Make 500 Smog-Legal Horsepower With Bolt-On Parts - Diesel World

Make 500 Smog-Legal Horsepower With Bolt-On Parts

Modern diesel engines are pretty efficient right off the lot. Even after racking up 282,000 miles, Clayton Putt’s early 2007 LBZ Duramax-powered work truck was still a great candidate to squeeze out more power and fuel efficiency. Like most people who buy a diesel for work, Putt is a contractor who depends on his truck to not only get him to and from his many jobsites, but also to carry all the tools and equipment needed to get the job done, including towing heavy equipment at times. As a small business owner, Putt has surely felt the effects of high fuel prices so he turned to Jonathan Jones and the team at No Limit Tuning & Design in Rossville, Georgia, to help him improve the driving efficiency of his work truck while improving its ability to handle heavy loads at the same time.


Just because it’s a work truck doesn’t mean it can’t be more powerful and more efficient.

To reach the performance goals without removing the emissions equipment on the truck, Jones and his crew opted to go with an emissions-legal cold air intake system from S&B Filters, including their under-bumper cold air intake scoop. On the exhaust side, they retained the catalytic converter, but installed an MBRP ceramic-coated and thermal-wrapped downpipe and T304 stainless steel cat-back 4-inch diameter exhaust system to help expel spent gasses more easily. Then to top off the emissions-legal performance bolt-on parts, they also installed a DSP5 switch from EFI Live and wrote five custom tunes for Putt, including a stock tune that’s optimized for the new intake and exhaust flow improvements and tunes for daily driving, towing, economy, street performance and hot performance. SoCal Diesel provided the switch, software licenses and an AutoCal that will allow Putt to upload future tunes as he continues to upgrade his truck, as well as read and clear any trouble codes that may appear.

The cold air intake kit from S&B Filters is emissions legal and includes everything needed to replace the factory filter and restrictive housing. Clayton Putt also opted to use the cold air intake scoop for improved airflow on the open highway.

To improve the exhaust flow while retaining the factory catalytic converter, Putt went with a T304 stainless steel cat-back 4-inch diameter exhaust system partnered with a ceramic-coated and heat-wrapped high-flow downpipe.

No Limit Tuning & Design writes custom tunes for the EFI Live software that’s loaded into the truck through the AutoCal interface.

Before starting the installation, Jeremy Mathis strapped the 11,000-pound 2WD work truck down to No Limit’s Dyno Dynamics chassis dyno for baseline performance testing that showed that the old truck was doing pretty good making 307 hp with about 650 lb/ft of torque. But everyone knew that even with the high miles Putt’s LBZ had, a lot more potential power trapped inside was waiting to be unleashed. After installing the S&B Filters intake system and MBRP exhaust components, another spin on the dyno showed a broader power band with 330 hp and 660 lb/ft of torque without any tuning changes to compensate for the additional airflow capability in and out of the engine.

Then after installing the DSP5 switch and uploading the custom No Limit Tuning & Design tunes, Mathis and Jones gave the truck another spin on the dyno with excellent results. Using a stock tune but compensating for the additional airflow, the truck put 385 hp and 685 lb/ft of torque to the rollers. While an increase of nearly 80 horsepower is nothing to sneeze at, the real performance improvements came when the DSP5 switch was turned to activate the No Limit performance tunes. Even the economy tune made big power, delivering 440 hp and 765 lb/ft of torque and the tow tune lit up the dyno for 479 hp and 830 lb/ft of torque, which will no doubt help carry nearly any load up a steep grade.

For a truck with more than 280,000 miles on the odometer, the engine bay is pretty darn clean. But the restrictive factory air cleaner assembly is holding back the potential of the 6.6L LBZ Duramax engine.

Jeremy Mathis kicked off the LBZ upgrades by disconnecting and removing the factory air cleaner assembly as well as the mounting plate below the assembly.

