How to you add power to a turbo motor? The obvious answer is simply to increase the boost pressure, but there are actually many ways to add power.

One way is to change the power output of the NA motor by replacing the factory heads, cam, and intake (or displacement), but what if we told you to look elsewhere, like the exhaust? Turbo motors thrive on maximum exhaust flow, not necessarily before the turbo, but certainly after the turbo. Restrict flow out of the turbo and it gets unhappy and inefficient. One way to increase the flow rate out of the turbo is to increase the size of the exhaust or downpipe exiting the turbine housing.

But Richard, what happens if the turbine is designed to accept a certain size exhaust pipe and V-band flange? Does it still help to up-size the exhaust after the turbo?

This is where the Power Cone comes into play. The Power Cone is simply a cone-shaped section of exhaust that steps up the exit size of the turbo to allow installation of a larger exhaust pipe.

The question is, does it work?

turbocharger power cone installed
What the heck is a Power Cone and does it add power? (Image/Richard Holdener)

To properly test the Power Cones, we first needed a test motor. We all know that the best test motors come from the wrecking yard, and our all-aluminum, 5.3L L33 was no exception. As our go-to LS test mule of choice, the 5.3L had been previously subjected to all manner of testing, including intakes (EFI and carb), spacers, cams, blower, turbos, and nitrous.

You name it, and this 5.3L motor has likely tested it.

A high-mileage unit when liberated from the yards, this test regiment had subjected the LS to nearly 700 dyno pulls as of this writing, with many more to come. Though this motor had long established itself as dyno soldier, ready and willing to serve, we took the liberty of verifying it was still in decent shape and ready for boost. Fresh from its last outing, the 5.3L was first run in near-stock trim, naturally aspirated trim. The only mods to the L33 included an aftermarket truck cam, BTR valve springs, and a TBSS intake (with a Fast 92mm throttle body).

Run with 1-7/8 inch dyno headers, 1,000cc injectors, and a Holley HP engine management system, the cammed 5.3L produced 436 hp and 420 lb.-ft. of torque.

Now it was time for some cones.

After running the motor in naturally aspirated trim, we installed the dyno turbo kit. Built for dyno use (not for a specific chassis), the turbo components included a pair of factory truck exhaust manifolds. The forward-facing manifolds fed a custom Y-pipe from Jason at JTFab77. The Y-pipe featured a number of flanges, including a pair for the twin 45mm Hyper-Gate wastegates from Turbo Smart.

The Y-pipe also featured a 3 inch V-band designed to accept either a V-band turbine housing or V-band-to-T4 (T3 or T6) adapters. This facilitated the installation of a variety of different turbo sizes and designs. For this test, we installed an RHP GTX3584RS turbo designed to accept a 3 inch V-band exhaust. Slightly larger (3.5 to 4.0 inch) Power Cones were tested on the larger G42 turbo (capable of 1,200 hp) with similar results. Boost from the RHP turbo was channeled through an air-to-water intercooler. The discharge tubing also featured a Turbosmart BOV.

The 1,000cc injectors (and Aeromotive brushless fuel pump) provided more than enough fuel flow (E85) to feed the boosted 5.3L.


To start the test, the turbo 5.3L was first run with a peak boost pressure of 11.75 psi. The boost was controlled using a manual boost controller, though once adjusted to this level, it was not touched for the 2nd part of the test. Run in this manner at 11.75 psi, the turbo L33 produced 739 hp and 778 lb.-ft. of torque. After back up runs repeated these power numbers, we swapped out the 3.0 inch, V-band exhaust and installed the 3.0 to 3.5 inch Power Cone.

The Power Cone was simply a transition section that stepped up the exhaust to allow installation of a 3.5 inch exhaust. We know that turbo motors respond favorably to increased exhaust flow after the turbo. The Power Cone just provided a nice, smooth transition from the smaller 3.0 inch V-band outlet of the turbine housing to the larger 3.5 inch exhaust.

Run with Power Cone and larger exhaust, two things happened simultaneously. Both the power and boost increased through the entire rpm range. We made no change to the manual boost controller, the added exhaust flow from the Power Cone and larger exhaust we responsible for the change. The boost jumped to a peak of 13.0 psi and the power output jumped to 773 hp and 812 lb.-ft. of torque.

