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Will have the C8 an engine with crossplane or flat crankshaft
Have someone Heard some rumor about crankshft type of the new c8 vette?
I hope for crossplane |
Nothing definitive is known.
If the displacement is above 5.0 liters it'll be a crossplane. |
There is no point for having a flat crank unless you want to rev it. Direct injection is heavy but can't rev high unless you make it much heavier. 50 lb 4000 psi fuel pumps require much HP to run at 8000 engine rpm. Turbo charging negates high revs anyway. High revs uses more gas. As Onpoint mentions, 5 liters is the limit for a flat crank in a V8. GM won't guarantee such a mill. You also can't modify the engine if you don't have access to and have know how to use very specialized expensive equipment. You increase primary and secondary shakes which requires a heavy and complex vibration damper and special engine mounts. The most closely guarded secret in race engines. Try taking a picture of one in the pits.
It is much lighter and has better throttle response up or down which is good for fast shifts. Ain't going to happen at GM. The LS engine engineers were given permission to do as they please and they explored a flat crank. It can't meet future smog and neither can OHV engines and has no virtues except for the above mentioned. It even sounds UTS. Can't even hear a F488 which is a 3rd of the car's value. |
Originally Posted by Shaka
(Post 1596669769)
There is no point for having a flat crank unless you want to rev it. Direct injection is heavy but can't rev high unless you make it much heavier. 50 lb 4000 psi fuel pumps require much HP to run at 8000 engine rpm. Turbo charging negates high revs anyway. High revs uses more gas. As Onpoint mentions, 5 liters is the limit for a flat crank in a V8. GM won't guarantee such a mill. You also can't modify the engine if you don't have access to and have know how to use very specialized expensive equipment. You increase primary and secondary shakes which requires a heavy and complex vibration damper and special engine mounts. The most closely guarded secret in race engines. Try taking a picture of one in the pits.
It is much lighter and has better throttle response up or down which is good for fast shifts. Ain't going to happen at GM. The LS engine engineers were given permission to do as they please and they explored a flat crank. It can't meet future smog and neither can OHV engines and has no virtues except for the above mentioned. It even sounds UTS. Can't even hear a F488 which is a 3rd of the car's value. |
Originally Posted by Shaka
(Post 1596669769)
There is no point for having a flat crank unless you want to rev it. Direct injection is heavy but can't rev high unless you make it much heavier. 50 lb 4000 psi fuel pumps require much HP to run at 8000 engine rpm. Turbo charging negates high revs anyway. High revs uses more gas. As Onpoint mentions, 5 liters is the limit for a flat crank in a V8. GM won't guarantee such a mill. You also can't modify the engine if you don't have access to and have know how to use very specialized expensive equipment. You increase primary and secondary shakes which requires a heavy and complex vibration damper and special engine mounts. The most closely guarded secret in race engines. Try taking a picture of one in the pits.
It is much lighter and has better throttle response up or down which is good for fast shifts. Ain't going to happen at GM. The LS engine engineers were given permission to do as they please and they explored a flat crank. It can't meet future smog and neither can OHV engines and has no virtues except for the above mentioned. It even sounds UTS. Can't even hear a F488 which is a 3rd of the car's value. And more RPM in a smaller engine doesn't equate to more fuel use. In fact the cruising fuel use typically goes down because the engine is smaller. I'm not advocating for a flat plane but it's really nice to have an engine that can rev to the moon. My M3's V8 redlines at 8,400 and it's awesome. |
IMO it's all about sound. I like the v8 cross sound more than v8 flat sound Also on an American car this should be an iconic character |
Originally Posted by vetteLT193
(Post 1596676247)
More RPM means you can use your gears better so why wouldn't you want to rev higher? Lingenfelter has built a flat plane LSx already. If they can do it in their shop I'd think GM could handle it with 100000 times the resources.
And more RPM in a smaller engine doesn't equate to more fuel use. In fact the cruising fuel use typically goes down because the engine is smaller. I'm not advocating for a flat plane but it's really nice to have an engine that can rev to the moon. My M3's V8 redlines at 8,400 and it's awesome. |
Originally Posted by vetteLT193
(Post 1596676247)
More RPM means you can use your gears better so why wouldn't you want to rev higher? Lingenfelter has built a flat plane LSx already. If they can do it in their shop I'd think GM could handle it with 100000 times the resources.
