Читать книгу How to Build LS Gen IV Performance on the Dyno - Richard Holdener - Страница 7
ОглавлениеWhether you have a stock, street, or strip LS application, the intake manifold is one of the three major players in terms of power production. The aftermarket has produced intake combinations for performance LS3 and LS7 applications. Intake designs do more than just allow airflow into the ports; they actually provide a tuning effect that aids in power production over a given RPM range. Not surprisingly, factory LS3 or LS7 intake manifolds were designed with a combination of peak and average power combined with ease of production and even fuel mileage.
The right intake can help you produce impressive power, especially when used in conjunction with the right cam and ported cylinder heads. More than any other single component, the intake manifold (most specifically the runner length) determines where the engine makes effective power. Match the runner length to produce power in the same operating range as the cam profile and you are a long way toward making an impressive LS combination.
For any engine (including LS3 and LS7), intake manifold design may be broken down into three major elements: runner length, cross section (and taper ratio), and plenum volume. These elements are listed in the order they most affect the performance of a given manifold. By this I mean that changing the runner length has somewhat more of an effect than altering the cross section or plenum volume. This is not to say that all of the elements are not important, it is just that proper care should be given to the elements in accordance with their eventual effect on performance. Take note, intake designers often spend countless hours altering the plenum volume in an attempt to change the effective operating range when they should have simply increased (or decreased) the runner length. Also, manifold design is sometimes limited by production capability or rather ease of construction. Building a set of runners with a dedicated taper ratio and a compound curve is difficult, if not impossible, for the average fabricator. Despite the fact that this design produces the best power, it simply isn’t going to get produced unless a major intake manufacturer (like FAST, Holley, or Edelbrock) steps up to the cost of such a complex combination.
Fabricated, short-runner intakes such as this unit from Speedmaster are popular among LS enthusiasts, but know that the design lends itself to power production higher in the rev range than the stock (long-runner) LS3 or LS7 design.
The first element in intake design is the runner length. The overall intake runner length actually includes the head ports, but the discussion will be limited to those in the manifold. Fuel-injected intake manifolds seem to be broken down into two distinct groups, long and short. Obviously not very scientific, the terms “long” and “short” do not properly describe intake manifolds. The reason for the long and short designations is that, generally speaking, the longer the runner length, the lower the effective operating rpm. Obviously the opposite is also true because shorter runner lengths improve top-end power. Production LS intake manifolds are typically of the long-runner design to help promote torque production. It is possible to design an intake that offers more low-speed or top-end power than the stock LS3 intake, but doing both has proven to be difficult. It should be pointed out that the “ideal” intake design varies with engine configuration as well because the power gains offered by a given design on a stock engine are most likely different on a wilder combination. This is why FAST designed its adjustable LS3 intake manifold to allow adjustment for individual combinations. Since the reflected wave is determined by the cam timing, its initiation point changes with different cam profiles. Thus, changing the cam timing may well require a different intake design.
The next element in intake design is cross section, or port volume. A related issue is taper ratio, but I will cover that shortly. The port volume or cross section of the runner refers to the physical size of the flow orifice. Suppose you have an intake manifold that features 17-inch (long) runners that measure 2.00 inches in (inside) diameter. It is possible to improve the flow rate of the runners by increasing the cross-sectional area. Suppose you replace the 2.00-inch runners with equally long 2.25-inch runners. The larger 2.25-inch runners flow a great deal more than the smaller 2.00-inch runners, thus improving the power potential of the engine. From a reflected wave standpoint, the increase in cross section has no effect on the supercharging effect, but it alters the Inertial Ram and Helmholtz resonance.
For the ultimate in LS3/LS7 induction systems, look no further than an individual-runner intake system.
Related to the cross section, taper ratio refers to the change in cross section over the length of the runner. Typically, intake manifolds feature decreasing cross sections, where the runner size decreases from the plenum to the cylinder head. The decrease in cross section helps to accelerate the airflow, thus improving cylinder filing, but the real difference is the effective change in cross section brought about by the taper.
