Tech Articles

Compound Boost! Turbo/Supercharged 3800 V6 (Part 2)

Every supercharged motor needs the same thing—a TURBO (and more boost)! (Image/Richard Holdener)

Quick, what is the one thing every motor needs?

The answer, as always, is BOOST!

What if your motor already has boost, like the junkyard, supercharged 3800 Series-3 V6 we pulled from the local wrecking yard? I mean, it already has a supercharger, so we are good, right? Yes, and at the same time, a resounding no! You see, having a supercharged V6 is head-and-shoulders better than having a naturally aspirated V6, but that doesn’t mean the boosted V6 can’t respond to even more boost.

Back in part 1, we added boost the way most performance enthusiasts go about it, by increasing the blower speed with smaller blower pulleys. This naturally resulted in more boost and (not surprisingly) more power. But there are limits to the power available from the factory M90 supercharger, and while we were not at the flow (or rotor speed) limit of the blower, we decided to go a different route here in part 2.

To further improve the flow and power potential of the supercharged V6, we decided it needed a turbo, and not in place of the blower, but rather in addition to the blower.

My friends, it’s time for some Junkyard Compound Boost! (Oh, and if you long for video footage of all this testing, check out the Richard Holdener YouTube Channel.)

Not sure on the difference between a supercharger and turbocharger? Read this.

A Quick Refresher Course

Backtracking a bit, we previously pulled this Series-3 L32 3800 motor from a 2004 Pontiac Grand Prix GTP. Thanks in part to the Gen-V M90 blower, the L32 was rated at 260 hp, a 20 horsepower increase over the previous L67 3800. Our junkyard L32 was not without its hurdles, as the stock heads were removed and repaired (valve job and seats) after initial testing revealed low power production.

Fixing the heads resulted in a sizable power gain (video available), but we wanted to make sure we had a healthy candidate for testing. Prior to this adventure, the fuel system on the supercharged L32 was upgraded with a set of 80-pound Accel fuel injectors. This allowed us to safely explore the higher power levels using the extra fuel flow required when running E85. For this test, the motor was configured with the stock Gen-V blower and pulley along with the stock manifolds and cross over pipe, feeding our three inch dyno exhaust (no muffler). Tuning was via a Holley ECU, with air/fuel kept near 11.7:1 (on the gas scale) and the timing (in supercharged trim) starting the load with 18 degrees and rising up to a peak of 23.5 degrees. Equipped with just the supercharger, the 3800 produced 289 hp and 292 lb.-ft. of torque at a peak boost reading of 9.7 psi. Now it was time to add the turbo system!  

Turbocharging the Supercharged Pontiac 3800 V6

Our turbo “kit” for the supercharged 3800 was actually a simple custom fabricated affair that consisted of a GT45 turbo capable of supporting 700+hp on the right application. Though we had no intention of testing the limits of the turbocharger on this supercharged 3800, it is always a good idea to have more turbo than you need to reach your desired power output. The extra torque offered by the supercharger ensured the compound system would have plenty of turbo response.

To make the compound system work, we needed to feed all of the exhaust from the supercharged combination to the turbo. This was accomplished with s simple three inch V-band clamp. We unbolted the exhaust elbow used on the supercharged motor and bolted on the turbo elbow. The elbow used to mount the turbo featured a three inch V-band fitting on one side and a T4 turbo flange on the other. The 90 degree bend allowed us to orient the turbo facing forward, with the exhaust running roughly parallel to the motor (toward the rear of the dyno cell).

The fact that this GT45 turbo was used previously with this elbow on another application, made installation a snap. The GT45 was previously set up with both and oil feed (T-fitting to the dyno oil pressure gauge) and oil drain (welded fitting in the oil pan (thanks Troy). The only thing left was connecting the 3.5 inch turbo exhaust, the Procharger ATW intercooler and remainder of the 3.5 inch aluminum discharge tube (to the modified factory DBW throttle body).

A few important notes are in order here: The first being the boost supplied by the turbo was controlled by a single Turbosmart wastegate. To ensure the turbo supplied a steady 7 psi to the supercharger, the waste gate reference line was run between the turbo and blower. Running the gate reference after the blower would have it open all the time because the blower (almost) always produced more than 7 psi.

The ATW intercooler was fed ambient dyno water for cooling, but the cooling only took place between the turbo and supercharger.

