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3 Bullet Bikes vs. 9,000 lb Lifted Megacab with Cummins. Who wins?

3 Bullet Bikes vs. 9,000 lb Lifted Megacab with Cummins.  Who wins?

I was prototyping our first set of triple turbos, so I had everything in my truck set to kill.  My wife was with me, along with two other couples, driving on the freeway. Three bullet bikes came flying by us, and one of the guys in my truck gives me the old, “You going let them just pass you like that?”

Of course the pressure was too much and I caught them.  They paid little attention to me, that is until I hammered it and pulled away from them. Although they were not racing me, this got their attention.  I slowed down to about 60 MPH, they caught up and it was game-on.

I started rolling into the throttle as we could hear the bikes downshifting.  I’m not going to lie, one of the bikes left the rest of us, he was way fast, really noisy, obviously heavily modified.  The other two bullet bikes, however, were not as supersonic.  We started pulling away from the one bike, and the 2nd bullet bike was glued to the side of us, we were accelerating exactly the same.  In fact when this rider turned to look behind him to see how bad he had supposedly beat us, he about wrecked his bike when he saw we were right next to him. 

Around 120 MPH, I ran out of RPM’s and was done. A minute later all three bikes came next to us giving us the thumbs up, probably as amazed as we were that only one of the three bikes could beat a lifted Dodge Megacab with 35” tires and weighing in a $9,000, plus the passengers, so right aroung 10,000 pounds altogether.  A very fun race.


Why Turbochargers Are So Exciting, and the Basics of How They Work.

As a teen, I really wanted to figure out how to make power in my own car.  After working on naturally aspirated engines for years, I got tired of the compromise of either having something drive able or having something with a lot of power.  Then along came pickups with diesel engines and turbochargers. By this time in my life I had received a Masters in Engineering Design, and combined what I now knew to start making advancements in this exciting field of turbo diesel engines.  The exciting thing is that a turbo diesel can make a lot of power, be very fast, and have still be daily driven.  This is largely because of the turbochargers used on today’s Ford, Cummins and Duramax diesels.

Here’s some of the basics to begin with.

A turbocharger is axial pump on the front on the compressor wheel. It is also a centrifugal pump on the back part of the compressor wheel.

If a compressor wheel is designed properly, it works great and is extremely efficient. It can push air in excess of a 4:1 ratio. A jet engine is an axial compressor and only compresses air in a 1.1-1.2:1 ratio, so a turbocharger it is much more effective in pressurizing the air through the compressor wheel.

Are you wondering why? It is because when a turbocharger compressor wheel is spinning, air enters the front of the turbo and passes through the centrifugal compressor and multiplies the air pressure ratio. Then, the air dissipates into the little snail shell we call a scroll or volute. As the air goes through the scroll, it slows down and becomes more pressurized and develops a higher density. It then exits the turbo charger then it enters into either the intercooler or engine.

On the exhaust side of things, a turbine wheel, which is usually made out of inconel, accepts the exhaust energy and causes it to spin which does two things: it takes the energy out of the exhaust in the form of pressure and also takes out energy in the form of heat. As a general rule, the air looses 10 degrees per pound of boost. So, if you are developing 30 PSI in a motor you are typically going to see exhaust temps drop by about 300 degrees after the turbine wheel.  The turbine does convert some of the heat energy into energy that goes back in form of boosted air, so it is also a heat exchanger and some of the heat energy is reused, instead of just being wasted.  This is one reason a turbo is more efficient than a supercharger.

The turbine wheel is actually part of the shaft, and the shaft is fastened to the compressor wheel. The shaft rotates in place by bearings, either journal and thrust bearing combination, or ball bearings which keep it from moving and side to side, front to back.  In very simplistic terms, it is one fan connected to another fan.  The one side spins by the exhaust and the other side spins and pushes air into the engine.

