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Hey good folks........so after getting my 21' WB Scat 6spd a few months back and getting back into the game of hardcore engine building after a decade or so......ive been looking at the upgrade path for my 6.4l........either an all out naturally aspirated street build.........or an all out boosted street build.

The concensus from amatuer and pro builders alike is that the bottom end( crank rods and pistons) can handle any build naturally aspirated you can throw at it WITH A SOLID PROPER tune. The hypereutectic pistons will be fine.

But with boost you are basically limited to about 5-6 psi from same said pistons. The universal reasons you read online is due to the top ringland being so close to the top of the piston and it being suceptible to breaking.

What seems to never be mentioned or talked about in depth is why other than vague bad tune or heat at piston crown ......detonation ringland just cant handle boost because too thin etc.

But ive had a few pro engine builders tell me that the stock pistons can in fact handle higher boost etc w no problem w proper tune but most amatuer builders and pro builders dont go down this path due to lack of knowledge or not wanting to pass up a higher ticket sale on parts for common street builds.

Whats being missed here? This has come up in discussion. Regapping the rings......top one especially. They have a very tight gap from factory. Combine that with boost builds that increase the heat and expansion on the top of piston and ringland.....it creates a ring that cannot expand properly and creates excess pressure where the thin top groove of piston will be suceptible to breaking/cracking.

Some boosted kits claim ur fine on low boost but in reality even on low boost setups the ring gaps should be rest accordingly on these pistons. But that means more labor and getting deeper into the engine teardown. So if your yanking out the rods and pistons......may as well do forged parts right? But now your looking at forged pistons with poor long term wear characteristics and greater expansion rates causing quicker piston, piston ring and cylinder wear on a street rig that will see alot more miles that a race motor.....2618 especially.

One of great things about Hyper pistons is the tight tolerances and low uniform expansion.........these engines stock are quarter million mile engines with proper care and maintenance.......when you increase power and performance longevity goes down.....but i personally would like to keep as much of that as possible still.

So thoughts on properly regapping the stock pistons and trying higher boost than what you see typically recommended? Told these pistons regapped can realistically handle boost into the 12-15psi range REGAPPED w proper tune. Has anyone actually done that?
 

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You've zeroed right on the issue.

10.9:1 CR and tight end gaps

the 5.7s run 10.3:1 CR and with the smaller combustion chamber there's less quench area and the rings don't have to be as high up on the piston.

Basically all engines have to meet the same emissions standards - the smaller displacement engines meet it more readily as they have less air in = lower combustion emissions.

go to larger displacement and the challenge of meeting emissions is greater...

a naturally aspirated engine will have tighter ring gaps for both less blow-by (which creates emissions) and this will tend to have longer service life with lower oil consumption.

compare this to the forced induction Hellcat (and derivatives) they are 9.5"1 CR and they ring gaps are larger than the N.A. engines.

two factors - the lower CR allows more boost and can live with pump gas (min 91 octane for SRT engines) and with knock sensors to keep detonation under control
 

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For many - if they're not a DIYer

the labor involved tearing an engine down - it would be conceivable to re-gap rings for forced induction.

they go "all in" and just replace pistons and do the ring gaps accordingly for the application.

Even then, going forced induction with 10.9:1 CR is going to have limits for the amount of boost probably in the low teens? because you're back to the limits of 91 - 93 octane fuel plus the stock CR and whatever boost.

for the record a standard Hellcat runs 11.6 PSI w/ the 2.4L s/c unit and 14.5 PSI w/ the larger 2.7L s/c setups
 

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Thought provoking and educational...that's why I like this place!
 

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Went with thin ring forged pistons on my N/A 426 stroker. Dialed in more gap (just in case I wanted to go nitrous down the road) and went gapless on the #2 ring. Works great with 0 oil consumption.
 

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So thoughts on properly regapping the stock pistons and trying higher boost than what you see typically recommended? Told these pistons regapped can realistically handle boost into the 12-15psi range REGAPPED w proper tune. Has anyone actually done that?
I realize you probably mean regapped the rings but as was mentioned once you do the labor to tear the engine down the vast majority of people are going to then put forged parts in so they have no worries about a lot of boost. Even with the rings gapped properly for forced induction you are still left with a higher than optimal compression ratio.

I don’t remember who did it but there was a magazine article quite a while ago were they just regapped the rings just to see how much boost it could handle. It was quite a bit as I remember but longevity wasn’t a factor in the experiment.
 

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I realize you probably mean regapped the rings but as was mentioned once you do the labor to tear the engine down the vast majority of people are going to then put forged parts in so they have no worries about a lot of boost. Even with the rings gapped properly for forced induction you are still left with a higher than optimal compression ratio.

