miliage(SIC). I think you meant mileage. Typically smaller displacement engines get better fuel economy, just for your information. Again, not his point, pecifically higher RPM engines get worse mileage (read that as amount of fuel to produce a given horsepower), friction goes up with the square of the speed of the engine. A 50% crease international rpm increases friction by 225%. Given that it takes the same hp to push the car down the road at a given speed, higher rpm means worse mileage.
And even your exact figure of $900 more to manufacture is laughable. Costs aren't that predictable and the cost difference will not be an exact number like that. You are right it could be way more to produce a DOHC. Price a replacement 660 hp Ferrari engine versus a replacement 650 hp Z06 engine. You are purposefully avoiding correct point that DOHC engines are more expensive to produce. Higher RPM engines are more expensive to produce as they need stronger materials to withstand he addition stress of the higher RPM.
..........
Melting Slicks
Joined: Dec 2010
Posts: 2,891
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From: Tempe, Az
That being said, there must be some efficiency benefits with going from a cpc to a fpc, because the C8R racecar is using an fpc on an engine with the same displacement as the cpc'd engine in the outgoing C7R. I don't think they would want to utilize something that would be detrimental to endurance racing.
Last edited by C3DeedlyDee; Dec 10, 2019 at 02:50 PM.
Safety Car
Joined: Nov 2007
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From: Bethesda MD
On this statement, he does mention high revving small displacement engines, which do in fact get pretty **** gas mileage. My C3 with a 5-spd, lt4 hot cammed 350HO is currently getting better hwy fuel economy than my Z3M Coupe, and it has about ~100hp more. The Honda S2000 is another example. 2.0L or 2.2L engines that rev to the moon but return fuel economy figures not much higher than a C6 Z06.
Pro
Joined: Jun 2018
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Likes: 104
It has a V10, so no it doesn't. The only way to use a FPC in a V10 is to use a split pin crank where opposing cylinders do not share a journal or to use on oddfire configuration where the timing between cylinders is not even. Given that I am pretty sure it doesn't.
Last edited by auburn2; Jan 14, 2020 at 08:49 PM.
Pro
Joined: Jun 2018
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Now V12s do not require the large crossweights of a cross plane V8, for that reason the counterweights are smaller, like those on a FPC V8 but the V12 ceranckshaft is not a FPC itself.
Here is an aventador crankshaft on ebay, you can see clearly that it is a crossplane crankshaft:
https://www.ebay.com/i/113924009493?...SABEgJEc_D_BwE
Last edited by auburn2; Jan 14, 2020 at 08:50 PM.
Burning Brakes
Joined: Aug 2019
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That is not true. In a flat plane crank the journals are all in one "flat" plane. No V12 has journals in one plane because a cylinder needs to fire every 60 degrees. You would need 3 banks of cylinders to make that happen with 12 cylinders firing on a crank with journals only at 0 and 180 (essentially a W12).
Now V12s do not require the large crossweights of a cross plane V8, for that reason the counterweights are smaller, like those on a FPC V8 but the V12 ceranckshaft is not a FPC itself.
Here is an aventador crankshaft on ebay, you can see clearly that it is a crossplane crankshaft:
https://www.ebay.com/i/113924009493?...SABEgJEc_D_BwE
Now V12s do not require the large crossweights of a cross plane V8, for that reason the counterweights are smaller, like those on a FPC V8 but the V12 ceranckshaft is not a FPC itself.
Here is an aventador crankshaft on ebay, you can see clearly that it is a crossplane crankshaft:
https://www.ebay.com/i/113924009493?...SABEgJEc_D_BwE
But man that lambo/ audi v-12 can rev, and sounds like a flat plane crank motor.
Le Mans Master
Joined: Aug 2000
Posts: 5,529
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From: Austin Texas
However, there is a vibration dampening system--which consists of a long shaft (a bit over 12") and a grease filled dual-mass flywheel at the back of the transmission.
Le Mans Master
Joined: Aug 2000
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From: Austin Texas
Some flat-6s have "horizontally opposed" cranks with 6 journals {0 degrees, 180 degrees, 120 degrees, 300 degrees, 240 degrees, and 60}