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2013 Challenger SXT
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Discussion Starter #1
So I might have my supercharged 3.6 Challenger sold on Monday, I was wanting to get a used Scat Pack to play with an add boost.

Thought I would just buy the largest Hemi,. the 6.4, tinker on it, get some 11s out of it in the 1/4- seen stock Scat Packs at the track with just drag radials run 12.20s. I figure that I could tinker one down into the 11s and then just add a supercharger to maybe dip into the 10s down the road- of course, I will be running an automatic.

Been reading that about 6 lbs of boost is all you should add to a stock 6.4. Are any of the modern Hemi engines strong enough to take more boost and end up with more than 600 rwhp or all of them pretty much too weak to add more than 6 psi in stock form?

I would consider an older Challenger or smaller Hemi if they could take more boost and have more hp than a 6.4 with about 6 lbs of boost.

Not really interested in tearing an engine out and installing pistons,cams or heads. I would just rather buy a car and just do bolt-ons. With my V6 Challenger, I took it from 15.20 @93.26, with 7 plus 0-60 mph times to 12.80 @ almost 106 (107 mph with slower e.t. ) 1.78 60 ft with 4.0 0-60 mph times. with just bolt-ons.

So, I would like to do the same with a Scat Pack or another Hemi Challenger with a possible stronger engine to boost.

So what's the word on the Hemis that can take some boost?

Side note- I am shoving up to 15 lbs of boost on my stock 3.6.
 

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2015 SRT 392
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The rumor is that 6 psi is what's safe, but there are exceptions to every rule.

I suggest that you give Tim Barth a call and ask him about running boost on a stock motor. You can ask him what he thinks and take it from there. It's just a phone call away.

Guy knows how to tune a Mopar!

For the 392 crowd | SRT Hellcat Forum

Same car as above with time slip:

392 scat pak with 700 rwhp track results! | SRT Hellcat Forum

Disclaimer: I've never used him, but haven't heard anything bad about his tuning abilities. Just a suggestion.

I hope that I didn't break any rules by posting another forum thread and if I did, then I Apologize.
 

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Discussion Starter #5
So I take it all the modern hemi's say 2011 and up are all weak piston engines that can't handle any big amount of boost?

Let's see most say the 5.7 is only safe to about 500 hp so any challenger with a 5.7 is out.

6.1 and 6.4 is pretty much the same they both can only handle maybe 6 psi at best.

This is an extremely simple broad understanding of what I'm reading on the net above.

I have ran hypers for years in my bbc's and sbc's and never broke any, but I have never ran them lean or under knock conditions, keep the engines cool and never prolong any engine to long durations of load, just mostly 1/4 mile and maybe some sprinted runs to about 160 mph in some cars.

I have heard for years about the hypers are just glass, to me this just has to be the tunes, you put a crap tune on any piston they will break, I see it from the other guys I'm around, they have the will to be a hot rodder but don't understand tuning and they break crap but I thought I would ask.

I didn't leave out any other modern hemi did I? other than the 6.2 but it's already supercharged and was designed for it and I'm not buying a hellcat or demon so those are out.

So I will probably just get a scat pack, tinker on it and put a supercharger on it with about 6 lbs of boost and call it good, not trying to build the worlds fastest car, just something to play with.

Wonder how long the 700 rwhp hemi lasted on stock internals with that supercharger in the post above. You keep the engine cool, keep plenty of fuel down the hole and back the timing off far enough for no pre ignition, engine should just be fine, beat on it and beat on it til the engine gets super hot, expand those piston rings and it will pop.

Most tuners I think tune the engine for a hard run with a cool down in between each run. But then you get it out on the street and pound the sh!t out of the car without cooling it down and the tune wasn't built for that, I can see popping a piston then, it wasn't ran that hard on the dyno so it wasn't tuned for those kind of temps.

You would have to have a tune where you make 3 or 4 pulls or more on the dyno in a row and get the temps as high as they will go and put the tune there, make sure it has plenty of fuel for the most extreme conditions, the hottest the engine will run, the warmest air the engine will take in, the hottest the intercooler will be running. that's a street tune.

You make a tune for a dyno pull and give it some time to cool off and settle back down then pull again, this is more less just a 1/4 mile pull with a cool down, so that tune is for cool air, cool water, cool block, and just enough fuel to cover those temps. take that out on the street and pound the crap out of it on a hot day, pop a piston in a heart beat. I can see that happening to the folks with stock engine and 8 lbs of boost or 7 or 6, I wouldn't put it all on the piston itself.