The cold air intake scoop comes in two pieces with the top section installed from the top and the bottom section secured to it with mounting bolts and support brackets that are included with the kit. S&B Filters also includes a plug for instances where owners are expecting to be crossing deep water to prevent water intrusion in the engine.

When installing the new filter assembly be sure to use the provided seals and mounting screws to mount the MAF sensor in the housing.

Not only is the engine bay of Putt’s truck dressed-up a little better, his LBZ can breathe easier now thanks to the high-flow cold air intake system.

The scoop is designed to work with the factory bumper and draws cool outside air directly into the air filter rather than hot air from under the hood.

The small-diameter factory tailpipe leaves a lot to be desired, even on a work truck.

Both of the performance-oriented tunes broke the 500 horsepower barrier with the street tune slightly edging out the more aggressive hot tune with 511 hp compared to 505 for the hot tune. Jones felt that this difference was due to the high mileage CP3 high-pressure fuel pump not quite being able to keep up with the aggressive demands of the hot tune and dropping rail pressure. The hot tune did reign supreme in torque, though, delivering just over 900 lb/ft of torque while the street tune put 885 lb/ft of torque to the rollers.

Installing both the S&B intake and cold air scoop was easy and straightforward where the old intake is removed and replaced by the new parts. A word of warning on the scoop, though—it’s designed to work with factory bumpers and should never be submerged. If your truck sits low or you’re expecting to cross through deep water, it’s best to put the provided scoop plug on to replace the scoop head. Under normal driving circumstances, water ingestion is not typically a problem but it is something to be aware of with this type of intake since ingesting water into your engine could cause catastrophic failure.

To make it easier to slip the hangars out of the rubber mounts, Mathis sprays them with a blast of Schaeffer’s Penetro and lets it soak while removing the clamps and cutting the exhaust pipe.

Cutting the exhaust pipe into sections makes it much easier to remove from under the truck, especially when you’re working on the ground in a shop or garage.

After removing the rear portion of the factory exhaust system, Mathis installs the included 3.5-inch to 4-inch tubing adaptor in the clamp behind the catalytic converter.

Then he installs the rest of the sections of the MBRP cat-back exhaust system using the supplied clamps and hangars.

Mathis aligns and installs the polished stainless steel double-wall 5-inch diameter MBRP exhaust tip that’s included in the kit. It looks much better on Putt’s work truck than the wimpy stock tailpipe.

Removing the factory downpipe is not as easy as the intake or cat-back exhaust system. Mathis had to work by feel on the backside of the turbo to remove the heat shields and band clamp securing the factory downpipe.

After removing the plastic fender liner, Mathis could
access the bottom side of the downpipe, but it’s very tight work here as well.

Mathis had to separate the heat shield from the downpipe, then, after a lot of wrestling, he was finally able to remove the factory downpipe from the bottom side of the truck.

Likewise, the cat-back portion of the MBRP exhaust system was easy to install, even working on the ground, since the ladder rack prevented the truck from being pulled into the old No Limit shop in Chattanooga, Tennessee, where the installation was performed. Removing the old exhaust system is easiest if you cut it into two or more sections to make it easier to get out from under the truck, especially if you’re working on the ground in your garage or driveway. It’s also easier to remove the rubber exhaust hangar bushings if you lubricate them with a penetrating spray like the Schaeffer’s Penetro that the crew at No Limits uses.

Installing the MBRP downpipe was a different story entirely. Mathis wrestled and fought with the truck every step of the way, including removing the original factory downpipe and then he fought to install the new tubular high-flow MBRP downpipe. It’s a very tight fit between the firewall and the engine, giving you little room to work in and making it difficult to disconnect the downpipe. But even once it’s disconnected, it’s hard to work the downpipe out of the truck.

Looking at the stock downpipe side by side with the new MBRP tubular downpipe it’s easy to see that the MBRP pipe will flow better than the dead-headed and pinched factory pipe.

It was a fight for Mathis to install the new downpipe too, but he did eventually get it into position, then secured it top and bottom with the factory band clamps.

