Longtube Comparison: JM/Southeast vs. KRC/Hooker vs. Spintech

Tanky said:

You guys need to remember, in exhausts, bigger isn't always better. if I have a factory motor, per se, would I benefit more from dual 2.5" piping or dual 3.5" piping? Motors do need to maintain some back pressure.

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A correction here... carbureted motors need a certain amount of backpressure maintained unless the carburetor is jetted to compensate for an increase or decrease in the backpressure. A modern fuel injected motor will be able to respond to a change in backpressure by adjusting the injector pulse.

Now, with that said, one thing I need to point out is KRC headers aren't true LT headers for lat emodel Magnum motors, but a mere conversion using adapter plates. Scott used the same trick on his mid lengths.

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True, but the topic here is the power comparison between the headers and not whether they have a bandaid approach or not. At the time those headers came out there was no vendor willing to sink money into designing a long tube specific to our trucks. The KRC adapter plates were designed to allow the use of an off the shelf header (Hooker SuperComp 5803, to be precise) with our chassis configuration. Personally I don't care for KRC and everyone knows that, but I think the adapter plate was a good short term solution. Typical for KRC, they decided their solution was worth a premium price at $799 (at the time) and they neglected to tell people that it was an off the shelf header with an adapter, instead leading people to believe that this was their special design. A Dakota owner could have gotten the same package by ordering the headers from Summit for about $300 and then taking a gasket to a CNC shop and using it for a template to make their own 1/2 inch plates.

If Spintech has LTs, I hope they are truely made for our trucks, not adapter plate conversion kits.

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I do too. I think the time for band aid approaches to our trucks is gone. With hundreds of thousands of these things on the road there should be no shortage of proper parts designed just for us.

I don't know anyone thats going to dyno, change to header 1, dyno, change to header 2 and re-dyno especially given 3-4 pulls to get a baseline and in same weather environments.

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Right. Unless one of the truck magazines or Mopar Muscle gets into it, it isn't going to happen. Even if it does, there's going to be a tiff over whether the PCM was tuned properly, were all other things equal, etc. Ultimately its still going to come down to the same thing it always was, and thats cliques of people supporting their preferred vendors. As always, the new guys are going to be the ones who have the hardest time, as they have to sift through years of thread arguments trying to figure out what the science is at the bottom of the holy wars.

I'm glad that Spintech is offering these parts, because it means there's more choice out there for the DD drivers. The more new parts, the more interest in our platform, and the more companies will take a serious look at us. As I mentioned before, there are hundreds of thousands of these trucks out there, and most of them are off warranty now, many are paid off, many are on their third or fifth owner. They're ripe for customization, and I think there's eventually going to be a wave of that, driven by new products.

Unless of course the gas prices make us all ride scooters.

Tanky said:

I doubt this sir. I'm no where near the car expert that many here are, and you sound like you know more than I on this stuff, but all the evidence out there proves what I said correct. I honestly have no technical backing to support this. My experience is on aircraft as a CC. But, from all things, doesn't this make since??

Think about it... makes more since. Why throw a 4" exhaust on a 318 when it can't really use it? Thats all I'm saying. I know most here have built up motors and all, but again, is bigger necessarily better?

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You're misunderstanding your question.

The issue is not the backpressure but the velocity. I've posted several threads in the past year where I've discussed this at length, but here it is again in 10 minutes or less:

You're understanding the cross sectional area concept pretty well, but you are using the wrong terms. A complete lack of back pressure is actually the optimum design, provided you have the correct cross sectional area and primary length. Unfortunately noise and emissions laws affect this, so every factory exhaust is a compromise, and when you throw the economic factor in there, cheaper and smaller always wins. Still, the OEMs are able to tune some pretty respectable performance into those things. Look at our stock 5.9 motors, choked down with multiple cats, a poor exhaust system, and a prehistoric EFI system, yet it gives us 245/345. Thats really pretty good for a smog motor that pretends to be a hotrod.

Pipe cross sectional area and pipe length are the two biggest factors (collector design notwithstanding) in figuring the major benefit of header design, which is exhaust velocity. Velocity of spent gases is more important than volume of spent gases, because a lot of spent gases moving slowly is not beneficial to performance. Velocity as it increases causes a corresponding increase in cylinder scavenging, where you evacuate more spent gases and provide more room for fresh combustibles. By increasing the velocity while using a performance cam (higher overlap than stock) you are also assisting the intake side during the overlap by using the exhaust gas velocity to create a vacuum that pulls the intake charge in. However, larger primary diameter, larger collector diameter, and larger exhaust pipe diameter or any combination of those three can actually cause performance loss, unless you augment the intake side and give it more intake charge.

The backpressure=performance concept occurred when people who were running stock or nearly stock vehicles decided to have their local exhaust shop "slap on some duals" to mimic the performance cars of the 60's. They would notice a drop in performance. I noticed it when I went to true duals on my 81 Z/28, even though I'd installed an Edelbrock Performer manifold and cam package, a Holley carb, and a recurved HEI distributor. Where did my acceleration go, especially out of the hole? Everyone knows that duals adds power, right?

In my case, its because I eliminated the performance barriers that existed in the exhaust, and then didn't recalibrate my A/F. I needed to rejet my carb, or even go to a bigger one, to take advantage of all that extra flow. Otherwise it was running way too lean. A carb can't rejet on its own, and most garden mechanics of the day didn't know what was going on. The exhaust shops would simply say, "Yep, changed out lots of factory y pipe systems for true duals and seen this happen almost every time. You lost too much backpressure."