Just my point of view.
 

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So I take it all the modern hemi's say 2011 and up are all weak piston engines that can't handle any big amount of boost?

Let's see most say the 5.7 is only safe to about 500 hp so any challenger with a 5.7 is out.

6.1 and 6.4 is pretty much the same they both can only handle maybe 6 psi at best.

This is an extremely simple broad understanding of what I'm reading on the net above.

I have ran hypers for years in my bbc's and sbc's and never broke any, but I have never ran them lean or under knock conditions, keep the engines cool and never prolong any engine to long durations of load, just mostly 1/4 mile and maybe some sprinted runs to about 160 mph in some cars.

I have heard for years about the hypers are just glass, to me this just has to be the tunes, you put a crap tune on any piston they will break, I see it from the other guys I'm around, they have the will to be a hot rodder but don't understand tuning and they break crap but I thought I would ask.

I didn't leave out any other modern hemi did I? other than the 6.2 but it's already supercharged and was designed for it and I'm not buying a hellcat or demon so those are out.

So I will probably just get a scat pack, tinker on it and put a supercharger on it with about 6 lbs of boost and call it good, not trying to build the worlds fastest car, just something to play with.

Wonder how long the 700 rwhp hemi lasted on stock internals with that supercharger in the post above. You keep the engine cool, keep plenty of fuel down the hole and back the timing off far enough for no pre ignition, engine should just be fine, beat on it and beat on it til the engine gets super hot, expand those piston rings and it will pop.

Most tuners I think tune the engine for a hard run with a cool down in between each run. But then you get it out on the street and pound the sh!t out of the car without cooling it down and the tune wasn't built for that, I can see popping a piston then, it wasn't ran that hard on the dyno so it wasn't tuned for those kind of temps.

You would have to have a tune where you make 3 or 4 pulls or more on the dyno in a row and get the temps as high as they will go and put the tune there, make sure it has plenty of fuel for the most extreme conditions, the hottest the engine will run, the warmest air the engine will take in, the hottest the intercooler will be running. that's a street tune.

You make a tune for a dyno pull and give it some time to cool off and settle back down then pull again, this is more less just a 1/4 mile pull with a cool down, so that tune is for cool air, cool water, cool block, and just enough fuel to cover those temps. take that out on the street and pound the crap out of it on a hot day, pop a piston in a heart beat. I can see that happening to the folks with stock engine and 8 lbs of boost or 7 or 6, I wouldn't put it all on the piston itself.

Just my point of view.
You make some good points, but I can only speak about what little I know about tuning a car.

When I tuned my old Vette (LS1 with a Vortech T-Trim at 10 psi and some meth), I street tuned it for the drivability because any real street car spends little time at WOT compared to part throttle driving. I tuned my WOT on the dyno just because it's safer than doing pulls on a public street. I did my partial throttle cell mapping/logging with the laptop on and plugged in, then I'd just use the filters to get rid of the noise (cells that weren't logging what I needed) on the street. To me, it took very little time to tune for WOT than it did to tune drivability. I still have a few hundred log files on my pc for the drivability part of the tune, but she ended up over 600+ rwhp and got 30 mpg on the highway and 22-24 in the city (not too mention, that she ran 10.52 @ 131 in street trim), so it was worth it.

I tuned with the meth to keep the IAT's down when the outside temps got hot and to add fuel when at WOT. It wasn't to add power, just a safety net. I set my tune up so that if the IAT's went past a certain point, it would pull some timing from the motor until they came back down. Like you said too, running it a little fat doesn't hurt either.

As far as the pistons, I don't think that it's so much the material that they're made out of, but the placement of the ring land to the crown of the piston. It's up kind of high for boost. I could be wrong, but that's what I thought was the problem. Like I said, there's a chance that I'm wrong because I'm far from an expert.

I can't answer your question about that Scat's longevity...Sorry.
 

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Came across an Engine Masters video -- I think Hotrod pulled these and they are only available by subscription now -- in which a 5.7l "crate" motor was supercharged -- with a centrifugal supercharger to nearly 20lbs of boost to where the engine was making close to "Hellcat" power.

'course this was on a dyno. The mixture was rich, very high octane gas was being used, and even so the timing dialed back a few degrees for extra margin. One of the presenters said something to the effect if one tried to run this engine on the street or track he'd be driving over the crankshaft.

