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This is how they got to 670 hp and they learned a lesson from Ford
I’m going to re-post some of my contact from another thread please read through it it’s very informative
When it’s comes to naturally aspirated engines you have two main ways to increase power. Either increase displacement or revs. With a pushrod engine you’re basically capped at 7000rpm or so depending on the situation. The main reason for this is parasitic loss related to the valve train. There is way too much going on in the valve train to be reliable or high engine speeds. This is why dual overhead cam will always be superior at high engine speeds and cylinder head flow. We could get into the nitty-gritty but no need to just be aware that by extending the rpm range and including the fact that you have to work on some other Aspects including cylinder head flow all sorts of other variables another 200 hp is a non-issue. Be aware that at 5.5 L actually comes in under horsepower per liter compared to the old Ferrari Speciale this is actually a good thing because the engine is actually a little bit understressed from an engineering perspective. Ferrari had to do all sorts of witchcraft to get to 600 hp out of the 4.5 L and rev to 9000rpm.
Now where things get interesting is talking about flat plane cranks. They are not superior to Cross-plane cranks in every metric, and in a lot of ways they have a lot of problems particularly NVH. Cough cough ford, The way Chevy got around this Is by using 120° V angle it’s almost flat eight this allows them to use very little counterweights for the crankshaft helping out with NVH. The only thing I’m really curious about is piston speed and we don’t know a whole lot about the engine as far as internals right now
Here is the rub and we have to go look back at ford as well. Flat plane crank engines are very difficult to tame if ya will the NVH will always be an issue. Ford found this out the hard way by basically rigging in a non traditional FPC into a coyote. While it’s a great engine and has a very unique soundtrack it’s definitely not the right way to make such an engine. Ford has paid the price for this with all the major issues over the years. I could go into advance detail all the issues with the engine but the main reason why the GT350 is a compromised design, it’s because of the packaging. Ford engineers wanted to lower the hood line and after the boss 302 development top brass wanted 100 hp per liter. At this time right around 2012-2013, this was a big problem because the coyote was still very new and they hadn’t even gotten the boss 302 out the door. So the solution was to increase the revs and use a FPC. This required all sorts of witchcraft to work, including changing the firing order which meant increasing the weight of the crankshaft up to 50 pounds which meant a savings of only 5 pounds vs the coyote. They couldn’t use equal length headers do they basically used an updated and hand welded variant of the stock coyote tube headers. They also could used a traditional twin throttle body and intake setup aka Ferrari which is why the firing order had to change. The reason why this is all important is because what Ford wanted the GT350 to be is what the new Z06 is. Ford also had piston speed issues in early development engines we heard all sorts of oddball engine failures in early development vehicles are going to post down below an early engineering document talking about estimated piston speed numbers back in 2012 talking about this engine so you can compare to the new z06 Engine / Bore x Stroke / Mean piston speed in feet per second @ redline
and with a 458 Speciale Ferrari had to run 14:1 compression and rev all the way to 9000 RPM including CNC machine heads. And that was with a 4.5 L and as much as I love the Italians “Ducati owner here” they like the fudge the numbers a little bit. 458 Speciale was rated at 597 hp but in the states it was lowered to 13:5:1 compression. The reason why this is important is because this may very well be the most powerful flat plane crank v8 ever made. I can see it making between 625 hp and maybe 660. Once you start going to past that it’s going to require more revs or higher displacement. Which in a flat plane crank engine is a major issue it’s the same reason why you don’t see huge 3 or 3.5 L four-cylinder‘s “ cough cough Porsche
This is an amazing engine and anyone who does it need to do a little bit of reading lol
if your math is correct, wouldn't 104 FPS put this engine in the ballpark of v10 F1 engines in terms of mean piston speed? That seems unlikely GM would push the envelope that much given the rebuild frequency isn't measure in 2 digit hours.
Last edited by Trojan man; 10-26-2021 at 03:21 PM.
Now where things get interesting is talking about flat plane cranks. They are not superior to Cross-plane cranks in every metric, and in a lot of ways they have a lot of problems particularly NVH. Cough cough ford, The way Chevy got around this Is by using 120° V angle it’s almost flat eight this allows them to use very little counterweights for the crankshaft helping out with NVH.
By all means, post more detail on this 120-degree v-angle. Specifically, its impact on the crank throws and balancing.
I think it's interesting that the LT6 has titanium connecting rods for light weight in order to achieve high RPM. There are issues with the LS7 titanium connecting rods abrading one another if the coating is lost. Evidently GM figured coated titanium rods are worth the risk in order to achieve the level of performance that was targeted. Coating technology may have improved as well.
I think it's interesting that the LT6 has titanium connecting rods for light weight in order to achieve high RPM. There are issues with the LS7 titanium connecting rods abrading one another if the coating is lost. Evidently GM figured coated titanium rods are worth the risk in order to achieve the level of performance that was targeted. Coating technology may have improved as well.
