Why 6.2 Liter?
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From a Motortrend article, at least explains why the Hellcat platform in particular went with 6.2
"While some Internet chatter has bemoaned that the 6.2L Hellcat is a few cubes smaller than its less potent 6.4L Apache Hemi stablemate, from a durability standpoint the reduction in displacement makes a lot of sense. The new 6.2L combines the 4.09-inch bore of the 6.4L Hemi with the 3.58-inch stroke of the 5.7- and 6.1L Hemis. The shorter stroke (3.72 versus 3.58 inches) offers three distinct advantages. First off, it increases the crank overlap—the portion of the main and rod journals that overlap each other—thus increasing strength. Secondly, considering that the Hellcat utilizes the same block-deck height and connecting-rod length as the 6.4L Hemi, the shorter stroke enabled Chrysler engineers to increase the compression height of the pistons. In a forced-induction application, having more piston material between the wristpin centerline and the piston crown not only provides more space for thicker ring lands but also allows pushing the top ring farther down the bore. This isolates it from the extreme cylinder pressure and heat generated through supercharging. Lastly, reducing the compression ratio is a must in any forced-induction combo, and the Hellcat Hemi relies on a larger piston dish to reduce compression from 10.9:1 to 9.5:1. A taller compression height makes it possible to fit a larger dish into the piston without compromising durability."
"While some Internet chatter has bemoaned that the 6.2L Hellcat is a few cubes smaller than its less potent 6.4L Apache Hemi stablemate, from a durability standpoint the reduction in displacement makes a lot of sense. The new 6.2L combines the 4.09-inch bore of the 6.4L Hemi with the 3.58-inch stroke of the 5.7- and 6.1L Hemis. The shorter stroke (3.72 versus 3.58 inches) offers three distinct advantages. First off, it increases the crank overlap—the portion of the main and rod journals that overlap each other—thus increasing strength. Secondly, considering that the Hellcat utilizes the same block-deck height and connecting-rod length as the 6.4L Hemi, the shorter stroke enabled Chrysler engineers to increase the compression height of the pistons. In a forced-induction application, having more piston material between the wristpin centerline and the piston crown not only provides more space for thicker ring lands but also allows pushing the top ring farther down the bore. This isolates it from the extreme cylinder pressure and heat generated through supercharging. Lastly, reducing the compression ratio is a must in any forced-induction combo, and the Hellcat Hemi relies on a larger piston dish to reduce compression from 10.9:1 to 9.5:1. A taller compression height makes it possible to fit a larger dish into the piston without compromising durability."
Interesting read. Good stuff, thanks.
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yes but lots of variables here. Hot Rod/Engine Masters has done some interesting tests in the past with same displacement but different bores/strokes.
10.9 static CR would have been just fine and utilized more power if they would have left it there. Higher compression engines do just fine with boost, and the old adage of "you have to lower the static CR for boosted applications" just doesn't ring true any longer.
Case in point... I held the record for the highest hp stock block S2000 for years and that engine lived and drove very well with it's 34 psi boosted 11:1 static CR engine, making around 900hp. Never once did it have any issues and in fact I have since fully built the engine for 50+ psi and it is still at 10.8:1 static CR. Higher static CR engines seem to drive much better off boost and on tip in to boost, over lowering the static CR, and they make more power throughout the powerband.
I believe they should have left the hellcat engine at the 10.9:1 static CR and it would have been that much better.
Case in point... I held the record for the highest hp stock block S2000 for years and that engine lived and drove very well with it's 34 psi boosted 11:1 static CR engine, making around 900hp. Never once did it have any issues and in fact I have since fully built the engine for 50+ psi and it is still at 10.8:1 static CR. Higher static CR engines seem to drive much better off boost and on tip in to boost, over lowering the static CR, and they make more power throughout the powerband.
I believe they should have left the hellcat engine at the 10.9:1 static CR and it would have been that much better.
I think it’s just GM and the Hellcats isn’t it? So basically 2 engines that both come in different configurations.
Granted there is a big difference between an Escalade 6.2 and a 755hp LT5 or even between the LT5 and LS3 (which debuted all the way back in 2008) but still based on the same bore and stroke.