I don’t remember who did it but there was a magazine article quite a while ago were they just regapped the rings just to see how much boost it could handle. It was quite a bit as I remember but longevity wasn’t a factor in the experiment.
Engine Masters did that I believe.
 

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2011 R/T 6M Bright White, 590whp 490wtq, Whipple 10psi, 274 cam, 1 7/8 LT headers, 429 gears
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Engine Masters did that I believe.
yeah it was Engine Masters... Ran it up to 1000hp.

Side note: Hypereutectic pistons are used in boosted engines. They are actually quite a bit stronger than just a cast piston and they are resistant to heat expansion which is key for boosted applications.

I would like to see how much abuse/boost a 5.7 could take long term with just adjusting the ring gap. Between the Hypereutectic pistons and the Nodular Iron crank they can take some abuse. The 5.7 crank is rated to take up to 700HP.
 

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I have seen first hand what happens to a super charged 6.4 liter engine when the boost was eight pounds. I friend of mine in Tucson did it with his Challenger, and completely destroyed the pistons in five cylinders as well as the heads and I don't know what else. I was shown the engine after it was torn down, and it was not a pretty sight. The repair ended up costing him a lot more than if he had forged the engine in the first place.
 

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Im digging this. So what happens the rings expand too much and break or burn out?
the ends of the rings butt together and they break off the ring lands - especially the top ring

those pieces of ring lands hammer around inside the combustion chamber hammer both the cylinder head and those pieces can also damage the cylinder walls.

if its really severe the pistons can crack

that heat under boost makes internal parts expand - when there's no room for clearance, parts break apart
 

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the ends of the rings butt together and they break off the ring lands - especially the top ring

those pieces of ring lands hammer around inside the combustion chamber hammer both the cylinder head and those pieces can also damage the cylinder walls.

if its really severe the pistons can crack

that heat under boost makes internal parts expand - when there's no room for clearance, parts break apart
Ok and the ring land is the space between the piston rings on the actual piston and that breaks not being forged and therefore more brittle? Is that the major weakness of the engines? I would have thought the top of the piston would actually start deforming.
 

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There are plenty happy stock 6.4's running 6 psi enjoying 100hp gains and have longevity. Edelbrocks EForce canned tune will not steer you wrong but you can have a tuner who knows how clean it up a bit.
Lots of tuners less on experience try for classic 11.8 AFR's when there is nothing to mine for up there. 11.3 is fine.

Some don't know how to calibrate enriching as IAT's raise. So when back to back runs are made and she get hot it will survive.

But.............. you gotta believe and know the traps.
 

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There are plenty happy stock 6.4's running 6 psi enjoying 100hp gains and have longevity. Edelbrocks EForce canned tune will not steer you wrong but you can have a tuner who knows how clean it up a bit.
Lots of tuners less on experience try for classic 11.8 AFR's when there is nothing to mine for up there. 11.3 is fine.

Some don't know how to calibrate enriching as IAT's raise. So when back to back runs are made and she get hot it will survive.

But.............. you gotta believe and know the traps.
I have been wanting to add some laughing gas to mine and I figure it is the same principle so even then the richer the afr during gas the less likely it will be to heat the cylinder excessively and blow up and so the tune would be the most important thing? So is it heat that destroys the rings and ring land or is compression?
 

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The top ring is very close to the dome

Stock piston
1023610

Aftermarket piston examples
1023611

1023612

1023613

A Guy
 

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4032 pistons are a nice middle ground between the 2618s and hypers imo.
But if you wanna try the stock pistons, and I'm all for it, I think running an alcohol fuel, Ethanol or Water/Meth, will help the pistons live longer by not only knock prevention but keeping heat down which is imo the biggest problem with the 6.4 pistons. You could even run a slightly thicker head gasket and drop CR a bit to help keep things safe too. Add on regapping the rings and I'm sure you could make a reliable 800whp motor on stock internals with a solid tune. I'm currently trying to push the limits on the 5.7 stock internals slowly and carefully. The long term goal is 700whp stock internals without regapping rings, hoping for 600whp this Saturday on Meth injection.
 
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Smog control :devilish:

I honestly don't know if that's why. But as an OEM, they made what will live as a stock engine no problem. Why they didn't build in ability to modify like other manufacturers is short sighted at least

A Guy
 

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Smog control :devilish:

I honestly don't know if that's why. But as an OEM, they made what will live as a stock engine no problem. Why they didn't build in ability to modify like other manufacturers is short sighted at least

A Guy
I’m tired of 5.7 guys saying all the cool things they can do reliably. If I would have known I would have bought a 5.7 put a cam maybe some headers and forced some air in it.
 

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You can do 6 - 7 lbs boost with good fueling and tuning reliably. It's the tuning where most go wrong I believe. 5.7 said to only do about 8 lbs reliably, so not a huge difference stock

A Guy
 
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