But a more conservative amount of boost with a suitable (precise) tune would (probably) be ok.

The 6.4l engine is a better engine that the 5.7l engine so there's that.

No promises but get the used Scat Pack and add a centrifugal supercharger and keep the boost down to around 6lbs and see what happens. It is a coin toss at around 6lbs of boost whether the ring gaps need opening up.

If you venture into higher levels of boost you need to think about the ring gap mode. At least.

With 6lbs of boost or 12lbs or more you need to be darn sure the fueling is spot on and things like the plugs, oil, engine air filter, engine cooling, all critical in a stock engine, became hyper-critical in a modified engine.

Added: Curious I just searched and found the video I mentioned above. Apparently these are still available to view. Maybe new videos will not be released to YouTube?

Here's the link:

 

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Barth's Scat mentioned above eventually went boom. I called his shop once and talked to the gal answering phones. I described a build I wanted to do and she said she'd have him call me. He never did return my call. Pretty lame IMO.

Keep in mind the stock 392 rings are not gapped for higher temps. that boost can and will create. Rings will close then over expand to the point of undue stress against the cylinder wall thus breaking the top #1 ring land. I believe the 392 crank to be forged but would highly recommend a set of drop-in forged pistons in the very least. Stock compression is 10.9:1. Why go through the expense of a new blower with fingers crossed? I went with forged "thin ring" pistons on my N/A 426 build for less friction. Gapped the rings for boost (just in case) and installed a gapless ring in the #2 position to reduce blow-by.
 

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buy a Hellcat or the drive train from a wrecked hellcat and do bolt on's (Long Tube Headers, Tune) and call it done. Or boost a 345 and get stock 392 power or get a 392 and grenade it, play stupid games win stupid prizes. I myself, if I had the money to blow (no pun intended) on a Supercharger set up, I would prefer a well built 7.0 liter or larger displacement N/A motor, just for reliability and drive ability. Injection is nice, some would rather be blown, but in the end, there is not replacement for displacement, bigger is better.
 

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You will be in the 11's no problem with a late model 6.4 automatic and tires if you are not at altitude or hot. Is the car going to be your daily driver? I recently went the supercharger route without forging at roughly 5psi (I tend drive the car daily but in winter usually just on weekends). In retrospect I think I should have stayed NA and invested the money in very good lightweight wheels for the track, high flow cats and perhaps exhaust/intake/throttle body, a HP tuner kit (to learn), a small dose of nitrous (75 shot) with a window switch and couple of race tunes for different octane/nitrous.
 

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The issue at hand is:

6.4> 10.9:1 CR - you have a very high static CR and trying to add forced induction to that.
-the proper way is lower CR to 9:1 and you gain more room for boost.

5.7> 10.3:1 CR - there's a bit more room for boost, up to a point

Look at any OEM with their NA engines vs. a forced induction system. They use lowered CR (dished pistons) and generally have beefed up the FI versions for the higher heat and in some applications oil squirters (like FCA does on their SRT application) to cool the pistons more.

You spend $$$ for a s/c and bolting in onto the engine is only doing it halfway. That's why the limit is 6# on the 6.4 as you're pushing things with pump gas and reliability.

The 5.7 has more margin due to the slightly lower CR

And going for the big power (if building a forged / built internals engine) then the next step is upgrades further along the driveline.

The owners with A8s are going to have to pay attention to hitting the limits of durability with those ZF trannys or what it takes to build an HP70 higher up to what the HP90 can take.

There's no such thing as cheap power with FI - as the consequences of mistakes get very expensive quite quickly. There's plenty of evidence out there to show the outcome.
 
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An engine built for boosting would have a lower compression ratio, that's for sure. My 996 Turbo had a 9.3:1 compression ratio and would develop 0.7 bar boost.

But even high compression engines can take some boost. I have not looked into any 6.4l or 5.7l boost kits but over the years got exposed 2nd hand to boost kits for Porsches which would deliver 5 or 6 psi of boost and this with a compression ratio of around 11:1. The engine picks up a nice bump in HP but is not sitting on the ragged edge. 'course, this is provided the engine's properly tuned and kept in good tune. A centrifugal supercharger doesn't make much if any boost at low engine speeds. At high engine speeds what "saves" the engine is the loading is less because even with boost the cylinders don't fill that full.

As for the transmission, I think the A8 automatic has some margin. AFAIK the A8 in the R/T Scat Pack with 485hp and 475lbs of torque is the same A8 in my Hellcat with 707hp and 650lbs of torque.
 