When did those issues show up in the LS7 con rods? From as far as I can tell not while the cars were in production. I owned a 2008 Z from 2009 through 2015 and although I lost an engine due to a dropped valve in 2011 I never had or heard of issues with the con rods. Once I traded the car at the end of 2015 I stopped paying attention to C6Z issues but basically if there are con rod issues they weren't considered very high on the list of issues discussed on the forum or other outlets from mid-2005 through 2015.
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When did those issues show up in the LS7 con rods? From as far as I can tell not while the cars were in production. I owned a 2008 Z from 2009 through 2015 and although I lost an engine due to a dropped valve in 2011 I never had or heard of issues with the con rods. Once I traded the car at the end of 2015 I stopped paying attention to C6Z issues but basically if there are con rod issues they weren't considered very high on the list of issues discussed on the forum or other outlets from mid-2005 through 2015.
Bill
Oh yeah, it's real. Not as prevalent as the dropped valve issue, though. Do some reading on the C6 Z06 forum and you will see it. My 2006 Z06 has 75,000 miles on it, and so far no sign of connecting rod trouble, so I consider myself fortunate. It's hard to predict when and where it will strike, but I'm sure it affects those cars that are driven harder.
When did those issues show up in the LS7 con rods? From as far as I can tell not while the cars were in production. I owned a 2008 Z from 2009 through 2015 and although I lost an engine due to a dropped valve in 2011 I never had or heard of issues with the con rods. Once I traded the car at the end of 2015 I stopped paying attention to C6Z issues but basically if there are con rod issues they weren't considered very high on the list of issues discussed on the forum or other outlets from mid-2005 through 2015.
Bill
Bill,
The Ti rod issue has come up primarily in some of the bigger build HCI LS7s and mostly after you moved on from the C6Z forum. I started to see it in my 593 rwhp build around 10K miles after the build and then got the bottom end forged including CrMo forged rods. New Ti rods, if you can find them go for $770 each whereas the CrMo intakes on mine build were $820 for the set of 8.
NASCAR 358 ci Cup engines ran Martinsville up to 10,400RPM but then they would get rebuilt after ~300 miles. Presumably the LT6 will meet emissions, get reasonable fuel economy and have at least a 3/36 warranty, maybe 5/50 on the powertrain.
NASCAR 358 ci Cup engines ran Martinsville up to 10,400RPM but then they would get rebuilt after ~300 miles. Presumably the LT6 will meet emissions, get reasonable fuel economy and have at least a 3/36 warranty, maybe 5/50 on the powertrain.
Props to chevy for raising the bar. As comlicated and impressive as this engine is...most def going to let others deal with the inevitable bugs that will arise...wicked package for sure
Don't forget there have been de-stroked LS7 engine running around for nearly 15 years now. With a 3.625 crank they rev them to past 8000 RPM, with a 3.25 crank and Honda "cheaper" rod bearings, they rev them up to 9500 RPM. When you look at the bore and stroke numbers the LT6 are not that far off from a 5.8L de-stroked LS7. The peak HP and torque figures of both the LT6 and those de-stroked LS7 peak at about the same RPM levels as well. The key with these de-stroked LS7 engines is the intake manifold. Options like the MSD atomic or a fabricated large plenum shirt runner unit really brings those de-stroked LS7 alive at higher RPM. The difference is that the LT6 is emission compliant and has a warranty as noted above. Plus the drivability of the LT6 is most likely much better too.
Besides those NASCAR engines, don't forget that +50 years ago they were shifting Chevy small blocks at 11,000 RPM at the drag strip. They also changed valve springs fairly often too
if your math is correct, wouldn't 104 FPS put this engine in the ballpark of v10 F1 engines in terms of mean piston speed? That seems unlikely GM would push the envelope that much given the rebuild frequency isn't measure in 2 digit hours.
Mean F1 piston speeds are not "very representative since they are fuel limited and don't run over 11,500 RPMs.
NASCAR engines (350 CPC V8s) at 9,000 RPM run 145 FPs.
The old V10s ran in the 140 FPs range, too.
I would say you are not quite within spitting distance.
From::
A Cup car's piston speed is 8,780 feet per minute at 10,000 rpm. Compare that with an F1 2.4L V8's peak piston speed of 8,349 feet per minute at 18,000 rpm. It takes serious engineering to make an engine last 600 miles with that piston speed.Mar 17, 2021
Stroke: 3.600
Bore: 4.190
Displacement: 397 cubic inches
Camshaft: Over 900 lift, 280º/286º at 0.050, 110
Now where things get interesting is talking about flat plane cranks. They are not superior to Cross-plane cranks in every metric, and in a lot of ways they have a lot of problems particularly NVH. Cough cough ford, The way Chevy got around this Is by using 120° V angle it’s almost flat eight this allows them to use very little counterweights for the crankshaft helping out with NVH.
10-26-2021, 03:09 PM
This is how they got to 670 hp and they learned a lesson from Ford