While the basic concept of a turbocharger is simple, the science in designing it to properly work, is extremely complex.  Aside from the designing of turbochargers, there are many variables that determine how well turbocharges will work with your engine, so be sure you are buying the from the right place, from someone who isn’t just selling you a general turbo, that they’ve heard works well.

Following the Air and Exhaust Through a Compound Turbo System.

There is nothing more exciting than figuring out HOW to make an engine run better, faster and more efficiently. My love of science stemmed from my love of cars and explaining how our products work to our customers and readers is one of the coolest things about my job.

Quite often I get questions as to how the air and exhaust move through our twin turbo kits, so here’s a quick overview.

A compound turbo kit is one turbocharger that charges another turbocharger which in turn charges the engine. This takes place as the air comes in through the air filters then moves to the air intake. It then hits the large turbo first which has to be significantly larger than the smaller turbo. The large turbo pressurizes the air and pushes it into the second, smaller, charger. This second turbo then multiplies the air pressure ratio which then puts it into the intercooler, then into the engine.

The exhaust exits the opposite way. It goes first through the small turbo, then the large turbo, then out the exhaust pipe. If you have a wastegate, (which all of our kits do) then some exhaust can bypass the first turbo. That is essentially how our compound turbo kit works. If you have any questions, feel free to post them. I will do my best to get you quick answers!

In a Nutshell. The Reason You Need Two Turbos On Your Diesel truck

Knowing why when it comes to your diesel pickup is important as you choose parts to enhance its performance, so I wanted to break down why compound turbos (twins) are far superior to single turbos.

  1. There is an increase in horsepower. With compound turbos, you don’t have to compromise between slow spool up and high end or quick spool up and no top end. A compound turbo has two turbos. Not only, does the smaller one allows it to spool up as quickly as most stock turbos and the large one provides a lot of air for the top end, but the pressure is multiplied between both turbos so a lot more air is available, then with either turbo by themselves. This equalizes the pressure between the exhaust driving pressure and the boost pressure so that the pressure exerted on the top of the piston during an intake stroke is similar to the pressure exerted on the piston when it pushes the exhaust out. This balanced pressure allows for less loss of horsepower because the power to push the exhaust out is recuperated as boost air comes back in as the intake valve opens.
  2. You engine stays cooler. With compounds, there are excess air molecules in the cylinder. There are enough air molecules to consume fuel and carry out the heat that isn’t involved in combustion. There is also more cool air going to the cylinder because the turbos are each spinning at lower pressure ratio, the air exiting the turbos is cooler than the air from single turbos and there is cooler, denser air entering the cylinder.
  3. Your turbos last longer. In a compound turbo, each one works less than it would have in a single turbo. Both turn at a lower pressure ratio yet produces higher total boost. This is great for the longevity of your turbos, and engine.

–Diesel Power Source

T4 Non Waste Gated Turbos: Are They Worth It?

There is a big trend in the diesel pickup market to use T-4 non-waste gated housings as a turbo upgrade from stock. For many, it seems like a great alternative. Without waste gates, these turbos are cheap, often between $500 and $800 instead of the typical $1500-$2000 price tag.

However, like most things in life, you get what you pay for. These T4 turbos, are generally created for OEM, are not manufactured for high performance vehicles but rather for small industrial, low RPM engines or gasoline cars that don’t have the same need most diesel truck drivers have like quick spool up, high top air flow, and high pressure ratios.

What people don’t realize is that these turbos are not bolt in applications. Without a waste gate, the housings have a high A/R ratio, somewhere around .9 or higher. This means the spool up is incredibly slow and while the top end performance is fair to good, the bottom end performance and drivability is really sacrificed.

There are also hidden costs. T4 housings were not manufactured to fit on a Dodge with a Cummins engine so you have to adapt the intake, the exhaust pipe, the exhaust manifold, and the intercooler tubing. After all these extra costs, you are still left with a turbo without a performance bearing structure. They hold up okay and are decently reliable, but they are not very drivable and will not have 360 degree thrust bearing or grooved journal bearings to keep oil on the shaft, at extremely high speeds. They are just not structured for high performance application, and are more suited to lower boost pressures.

