There is nothing better than finding some junkyard V6 boost! (Image/Richard Holdener)

The only thing better than going to the junkyard and grabbing a running motor is to grab a running motor with boost.

Click here to see Part Two of this Compound Boost Series.

While our supercharged Pontiac/GM 3800 Series-3 L32 certainly qualified on both accounts, it was actually lacking slightly in the running department when we made our initial dyno pulls. Sure, it ran, and there was boost, but the power was certainly down from where it should have been given its rated output of 260 hp.

In truth, this was actually our second attempt at junkyard boost, as our first netted the predecessor of our L32, the 240-hp L67 3800 Series-2 V6. Unfortunately, the L67 was down more than a few holes and thus a suitable replacement became mandatory for our Junkyard Boost dyno adventure. After the initial pulls on the L32, we eventually removed and repaired the stock cylinder heads. Thanks goes to Derrick and the gang at L&R Automotive for the quick turnaround on the heads.

After the installation of new valve seats and a fresh valve job, the heads were reinstalled on the awaiting V6 with impressive results. For a full rundown video on the head test, as well other as all the results on this test motor (compound boost!), check out the Richard Holdener YouTube Channel. With 80 pound injectors and a Holley HP management system, the otherwise stock L32 produced 289 hp and 292 lb.-ft. of torque at a peak boost of 9.7 psi.

Improving Power at the Intake

After establishing the baseline, we started looking for ways to improve the power. Knowing that more airflow into the blower equals more boost and power out of the blower, we decided on a radiused air intake as the first modification to the supercharged, junkyard V6.

Pulled from a 2004 Pontiac Grand Prix GTP, the supercharged L32 featured an electronic drive-by-wire throttle body. We replaced the electronics with a simple cable by welding on a throttle arm. This allowed us to mechanically open and close the throttle body. To improve the flow rate of the throttle body, we installed a radiused air inlet using a silicone coupler. While this set up certainly improved the flow rate, the same can’t be said for power production, as the air intake managed to increase the peak power by a scant 2 horsepower (to 291 hp) and 2 lb.-ft. (294 lb.-ft.).

Apparently, the stock throttle body had no trouble supplying the necessary airflow requirements at the stock power level. It should also be pointed out that the motor was run with full accessories, run on E85, and tuned to perfection with the Holley HP management system. The installation of the 80 pound Accel injectors was deemed necessary to supply the additional fuel flow required not only for the use of E85, but we would eventually run more boost and even add a turbo in part 2 (compound boost) coming soon!

Upgrading the Pontiac 3800 Exhaust System

Since the inlet side of the supercharged 3800 netted no power gains, we turned our attention to the exhaust side, and decided to replace the stock exhaust system, including the front, factory cast iron exhaust manifold, the cross-over pipe, and rear manifold and exhaust outlet.

One look at the design of this system should just scream “turbo me!” But instead, we replaced the stock components with tubular headers. Headers are a popular upgrade for the FWD 3800 motors, but we wanted to see just how much power they were actually worth. The only component retained in the header swap was the three inch exhaust used after the three inch V-band. The dreaded factory downpipe was even replaced, as (according to internet lore) this was a sure source of exhaust restriction. The tubular headers offered little in the way of primary length (think of them as a mid-length header at best), we nonetheless had high hopes for power.

Unfortunately, like the air intake, the headers offered only minor changes in power. What did happen, which might certainly be beneficial, is that the exhaust modification actually dropped the peak boost pressure from 9.7 psi to 9.1 psi. We wanted more power, but we will also accept the same power at a lower boost level if it means reduced knock retard in the vehicle.

More Boost!

We obviously saved the big gains for last, as the best way to improve the power output of a boosted junkyard motor is to add more boost!

To that end, we replaced the factory Gen-V blower with another (factory) Gen-V blower. Why the seemingly redundant blower swap? Well, the replacement blower featured a pressed-on drive hub ready to accept bolt-on blower pulleys. Smaller blower pulleys increase the speed of the blower, which adds power and boost.

To get things started, we installed a 3.4 inch blower pulley. This resulted in a jump in boost pressure to 12.8 psi, which pushed peak power to 326 hp and 338 lb.-ft. of torque. As we have come to expect, the pulley swap netted power gains through the entire rev range, from top to bottom.

The next pulley swap, to the smaller 3.2 inch pulley, followed suit, increasing the boost pressure to 15.1 psi. The 3.2 inch pulley increased the power output of the 3800 to 340 hp, while the peak torque checked in at an impressive 359 lb.-ft.. 