So the myth took root and stuck. The only truth to it is that on a carbureted motor, reducing backpressure can lean out the motor so much that you burn up the exhaust valves. Fuel also cools the exhaust, the more you use the cooler it runs.

On a modern EFI engine, your O2 or Lambda sensor will read the spent gases and then change the injector pulse width to alter the A/F until its within spec. If you have a factory EGT sensor on there, it can really do some fine tuning.

At the end, only an EFI motor can self-adjust for the increase in velocity ("loss of backpressure"). A carbureted motor will suffer from increased velocity until you adjust it yourself (rejet or upgrade the carb to a larger one).

Tanky said:

My first post was basically saying from my own understanding is S&S went with this type of collector for a reason, to maintain some back pressure to maintain torque. I was merely warning those not to hop on the hype express (if so) that A brand or B brand has this and that. Maybe a 3" collector is better, I can't say. S&S went 2.5" for a reason.

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They did, at that. If you remember the original interviews John had with S&S, even John pushed for the bigger collector because of his prior experience with race motors for E and A body Chryslers, until Loren showed him the math and proved that the 2.5 inch collector would be best for the majority of his customers. A 4400 lb truck needs torque out of the hole and big midrange power to move it down the track. They're better in the eighth mile than the quarter because of this. The smaller collector is designed to move the torque down low by giving the maximum scavenging at lower rpm. The special design of the collector (tri-y) collects pairs of tubes and gives even more low rpm scavenging. These are long tube performance headers for a heavy truck, not a 2800lb E body race shell.
So many people couldn't understand that, and some people posted pics of breathtaking examples of custom headers. There is a place for those type of pipes and it isn't on a motor with bolt-ons. If someone builds a full on, big cube small block with a monster cam and sewer pipe heads, the big tubes and collectors have a place. If you're going to take a motor and rev the dung out of it and expect power all the way to the top of the band, you'll need the big pipes and collectors.

There is a whole branch of mathematics that header theory is built on. Its called "Fluid Dynamics" because a volume of air in a system is considered a fluid medium. Air is mathematically equivalent to water when you talk about its interaction with the physical world, so the same rules apply. Once I understood that, it was easy to get past the myths.

KicknAsphlt said:

Actually, Marty does more than just give you an off-the-shelf header with some spacer plates. They hack 3" off of the collector and reweld it first. Another clearance issue...lol.

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I'm not arguing here... but are you sure about that? The 5803 was designed for the LA motor early Daks with the 46RH transmission (or was it the 44?) so where is the big clearance difference between the two chassis and drivetrain combos that would require shortening the collector? I just spent a few minutes trying to find the pics that were up on the KRC site (what a mess that place is) of the headers installed in a truck that was up on a lift. I don't remember any clearance problems existing aft of the collectors.

KicknAsphlt said:

And just out of curiosity, how does the PCM know how to compensate for backpressure or exhuast velocity...? That's all determined by hardware, all the PCM can control is air/fuel mixture and ignition timing.

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Which is my point, indirectly.
I'm sorry I spent so much time talking about the exhaust flow without giving you the other side of the equation, and showing the real reason all this affects us. The Dodge PCM is the heart of a MAP system that measures manifold pressure and makes a guess of what is going in the cylinder based on prewritten tables. Our PCM has no idea of whats actually going on aside from reading the A/F as the spent charge leaves. It can compensate a little for an increase in that charge velocity, but as anyone here who has tried to see how far they could go with a cam or boost can tell you, you will exceed the tables and end up with a MAP code before you get very far. Any change in the flow and you have to have the PCM reflashed to take advantage of it.
If this were a MAF system, the system would sense the extra flow going into the throttle body and it would bump the fuel when the exhaust velocity pulled more air into the cylinder. All you have to worry about then is exceeeding your injector ability, which can be helped by simply going to a larger throttle body/MAF and matching injector increases.

Tanky said:

I'm just saying be leary of false claims and promised numbers. MBRP did this on their cuda kit using Terry Delong as their role model saying their exhust system would give 'at least 10 more hp' than the competition. And when someone dyoned it, flowmaster to that, it yielded 1.5 more horses, if memory serves.

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Tanky, I forgot to address this earlier. I'm not arguing against your point here, but I felt it necessary to point out that not only are manufacturer claims not to be trusted wholly, but also customer claims and "independent" claims. Unless you care to exactly duplicate the conditions of the manufacturer's dyno pulls, you're wasting time. Prior to purchase, manufacturer dynos are only useful as guidelines, not gospel. After purchase, I think a baseline dyno is useful, but only for same vehicle comparisons.

My favorite example came from my BMW days, when Steve Dinan got sued by a bunch of E39 M5 owners who bought his S2 package and got angry when they dyno'd they're completed installs and found that their 400hp/400lb-ft cars made less power than stock with his parts installed. A class action suit was mounted against him, but he destroyed it with a single open letter he posted on his website by describing his dyno setup. He asked the owners just how many of them had a 250,000 cfm wind tunnel turbine as a supply fan. No one pursued the lawsuit after that.

I bolted a bunch of parts on my M3, along with software that seemed to make a big difference. I GTech'd the car and found a .5 second reduction in my 1320 time. I know that a GTech isn't the end-all of automotive telemetry, but its a useful tool as long as you use the same GTech on the same vehicle. When the local BMW crew organized a dyno day I jumped at the chance. I ended up showing stock power all the way up the chart. I was disgusted and felt that I ripped myself off by spending money on boltons for the car. Then I realized that the shop used an office fan for an air supply, so the car was starving all the way up the rpm band. The dyno was useless to me, because I didn't baseline the car on that same dyno.