Hellephant exhaust design questions

[Grant]

Hello,

Mopar should be releasing more details on their 1,000 hp "Hellephant" crate motor any day now (I'm expecting it on 4/26). Unless it's horrendously expensive, my plan is to put one in my SRT8 Magnum. My goal is to leave the motor as it came for maximum reliability, and try to get as much power as possible out of it with exhaust work. To that end I've been playing with PipeMax to design an exhaust, as well as reading posts here. I've got a few questions you guys can probably answer easily:

1) PipeMax recommends dual 4.5" exhaust. The stock exhaust is only 2.75", so this obviously isn't going to fit. However I noticed PipeMax recommends the same total surface area (15 sq-in) regardless of whether or not the motor is a V with dual exhaust or an inline with a single pipe. From what I understand, a good X or H-pipe will share exhaust load between banks, because a pulse from one bank will not arrive at the same time as a pulse from another. Am I right in thinking PipeMax is not taking this into account?

2) How much of a point is there in doing a properly-designed long-tube header with a supercharged motor? PipeMax recommends 2.5" primaries, which also probably won't fit. I have 2"s on my current motor, and they're pretty tight. The Hellephant seems to come with shorties, pictured here:

hellephant_shorties.jpg

3) Similar to question #2, is there much point in termination boxes on a supercharged motor? My thought was to forgo an X or H-pipe and instead use a large common chamber to reduce the effective exhaust system length. PipeMax puts the first four harmonics at 135, 67, 34 and 17 inches. Would this chamber need to be double the normal size because the supercharger provides ~200% VE?

Thanks for any help.

Known Hellephant engine specs are as follows:

Engine Type: GEN III HEMI® V8
Displacement: 426 cu in
Bore: 4.125 in
Stroke: 4.0 in
Block: Cast Aluminum Block with 4 Bolt Steel Caps
Crank Material: Forged Steel Crank Material
Connecting Rods: 6.125" H-beam Forged 4340 Steel
Piston Material: Forged Aluminum Piston Material
Camshaft: Billet Steel Camshaft
Valve/lift duration@ 0.15mm
Int: 15.24mm (0.600") - 286 deg.
Ext: 15.24mm (0.600") - 301 deg.
Cylinder Heads: Aluminum, Hemispherical Chamber Cylinder Heads
Intake Valve Size: 54.3 mm
Exhaust Valve Size: 42 mm
Compression Ratio: 9.5:1
Peak RPM: 6700
Boost: 15 psi

[Orr89rocz]

I dont believe pipemax models boosted motors. I dont have the latest version tho but the older ones dont

4.5 is way excessive. 2.5 is way excessive. Hence my statement about it doesnt model them right assuming you dont have an incorrect value input somewhere

2” is fine for that power if you got them. 3.5” exhaust would work great if you can fit it. The cylinder pressure in boost is gonna find its way out. If you have to run dual 3” then it is what it is, it may be restricted some but i have seen alot of latemodel boosted stuff make big power on 3-3.5” exhaust.

[Grant]

The VE field in version 4.30 contains this text, so I set mine to 210%:

Potential Trapped Volumetric Efficiency % PerCent ( Valid Range= 60.0% to 400.0% VE ) ( up to a maximum 400.0% VE for Blower / Turbo Engines )

PipeMax recommends 1-7/8 to 2" primaries on my current motor (a 7.36L), so I'd think you'd want much larger tubes with a similar engine seeing 15 psi of boost.

[Newold1]

Haven't seen the exhaust port on these heads on this engine but with a 1.65" exhaust valve I doubt the area of the port is probably in line with a 1.78" to 2" round exhaust port.

I have had a lot of experience with blown BBC's in marine race engines that were running about 10-15 lbs of boost and about the same 6500 rpms with cubic inches in the 427 -525 range and we always made better power when we stayed away from long tube and long tube equal length header systems. We had the best results when the primaries were about 12- 15" and dumped into a larger collector 5" and then exited with marine thru the transom exhaust or short vertical 4" water jacket cooled dry uprisers through the top of the engine hatch.

I would think a 2.5" exhaust would be a good compromise and if you have a long exhaust to the back of the car and can fit a 3" exhaust that might squeak out a bit more high rpm 4500-6500 power but if fitment is a nightmare, stay with a 2.5" and a low back pressure muffler.

[GARY C]

Old school thinking was that boosted and nitrous applications need bigger headers, modern day argument is that both boost and nitrous raise cylinder pressure, most modern day tests show that raised cylinder pressure actually respond to smaller headers?.

[Grant]

Haven't seen the exhaust port on these heads on this engine but with a 1.65" exhaust valve I doubt the area of the port is probably in line with a 1.78" to 2" round exhaust port.

Is there no point in running a primary significantly bigger than the exhaust port? If I bought Burns Stainless collectors I guess I'd get their header design service for free.