The reason waste gated housings costs so much and people are willing to pay that price is because a waste gate is the most simple form of a variable geometry housing. This means that a smaller turbine housing can act as a larger turbine housing by virtue of the waste gate which allows the exhaust to bypass efficiently. This increases the capability of the housing to flow 10-15% more without sacrificing spool up. A T4 might flow well on the top, but it will generally be a dog on spool up and drivability.

Before you go buy a big, inexpensive T4 turbo, give us a call and ask a few questions so you can be an informed customer. We understand the sacrifices made to be able to drive a great truck with a great engine and know there is nothing worse than buyer’s remorse. We can give you quality parts and guarantees so that you get the most value for the truck you love.

Turbine Housings Basics

The turbine housing is the housing that covers the turbine and directs the exhaust gasses into the turbine wheel. The turbine housing is one of the most crucial parts of the turbo-charger, to determine how the turbo will peform.  For this reason we cast our own turbine housings for most of our DPS Turbos.

Turbine housing science can be broken down into 5 different main categories.

Wastegated Housing: A turbine housing with a wastegate has valves that control the exhaust around the turbine so a portion of the exhaust bypasses the turbine when it is open. This is the simplest form of a variable geometry turbine housing. It can allow between 10-15% more exhaust gas to bleed off past the turbine. This helps reduce exhaust drive pressure, it can control boost and exhaust pressure and decreases turbine speed.

Non-Wastegated Housing: In non-wastegated housing there is no way of regulating the boost or turbine speed from the exhaust end of things. These housings are typically a little larger and are much cheaper, but they do not have as wide of an operating range as wastegated housing does.

Volute/Scrolls: Scrolls or volutes are snail shaped passages of the turbine housing. If you were to stretch the scroll out, you would find that it is a cone that is wrapped around the turbine and has a slot in the center that allows exhaust to pass through into the turbine wheel. The A/R ratio is measured starting at the tongue or inlet and is the AREA over the RADIUS from the centroid of the turbine scroll (notice I did not say “center”). A smaller A/R means that the “cone” is tighter and smaller which allows exhaust gasses to pass through at a faster rate, which helps the turbo spool faster. This is more conducive for low end drivability and quick spooling. A ratio of 1.1 to 1.35 is on the larger side of ratios, and will be indicative of slower spooling with exhaust flow being high on the top end but not as quick spooling or nearly as drivable.

Divided Scroll: In a divided scroll, on a 6 cylinder Cummins for example, the front 3 cylinders are separated from the back 3 cylinders by a divider. This means that only 3 cylinders have to pressurize in exhaust manifold so the exhaust pulses are much stronger as they pass into the turbine wheel. This allows for faster spool up.

Open or Non-Divided Scrolls: In an open scroll, the volute has only one open hole and it is not divided. This means the exhaust gasses have pressurize through the entire manifold to fill up the turbine housing before it can spool the turbo, and exhaust pulses are less powerful. This means the spool up will be much slower. However in theory an open scroll can flow slightly more at top end, although our experience does not necessarily support this theory.  In other words, we like a divided scroll on a most diesel engines.  We believe that this theory is may be correct on gas engines, where RPM’s are much higher.

The ideal combination is a divided manifold with a divided turbine housing. With this option on a 5.9 Dodge Cummins you will see typical spool ups of 100-200 RPMS quicker. For this reason, we only build full divided scroll manifolds. we highly advise any 3rd gen Cummins owners who purchase our turbos to also purchase our 2-Piece Exhaust manifold because the combo makes your driving experience more enjoyable.  

Diesel Power Magazine

Truck Trends Logo

Nothing says "bang for the buck" like the '94 to '98 12-valve Cummins. Gaining horsepower can cost next to nothing, and even if the project takes a turn toward the extreme, big power can still be had without breaking the bank.

