What is the best way to make more power with a supercharger?

The most obvious answer is to simply to add more boost, right? I mean if seven psi is good, then ten psi must be even better! This stands to reason, as more boost usually adds more power.

But what happens when you can no longer add boost? What happens when you are at or near the rpm and/or flow limit of the supercharger? What happens when you can’t simply crank up the blower speed to add boost? Does that mean there is no more power to be had?

The reality is that the flow rate of a supercharger is a function of many things, including the size of the blower, the speed of the blower, and (drum roll please…) the power output of the motor you apply the blower to!

Working with blower size and speed (relative to engine speed), the final element helps determine the boost pressure supplied by the blower. Since boost is actually a measurement of a restriction inherent in the system, lowering boost (at the same blower size and speed) can actually improve the flow and power supplied by said blower.

What manner of sorcery is making more power with less boost? Let’s check out how we waved our proverbial magic power wand to coax over 600 hp from a junkyard M90 blower.

Getting 600 HP from a Junkyard M90 Blower

The quest came about after running a junkyard Gen. V M90 on our 4.8L LS.

Originally designed for the 260 hp 3800 V6, the Gen. V blower was modified with minor porting to the opening, the installation of a larger 92mm throttle body, and (of course) spinning the snot out of it with a 2.6 inch blower pulley and 7.5 inch crank pulley. Using a Super Richie adapter plate, the V6 blower was bolted to the 4.8L V8 equipped with a Holley Hi Ram intake (but it also works with a Lo Ram).

The 4.8L test motor also featured a revised cam and valve springs from BTR, 1-7/8 inch long-tube headers, and Holley HP management system controlling the 80 pound injectors. Run in naturally aspirated trim, the modified 4.8L produced 411 hp and 355 lb.-ft. of torque. After installation of the Eaton M90 blower and 92mm throttle body, the peak power jumped to 537 hp and 491 lb.-ft. of torque at a peak boost near nine psi (but a falling boost curve near eight psi).

The question now was, how could we further increase the power output of the M90 combo? While we considered ported heads and wilder cam timing on the 4.8L, we already had a test motor so equipped, and it was bigger to boot!

supercharged ls engine on a dyno during test run
How do you make even more power with a junkyard M90 blower? Easy, just make the test motor bigger and better! (Image/Richard Holdener)

Enter the 5.3L L33

An original score from a local wrecking yard, the 5.3L L33 had been subjected to all manner of performance upgrades, including turbos, nitrous, and many, many different cam profiles. In its latest configuration, it was sporting a very big cam, ported heads, and a BTR Trinity intake, which allowed it to make 552 hp. For our blower test, we obviously needed to swap out the short-runner BTR intake in favor of the Hi Ram that allowed installation of the Super Richie adapter plate and M90 blower.

Considered big for a 5.3L, the BTR Stage 4 LS cam featured 636 lift (intake and exhaust), a 233/25X duration split and 113 LSA. The added Trick Flow 220 as-cast heads were no longer as cast, as the boys from BTR subjected them to both porting and milling. When combined with the Holley Hi Ram intake, the NA 5.3L produced peak numbers of 545 hp and 428 lb.-ft. of torque, bettering the milder 4.8L by 134 hp.

The question now was how would this change in NA power translate to power once we added the junkyard Gen. V M90 blower?

Adding the Supercharger

To find out, we installed the awaiting M90 supercharger, but not before making a few changes.

Since the boost and power provided by any positive displacement supercharger was a function of the airflow into the blower, we further increased the flow rate of the M90. The port-matched (factory) throttle entry was first cut off on the bandsaw, then milled by Gary and John at Accufab Racing. The ball-milled opening (near 92mm) was then blended (by yours truly) using a head porting aluminum bit and more than a few cartridge rolls.

The final step was to have Jason at JTFab weld on a short section of 3.5 inch aluminum tubing, to which we could install our throttle body adapter designed to accept either a 92mm or 102mm throttle body. This configuration allowed us to orient the throttle body in any position to facilitate the throttle linkage.

The final mod was to sandwich a Tick ATW intercooler core (designed for 1,000+ hp turbo LS applications) between the adapter plate and Holley Hi Ram. Our custom Super Richie plate presented a problem, as it positioned the discharge of the blower within a half inch of the intercooler core, meaning the blower was only using roughly one-third of the available surface area of the core. We plan to rectify this situation later with a much taller spacer, but run in this manner, the core still managed to drop the air temps of our low-boost (six psi dropping to just four psi) M90 5.3L from 162 degrees to 90 degrees.

The Dyno Results

The intercooled 5.3L M90 combo exceeded 600 hp, with a peak of 614 hp and 547 lb.-ft. of torque.