I think I can fit dual 3.5" pipes under the car.

[SchmidtMotorWorks]

What tires are you planning to run?
Have you driven a supercharged car like this?
In my experience, they have too much power for the tires already.

[In-Tech]

Hi Grant,
I have been involved in a few exhaust tests with supercharging and I hope you understand that I don't want to hinder you in your testing.

Side effect, as much as people want to pick on Jon about NDA, it is a real thing, and want to note that he is speaking real world with tires/traction, really hard to find anyone on the street that can actually drive ~1000rwhp.

One thing to consider is boost is a restriction to flow. While I really want to see what you can accomplish I hope you can understand that each object is a mass flow device.

If the mass flow device(the front one, a supercharger) is set to flow an amount of mass flow, it doesn't really matter what it does after. That is, of course, without stupid affects after.

You can help the after affect with better exhaust(or pumping ability) but all you have done is lower the boost. Basically the only way to gain more horsepower is to now change the pulley to regain the boost loss. That doesn't mean a crap because you just increased the mass air flow into the engine. I so tire of people saying that so and so engine will be fine at 12lbs of boost. I have, plenty of times, increased a lot of hp with less boost and more pulley because with a cam change was needed to INCREASE the internal cylinder pressure due to more mass in the engine. The biggest trade was "better air" since the blower had less intake air temp output and was more efficient due to not beating and heating the air. Bottom line, quit thinking boost is a horsepower number instead of thinking it is one engine on the outside of the other engine. They are both air pumps, make them work together as efficiently and as good as you can. They are both heat pumps.

Again, I am not trying to slow you down on your endeavor.

I will give you an example that of course NDA doesn't allow me to say brands or sizes.

We did a newer Camaro with 10lbs of boost and installed "a" company's headers. This is with 10 widebands as well as many other things to monitor. It gained an average of 0(zero) hp throughout in boost and did not change the boost. Yes this was with stock exhaust, just the headers.

I have also done an ~1140fwhp BBC with 2 1/2 dual full length exhaust and running open exhaust(open header) made ~ 10hp more. I was truly expecting at least ~100.

What happened in the last instance since it was carbureted, the AFR changed a little and lost some pumping losses and made it a bit happier. It did lose around 2lbs of boost. It lost boost because of the backside.

I guess, what I am trying to say, if you have a mass air flow based system, it will measure and adjust the change accordingly. A carb is a MAF based system.

You say that you want to keep it the same so it is "reliable". I am not familiar with how the hellplant does its' efi control but I hope it is MAF based and not strictly MAP, otherwise you will need to get into the software if the ecu MAP based has no way to know how much you changed the dynamics inside/outside.

I am not trying to start a fight, just letting you know I have done a LOT of supercharged applications and the key point would be that you CAN make some more horsepower if you can control and/or use the heat better. IMO, you will still need to get into the tune to make that happen.

Understand you are chasing/playing with MASS air flow.

Also understand that I am not saying a blown alcohol dragster could use a stock exhaust manifold.

[In-Tech]

Sorry, I guess I am saying, if you don't change the pulley nor the tune, don't expect a lot.

But good luck and I hope you let us know.

[Grant]

What tires are you planning to run?

Nothing good enough. It won't hook. 1,000+ bhp is not at all practical, but I want it anyway.

Have you driven a supercharged car like this?

I have a Corvette with a similar power/weight ratio. It spins into third. The Tremec Magnum trans going into the car has slightly taller gearing.

If the mass flow device(the front one, a supercharger) is set to flow an amount of mass flow, it doesn't really matter what it does after. That is, of course, without stupid affects after.

Yup I get how positive displacement pumps work. However more flow from the engine should mean less boost, which is less heat going into the intercooler, less parasitic drag on the crankshaft, and (from my reading of compressor maps) slightly more mass air flow from the supercharger.

The car is set up to handle quite well for it's size. It's got 305 square tires, dual wishbone front and multi-link rear suspension, bigger brakes from a Hellcat, reasonable roll stiffness, camber, and weight trimming (50/50 balance due to the aluminum block, which the Hellephant shares). I occasionally track it with the current motor, and would probably do so with the Hellephant too. Is this sensible? No not at all, but it's fun to surprise people in a giant wagon. I'll probably put a larger pulley on the supercharger to control heat when it sees the track, so lower boost with the same power would be a good thing.

I have also done an ~1140fwhp BBC with 2 1/2 dual full length exhaust and running open exhaust(open header) made ~ 10hp more. I was truly expecting at least ~100.

Crap. I was hoping headers would make more than 10 hp. If that's the case then I agree, they aren't worth bothering with. I need to do the rest of the exhaust anyway though.