And more RPM in a smaller engine doesn't equate to more fuel use. In fact the cruising fuel use typically goes down because the engine is smaller. I'm not advocating for a flat plane but it's really nice to have an engine that can rev to the moon. My M3's V8 redlines at 8,400 and it's awesome. The flat-plane design used in my GT350's engine is pretty nice at times, but also causes lots of vibrations that require lots of engineering to quell. I think it would be nice if the C8/Mid Engine Vette get a 4 valve, cross-plane design that is designed to rev a bit higher than the LT1, but not sacrifice too much for an 8000+ RPM redline. In the end, if the displacement is ~5.0 liters and they want 100 hp/liter (500 HP total) it will still need to rev to make that power. Really looking forward to seeing how this next gen Vette turns out. -T |
Originally Posted by Trackaholic
(Post 1596694283)
Your M3's V8 is a cross-plane configuration. Nothing about a cross-plane design prevents it from revving high. It just requires more crankshaft balance mass, but once the mass is added it is actually much smoother than a flat-plane design. It may not have quite the no-load throttle response of a flat-plane design, but it can certainly rev out if designed that way.
The flat-plane design used in my GT350's engine is pretty nice at times, but also causes lots of vibrations that require lots of engineering to quell. I think it would be nice if the C8/Mid Engine Vette get a 4 valve, cross-plane design that is designed to rev a bit higher than the LT1, but not sacrifice too much for an 8000+ RPM redline. In the end, if the displacement is ~5.0 liters and they want 100 hp/liter (500 HP total) it will still need to rev to make that power. Really looking forward to seeing how this next gen Vette turns out. -T The Chevy engineers built a flat crank LS engine, but they abandoned it because it doesn't meet any profitable production criteria. Lingenfelter plays with this GM design now. There is a dude here who installs Chevy mills in BMWs including the 840 and a variety of front engine Porsche including 928s. A thriving business he has. My low revving LS7 427 is lighter than those German V8s and I don't even have to change gear if I don't want to. It uses less materials than the German V8s to make and will last longer. Over 30 mpg is normal. Mercedes and Audi V8s are better than BMW V8s but no where near low Cg Chebby injins with pushrods. https://cimg6.ibsrv.net/gimg/www.cor...9ccf242c8c.jpg |
The flat plane crank V8 is even firing with the main advantages being reduced rotating mass and superior exhaust scavenging compared to a cross plane V8. The trade off is a big increase in vibration. The vibration becomes especially noticeable when engine displacement gets above about 4 liters that’s why you don’t see many large displacement flat plane V8 engines in road cars. Space permitting, it is sometimes possible (see the original Ford GT “bundle of snakes exhaust”) to use a cross plane crank with a 180 degree exhaust system to achieve more optimal scavenging similar to that achieved with a flat plane crank.
Regarding revs, power is power, 500 HP at 4000 rpm is just as strong as 500 HP at 8000 rpm, however the torque curves would look quite different! All things being equal the 4000 rpm engine would be more fuel efficient because internal friction increases logarithmically so that 8000 rpm engine suffers from significantly more internal drag at a given power output. That friction issue is why Corvette engines are designed to stay under 2000 rpm in most cruise conditions. Revs can be fun but due to fuel economy considerations the trend is to reduced cylinder count (less friction per unit of displacement) and turbo charging (more power per unit of displacement at lower rpm) to keep friction losses low and efficiency high. |
Originally Posted by Guard Dad
(Post 1596700932)
The flat plane crank V8 is even firing with the main advantages being reduced rotating mass and superior exhaust scavenging compared to a cross plane V8. The trade off is a big increase in vibration. The vibration becomes especially noticeable when engine displacement gets above about 4 liters that’s why you don’t see many large displacement flat plane V8 engines in road cars. Space permitting, it is sometimes possible (see the original Ford GT “bundle of snakes exhaust”) to use a cross plane crank with a 180 degree exhaust system to achieve more optimal scavenging similar to that achieved with a flat plane crank.
