Tech Articles

Clash of the Turbo Titans: Summit vs. eBay Turbos

Cost favors the GT45, but how does the eBay turbo compare to the Summit turbo on the dyno? (Image/Richard Holdener)

Turbos rule.

If you’re a turbo guy (or gal), there has never been a better time to be an enthusiast. Just look around, turbos are everywhere and on everything.

Not long ago, many people didn’t even understand how turbochargers work, let alone attempt to install them on their hot rod. Unless your name was Gale Banks or Corky Bell, you left turbos alone.

Fast forward a few decades and the advent of automotive internet forums, YouTube, and eBay have ushered in the modern turbo era.

Never in history have turbos been so available and affordable, but it is this over-abundance that creates confusion. The massive availability of cost-effective, offshore turbos has everyone jumping on the boost wagon, but many are doing so without a basic understanding of the differences between various turbo offerings.

The offshore turbos have many enthusiasts selecting them based solely on price—because a turbo is just a turbo, right?

While everyone wants a good deal, there is more to turbo selection than simply price.

To illustrate the difference a turbo cam make, we selected a pair of popular turbos, one from eBay and the other from Summit Racing. Though eBay doesn’t manufacture their turbos, this popular GT45-style turbo offered the best combination of price and power potential.

To ensure the turbos were run with proper cam timing, we installed the Summit Pro LS Stage 3 turbo (specific) cam that offered a .600/.575 lift split, a 231/234-degree duration split and 115 +5-degree duration split. (Image/Richard Holdener)

This turbo can be sourced through a variety of resellers, as most repackage or simply resell the same product under their own name. Our eBay turbo actually came from the folks over at DNA Motorsports.

There might be some confusion about this turbo, as there seems to be different versions available. If our spec sheet is to be believed, our GT45 featured a 50-trim compressor wheel, with a 68.9-mm inducer, and 98-mm exducer.

The T4 exhaust featured a 1.05 A/R ratio, an 88.7-mm inducer, and 77.5-mm exducer. Though offered at a variety of different price points, ranging from our cost of $163 to over $400, the eBay turbo was certainly affordable.

On the hot side, the T4 eBay turbo featured a 1.05 A/R, 88-mm inducer and 77.5-mm exducer. The hot side was set up to accept a 3.5-inch exhaust using the cast V-band flange. (Image/Richard Holdener)

By contrast, the $649 S475 turbo offered by Summit Racing was considerably more expensive.

The spec sheet on the Summit turbo made up for at least some of the cost difference, as the T6 turbo offered a larger 75-mm inducer, and 100-mm exducer on the compressor side and a hot side equipped with an 88-mm exducer, and 96-mm inducer. The T6 housing also featured a 1.32 A/R ratio to further improve exhaust flow.

Out back, the hot side featured a 96-mm inducer and 88-mm exducer. The larger V-band flange accepted up to a 5.0-inch exhaust. Honestly, we’d like to see something smaller made available on the Summit turbo (even a T4 housing), as there is often little room to run a 5-inch exhaust, and the 4.5-inch (or even 4.0-inch) exhaust will not limit power with this turbo. (Image/Richard Holdener)          

Spec sheets are all well and good, but how do they actually perform?

For most people, a turbo is just about boost, more boost equals more power, right?

I mean, all you have to do is keep cranking up the boost, and the turbo will keep making more power.

Neither of the turbos were supplied with oil feed or drain fittings, so make sure you get them before attempting installation. (Image/Richard Holdener)

Unfortunately, like any air pump, there is a limit to how much a turbo will flow.

Forget about the boost and think more about airflow.

A turbo will only flow so much, and boost is simply a measurement of the restriction inherent in the engine it happens to be flowing air into. At some point, the turbo will be unable to flow additional air, either because of a limitation in the compressor or turbine side, and then boost will drop.

This is exactly what we saw in this comparison, but first we need to quickly cover the test engine.

The 5.3L LM7 Test Engine

The test motor was a 5.3L equipped with forged K1 rods, Wiseco pistons and a set of TFS 205 heads. (Image/Richard Holdener)

On loan from Roadkill’s David Freiburger, the 5.3L LM7 featured a stock block and crank combined with forged rods and pistons. The powdered-metal rods and cast pistons were ditched in favor of a set of 6.125-inch, K1 rods and Wiseco forged pistons. The motor also received a set of TFS 205 heads and FAST LSXR induction system. In addition to the intake, FAST also supplied a set of coils, injectors and a 102-mm, Big-Mouth throttle body.

On loan from Roadkill’s David Freiburger, the 5.3L LM7 featured a stock block and crank combined with forged rods and pistons. The powdered-metal rods and cast pistons were ditched in favor of a set of 6.125-inch, K1 rods and Wiseco forged pistons.