Recently, we hooked up with Russ Kennel of Maximum Diesels in San Jacinto, California. He's a diesel shop owner who's becoming more and more involved in the old-school diesel aftermarket-mainly due to how fun and affordable it is. When we bumped into him, he'd transformed a $3,000 '94 Dodge Ram 2500 into a 12-second quarter-mile performer-and had done so on a very tight budget. But he wanted more.

With plenty of fuel on tap, Kennel recently upgraded to a set of twin turbos. By retaining his quick-spooling Tech 64 unit from Diesel Power Source and using it as the high-pressure charger, Kennel threw an S480 (also from Diesel Power Source) into the mix. Still within budget, the addition of the low-pressure charger and new plumbing propelled his standard cab Dodge into the 11s in the quarter-mile, and the truck picked up 145 hp on the dyno.

Is the 12-valve still the king of cheap diesel power? You betcha! Follow along as we give you Kennel's power recipe, dyno results, and elapsed time improvement from adding twins.

Read the full article: DieselPowerSource

Melted a Piston Lately?

On the 2003-2007 Dodge Cummins common rails there have been a large amount of pistons "sticking" or failing. This is especially the case on 2004.5-2007 years.

One main reason for the engine failures: Common rail engines have a different exhaust manifold than the older style engines, and they have a significant flaw, in exhaust flow, on the back three cylinders, especially cylinders 4 and 5. If you look at the stock exhaust manifold cylinders 4 and 5 actually blow directly into each other. When a pyrometer probe is placed in each cylinder, cylinders 4 and 5 run approximately 200 degrees hotter than the front 3 cylinders, and cylinder 6 runs over 100 degrees hotter than the front three. So if your pyro probe is in the collector, chances are cylinders 4, 5 and 6 could be as much as 200 degrees hotter than your probe is reading. So if you read 1500 degrees, you're actually at 1700 degrees on those hotter cylinders, resulting in premature piston and engine failure. In many cases the piston (which is aluminum) expands so much in the cylinder, that it actually wedges itself in the cylinder, resulting in the piston material rubbing off onto the cylinder walls, what mechanics call a "stuck piston".

Solution: Diesel Power Source's, 2-Piece Manifold, reduces EGT's in the rear three cylinder by 150-200 degrees, due to a better flowing design. Our manifold flows much better in the rear three cylinders than the stock manifold does, as well as flowing better in the front three cylinders. EGT reduction in front cylinders of 30-60 degrees, and the rear cylinder of 150-200 degrees makes the temperatures in the cylinders much more balanced, and cooler overall. This could literally save the life of your engine.

With only a $359 price-tag, it could save you an engine rebuild, and have a crack-proof manifold. Not a bad investment.

Purpose of groove on turbocharger

We have received many questions about turbochargers. One being about the groove in the compressor housing (also called the MWE groove, MAP WIDTH enhancement groove), the purpose and effect of changing it.

This groove also called the Surge Groove. This groove is placed in a turbo to move the surge line on the compressor map to the left and widen the map. The larger the groove the better surge characteristics, but at the sacrifice of top end air flow. In other words the larger the groove the less surging a turbo will do, but at a slight sacrifice to max air flow.

A groove that is properly sized and positioned will allow a larger compressor wheel to be used, which would normally surge. So while a surge groove causes a small sacrifice to top end, it allows a much higher flowing compressor wheel to be used. This ultimately flows much more air than a smaller wheel with a small or no surge groove. (This is exactly what we do on our D-Tech 64mm, a huge flowing wheel with lowered surge line.)

What is surge? Surge is when boost pressure exceeds the driving force of the turbine/compressor wheel, ultimately stalling or reversing the direction of air flow and the spinning wheels.