Some Math & The Dyno Result…

While common sense might suggest that if the turbo supplies 7 psi to the 9.7 psi offered by the supercharger, the result would be a combined 16.7 psi, the compound system actually produced a peak of 23.3 psi.

The reason is that in this compound system the pressure ratios are actually multiplied (7+14.7)/14.7=1.476, then (9.7+14.7)/14.7=1.659, then 1.479 x 1.659=2.453, then 2.453 x 9.7 psi gives us 23.75 psi or pretty close to our measured peak of 23.3 psi.

Close enough, especially since we did not directly log the actual pressure supplied by the turbo.

Math aside, adding the turbo to the supercharged combination resulted in a jump in power from 289 hp and 292 lb.-ft. of torque, to 479 hp and 465 lb.-ft. of torque, at our previously discussed peak boost level of 23.3 psi.

Compound Junkyard V6 Boooost baby!      

The best way to increase the power output of any motor is to add boost! That statement holds true even if the motor already has boost, like our junkyard, supercharged 3800 Series-3 V6. Just take a look at the dramatic gain in power offered by the installation of a an expensive GT45 turbo on the already supercharged 3800 V6. Using nothing more elaborate than the factory V6 exhaust system, we used the single (intercooled) turbo to feed (roughly) 7 psi to the M90 supercharger. The result of adding the turbo was to increase the power output of the supercharged V6 from 289 hp and 292 lb.-ft. of torque to 479 hp and 465 lb.-ft. of torque. Of course, this came at a very high 23.3 psi of compound boost, but the combination of intercooling (between the turbo and blower) and the use of E85 allowed us to successfully run this elevated boost and power level. (Dyno Chart/Richard Holdener)
After having no luck with our first supercharged 3800 (Series-2) L67 from the wrecking yard, a second trip netted us a Series-3 L32 from a 2004 Pontiac Grand Prix GTP. (Image/Richard Holdener)
Thanks to the Gen-5 M90 Eaton supercharger, the later Series-3 L32 produced an extra 20 hp (260 hp) over the previous L67 (240 hp). (Image/Richard Holdener)
Knowing we planned on running E85 (which required more fuel flow) AND cranking up the boost, we replaced the factory injectors with a set of 80-pound Accel injectors. (Image/Richard Holdener)
After an impromptu head repair, we installed the near-stock L32 up on the dyno for testing. For testing, we retained the front accessories on the supercharged 3800 V6. (Image/Richard Holdener)
Rather than rely on the stock ECU, we tuned the supercharged V6 with a Holley HP management system. (Image/Richard Holdener)
For this compound turbo/supercharging test, we retained the stock 3800 exhaust system, including the cast-iron manifold feeding the rear tubular exhaust. (Image/Richard Holdener)
Run on the dyno with the stock blower pulley and stock exhaust (on E85), the supercharged 3800 produced 289 hp and 291 lb.-ft. of torque at a peak boost reading of 9.7 psi. (Image/Richard Holdener)
Now it was time for some (cheap) boost. While we might later employ something bigger (like the S475 turbo from Summit Racing), we decided to start with this smaller GT45. (Image/Richard Holdener)
Because the compound boost would be considerably higher with both forms of forced induction, we installed the Procharger ATW intercooler between the turbo and the blower (using ambient dyno water). (Image/Richard Holdener)
Hooking up the turbo was very simple, as the three inch V-band clamp used for the exhaust connected right to the elbow used to mount the turbo. (Image/Richard Holdener)
Ensuring full (post-turbo) exhaust flow was a stainless, 3.5 inch, V-band exhaust. (Image/Richard Holdener)
Controlling the boost supplied by the single GT45 turbo was a 45mm TurboSmart HyperGate. To ensure the gate remained closed until the turbo supplied 7 psi, the wastegate reference was run between the turbo and the supercharger. (Image/Richard Holdener)
The turbo supplied boost through the intercooler via a 3.5 inch aluminum discharge tube. (Image/OnAllCylinders)
The discharge tube was attached to the stock (now drive-by-cable) throttle body. The discharge tube also featured a TurboSmart blow-off valve. (Image/Richard Holdener)
After hooking up the single turbo system to the supercharged V6, the compound system (with 7 psi from the turbo and 9.7 psi from the blower) produced a peak of 23.3 psi in the manifold (under the blower). The result was an increase in power from 289 hp and 292 lb.-ft. of torque, to 479 hp and 465 lb.-ft. of torque. (Image/Richard Holdener)

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