Regarding revs, power is power, 500 HP at 4000 rpm is just as strong as 500 HP at 8000 rpm, however the torque curves would look quite different! All things being equal the 4000 rpm engine would be more fuel efficient because internal friction increases logarithmically so that 8000 rpm engine suffers from significantly more internal drag at a given power output. That friction issue is why Corvette engines are designed to stay under 2000 rpm in most cruise conditions. Revs can be fun but due to fuel economy considerations the trend is to reduced cylinder count (less friction per unit of displacement) and turbo charging (more power per unit of displacement at lower rpm) to keep friction losses low and efficiency high. I agree that power is power, but an engine making 500 HP at 4000 RPM is also making ~650 lb-ft of torque. That's not happening on a NA engine. So, if it is going to be "small", then in order to make 500 HP it will need the revs. Just for fun I looked up the volumetric efficiency of many top N/A engines (torque/liter). Here is what I found: Honda S2000: 155 lb-ft, 2.0 L = 77.5 lb-ft/L 163 lb-ft, 2.2 L = 74.1 lb-ft/L Lambo Huracan: 413 lb-ft, 5.2 L = 79.4 lb-ft/L Ford GT350: 429 lb-ft, 5.2 L = 82.5 lb-ft/L Ford Gen3 Coyote V8: 420 lb-ft, 5.0 L = 84.0 lb-ft/L GM LT1: 460 lb-ft, 6.2 L = 74.2 lb-ft/L GM LS7: 470 lb-ft, 7.0 L = 67.1 lb-ft/L BMW M3 V8: 300 lb-ft, 4.0 L = 75.0 lb-ft/L The main point here is that the advanced 4 valve, high performance engines are able to make around 80 lb-ft per liter. If you optimize a 5 liter engine for power, you will likely give up some of that mid range torque in order to have better breathing up top for more power. If the engine can make 350 lb-ft at redline, it would need to rev to 7500 to make 500 HP. I would honestly love an updated version of the LS7 for the ME vette. I think that is one of GM's most exciting engines (reliability concerns duly noted); it makes great power with excellent torque, and with DI updates could be even more potent. Anyhow, I think I just wasted a bunch of time, but I did have fun looking at various engine specs, so there is that. -T |
For the engine guys.
http://www.epi-eng.com/piston_engine..._yardstick.htm |
They want the engine small and that doesn't necessarily mean small inside. They need a compact, light engine and OHC engines historically haven't provided that. Look at the people replacing Porsche 944 4 cylinder turbo'd OHC engines with a simple LS1 that weighs 40 lbs more and comes in a physically smaller package. Replace a 2.5 L Turbo Four producing 247 HP with a 5.7 L 350 HP NA engine with a much better torque curve. The LS1 weighs about 40 lbs more and can be set back further in the chassis due to its smaller size. What if they decided to throw in an LS6 or LS3 which weigh about the same as the LS1? You are then talking about Sudden Impact.
I have ridden in one of those light weight cars with a 350 Horse LS1 and they go like stink. With the engine set back further, the chassis is well balanced and you are sitting at less than 2900 lbs with a non stripped car. Strip the car down, add a cage and you are less than 2800 lbs. Why should GM constrain themselves to a physically larger and heavier engine to have a pure DOHC that makes more HP per Liter but less HP per pound and unit of total volume? Bill |
Three engines. Normal LS based New OHVT flat crank 5.x New forced induced Information came from a source in the know. |
Originally Posted by Bill Dearborn
(Post 1596704239)
They want the engine small and that doesn't necessarily mean small inside. They need a compact, light engine and OHC engines historically haven't provided that. Look at the people replacing Porsche 944 4 cylinder turbo'd OHC engines with a simple LS1 that weighs 40 lbs more and comes in a physically smaller package. Replace a 2.5 L Turbo Four producing 247 HP with a 5.7 L 350 HP NA engine with a much better torque curve. The LS1 weighs about 40 lbs more and can be set back further in the chassis due to its smaller size. What if they decided to throw in an LS6 or LS3 which weigh about the same as the LS1? You are then talking about Sudden Impact.
I have ridden in one of those light weight cars with a 350 Horse LS1 and they go like stink. With the engine set back further, the chassis is well balanced and you are sitting at less than 2900 lbs with a non stripped car. Strip the car down, add a cage and you are less than 2800 lbs. Why should GM constrain themselves to a physically larger and heavier engine to have a pure DOHC that makes more HP per Liter but less HP per pound and unit of total volume? Bill The cam-in-block architecture is excellent from a weight and packaging perspective, but you are limited with what you can do with valve timing. In reading about the Viper engine, they had to move to a cam-in-cam design that allowed them to vary the exhaust timing. This allowed them to hit emissions requirements and still achieve their power goals. Maybe that tech is an option if GM wants to stay with the pushrod design. I do wonder a bit if there will be a general feeling that pushrod is too old fashioned for a mid-engine, modern sports car. That might be another reason to go with a DOHC architecture. Here is the article on the viper engine: http://www.hotrod.com/articles/how-t...ts-horsepower/ -T |
Possible 4 liter Dohc twin turbo in valley v8 is a GM design.