How does the surge groove help with this? A surge groove is positioned just after air begins to pressurize in the compressor housing. This allows some of the pressurized air to escape and return into the intake increasing the pressure in the intake at low turbine speeds. This makes the pressure differential between boosted air and intake air not quite as different. This is why a turbo surges less at low altitude then high altitude, because of the higher pressure at low altitude. At high turbine speeds the air is moving so fast that a lower percentage of air escapes through the groove so the groove has very minimal effect on max air flow compared to the benefits (but does have some).

Our DTech 64 turbo has a specially engineered surge groove to allow a smaller, quick-spooling turbine wheel to be used with a very high flowing compressor wheel (1190 CFM). With comparatively great surge characteristics.

Twin Turbos vs. Single Turbos

Why would I choose compound turbos over a single turbo?


There are certain  facts and laws of nature that work against every diesel driver. Among these are 1. Ambient (atmosphere) air pressure is approximately 14.7 psi at sea level. 2. Turbochargers only function at their best in a limited band of RPM's.


Because of this, most diesel drivers have to choose either:

  1. A small turbo (like a stock turbo) which functions very well with most engines at low RPMs, but limits high end power, or

  2. A large turbo which functions well at wide open throttle (WOT), but is horrible to drive around town because it won’t spool up (takes too long to produce a boost) and has surging issues), or

  3. A medium size turbo which spools up relatively well and at WOT still has some exhaust restriction but allows a lot more power and cooler EGTs than the small turbo.


To help alleviate these problems, DPS offers Turbochargers that offer quick spool up and a good increase in airflow and 10%-13% increase in horsepower over a stock turbo. However, single chargers, even with enhancements, all have limitations.

Why is air pressure a factor for my turbo?

Here is a quick science lesson: If you see boost pressure on your truck at 35 psi, this is actually the gauge pressure (psig). The zero on the gauge is actually 14.7 psi (at sea level), so the actual pressure is what you read on your gauge (35) + 14.7 which equals 49.7 psi.


What does this mean for my turbo?

What this means is that the pressure trying to get into the turbo is only 14.7 psi, and despite how fast you spin the turbo, there is only 14.7 psi pushing air in. So, if you spin the turbo too fast it becomes inefficient at bringing new air in, and it becomes increasingly harder to get exhaust out.


Is there an easy way to fix the air pressure problem?

There are ways to lessen the problem. With a single turbo, people increase the sizes of compressor and turbine wheels as well as the turbine housings.  This can increase the amount of airflow, but ultimately hurts low end drivability and spool up, and all because the engine is up against those pesky laws of physics. A certain size of hole (the turbo air inlet) will only flow a limited amount of air at a given atmospheric pressure. Atmospheric pressure becomes a huge limiting factor.


Is there a way to get my turbo to function well at low RPMS, at WOT and without surging or spooling issues?

Yes! The solution is compound turbos (aka: twin turbos, sequential turbos)


Why do compound turbos work so well?

Compounds are two turbos placed sequentially, one flowing into the other. They must be sized perfectly so they complement each other instead of work against each other. These turbos consist of a smaller charger and a larger charger. The small turbo gets exhaust from the engine first and the large turbo gets fresh air first. Fresh air enters the larger turbo which spools slower. It is then pressurized and fed into the small, quick spooling turbo. The small turbo multiplies the already pressurized air, and then feeds that air into the engine.


For those who enjoy numbers, here is a quick illustration:

Turbos multiply atmospheric pressure. Therefore if the small turbo as a single can take air at 14.7 psi, and produce 40 psi boost, it is multiplying the air by 3.72 times (14.7 psi x 3.72 = 54.7 psia, minus the 14.7 atmospheric gives 40 psig (gauge pressure)). The large turbo can do a similar job. Therefore let's say that the large turbo multiplies by 2.2 times, it takes 14.7 psi (atmospheric pressure) and makes 17.6 psig (actual pressure 32.3 minus 14.7 atmospheric, not taking into account adiabatic efficiencies), now the small turbo will see 32.3 psia at it's air inlet (instead of the 14.7 psia, that it would normally see as a single turbo), but the secondary/small turbo thinks it's only seeing atmospheric pressure.  Then when the secondary turbo multiplies the 32.3 psia by 2.4 times you get about 65 psi.  A lot of cool air to help in combustion and carry heat out of the cylinders.