The motor also received a set of TFS 205 heads and FAST LSXR induction system. In addition to the intake, FAST also supplied a set of coils, injectors and a 102-mm, Big-Mouth throttle body.

To ensure plenty of flow for both turbos, we also installed this FAST LSXR intake and matching 102-mm throttle body. FAST also supplied the necessary 89-pound injectors. (Image/Richard Holdener)

Because we were testing a pair of turbos, naturally we needed some kind of turbo kit.

Less a kit then a DIY project, the turbo system consisted of a pair of stock truck exhaust manifolds feeding a custom Y-pipe.

The DIY turbo system featured a pair of forward-facing, stock truck manifolds. Basically we just swap sides on the manifolds. (Image/Richard Holdener)

The Y-pipe merged the exhaust flow from each bank of cylinders in the V8 to a single three-inch, V-band outlet. The three-inch V-band was used to allow us to run both T4 and T6 turbos, using the respective adapters.

The key to the DIY turbo kit was this custom Y-pipe that merged the exhaust flow from the two banks of cylinders to a common outlet. (Image/Richard Holdener)
We equipped the Y-pipe with a single, three-inch V-band flange. We did this to facilitate installation of both T4 and T6 turbos using custom adapters. (Image/Richard Holdener)

One of the mistakes we made—and why there will be a part two follow-up to this test—is that we relied on a manual waste-gate controller to raise the boost.

To adjust the boost pressure up from the 7-psi springs run in the TS waste gates, we ran this manual waste-gate controller. This was our first mistake in this test, as it did not provide flat, consistent boost curves, though the comparison between the absolute flow of the turbos was pretty evident. (Image/Richard Holdener)

The manual controller resulted in slightly different boost curves for the two turbos, despite the use of a pair of Turbo Smart Gen-5 waste gates.

Controlling boost was a pair of Gen-V, HyperGate45 waste-gates from Turbo Smart. (Image/Richard Holdener)

Boost from each of the turbos was run through an air-to-water intercooler from ProCharger. Both turbos were run with the same 11.8:1 A/F ratio and with 20 degrees of total timing at the power peak (less at the torque peak). With our DIY turbo system ready to accept both turbos, it was time to test.

Turbo Smart also supplied this blow-off valve (BOV). This OG design has long since been replaced by a much slicker, and more effective version, but we keep using it because it keeps working! (Image/Richard Holdener)
Both turbos were run through this air-to-water intercooler from ProCharger. We’ve run this cooler on 1,300-hp applications with good results, so it represented no restriction at the lower power levels produced by these turbos. (Image/Richard Holdener)

eBay GT45 Turbo Test

First up was the eBay GT-45 style turbo. According to the listed specs, this T4 turbo offered a 50-trim wheel with a .66 A/R, 68.9-mm inducer and 98-mm exducer. (Image/Richard Holdener)

First up was the eBay GT45 turbo. To ensure we had the tune nailed down, we started out running on the waste-gate springs of 7 psi. Using the manual controller, we raised the boost pressure until we started to get diminishing returns from the turbo.

Installation of the T4 turbo was made easy using this T4-to-3-inch V-band adapter we fabricated. The same thing was done for the T6 Summit turbo. (Image/Richard Holdener)

After reaching a peak boost of 14.5 psi early in the run, the boost pressure dropped down to just 10.1 psi at 6,500 rpm. The falling boost curve produced a peak power reading of 776 horsepower at just 5,600 rpm. The upside to having lots of boost at lower engine speeds was a healthy peak-torque reading of 786 foot-pounds at 4,500 rpm.

To give you an idea, run naturally aspirated, this combination would make peak power closer to 6,500 rpm, so the turbo and dropping boost curve were definitely altering the power curve. Though available maximum flow, from what is likely an 800-hp turbo, was certainly the major contributor, the method of boost control was also a factor.

We ran the eBay turbo on the dyno at various boost levels, keeping the A/F ratio at 11.8:1 and the total timing (at the power peak) at 20 degrees. We eventually ran the boost as high as 14.5 psi, but the eBay turbo did not maintain this boost level out to the power peak. Thanks to a lack of flow potential and our boost control method, the boost dropped from a high of 14.5 psi down to just 10.0 psi at 6,500 rpm. The boost pressure registered 10.6 psi at 5,600 rpm, where the little eBay produced peak power readings of 776 hp and 786 ft.-lbs. of torque. (Image/Richard Holdener)

Had we run an electronic (three- or four-port) boost controller, the boost curve would be more consistent. We know the eBay turbo should be able to run a consistent boost level of 10 psi, but we doubt it will go more than one or two extra psi before it runs out of flow.

