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I'm wondering how much boost you could run to a stock 5.7L if you lowered the compression ratio with thicker head gaskets but didn't tear into the short-block. In theory it sounds great but I worry about the stock ring gaps being too small and the crank. The idea of running 11-12PSI (with the proper cooling system) sounds awesome. Anyone have experience with this?
 

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I'm wondering how much boost you could run to a stock 5.7L if you lowered the compression ratio with thicker head gaskets but didn't tear into the short-block. In theory it sounds great but I worry about the stock ring gaps being too small and the crank. The idea of running 11-12PSI (with the proper cooling system) sounds awesome. Anyone have experience with this?
API told me of a customer running 10psi with water/meth injection and the tune was adjusted for it. At that time the individual was running that set-up for over half a year and no issues. Although API highly recommends forged pistons at those boost levels.
 

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From what I've gathered around the forums, the 5.7's fair a lot better than the 6.4's where boost is concerned. That being said, I'd still regap rings at a minimum if you are planning boost above 7-8 psi on any of these modern Hemi's. As you may know the ring lands on the pistons are what cause failure under boost. Couple that with the mattern the Hyper Eutectic pistons are made out of is a recipe for disaster. If your tune is spot on you may be able to avoid failures that said, I wouldn't take any chances on a newer platform vehicle. You are already spending the money to boost it, you minds well do things right the first time around.
 

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Bringing this thread from the dead as I always believed the 6.2 had more generous piston ring gaps but according to the FSM it appears the 5.7 has a slightly bigger top ring gap spec of all 3 engines?

979292
 

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ChallyTatum, How in the world do you find all of this information...... I have a FSM also, but my goodness you are like the Hemi knowledge base....... I'm seriously going to DM you next time I need to look any spec up lol. This is a great find especially for those of us that build our own engines....... I'm actually surprised that the factory specs for the 6.2 are so conservative........ But I'm not surprised they are similar to the 6.4's. The bores on both blocks are identical so this makes sense to me. Thanks again my friend
 

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ChallyTatum, How in the world do you find all of this information...... I have a FSM also, but my goodness you are like the Hemi knowledge base....... I'm seriously going to DM you next time I need to look any spec up lol. As always great find sir.
I found it on the chilton site (most of the info is same as FSM) but I am pretty sure it is in the FSM under engine mechanical> displacement> specifications. I still want to cross reference this with the New Hemi books I bought a while ago. Only reason I was looking into the ring gaps is I always heard and believed gapping the rings wider is required in boost application, which I still firmly believe, but seeing the 6.2 has similar ring gaps I am a little puzzled. I would have expected it to be a little bit more open. However, I have little faith in FSM specs as I have found numerous errors.
 

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Agreed, from every engine builder I've ever spoken to, I've been told to gap between .022-.028 for boost and .018-.022 for nitrous. Factory gaps should follow manufacturer's recommendations
 

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I found it on the chilton site (most of the info is same as FSM) but I am pretty sure it is in the FSM under engine mechanical> displacement> specifications. I still want to cross reference this with the New Hemi books I bought a while ago. Only reason I was looking into the ring gaps is I always heard and believed gapping the rings wider is required in boost application, which I still firmly believe, but seeing the 6.2 has similar ring gaps I am a little puzzled. I would have expected it to be a little bit more open. However, I have little faith in FSM specs as I have found numerous errors.
It might also depend on the ring material too. Different metals expand at different rates. It might also have to do with the compression rings on the Hellcat are PVD (Physical Vapor Deposition) coated with Chromium Nitride to toughen them up and make them more heat resistant.

Something like this:

https://www.cp-carrillo.com/n-12068-pvd-rings.html
 

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Could very well be coating but I would still think they would run a wider gap. However, according to "New Hemi Engines" book file to fit rings typically have top compression ring gaps that vary per application and what is interesting is the "rule of thumb" gap for FI is what is used for NA street apps.
File to fit ring gap guide line
[inch]
Street -0.025
Drag0.018-0.020
Nitro Street0.020-0.022
Nitro Drag0.028-0.030
Forced Induction0.024-0.026
 
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