You say that you want to keep it the same so it is "reliable". I am not familiar with how the hellplant does its' efi control but I hope it is MAF based and not strictly MAP, otherwise you will need to get into the software if the ecu MAP based has no way to know how much you changed the dynamics inside/outside.

I'm pretty sure it will be MAP-based like all Gen 3 Hemis. However Mopar has said the controller is completely tuneable, so I'd just adjust their VE tables until actual AFR was the same as commanded AFR. On the Hellcat PCMs the other tables (like ignition timing) are based off of calculated load and not MAP, so my guess is adjusting the Hellephant's VE tables will put the others where they need to be.

Externally the Hellephant PCM looks like a Hellcat's, so I'm guessing it's the same thing with a different tune on it. I can't think why they'd want to re-invent this wheel.

[In-Tech]

Hiya,
I'm glad to hear you will be involved with your tuning.

Keeping in control of the heat is incredibly important and losing the heat with a well designed exhaust system is just as important regardless of the initial hp gain. I deal with that a lot in making stuff live at an hour at a time full throttle.

1000hp on the street is what everyone wants till they get it.

It's kinda funny how we can build some bad ass stuff and then know they can't stay on the throttle long enough to hurt it.

I will enjoy hearing of your progress.

[Grant]

1000hp on the street is what everyone wants till they get it.

I don't think I'll be that guy, but we'll see.

A friend of mine is about to do shorty headers on his positive-displacement supercharged S55 AMG Mercedes. He's got tons of data and logs with the stock manifolds, so differences in temps and power should be obvious. I'll post the results. He's certainly hoping for more than 10 hp. I'm thinking he'll mostly see a reduction in temps which will pay off on longer pulls.

[In-Tech]

1000hp on the street is what everyone wants till they get it.

I don't think I'll be that guy, but we'll see.

A friend of mine is about to do shorty headers on his positive-displacement supercharged S55 AMG Mercedes. He's got tons of data and logs with the stock manifolds, so differences in temps and power should be obvious. I'll post the results. He's certainly hoping for more than 10 hp. I'm thinking he'll mostly see a reduction in temps which will pay off on longer pulls.

Yes, temp control is critical.

It's great to hear from someone "in the know", thanks.

Do you know where he was measuring temp and will it be the same distance from the exhaust valve? (Not that it matters, just curious if temp is measured versus time too vs dissipation vs material in between, doesn't matter if steady state was achieved.)

Again, I am not trying to nitpick. Details mind so I can sleep. And thanks.

[Olds455]

Just curious but it's been known about for 6+ months, correct? What exactly could they say that we don't already know about it other than price? I'd expect 35k for it if the Hellcrate is 20k.


You're actually planning on spending what will likely be $35k for 1000hp gen 3 hemi? Serious question here. Are you on crack? Guys build boosted 1000hp LS engines for about 1/17 of that price lol. I just can't see spending $35k just to be able to say it's a hemi. That's the only thing you get with that 35k, imo, that you can't get anywhere else for way less.

[enigma57]

Grant, I believe you will be OK to run 3.5" dual exhaust. From reading over David Vizard's works on zero sum loss exhaust systems some while back...... As I recall, a straight piece of exhaust tubing of around 2 ft. length will flow 115 CFM per sq. in. cross sectional area. Additionally, 2.2 CFM flow rate per HP generated is required to produce a zero sum loss full length muffled exhaust system......

https://www.musclecardiy.com/performanc ... ail-pipes/

Tubing is measured OD (outside diameter). Typical 16 gauge exhaust tubing has a wall thickness of 0.065". If we subtract 2 wall thicknesses, we have 3.37" ID (inside diameter). So in theory, a short piece of 3.5" OD tubing should have sufficient flow capacity to support 446 HP (892 HP for dual exhaust), after which friction losses will gradually allow back pressure to begin limiting further HP gains. Of course, you will have friction losses in the system each time you must offset (bend or change direction) or change shape of tubing even when maintaining consistent cross sectional area throughout (mandrel bends). Bear in mind as well, that the longer the tubing and the tighter the bends or offsets in your tubing runs, the more friction losses you will have. So plan your exhaust system to be as straight as possible, make offsets only when necessary and use as large a radius as possible when you must make bends.

H-type or X-type crossover (balance) pipes...... Yes. Either will work for you and neither is better than the other as a matter of course. Each system under each car being different, you would have to construct systems utilizing both types and do back to back testing on a chassis dyno to see which (if either) has any advantage over the other. If making H-type crossover, use connecting pipe same diameter (or 1 size smaller) than your exhaust tubing on either side. Any smaller than that will not be as effective). Not always possible due to clearances, but ideal placement for balance pipe (center of X-type or points of connection for H-type) would be where tuned length of collector extensions would terminate if you were running open headers on the track. NOTE: We were not permitted to run a balance pipe at EMC 2012 and priour. I hope that has been addressed now.