No wonder smaller blower pulleys are one of the most popular upgrades available for not only the supercharged 3800 V6, but for most factory supercharged applications. Check back for part 2, where we add even more boost with a single turbo feeding the M90 supercharger. Make sure to check out all the 3800 upgrade videos on my YouTube Channel.

You need to look very closely to see any gains from either the radiused air intake or the tube headers on our supercharged L32 Series-3 3800 V6. Run on the dyno with E85, the stock blower pulley, open throttle body and factory exhaust manifolds, the supercharged V6 produced 289 hp and 292 lb.-ft. of torque. The radiused air intake offered an extra 2 hp and 2 lb.-ft., but the header showed little or no change in power (adding 1 hp and dropping 1 lb.-ft.). The most interesting thing about this round of testing was, despite no change in power, the tube headers dropped the peak boost pressure from 9.7 psi to 9.1 psi. This can come in handy on knock-limited (in car) applications where the stock ECU can pull timing based on knock sensor activation (Knock Retard). (Dyno Chart/Richard Holdener)
After finding limited success with the air intake and headers, we installed a couple of sure things! Increasing the blower speed relative to the motor improves airflow (we see as boost pressure) and therefore power. To replace the factory blower pulley, we actually replaced the factory blower and pressed pulley with another stock Gen-V blower equipped with a hub adapter that allowed simple bolt-on pulley modifications. Our first test was to install the 3.4 inch blower pulley, which resulted in a peak boost pressure of 12.8 psi, and peak power numbers of 326 hp and 338 lb.-ft. of torque. Stepping down to the 3.2 inch pulley resulted in 340 hp and 359 lb.-ft. of torque at a peak boost pressure of 15.1 psi. (Dyno Chart/Richard Holdener)
Pulled from a 2004 Pontiac Grand Prix GTP, the supercharged test motor was a 3800 (Series 2) L67, fresh from the yard. (Image/Richard Holdener)
Though the motor was a runner, it was down on power until we repaired the cylinder heads with new seats and a valve job from L&R Engines (thanks Derrick). (Image/Richard Holdener)
After the head repair, they were reinstalled using fresh Fel-Pro head gaskets. We reused the stock head bolts, but this motor will get ARP hardware soon enough. (Image/Richard Holdener)
The Series-3 3800 featured the upgraded (compared to the previous L67) Gen-5 M90 Eaton supercharger. Thanks in part to the new blower, the L32 offered an extra 20 hp (260 hp) over the previous L67 (240 hp). (Image/Richard Holdener)
To get things started, the 3800 was run with the stock cast-iron exhaust manifolds. (Image/Richard Holdener)
The factory exhaust system featured the cast iron (front) manifold feeding a cross over to the rear manifold assembly and downpipe. We employed a short section of the factory down pipe, attached a three inch V-band and then ran a short three inch exhaust. (Image/Richard Holdener)
Run on the dyno with the stock exhaust, stock blower pulley and open throttle body (converted to cable operation), the Series-3 3800 produced 289 hp and 292 lb.-ft. of torque on E85 at a peak boost of 9.7 psi. (Image/Richard Holdener)
Our first test involved an attempt to improve airflow into the blower with the installation of a radiused air entry on the throttle body. (Image/Richard Holdener)
Unfortunately, the radiused air entry offered only a couple of extra hp, with peaks up to 291 hp and 294 lb.-ft. of torque. Obviously the stock throttle body flowed enough to support the current power level. (Image/Richard Holdener)
Thinking the supercharged motor might respond to improved exhaust flow, we replaced the cast iron manifold with a tubular header. (Image/Richard Holdener)
The rear section was also replaced with a dedicated cross over feeding tubular rear header and downpipe. The three inch dyno exhaust section was retained. (Image/Richard Holdener)
Run on the dyno, the exhaust mod added no power, but did manage to reduce the peak boost pressure from 9.7 psi to 9.1 psi. (Image/Richard Holdener)
Having minimal luck with the intake and exhaust mods, we turned our attention to making more boost. This was accomplished by replacing the factory blower and pressed-on factory pulley with another stock M90 equipped with a pulley hub that allowed bolt-on pulley swaps. To start, we installed the 3.4 inch pulley, then dropped down to the 3.2 inch pulley. (Image/Richard Holdener)
The increased airflow and boost pressure offered by the blower pulleys resulted in sizable power gains. Equipped with the 3.4 inch pulley, the supercharged V6 produced 326 hp and 338 lb.-ft. of torque. These numbers jumped to 340 hp and 359 lb.-ft. of torque with the installation of the 3.2 inch pulley. (Image/Richard Holdener)

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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.