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The HP70 transmission in the Scat Packs are not as strong as the HP90 in the Hellcat, that being said if you don't monkey around with torque management the HP70 will handle the power/torque you can make with the stock pistons.
 

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Thanks for the info. I made the mistake of assuming because they both had 8 speeds, and from my 2 month experience with my R/T Scat Pack before moving to a Hellcat the transmissions felt/acted/seemed to behave the same, the two transmissions were the same.
 

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The HP70 transmission in the Scat Packs are not as strong as the HP90 in the Hellcat, that being said if you don't monkey around with torque management the HP70 will handle the power/torque you can make with the stock pistons.
And piggybacking on that, the drivetrain components past the trans from a scat pack and above should provide the extra safety net as well.

In the middle of the same issue. Just had a 2.8 KB out on a scat with w/m injection for added safety.

There is replacement for simple displacement- density increase in the same space.

The problem becomes this- the total platform beyond the motor is something to consider. If you’re committed to changing everything, then start with the least expensive anyway.

If you’re not, I have a biased opinion that the scat is the strongest compromise to probably around 675ish rwhp. After that, I defer to others experiences. As memory serves, the problems start coming up from there.

If you understand the way hypereutetic pistons are fit, and just how tight that is, it makes two things really, really apparent.

1) Heat expansion of the piston does not allow for much of a gap, and the rings take the pressure. Think distortion and ring gaps closing.

2) Heat expansion of the rings decreases ring gap, in addition to any change in piston size. The top ring being so high, it’s a compounding effect. With an NA ring gap, you don’t have much heat tolerance to play with.

So, which engine can you get the most horsepower with by bolting on a blower? The one you need to add the least heat to with the largest overall discplacement... if you’re not buying a short block, then the 6.4 fits the bill.
It also means that managing the extra heat is a little easier... which is the argument for water/methanol with boost.

Given equal modifications of adding a blower and maybe a w/m injector, it will get you to the highest horsepower with the least modification i.e. a piston swap up to the point you’re looking at stroking the motor, injectors, fuel system, etc.

So, if you’re only talking engines, and not talking platform complete... I still vote for the 6.4.

You can put less boost into it than either the stock 5.7 or stock 6.1... but the displacement makes up the difference. Which means when it’s all said and done, you can still make more power with it.

If and when you decide to swap parts... you still have a 6.4 with just a drop in piston swap. Cheapest way to run a few more pounds.

If you stroke it to another displacement, and it’s going to be the first thing you do, it’s a toss up with the 6.1 depending on how big you want to go. Still a fan of the 7.0/426 stroker upgrade to the 6.4 with 9.5 CR pistons.

EIther way, the platform as a whole will run into other limits, such as fuel, driveshaft, axles, transmission, etc. before you can push much past 6 lbs on the 6.4 anyway.

Of the three, I would look at the price difference of upgrading a 5.7 platform vs buying a used scat pack. At that point, you would have some decisions to make about how much you want to spend above and beyond the blower to get to the same places.

Me, I’m going to replace the driveshaft and work on the suspension next. I figure 550ish to the wheels is plenty fast for a year or two until I can afford to do the transmission, axles, fuel system, and then stroke it with a block refresh.

Oh yeah, and the 305s are going on the back- if it’s still smoking those hard, not sure what the point is until I can finish getting it governs the ground safely.

Horsepower isn’t everything until the means to support, control it, and use it effectively exist.
But if numbers are what you’re after... several vendors make a stroked hellcat block that will do what your asking if you already have a platform to put it in, and it’s an option to consider for a few thousands more if you’re going to take the long view on boost applications anyway.


Cheers,

Chuck
 
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The rumor is that 6 psi is what's safe, but there are exceptions to every rule.

I suggest that you give Tim Barth a call and ask him about running boost on a stock motor. You can ask him what he thinks and take it from there. It's just a phone call away.

Guy knows how to tune a Mopar!

For the 392 crowd | SRT Hellcat Forum

Same car as above with time slip:

392 scat pak with 700 rwhp track results! | SRT Hellcat Forum

Disclaimer: I've never used him, but haven't heard anything bad about his tuning abilities. Just a suggestion.

I hope that I didn't break any rules by posting another forum thread and if I did, then I Apologize.
Tim would not be bothered
 

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You can also put in a little boost safety factor by increasing the stock ring gap to 28-30 thou. if buying forged internal parts is out of budget.
 
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