Before installing the DSP5 switch and working with the ECU harness, Mathis disconnects the negative battery cable on both batteries to make sure there are no shorts or spikes to the ECU while working on it.

Mathis routed the DSP5 harness from the cab through an existing grommet in the firewall, being careful to avoid moving any hot parts under the hood as well as under the dash.

Unfortunately, you’re not out of the woods once the factory downpipe is removed, since the larger tubular MBRP downpipe still needs to be installed. Squeezing the high-flow MBRP downpipe into position to replace the restricted factory pipe can be extremely frustrating and will likely test your patience, but it’s possible and can be done. After muscling the downpipe into position, it’s secured to the turbo and the rest of the exhaust system with the factory band clamps for a secure and leak-free fit.

The baseline dyno testing, intake installation and exhaust upgrades were handled on one day then Putt returned to the shop the next day for the DSP5 switch installation and to have the custom No Limit tunes flashed to the ECU. Mathis mounted the switch in the cab under the dash and routed the cable through the firewall into the engine bay to the ECU. At the ECU, the pre-terminated connectors are installed in the larger ECU plug in vacant positions with the gray wire going to pin 46 and the black wire going to pin 54.

On an LBZ like Putt’s, the lower connector on the ECU (see arrow) is the one that’s modified to work with the EFI Live DSP5 switch for tune selection, but the top connector must also be unplugged to get to the bottom connector.

After carefully opening the connector, Mathis installed the gray wire in position 46 and the black wire in position 54 (see arrow), making sure that the pins are fully seated in the connector before reassembling the connector.

He installed the DSP5 switch below the dash near the parking brake release where it’s accessible but also out of the way.

27 and 28 Jonathan Jones loaded his custom tunes onto the AutoCal before Mathis uploaded them to the truck.

On the dyno, Putt’s truck made more than 500 horsepower and about 900 lb/ft of torque for an improvement of more than 200 horsepower and 250 additional lb/ft of torque with the intake and exhaust upgrades and custom tuning.

While the wiring of the DSP5 switch into the ECU harness connector is critical, it’s definitely something that most experienced DIYers can certainly handle. Mathis handled the installation and loading the No Limit custom tunes in about an hour and a half, including the typical photography slowdowns, and we expect that most DIYers would need a similar amount of time. When running wiring through the truck in the engine bay and under the dash, be sure to avoid hot and/or moving objects, especially the steering and pedal mechanisms as a problem in that area could potentially be fatal.

Mathis and Jones performed the dyno testing and installation in about a day and a half, including time to fight with the downpipes, so if you plan to install this combination yourself be sure to set aside the better part of a weekend. If you leave out the downpipe, you could easily do the installation in a day, but you will be leaving some performance on the table by retaining the factory downpipe. As always, practice safe shop techniques whenever you’re working on your truck and if the techniques mentioned and shown here seem to be beyond your skill level have your local diesel performance specialty shop perform the installation for you. DW

Dyno Results:
Stock (before upgrade) 307.3 @ 2,510 rpm 650 @ 2,425 rpm
Stock (with upgrades) 329.8 @ 2,675 rpm 660 @ 2,610 rpm
Stock (tuned for upgrades) 385.2 @ 3,390 rpm 685 @ 2,450 rpm
Economy 440.9 @ 3,100 rpm 765 @ 2,600 rpm
Tow 479.4 @ 3,150 rpm 830 @ 2,655 rpm
Street 511.5 @ 3,350 rpm 885 @ 2,945 rpm
Hot 505.1 @ 3,190 rpm 900 @ 2,830 rpm


EFI Live
Dept. DW

Dept. DW
315 Old Ferguson Road
Huntsville, Ontario, Canada P1H 2J2

No Limit Tuning & Design
Dept. DW
419 West Lake Avenue
Rossville, GA 30741

S&B Filters
Dept. DW
15461 Slover Avenue
Fontana, CA 92337

SoCal Diesel
Dept. DW
27833 Avenue Hopkins, Suite #6
Valencia, CA 91355