Choosing the right turbo for your truck is difficult. It's almost like choosing a girlfriend. The decision is almost always full of compromise. Believe it or not, the turbo you run on your truck makes all the difference in the world. A different turbo can dramatically change the way a truck drives and performs.
You can go with something smaller for quick response and a sharp spike in boost pressure, but the trade off is less air volume or CFM (cubic feet of air / minute) allowing less fuel and less power as the engine climbs its power curve. This is great for stop-and-go driving, but leaves something to be desired when you want to rocket up an on-ramp or try the drag strip.
A larger turbo will provide higher horsepower and torque once it has spooled up, but they can take a while to get there. They are a must for heavy towing with increased fuel. Larger turbos keep EGTs lower because of their larger exhaust housing and the greater volume of air they supply. If you've ever driven a truck with a large turbo, you know it can be frustrating to have to wait through the longer lag before the turbo spools and gives you the power.
If you are tired of compromise, then it's time to consider a compound turbo set up. The idea behind compound turbos is that you get the best of both worlds. They use a smaller primary turbo that spools quickly and earlier under light acceleration, and a larger secondary turbo that spools after the primary turbo to provide a massive amount of air to the engine.
We tested the ATS Aurora Compound Kit on a '98.5 24-valve Dodge Cummins. ATS has combined their smaller Aurora 3000 turbo with their larger Aurora 5000 turbo. The kit comes pre-assembled with an ATS Pulse Flow manifold which ATS says decreases time for turbo spool-up and lowers manifold backpressure. The manifold is in three pieces to allow it to expand and contract while under extreme temperatures generated by modified engines.
Exhaust travels through the manifold, into the exhaust housing of the Aurora 3000, then through a wastegate housing, through the exhaust housing of the Aurora 5000, and finally into the exhaust down pipe.
The air intake is as follows: Air gets sucked in through the AFE filter, into the Aurora 5000 intake and through the 5000, into a 3-inch tube, into the intake of the Aurora 3000, where it's initially compressed and sent as charge air into the intercooler and then force-fed to the engine. The 3000 compresses the air early on as the 5000 follows with serious air mass.
This system completely changes the way this truck drives. We had been running an Industrial Injection Super Phat Shaft 62 prior to this kit, which produced good power with a fair amount of turbo lag. The ATS compounds provide effortless turbo spool, early on as the truck accelerates, as the secondary turbo boosts to provide that heavy-hitting power you'd expect from a large charger like the 5000. The power curve is smooth and comes on earlier than it did with a single turbo. It's now a pleasure to drive through the city. Stopping at traffic lights and stop signs is somehow tolerable now that this dually truck accelerates like a sports car.
In order to get an idea of how the ATS compounds stack up to our previous single turbo, we did not change the fuel system on the truck. We wanted to with all this extra air, but had to refrain in the name of science. Here are a few of the numbers:
It should be noted that this Dodge has a lot of hard miles (220,000) on it. We are seeing a large amount of blow-by due to its tired piston rings. When the engine boosts above 50 psi, it evacuates a large amount of air and oil from the blow-by tube on the bottom of the engine. We expect to see more dramatic numbers on a younger engine.
Boost pressures are consistent between the SPS62 turbo and the ATS compound. Both setups are pushing up to 52 psi with the same amount of fuel. ATS says the compound kit will flow 1708 CFM, so there is a lot of potential for power as we add more fuel in the future. Keep in mind, you will need to replace the stock head studs if you want to exceed 45 psi boost pressure without losing your head gasket.
Installation of the ATS compound kit was somewhat time consuming. It took our tech about six hours to install it. The kit came with all of the parts needed to install the turbos. The instructions were easy to follow and fairly thorough.
We installed a set of BD Diesel's high-pressure intake hoses and clamps.
The 5"_ exhaust helps keep EGTs low while the truck does its heavy breathing.
Turbo Noise (towing): The II SPS 62 reaches its resonating, ear piercing, make you-want-to drive-the-truck-into-a-pole sound at about 20 psi. The ATS compound turbos activate their siren song at about 30 psi.
