How much is too much?

[Speedy!]

That's a good picture right there.

 

[BULL]

I'm not familiar with what you're referring to above.

The difference between the HC and H.O. mode of the Demon motor is only 133hp.

This is a small bump in HP by most people's standards, yet look at all that was done to make that viable in the eyes of SRT.

And then the small difference in rpm between the two motors.

They didn't just tweak the valve train, they upgraded it, not because they wanted to, but because they felt like they HAD to survive the few hundred rpm they added.

If there was margin left in the HC motor, they would have used it for what is a modest HP increase, they didn't.

Clearly the other side of the coin is all of the empirical evidence from everyone going well beyond factory specs.

Has something changed in parts??

I'm sure we'll never know.

 

[Stl376]

On the 5.7 and 6.1 HEMI platforms (and especially the 6.4), the ring lands were a problem. .

I can attest to to 6.4 ring lands....

 

[BULL]

I can attest to to 6.4 ring lands....
View attachment 2250

Was this on a stock engine, modified, with or without boost?

 

[Hpindy]

I can attest to to 6.4 ring lands....
View attachment 2250

That's only a lager valve relief for larger valves

Sent from my BBF100-2 using Tapatalk

 

[Stl376]

Was this on a stock engine, modified, with or without boost?

No boost. Just ported heads, long tubes, cam and tune. Stock internals.

 

[Speedy!]

@BULL - gotcha, the way it was worded I thought someone here had done some kind of build or something. 133 more HP his about 19% more, and with the Demon maybe they figured folks would beat on them since they planned to advertise it as an off the show room drag race ready car you could drive to and from the track. Your point is well taken though.

@Stl376 - that looks like the exhaust side of the piston. From memory I think it was usually the intake side that broke on supercharged applications at least. Looks like in your case it just got the ring hot, probably from running a bit lean.

 

[Stl376]

@Speedy! I agree.

 

[BULL]

Right, so kind of repeating myself, and others, and even some of what you're saying/asking.

Yes, there's a curve of increased hp vs durability, and what does it look like?

Hell, how could you quantify that? And then even if you could, how would you interpret it, or agree on where the sweet-spot is?

I certainly couldn't say.

Put all of the respected Tuners in a room, lock the door, 'tell them they can't come out or eat until they spit out the following numbers:

• Mild street tune
• Aggressive street tune
• Hobbyist Drag racer
• Serious Drag racer
• Crazy Drag racer
• Hobbyist Road racer (different eng loading)
• Serious Road racer (different eng loading)
• Crazy Road racer (different eng loading)
• Max HP, it might blow on the next WOT

Yeah, on second thought, they would die before they agreed on the first number...

 

[DGatzby]

I might take a tweek for 93 octane someday, but the more I read from you guys, I am sticking to suspension upgrades. It's plenty to work with on a road course as it comes for power. I use the best 93 octane I can find and add some Turco for the track to keep it happy, that and a catch can (which is collecting almost nothing on this engine) is as daring as I want to get for a while. It's good reading gents, thanks!

 

[Jack_Toepfer]

Interesting that the ringland failures were favoring a certain part of the piston. I find it very unlikely that the ring gaps were all in that orientation from the factory and remained that way throughout the lifespan of the engine. Would be very interesting if that was the case.
Of course I’m assuming that the primary point of failure would be where the gap is sealed and the 2 ends are fighting for space.

 

[Speedy!]

 

[Speedy!]

Interesting that the ringland failures were favoring a certain part of the piston. I find it very unlikely that the ring gaps were all in that orientation from the factory and remained that way throughout the lifespan of the engine. Would be very interesting if that was the case.
Of course I’m assuming that the primary point of failure would be where the gap is sealed and the 2 ends are fighting for space.

Seems intake side was prone to over heating.

 

[Magnified]

Now I'm really curious. Have any of these other cars that went down had the other rods examined for bend? On cylinders that didn't grenade? If Speed and others (who aren't novices) have looked at these and the bend was not noticed, I'm wondering if there are more bad rods out there that just have not been noticed or caught. Still, it doesn't explain why the #7 tends to be the one to finally fail, but I am concerned if I keep the car and start building on it.

 

[Speedy!]

I've not held anymore in my hands personally, but people have sent me pictures of bent rods from Hellcat and RE engines. Now that Mike pointed out the bent rods I sent him, it is super obvious, not sure how I missed it honestly.

The fuel pump in the Hellcat is variable, it's "supposed" to increase volume with boost. I'd take a look to make sure that's occurring in your situation.

 

[vortecd]

No boost. Just ported heads, long tubes, cam and tune. Stock internals.

What did it run at the track?

 

[WhipCat]

Are we all surprised you need to upgrade to stronger internals past 800-900 whp let alone 1000whp. For all the money and time we drop in these rides. We all continue to do the same thing every time, we always say we are done modding from here. It’s not gonna happen to me.

Eliminate all the weakest links. Cover all the bases, the engine reliability is number one. If you question whether or not it’s gonna take it, your not having any fun.

 

[Stl376]

What did it run at the track?

Stock with just a tune and tire; 12.1@114 in April. With all the mods 11.76 @118 in July. Never got to run it in better air before the engine went south.

 

[Phast Hemi]

If I'd had time I'd have pulled all the pistons out, but I was pressed so just boxed it up and shipped back to Mopar for core once we found the one disintegrated. I received some piston/rod assemblies from a performance shop (3 assemblies) from a failed engine. They didn't give me details on what failed, but @16GoManGoHC2 has experience testing parts failures so I shipped two of them to him to do some catastrophic tests on out of curiosity. I also sent him what was left of my #7 cylinder piston. Piston tops looked ok on the three test subjects, but had some scoring on the sides.

Turned out the piston assemblies I sent him were bent (granted not from my motor but AJ has mentioned bent rods more than once now). I kept one for myself as a souvenir and when Mike told me the others were bent I checked the one I kept, sure enough it's bent. The piston from my engine exhibited very similar wear characteristics on opposing sides as the assemblies I provided with bent rods. Mike's experience suggests the rod failed and caused my piston to fail. All just educated theory though really.

Had another shop reach out to me last week. Three Hellcats and a Demon all broke #7 and his analysis showed rod issues so they now recommend a piston/rod upgrade after 800rwhp.

In hind sight, an autopsy of your old engine may have yielded some information that could have helped you answer your own question, especially as it pertains to your specific use. It would have been beneficial to inspect the other 7 rods to see if any were bent/stretched and if so, why? Due to excessive cylinder pressure possibly? Detonation? RPM?

Combine that with your discovery of broken spark plug ground straps and the answer may have become more evident and less speculative.

 

[16GoManGoHC2]

In hind sight, an autopsy of your old engine may have yielded some information that could have helped you answer your own question, especially as it pertains to your specific use. It would have been beneficial to inspect the other 7 rods to see if any were bent/stretched and if so, why? Due to excessive cylinder pressure possibly? Detonation? RPM?

Combine that with your discovery of broken spark plug ground straps and the answer may have become more evident and less speculative.

Being the heads came off I would have had to have flipped it over and at least unbolted the rods from the crank and popped each out to inspect each assembly, each bore and the rod bearings. They would have waited on the core. The hints to its failure where buried with it unfortunately.