Retro 5.0 Makes Over 800 horsepower With A Vortech Supercharger

Last month, we brought you Project Retro 5.0 and its naturally aspirated story arc. A simple Trick Flow 11R top-end kit with a Stage-1 camshaft and Holley SysteMAX intake manifold netted way more power than the top-end kits of yesteryear advertised. So, it should come as no surprise that when adding a supercharger, the numbers would be equally impressive.

Back in the heyday of the Fox body, it was often a question of “heads, cam, and intake” or “blower”. However, if you opted for the former, you were usually going to end up adding the latter, because — let’s face it — there is no such thing as enough, especially after you’ve gotten used to your newfound power. So, in that same vein, we did what any Mustang enthusiast would do in the ‘90s. We called up Vortech Superchargers.

The Venerable S-Trim And Its Successor

For a brief history lesson, let’s look at the infamous S-trim blower from Vortech. This is important because it is the bar that most power adders were measured by back in the day. The original V-1 S-trim blower was advertised as having a peak efficiency of 72 percent, and could be spun to 50,000 rpm, moving 1,000 cfm of air at 20 psi, for a rated maximum output of 680 horsepower. While looking at those numbers today might not seem all that impressive, back in the 1990s, it was a beast.

There have been several successors to the original S-trim over the decades, with the latest being the Si-trim impeller design. The new compressor design bumps the maximum impeller speed up 2,000 rpm to 52,000 rpm. Maximum boost pressure is now listed at 22psi, with a maximum efficiency of 78 percent. All of those efficiency improvements add up to a new listed peak airflow of 1,150 cubic feet per minute and a maximum horsepower of 775.

Retro 5.0 Vortech Si-Trim Supercharger

The Vortech V-3 Si-Trim supercharger is the same physical size as the original V-1 S-trim blower, but has enjoyed 30 years of advancements in gearcase and compressor wheel design.

More than just a compressor upgrade, the Si-trim supercharger is available in both V-2 and V-3 gearcase designs. The V-2 is an improved version of the original engine-oil-fed V-1 gearcase, while the V-3 is Vortech’s latest self-contained-oiling gearcase design. The self-contained design makes installation incredibly easy and straightforward. There is no performance difference between the V-2 and V-3 on the airflow side, it’s simply differences in the gearcase.

The V-1, V-2, and V-3 superchargers all have the same inlet and outlet sizes, which not only allow for upgradability without having to change a lot of bracketry, but has also allowed the supporting components to stay the same. The Fox-body kit built around the S-trim has more or less withstood the test of time, being materially the same today as it was in say, 1996.

What Comes In The Kit And The Installation Process

Since we already have a Holley Terminator X system installed and running Retro 5.0, we opted for the tuner kit, which doesn’t include any form of fuel management components. What the kit does come with is so well engineered, it made the installation the easiest part of working on the engine the whole week.

Included with the supercharger unit itself is a mounting bracket for the supercharger that relocates the alternator and smog pump (more on that in a bit), a new crank pulley that incorporates both the serpentine drive and the blower drive, on separate belt systems, a cast discharge tube with a fitting for the included recirculator valve (which is especially important in a mass-air application), a tensioner relocation bracket, the appropriate supercharger belt, a piece of pre-bent hard tubing to replace a section of radiator hose, and all of the required hardware for everything. The kit is incredibly complete, with nothing left to source yourself.

The included crank pulley incorporates not only the serpentine drive pulley, but the blower drive as well.

Now, we mentioned the smog pump earlier. This is important because Retro 5.0 isn’t running a smog pump. While that might not seem like a big deal, the smog pump housing acts as a structural member in the mounting of the alternator with the kit. While the parts store had a smog pump in stock, we were able to repurpose our Powermaster billet alternator mount and eliminate the need for the smog pump entirely.

Other than that, the only other hiccup we ran into was that we were already running our belt tensioner in an air-conditioning eliminator bracket. So when we used the provided tensioner relocation bracket, our routing was a little off. We simply made an additional idler out of a spare pulley, a bolt, and some hex stock to gain the belt routing we needed. As long as you are installing the kit as it was designed, you’ll never even know these issues exist, but since we’re not running a stock application, we figured we’d mention the hiccups and how simply they were resolved.