Granted there is a big difference between an Escalade 6.2 and a 755hp LT5 or even between the LT5 and LS3 (which debuted all the way back in 2008) but still based on the same bore and stroke.
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Out of curiosity, how many miles you put on that engine tuned that way? Sounds like an amazing engine to race!
I bought the car new in 2003 and at 3k miles i had one of the first boosted s2k's in the country. At around 9k miles i made some turbo kit changes and got into the hp record with the stock block. It stayed there with a lot of street racing until 16k miles without a hickup. So, about 7k hard miles at over 800 whp. I have since made some major changes to it with everything being built now. If you know the name Carey Bales from Indy, he is building my s2000 now.
The F20c engine that comes in the s2000 is forged from Honda and very strong with a crank girdle instead of caps.
On your article, I quote a similar stat with the crank overlap when talking with people who want to boost a 6.4L. "Oh I have a fully forged build, I'm fine man." My reply: "No, you're not and here's why..."The Apache is a fragile engine... not just because the ring lands are shallow, but because the stroke is long and boosting it will put a lot of pressure on the rod journals."
There's a guy in a FB Mopar group I belong to that has more money than sense. He's one of these streamer kids with a Lambo Urus and a 50th Scat Pack. He just throws money at his cars and films other people doing all the work. He's currently turbo boosting his 6.4L to 16psi (so he claims) and really only put forged rods and pistons in for the lower internals. No dampener upgrade, no crank upgrade... all still stock. In DMs, I told him the above about the inherent problem that his engine builder seems to be overlooking (or not caring, as most will build exactly what you tell them to when money is involved). His reply, "Yo, my builder is well respected in the Miami scene bro. We fine." This same builder also installed an air ride suspension and insists that the stock 8HP70, rear end, and drive shaft are fine to hold a 392 on 16psi.
This convo was about 3 weeks ago after his FB live video unsuccessfully tried to film the initial startup. Car didn't start (PCM/wiring issues of some kind). They still haven't gotten it to turn over yet. I'm eagerly awaiting the first start and the soon to follow drivetrain explosions. I don't like to wish ill on people, but I have a macro made for "I told you so" preloaded onto this keyboard.
I have some experience with modding the 392, and it is not a cheap nor easy job. When I was parting together my build, I was looking at just shy of $30,000 to get the 392 to hold on to 900whp. This is why I own a Hellcat and nixxed the thought of that build. The Hellcat is a much more robust platform where the 392, even if it's built out to the Nth degree, will still have that fundamental architectural weakness unless you swap out the crank and practically start from scratch.
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So what’s your thoughts on putting a 6.4 crank in a Hellcat block with a good Rod like a Molnar H beam with a Diamond Piston on 18-19 psi of boost on E85?
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The basic "architecture" in the 6.4 and 6.2 is the same and the 6.4 crank IS forged.
I swear to god there is so much FUD mixed in with some cogent points that it would take more time and effort than I'm willing to invest to sort it out.
The cliffnotes version is some Yes and mostly No.
The crank is different, hence the shorter stroke in the 6.2L and added overlap benefit. That's basically the difference between a mobile home and a brick house on the same size lot.
If you want to get down to brass tacks though, all pushrod V8s share fundamental similarities in architecture... but what makes the Apache fragile for boosted applications is directly related to the stroke and associated increased force applied to the rods.
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Some of the theoretical weaknesses you reference may be valid at 900hp but not at 600-650.
A different architecture but I ran a stock cast piston 383 with OEM steel shim head gaskets at 12psi with no issues even though 'smart guys' would say it's a no no. Good tune and paying attention and it was fine.
A different architecture but I ran a stock cast piston 383 with OEM steel shim head gaskets at 12psi with no issues even though 'smart guys' would say it's a no no. Good tune and paying attention and it was fine.
If you look at the crankshaft from one end consider the diameter of the main bearing journal. Then imagine how the diameter of the connecting rod journal overlaps it. It would look like a Venn diagram with one circle overlapping the other by say 40%. When the stroke is reduced the connecting rod journal moves towards the centerline of the main bearing journal and the overlap is increased. Doing that produces a stiffer and stronger crankshaft, and both reduce the chances of a fracture.
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