If my engine runs a twin turbo, how will that change things?

The beauty of the whole staged, two turbo concept is this: You can have all of the benefits from a small quick spooling turbocharger, with more-than-all of the benefits of a very large turbocharger.


With a twin turbo, the engine can receive over double the amount of air than a single turbo, would be able to move because that’s all atmospheric pressure would allow. Because with twins we can literally cram over double the volume of air into the same inlet hole size in the small turbo (we have just turbocharged the small turbo).


How does this affect the efficiency of my engine?:

Efficiency is the amount of energy which is converted into heat during the compression process. The higher the efficiency the less heat is made from compressing the air. Most compressor maps for turbos end between a 3.5:1 and 4:1 ratio because the efficiency of the compressor drops beyond that point so dramatically. Most compressors have their highest efficiency between 1.5:1 and 2.5:1 ratio. Our DPS 62mm will run at 78% efficiency below 2.3:1 ratio, which is where it typically will run on twin turbos, running appx. 55-60 psi boost. Whereas at 40 psi boost when run as a single turbo the ratio is 3.7:1 and the efficiency drops to 70%, or 8% less than at 2.3:1 ratio (which is still very efficient at that level compared to most other turbos but is significantly lower than the twins at a much higher boost level, in contrast-the stock turbo at this same ratio is 5% less than that). By 45 psi most single turbos are running off the compressor map at efficiency below 68%. In other words our Twin Turbo Kit at 55 psi boost is running much more efficiently than any single turbo running at only 40 psi boost.


More efficient engines mean more usable, cool air entering the engine. To show the increase in compressing efficiency, our Twin Turbo Kit at 58 psi of boost produces compressed air temps (before the intercooler) of appx. 375 degrees F, while at 40 psi the stock turbo produces air temps of appx. 495 degrees F.


Our Twin kits actually put extra air molecules into the cylinder which are not consumed during combustion, but do carry heat out of the cylinder, keeping things much cooler. This is similar to the bypass ratio used on jet engines to keep the exhaust stream cool.


How does the exhaust to boost pressure affect my engine?

The exhaust to boost pressure ratio is the ratio of the exhaust pressure (pre-turbo), to the boost pressure. You want the exhaust and boost pressures to be as close to equal, or 1:1 as possible.  Single turbos rarely can do this.  For example,  the stock turbo you typically see is about 70 PSI exhaust pressure at 40 psi boost pressure.  


How do DPS Compound Kits improve my exhaust to boost pressure?

Compared to our compound kits, at 60 psi of boost pressure, we typically see 58-60 PSI of exhaust pressure.  This results in direct horsepower gains, because the power required to push the exhaust out, is regained by the high boost pressure, which pushes the piston down on the intake stroke, with our Compounds.  This adds horsepower.

Because of the high psi produced by our Compound Kits, the wastegate completely opens about 2/3 the way up the boost scale.  By allowing the small turbo to wastegate like this, it also lowers the exhaust (drive) pressure. Again helping with power and EGT’s.


What are your final thoughts on Twin Turbos?

With a lot more cool air in the cylinder, lower exhaust drive pressure, and quick spool-up, there is plenty of air for top-end performance, yet great drive and tow ability. A properly engineered Compound/Twin Turbo Kit, will translate into much more horsepower, much lower EGT's, better fuel mileage, a much broader RPM range (quick spool up, with huge high end WOT potential), and, overall, a much more drivable, high performance truck. All of this while the turbos don’t have to work as hard, making them more reliable and able to last much longer. So, next time you see a company trying to sell a single turbo, claiming it will compete with our Twins, remind yourselves that the laws of physics just don’t allow it. Our customers all say that once they have installed our Twin Turbo Kits, they could never go back to a single turbo.