With the supercharger kit installed, it was simply a matter of running to the parts store for a new serpentine belt (which was needed thanks to our custom accessory routing) and then firing up the dyno.

Here you can see the blower mount bracket that normally incorporates the smog pump as a structural component in order to mount the alternator. However, we were able to reimagine Powermaster's high-mount alternator bracket components in a way that works with the Vortech kit, and doesn't need a smog pump.

A quick recap of the engine configuration as it sits. Using an F1SE block and E7AE crank out of a 1993 Thunderbird, a set of flat-top ICON forged 2618 pistons are hung off of a set of super-budget Speedmaster connecting rods (we paid $138 for them on Black Friday), with coated Clevite H-series bearings throughout. A Trick Flow Stage-1 cam is part of the 11R top end kit we installed, topped off with a Holley SysteMAX intake manifold with BBK 75mm throttle body and EGR spacer. The engine is also still running the same 1-5/8-inch JBA GT-40P shorty headers for a 1965-’73 Mustang that we baselined with.

Making Noise On The Dyno With Retro 5.0

You might remember from earlier installments of Retro 5.0, that we sized our Deatschwerks fuel injectors to match the listed maximum output of the supercharger on E85 — that is 78 lb/hr of flow at 43.5 psi. Originally, we had planned to start on 93 octane and then add BOOSTane Professional before switching to BOOSTane’s Race E85. However, circumstances kind of changed the plan slightly.

With your author and Director of Editorial, Brian Havins, left to our own devices on the dyno due to circumstances beyond anyone’s control, we decided to start with the safest, most forgiving option, and then let KPE Racing’s namesake, Tommy Keeter, go back and complete the fuel testing at a later date (so keep an eye out for that article coming soon).

BOOSTane’s E85 Race is proving its mettle once again in a big-power EngineLabs project. Some love the corn juice, some hate it, but the fact is, it’s the easy button in a lot of situations.

BOOSTane’s Race E85 is, as the name suggests, a premium ethanol-based fuel consisting of 85 percent ethanol and 15 percent 105-octane race gas. Besides the octane advantage, the E85 offers increased cooling effects thanks to the ethanol’s increased latent heat of evaporation – or how much energy it absorbs as it is vaporized. While E85 won’t act as a replacement for an intercooler like methanol can, it will certainly help keep temperatures in check, since we are running the non-intercooled supercharger configuration on Retro 5.0. Although, Vortech’s are known for their control of post-compressor temperatures, and we never ran into any IAT concerns throughout testing.

With E85’s altered stoichiometric ratios compared to gasoline, normally you need to do some math, but the Holley software made it easy, simply noting the fuel switch and offering to automatically update the fuel maps accordingly. After starting the engine with the supercharger and ensuring that everything was operating as expected, we made our first tentative pull.

Our Si-trim supercharger has the stock 3.33-inch-diameter blower pulley on it. We actually reached out to Vortech to make sure that we had the right pulley after seeing the boost numbers. They explained that the kit is designed around the stock Fox-body rev-limiter and that at 7,000 rpm engine speed, 17 psi is totally normal.

Now, before we made any pulls, we were looking at what Vortech advertised the kit as making on stock engines, and doing some calculations based on projected boost levels and what Retro 5.0 made naturally aspirated. We all had a conservative number in our heads of what we were hoping to make. Well, that went right out the window after the first super-conservative pull. The dyno showed 631.3 horsepower and 589.5 lb-ft of torque. So much for our guesses.

The next pull saw us pick up 15 horsepower and 15 lb-ft with minor changes. After a few more pulls, where the engine just seemed to love everything we gave it, we were sitting at an impressive 687.5 horsepower and 616.6 lb-ft of torque, at about 11 psi, only turning the engine to 6,500 rpm. We were more than 15-percent over the power number we all quietly expected, and everything was going a little too smoothly. Reality started to creep into the back of our minds, and both Havins and your author decided to take the W, and leave Retro 5.0 in one piece for Tommy to take care of the fuel testing with.