It is amazing that the junkyard M90 can support this power level, and we feel that there is even more to be had with additional porting (blower already shipped off to Jokerz Performance for internal porting).


engine dyno chart
This graph illustrates the differences in power offered by our two test motors. This comparison was not simply a change in displacement, but the change in naturally aspirated power output, part of which included the change in displacement. The 4.8L was equipped with a milder (BTR Red Hot) cam, 799 heads (which added no power over the stock 706 heads), and the Holley Hi Ram intake. Equipped with the 1-7/8 inch headers and mufflers, the 4.8L produced 411 hp and 355 lb.-ft. of torque. By contrast, the 5.3L was equipped with a much larger (BTR Stage 4 LS3) cam, ported and milled Trick Flow 220 heads, and the same Holley Hi Ram. The larger 5.3L produced 545 hp and 428 lb.-ft. of torque. The difference between our NA test motors was a solid 134 hp! (Dyno Chart/Richard Holdener)
engine dyno chart 2
After adding the M90 supercharger to the mix, the difference in power between the two combos continued. Though the 4.8L runs featured a mildly ported entry and 92mm throttle body, the 5.3L runs featured additional porting to the entry. In fact, the ported throttle body flange was cut off, the opening milled and then a 3.5 inch section of aluminum tubing was welded in place. This was done in preparation for internal porting from Jokerz Performance (to be tested later). Run on the 5.3L with the modified M90 and Tick ATW intercooler, the power output jumped to 614 hp and 547 lb.-ft. of torque. The NA 5.3L made 134 hp more than the NA 4.8L, but only increased the power output by 77 hp under boost. Clearly we were getting near the flow limit of the little M90, but over 600 hp was still pretty impressive. (Dyno Chart/Richard Holdener)
close up of intake on an ls engine on dyno
The 4.8L test mule was equipped with 799 heads, a BTR Red Hot cam and Hi Ram intake manifold. Run in this configuration, the naturally aspirated 4.8L produced 411 hp and 355 lb.-ft. of torque. (Image/Richard Holdener)
adapter plate template on an intake manifold
The Hi Ram intake allowed us to employ this (Super Richie prototype shown) adapter plate designed to allow installation of the junkyard M90 supercharger. (Image/Richard Holdener)
blower mounted atop an ls engine
Using the adapter plate, we installed the Gen V. blower from a factory supercharged L32 3800 V6, pulled from a scrapped Pontiac Grand Prix GTP. (Image/Richard Holdener)
man tuning engine at a computer
All tuning for the E85-equipped, supercharged motors (both the 4.8L and 5.3L) came from a Holley HP engine management system. (Image/Richard Holdener)
close up of fuel injector on an engine
To ensure adequate fuel flow for our supercharged combo using E85, we ran these 80 pound Accel fuel injectors. (Image/Richard Holdener)
exhaust headers on an ls engine on a dyno
The exhaust system consisted of a set of 1-7/8 inch, long-tube Hooker Headers feeding simple collector extensions and Magnaflow mufflers. (Image/Richard Holdener)
close up of blower pulley installed with belt
The blower was equipped with a ZZP 2.6 inch blower pulley combined with the factory truck damper. The pulley combination produced a peak blower speed near 18,700 rpm at our engine speed of 6,600 rpm. (Image/Richard Holdener)
serpentine belt with supercharger on an ls engine
The M90 blower was driven off the same six-rib belt used for the alternator, power steering, and factory water pump. For this test, the alternator was eliminated. (Image/Richard Holdener)
supercharged engine on a dyno test run
Run with the M90 blower producing a peak of nine psi, the supercharged 4.8L maxed out at 537 hp and 491 lb.-ft. of torque. (Image/Richard Holdener)
btr camshaft in a box
The L33 was equipped with a BTR Stage 4 LS3 cam that offered 636 lift (intake and exhaust), a 233/25X duration split and 113 LSA. (Image/Richard Holdener)
trick flow cylinder head installed on an ls engine
Additional upgrades to the 5.3L included a set of Trick Flow as-cast 220 heads that received further porting from the gang at BTR. (Image/Richard Holdener)
combustion chamber in a cylinder head
In addition to the porting, the TFS cylinder heads received milling and chamber work to further enhance the NA power output. (Image/Richard Holdener)
intake manifold on an ls engine with top removed
Like the 4.8L, the 5.3L was first run in naturally aspirated trim with a Holley Hi Ram intake. (Image/Richard Holdener)
holley efi throttle body installed
The Holley Hi Ram was configured with a 105mm throttle body. (Image/Richard Holdener)
ls engine on a dyno test run
Run on the dyno in naturally aspirated trim, the modified (but still stock bottom end) 5.3L produced peak numbers of 545 hp at 7,300 rpm and 428 lb.-ft. at 6,100 rpm. (Image/Richard Holdener)
throttle body port on an intake manifold
Prior to running on the 5.3L, we modified the entry of the M90 supercharger even more. The mods included cutting off the throttle body mount and milling (thanks to Gary and John from Accufab) the opening to accept a 92mm throttle body. (Image/Richard Holdener)
drive by cable throttle body getting installed
Jason from JT Fab then welded on a 3.5 inch stand-off to allow us to mount the throttle body with a silicone coupler. (Image/Richard Holdener)
heat exchanger installed on a blower
Though our boost was considerably lower (down to six psi) on the more powerful 5.3L, we decided to try this ATW intercooler from Tick Performance. The 1,000+ hp intercooler was overkill on this application, but it did drop temps from 162 to 90 degrees. The proximity of the blower discharge to the core likely hindered its flow potential. (Image/Richard Holdener)
supercharged ls engine during dyno test run
Run on the dyno with the M90 and Tick intercooler on E85, the supercharged 5.3L produced 614 hp and 547 lb.-ft. of torque. The boost curve dropped from six psi down low to a max of just four psi at the hp peak, but we now know the junkyard blower will support 600+ hp! (Image/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.