Smoke (towing): The compounds clean up the smoke very quickly when towing. The turbos start doing their work right off of the line, where the single 62 takes some time to spool and clean up the smoke. Both the compound and the single run clean once the truck is moving at cruising speed.
Acceleration (towing): As the smoke indicates, the compound turbos spool quickly under heavy load and deliver responsive power early on in the power curve. The single takes some time to get up to speed, making for a sluggish power curve, especially while towing.
Application: Towing 15,500 lbs on a 30' flatbed trailer traveling same route
Fuel Setting: II (Industrial Injection) SHO VP44, FASS, 5 hole injectors, Smarty level 3 software
|Turbo||II SPS 62||ATS Compound|
||850 - 1050
||720 - 950
||30 - 50
||20 - 35
||8.5 - 10
||8. - 10
|Intake Temp (degrees above outside temp)
||40 - 70 *
||50 - 80 **
*AFE Stage II intake with heat shield **AFE filter without heat shield
Dyno testing indicates that the SPS 62 we ran on the truck prior to the ATS compound install was making good power with all of the fuel we were supplying to the engine. The SPS 62 gave us slightly higher numbers on the stock software setting. Notice the abrupt power curve as the turbo spools and delivers power around 2000 rpm.
The ATS compound on stock software setting shows us the impressive power curve that compounds can deliver. Note the smooth arc that begins a steep climb at 1500 rpm.
Smarty software program 5, a setting we commonly use for towing on this truck. Again, note the sluggish power curve while we wait for the single turbo to boost. But in the end, the single is generating good power.
Smarty program 5. The power curve feels even better under your foot than it looks on paper.
Smarty program 8 (max fueling) stacked with Edge Juice w/ Attitude on level 5 (max fueling). When we throw more fuel at the single turbo, it struggles to keep up, but it does provide enough air to burn all of the fuel. Max HP and torque is achieved at 2500 rpm.
Smarty program 8 (max fueling) stacked with Edge Juice w/ Attitude on level 5 (max fueling). The compound turbos begin to show us that they want more fuel. The power curve gets more steep and we still get max HP and torque just past 2200 rpm. We can't wait to upgrade the fuel system.
We used Gillett Diesel's Mustang Dyno, in Bluffdale, Utah for the numbers shown. The results are uncorrected, raw numbers from the same dyno, running the same fuel system on our test truck.
Single Versus Twins Dyno Testing
For the exhaust system, we chose a 5-inch turbo-back single exhaust kit from Diamond Eye Performance. We liked the fact that the 5-inch muffler on this system had a true 5-inch inside diameter. Some 5-inch exhaust systems reduce down to 4-inch mufflers. The ATS kit came with a 4-inch down pipe to use with their turbos (as the secondary turbo sits lower than stock), but we wanted to run a complete 5-inch exhaust, so we ordered a 5-inch down pipe for a 3rd generation (2003-up) Dodge from Diamond Eye that would need some modification for this project. We cut the 4-inch mounting flange off of the ATS down pipe and cut the 5-inch Diamond Eye down pipe down so that the two would slide together to fit our application. We then joined them with a 5- to 4-inch reducer and welded them together.
After we completed the comparison between the single and compound turbos, we replaced our set of 5 hole (90 hp) injectors with a set of Industrial Injection's 10 hole (140 hp) injectors to see how the ATS Aurora compound would react. We've noticed how difficult it can be to remove chunks rubber off the dual Toyo M/T tires from our new 6-inch stainless steel exhaust tip. We also know for a fact that the turbos were boosting past 65 psi when we knocked out the counter shaft in the truck's NV4500 5 speed manual. On Gillett's Mustang Dyno, it ran at 515 hp and 1136 lb ft as it blew about 2 quarts of oil on the floor. It seems like it might be about time to build a hot Cummins to stick under the hood.
ATS Diesel Performance
Diamond Eye Performance
Gillett Diesel Service
Industrial Injection Service
Editor's Note: To see more images from this Diesel Tech feature, go to www.dieseltechmag.com.