Retro 5.0 on the dyno.

All the belts routed, tensioned, and ready for the dyno.

Experience Proves Invaluable For Retro 5.0

Once Tommy got to the engine, he noticed that the coupler from the supercharger outlet to the intake tube was askew. We noticed that as we were wrapping up the dyno and assumed that it had happened on decel from the last pull, as we were seeing 11 psi, and the kit was advertised as a 9-10 psi kit. Well, we were wrong. Once Tommy resealed the coupler and made a 6,500 rpm pull, he saw closer to 15 psi. So, it was time for him to work his magic on the keyboard and clean up the map north of 11 psi, and start leaning on it.

While we might not have had the confidence in our plug reading skills to trust that there was more timing to be put into it, Tommy suffers from no such insecurities and confirmed that there was room for a few more degrees. After a few more pulls, he sent your author some updates via text message indicating that not only had he made an additional 100 horsepower from the combination, but that he thought there might be some more in it.

The Holley Terminator X really made tuning this combination incredibly simple. The software is an interesting mix of user-friendliness combined with a lot of powerful, advanced capabilities.

We had a quick conversation, because at this point, we were beyond the listed maximum horsepower of the Si-trim supercharger (but not near the max boost pressure) and the rated capacity of the injectors. However, your author was getting genuinely greedy, being so close to that magical 800 horsepower number. Tommy confirmed that upping the base fuel pressure would safely extend the injectors’ capacity, and that adding a few hundred RPM would give us a little extra boost from the supercharger.

However, his concern was a flat spot appearing at the top of the curve, which might be valvesprings losing control of the valvetrain. While I’d like to say that I had some kind of insight or knowledge that the flat spot was just a flat spot in the map, in reality, I didn’t care. We had come this far, the block was in one piece, and in the back of my head, I thought, “what’s the worst that happens on a single run where we float the valves?”

After we threw in the towel, Tommy Keeter of KPE Racing managed to find another 140 horsepower in the combination.

Whether Tommy agreed with my logic or just wanted to see what would happen at 7,000 rpm, he reset the sweep range on the dyno, and let her eat. The result? Well, the engine worked through the flat spot and started making power again. To the tune of 828.9 horsepower at 7,000 rpm and 673 lb-ft of torque at 6,100 rpm, while registering 17 psi of boost pressure.

Hero run accomplished, it was time to stop for the day, as there was still 93-octane testing to be done with the engine, and the engine was in one piece. So, that’s where it ended. 829 horsepower, the stock 5.0L block is still apparently in one piece, and our $138 Speedmaster Black Friday connecting rods were still in the block, all with zero indications of any problems in the engine.

Retro 5.0 dyno graph

Here’s the final result: 828.9 horsepower at 7,000 rpm, and 673.3 lb-ft of torque at 6,100 rpm. We’ve come a long way from that baseline pull of 260 horsepower in a short amount of time.

While we won’t spoil everything, we will share that the engine successfully completed quite a few more pulls at full-boogie for the fuel testing with no apparent issues. We’ll be conducting a full teardown of this engine in an upcoming article. While it seems like a shame to take apart a perfectly good 800-horsepower engine, the fact is, that there is no way I’d ever be comfortable putting this in my car, as I’d expect it to be a time-bomb, just wondering when, not if, the block decided to let go.

So, while part one of the project is over — with more success than I could have ever asked for from this little 302 — Retro 5.0 is far from dead. So that we can finish testing the modern parts we already have (we never expected to make so much power so early on in the project) we’re going to put together a short-block capable of taking anything we can throw at it.

Our new goal is to build an incredibly modern small-block Ford that blows past the 1,000 horsepower mark — since it seems that everyone is making that these days. We’re thinking 1,200 horsepower sounds like a nice round number to us. So stick with us as we continue on our journey with Retro 5.0.

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About the author

Greg Acosta

Greg has spent nineteen years and counting in automotive publishing, with most of his work having a very technical focus. Always interested in how things work, he enjoys sharing his passion for automotive technology with the reader.
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