Flat plan crank version is entirely possible for corvette Zora (like 488) while the Cadillac version if produced could have a more traditional build for smoothness. If creating both versions with the same block is possible? I'm not a fan of Dohc extra weight and exterior sizing but for eurosnobs that seems to be considered something to have...so if Cadillac gets a version of the c8 chassis it will surely have the Cadillac twin turbo v8 that was set for its large TT v8 sedan lineup that has been put on the shelf... How far that twin turbo 4.0 v8 production went...nobody knows....but it was scheduled...very close to a reality. I doubt it's a flat pan crank for Cadillac since smoothness would be a high priority.. I'd rather have a LT1 , LT4 and LT5 than a twin turbo 4 liter v8 ...flat plane crank or otherwise... Complication and cost are concerns.... |
At this point a flat plane crank would seem like a me-too. While GM is not above following Ford with a me-too, they really don't want it to look like Corvette is following Mustang. They would rather do ANYTHING else.
Even if that wasn't a concern, I think after seeing lawsuits spring up over LS7, LT4, and GT350, GM would rather play it safe with future high-performance powertrains. I would love a screaming flat plane crank mid-engine Corvette, but I don't think it's in the cards. |
There is a good possibility of them producing flat-plane engine as a competitive response to Ford.
But probably they gonna continue with cross-plane for now. |
Originally Posted by King Dranzer
(Post 1596741043)
There is a good possibility of them producing flat-plane engine as a competitive response to Ford.
But probably they gonna continue with cross-plane for now. |
Another thing about flat crank V8s is that they have to be square or over square to reduce piston speed. Not good for piston loads that low revving turbo charged engines produce. I will have lower crank stress due to the lower peak piston acceleration for the same engine speed and will have has better pumping efficiency because of bigger valve/bores ratio at high RPM. Increased piston and head surface area and high bore/stroke ratios cause increase in heat loss and poor thermal efficiency. (Gas guzzler tax)
The large size/width of the combustion chamber at ignition can cause increased inhomogeneity in the air/fuel mixture during combustion, resulting in higher emissions. Because these characteristics favor higher engine speeds, oversquare engines are tuned to develop peak torque at a relatively high speed, which contradict turbo duties. The reduced stroke length allows for a shorter cylinder and a shorter connecting rod, generally making oversquare engines less tall but wider than undersquare engines. The F488 is a magnificent car but it ain't cheap and you gotta stop for gas often which is bad for track days for that reason. Here is one of the greatest engines to come from Detroit or anywhere. The magnificent over square 8000rpm 90' crank, 302 CI, 'Screamer' mill from Chevy in 69. Only 100 Z28 Camaros with the JL8 option and dual quad carbs and 8000rpm tach were built with this engine. 100 cars had to be built for amoligation in Trans Am. The most beautiful sound a V8 has ever made. It didn't even have 180" headers. Could not even meet 1970 smog laws because of it's over square architecture. If it had a flat crank, terrorist would still be making them. https://cimg0.ibsrv.net/gimg/www.cor...017116e076.jpg https://cimg2.ibsrv.net/gimg/www.cor...62e509be75.jpg https://cimg3.ibsrv.net/gimg/www.cor...64ea5c6fb1.jpg https://cimg4.ibsrv.net/gimg/www.cor...d63f003e28.jpg https://cimg5.ibsrv.net/gimg/www.cor...e94d4dc574.jpg What happened to all those left over 'Screamers"? Well, 100 Chevy SS cars (English Vauxhall Firenza) were built by GM with these Camaro parts. It was the fastest production car in the world at that time. https://cimg7.ibsrv.net/gimg/www.cor...5e66aa67b6.jpg https://cimg8.ibsrv.net/gimg/www.cor...3a4385d506.jpg https://cimg9.ibsrv.net/gimg/www.cor...7f8160a61a.jpg https://cimg0.ibsrv.net/gimg/www.cor...a4c2a24c6c.jpg |
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