The main point of restriction in your system downstream of collectors (assuming you do not run cats) will be your mufflers. Straight through inner flow tube will give you more flow capacity than most other designs...... But it will be louder than most others, as well. One thing I found is that you can install a straight through muffler having an inner core size 1 size larger than your exhaust tubing and gain back the 20 -25 HP lost there. But again...... It will be louder than a similar muffler having same inner flow tube size as your exhaust system. So run as long a muffler as you have physical space for. Or a couple shorter mufflers on each side in series if need be. I have seen weld-in straight through mufflers having 3.5" and 4" inner flow tubes (these are spec'd for diesel truck performance replacements generally). You could use either of them with a 3-1/2" exhaust system. Use the 4" version if you want to pick up some flow...... Use the 3-1/2" version if you want your system to be quieter......

http://www.classicchambered.com/classic/Diesel.html

Yes, you can run what David Vizard describes in the article as a pressure wave termination box. Or boxes. There is a specific way the inlet and outlet pipes should be configured at each end of such boxes (see illustrations in article) and internal volume should equal (or exceed) twice the displacement of the cylinders discharged through the box. So 427 cu. in. per side if using 2 boxes. You can also accomplish a similar effect if you place your mufflers as far to the rear as practicable and utilize the internal volume of your exhaust tubing upstream of muffler inlets to do the same thing. In other words, with 3.5" OD/3.37" ID tubing, a run of tubing 48" (or more) between collectors and muffler inlets will provide same 427 cu. in. volume as a pressure wave termination box.

Some things we found when running Dan Miller's EMC engine on the dyno......

* What works well on the track when runninng open headers an tuned collector extensions does not necessarily work the same way when running a full length muffled exhaust system. We discovered this the hard way. Dan had been running a set of off the shelf Hot Heads street rod headers for several years with good results. But he wanted to see if he could pick up some power with a set of custom made headers. So he built a beautiful set of headers having very nearly equal length primaries of the 'correct' diameter and length as per PipeMax and used merge collectors, etc. Invested a lot of time and effort into constructing them. Problem was...... When coupled into the mandated 3-1/2" straight through mufflers and long exhaust run at EMC...... The off the shelf Hot Heads headers made more power. So we set about measuring the Hot Heads street rod headers and trying to figure out why. Our conclusions......

* With a full length muffled exhaust system, you have to look at the entire system as a whole. You cannot necessarily run a set of headers optimized for the track...... Then add mufflers and a long run of tubing downstream......And expect them to perform as they would on the track through open collectors.

* The off the shelf headers had unequal length primaries that were too short and too large a diameter according to PipeMax. So why did they make more power than the custom built equal length headers having 'correct' primary diameter and length?

1. We found that when running through a full length muffled exhaust system, so long as primary diameter was large enough to not obstruct the exhaust port exit where the header flange bolted on (or was larger, the mismatch in port size acting as a reversion dam)...... Primary length was not as important as collector length. Nor was having primaries of equal and 'correct' length. If anything, the unequal length (our primaries with the off the shelf headers varied as much as 2" in length)...... Only served to broaden the powerband a bit. What I did find (and this was as much by sheer dumb luck as anything)...... Volume mattered more than length and diameter, both for primary tubes and collectors...... With the caveat that diameter was at least as large (if not larger) than calculations called for. In other words, we had larger tubing (and this applied to primaries and collectors alike), but it was shorter as well and it just happened that interiour volume was very close to what we would have had with the longer, smaller diameter 'correct' tubing size. And further...... The average volume of all 8 primaries (even though they were of varying length) came out very nearly the same as if all had been equal length and 'correct' diameter and length.

2. Regarding collector length and where to place 'X'-type or 'H'-type balance pipes...... You can increase effective length of collector in multiples of 2 to 3 times single length without losing tuned collector length. So if collector length (measured from ends of primary tubes to end of collector extension) works out to say, 18"...... You can extend it in multiples of 18" (36", 54" for example) without losing tuned length. So keep volume and resonance in mind when building your full length, muffled exhaust system.

Hope this gives you some ideas,

Harry

P.S. >>> That said...... As has been pointed out by others...... Be careful of overpowering your chassis...... And tires. All the power in the world won't move your car if you cannot (controllably) put it to the ground.

P.P.S. >>> Might not be the consensus now of days...... But when I was building engines many moons ago, I was told to limit redline RPMs such that piston speed did not exceed 4,000 ft. per second. Rough rule of thumb. Even if using the best of everything. With a 4.0" stroke that works out to 6,000 RPMs if sustained for any length of time. Yes, you might be able to exceed that a bit if running on a drag strip under full power less than 12 second runs, but do keep it in mind. The engines we built were for circle track cars and transporters mainly.