While the power change is a function of the additional boost, the added exhaust flow altered back pressure before the turbo, which altered the wastegate opening, which altered the boost. The bigger exhaust would certainly come in handy at higher power and boost levels, but note that the change increased boost and power through the entire rev range.

turbo cone dyno chart test results
Power Cone Exhaust Test (Turbo 5.3L) – Prior to testing the Power Cones, we started off by running 5.3L in naturally aspirated trim. Run with an aftermarket truck cam, BTR springs, and 1,000cc injectors through long-tube headers, the cammed L33 produced 436 hp and 420 lb.-ft. of torque. We then added the GTX3584RS turbo and an ATW intercooler to the mix. The GTX3584RS turbo was first equipped with a 3 inch V-band exhaust. Run with the 3 inch exhaust, the turbo 5.3L produced 739 hp and 778 lb.-ft. of torque at 11.75 psi. After replacing the 3 inch exhaust with the Power Cone transition section (from 3.0 to 3.5 inch) and adding a section of 3.5 inch exhaust, the power jumped to 773 hp and 812 lb.-ft. of torque. Though we made no change to the manual boost controller, the boost increased by 1.25 psi up to 13 psi. (Dyno Chart/Richard Holdener)
piston and rod removed from engine
The test mule was an all-aluminum 5.3L L33 from the local junkyard. With boost in the cards, the motor was opened up to check for the necessary ring gap. (Image/Richard Holdener)
man holding camshaft near truck
For the Power Cone exhaust test, we equipped the aluminum L33 with a mild truck cam. Almost any milder truck-style cam from Summit Racing or Brian Tooley would provide similar results. (Image/Richard Holdener)
799 casting mark on an ls engine cylinder head
The aluminum L33 motor came factory equipped with flat-top pistons and high-flow, 799 cathedral-port heads. The heads were upgraded with BTR 0.625″ lift springs, if we want to run a bigger cam later. (Image/Richard Holdener)
TBSS installed on an ls engine
Topping the cammed L33 was a Trail Blazer SS intake and 92mm Fast throttle body. (Image/Richard Holdener)
fuel rail with injectors disconnected
To ensure adequate fuel flow under boost (with E85), we equipped the turbo test motor with a set of FIC 1,000cc injectors. (Image/Richard Holdener)
coil packs on an ls cylinder head valve cover
All of our turbo testing was run with factory LS3-style coils. These have proven effective at over 1,500 hp. We liked that coil brackets on these BTR valve covers allowed easy removal of the covers without coil removal. (Image/Richard Holdener)
holley ep efi engine control unit
All tuning was performed by the Holley HP management system. This allowed us to dial in the A/F and timing on our turbo combos. (Image/Richard Holdener)
ls engine with tbss intake on dyno run
The cammed L33 was first run naturally aspirated before installation of the turbo set up for the Power Cone test. (Image/Richard Holdener)
reverse exhaust manifold on ls dyno test
The turbo “kit” consisted of a set of stock truck exhaust manifolds reversed to face forward. (Image/Richard Holdener)
exhaust tubing for ls engine turbo system on dyno
The stock manifolds fed a custom Y-pipe designed with dual waste gate flanges and a single 3 inch V-band for the turbo. (Image/Richard Holdener)
air-to-water intercooler for an engine dyno
To minimize the inlet air temp, we employed this air-to-water intercooler, running dyno water. (Image/Richard Holdener)
turbocharger impeller inside a housing
For the initial test, we equipped the turbo 5.3L with an 800+ hp GTX 3584RS turbo. (Image/Richard Holdener)
turbosmart wastegate installed
Boost was controlled by a pair of Turbosmart 45mm Hyper-Gates. (Image/Richard Holdener)
log manifold installed
The first test involved equipping the turbo with the standard 3 inch V-band exhaust. (Image/Richard Holdener)
exhaust tubing sections on floor
We wanted to compare the standard 3 inch exhaust with a larger 3.5 (actually 3.75 inch) exhaust, but needed a transition for facilitate the test. (Image/Richard Holdener)
turbo cone installed on dyno
The Power Cone was simply a cone section of tubing that transitioned the 3.0 inch V-band flange to the larger 3.5 inch V-band flange and exhaust. The ugly prototype is shown. (Image/Richard Holdener)
turbo cone setup on an engine dyno test
The Power Cone facilitated installation of the larger 3.5 inch exhaust section. The larger exhaust increased response, boost and power all in one fell swoop—see the dyno chart. (Image/Richard Holdener)
looking at a turbo impeller inside the housing
We actually ran a similar test with the larger G42 turbo on the 5.3L with similar results. Turbos like big exhaust! (Image/Richard Holdener)

Keywords
dyno test , turbocharger
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Author: Richard Holdener

Richard Holdener is a technical editor with over 25 years of hands-on experience in the automotive industry. He's authored several books on performance engine building and written numerous articles for publications like Hot Rod, Car Craft, Super Chevy, Power & Performance, GM High Tech, and many others.