Summit Racing S475 Turbo Test

Next, we installed the larger S475 turbo from Summit Racing. The T6, S475 featured a compressor wheel with a 75-mm inducer and 100-mm exducer. (Image/Richard Holdener)

After running the eBay GT45 turbo, off it came and on went the T6 Summit S475 turbo. The turbo was configured to flow through the same ProCharger intercooler and was run at a variety of different boost levels up to a peak of 17.3 psi.

Because the larger S475 turbo was capable of supporting more power, the boost curves were slightly flatter on the Summit turbo. It wasn’t until we ran the boost up that we started seeing a dropping curve, but nowhere near as dramatic as the smaller turbo.

Run at a peak boost of 17.3 psi (at 3,700 rpm), the boost dropped to 14.7 psi at at 6,500 rpm. The dropping boost curve meant the turbo motor produced peak power at 6,100 rpm, but this was still at a higher engine speed than the smaller GT45 turbo. Even with the dropping boost curves, it is obvious the Summit turbo had more to offer than the smaller GT45, so if all you need is 800 (flywheel) hp, then go for the eBay unit. If, like most turbo owners, you plan on cranking it up, then the Summit turbo is definitely worth a look.

The more expensive Summit turbo showed why it cost a little more, as it allowed the 5.3L test motor to exceed 920 hp, with peaks of 922 hp and 886 ft.-lbs. of torque. The Summit
turbo allowed us to run the boost as high as 17.3 psi, but, like the eBay turbo, the falling boost curve dropped the pressure to just 15.3 psi at the power peak. We plan to redo this test with a three-port, electronic waste-gate controller to get a better handle on the boost curves, but we still expect the difference between the turbos to be somewhere near 200 hp! (Image/Richard Holdener)     

On our next test, we plan to monitor the backpressure to show how the power output affects the exhaust flow, and therefore the backpressure. This backpressure works to open the waste-gate valve, reducing the boost. With boost pressure applied to the top of the valve, we hope to counter this effect, but the change in boost curves and absolute max outputs will have to wait until next time.

5.3L Turbo Test: EBay GT45 vs Summit S475 (HP & Torque)

In an all-out power comparison between the eBay and Summit turbos, there really was no contest. The Summit turbo was able to supply more boost, and therefore more power than the smaller eBay GT45. The question about maximum power has obviously been answered, as the Summit turbo produced 922 hp to just 775 hp for the eBay GT45. The real question might be, how much power do you really need? Are you looking for 1,000 hp, or will your needs be served by a less-expensive turbo, good for only 800 horsepower? If all you ever want is 600-700 wheel hp, then the eBay GT45 might be a good choice. It should be pointed out that this dyno test tells us nothing about the quality, reliability or warranty offered by either of the two. The problem that often occurs when selecting a turbo good for 800 hp, is that once we get there, we almost always want to go up! More power costs more money! (Image/Richard Holdener)

Boost Curves — 5.3L Turbo: eBay GT45

These graphs show the changes in the boost curves created by our manual boost controller. By adjusting the controller (bleeding the boost signal), we tricked the waste gate into staying closed longer, thereby raising the boost. These graphs show the different boost curves generated by the eBay GT45 turbo. Note that as we raised the boost pressure, the boost increased much more at lower engine speeds that at the top of the rev range. This is an indication that we were getting near the flow limit of the turbo, but it also hinted at a possible increase in backpressure. Increased backpressure would tend to open the waste gate sooner. An electronic controller should cure this problem and allow us to produce a flat curve and explore the absolute limits of the GT45 turbo. Even with the change, we still don’t expect much over 800 hp. (Image/Richard Holdener)

Boost Curves—5.3L Turbo: Summit S475

The boost curves posted by the Summit Racing turbo showed a slightly different trend, as they started basically flat at lower boost and power levels. It wasn’t until we cranked up the boost that we started seeing a more pronounced dropping boost curve. If we compared both turbos at a peak of 13.5 psi, the boost dropped by over 3 psi on the smaller GT45 turbo, but less than 2 psi on the Summit turbo. Like the eBay GT45, we suspect the increased backpressure brought about by increased exhaust flow (from the higher power level) played a part in the shape of the curve. With flat boost curves from an electronic controller, we hope to push this Summit Turbo over the 1,000-hp mark. (Image/Richard Holdener)
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4 Comments

  1. Is it worth it compared to the ease of install and low cost of nitrous?

  2. Wait… Two different size turbo’s? How is that a “comparison”? Forget about the boost controller, that’s the least of your worries.

  3. This composition only prices that a bigger turbo makes more power, how come I didn’t think of that before?

  4. Luis Corbalá says:

    This comparison only prices… That autocorrector

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