The final element of an LS intake manifold is plenum volume. This refers to the size of the enclosure connecting the throttle body to the runners. Typically the plenum volume is a function of the displacement of the engine. Most production intake manifold applications feature plenum volumes that measure smaller than the displacement of the engine (somewhere near 70 percent), but this depends on the intended application. A number of manufacturers have recognized the importance of the plenum volume and incorporated devices to alter the plenum volume to enhance the power curve, but the LS3 and LS7 manifolds rely on a fixed volume.
Contrary to popular opinion, increasing the plenum volume does not increase the air reservoir allotted to the engine as much as it affects the resonance wave. When excited, the area in the plenum resonates at a certain frequency. Changing the plenum volume changes the resonance frequency. The Helmholtz resonance wave aids airflow through the runner (acoustical supercharging). Where this assistance takes place in the RPM band is determined by a number of things but primarily by the plenum volume. The air intake length, inside diameter, and a portion of the cylinder (when the valve is open) are also used to calculate the Helmholtz resonance frequency (and why air intake length and diameter have a tuning effect on the power curve).
LS applications also run very well with carbureted intake systems such as this dual-quad Holley Hi-Ram.
Test 1: Holley Single- vs Dual-Plane Intake on an LS3
When it comes to carbureted engines (including LS), the choice basically comes down to single- or dual-plane. That particular induction argument predates the LS engine family by multiple generations, but carbureted LS owners must ultimately choose. We all know that the LS was originally equipped with factory fuel injection, but MSD made the carb conversion ultra simple. Carb swappers were soon faced with the same induction question that plagued previous small-block Chevy owners. Choosing the proper intake design is critical for maximum performance, but just what defines the term maximum?
In most cases, it doesn’t mean peak power, but rather maximized power through the entire rev range. Now throw in things like drivability, fuel mileage, and even torque converter compatibility, and you start to understand the dilemma. You see, despite similar peak power numbers, the two Holley (carbureted) LS intakes tested here offered decidedly different power curves (and likely street manners). We all like to brag about peak power numbers, but the reality is that the vast majority of carbureted LS engines spend most of their time well below the power peak. In fact, street engines spend most of their time well under the torque peak and even during hard acceleration, the engine operates primarily between peak torque and peak power.
Holley’s single-plane intake was designed to optimize power production higher in the rev range than the dual-plane. Just make sure to apply it to the proper combination that can take full advantage of the top-end power production.
The choice ultimately comes down to where you value power production. For those new to LS performance (though this applies to every type of V-8 regardless of generation or manufacturer), the intake debate between single- and dual-plane manifolds is a simple matter of operating (engine) speed. The dual-plane was designed to enhance power production lower in the rev range than the single-plane. This simple fact makes the dual-plane ideal for the vast majority of street applications.
Run on the LS3 test engine (with mild Comp cam), the Holley dual-plane produced peak numbers of 544 hp at 6,900 rpm and 471 ft-lbs of torque at 4,300 rpm. After installation of the single-plane intake, the peak numbers changed very little to 552 hp at 7,000 rpm and 463 ft-lbs at 5,200 rpm. Despite minor changes in peak power, the power curves were decidedly different. Check out the curves and decide where you want your LS3 power production.
Most street and street/strip (carbureted) LS3 applications prefer the dual-plane design because of improved throttle response at lower RPM. The dual-plane was designed to maximize low- and mid-range torque production where it can be enjoyed most often.
Holley Single- vs Dual-Plane Intake on an LS3 (Horsepower)
Holley Dual-Plane: 544 hp @ 6,900 rpm
Holley Single-Plane: 552 hp @ 7,000 rpm
Largest Gain: 14 hp @ 7,200 rpm
The horsepower curves show a number of things, including the fact that the single-plane intake did indeed make more peak power than the dual-plane design, but not by much. Starting at 5,000 rpm, the single-plane pulled ahead, but the power difference was minimal. Run out to 7,200 rpm, the single-plane showed its worth by besting the dual-plane by 14 hp.
Holley Single- vs Dual-Plane Intake on an LS3 (Torque)
Holley Dual-Plane: 471 ft-lbs @ 4,300 rpm
Holley Single-Plane: 463 ft-lbs @ 5,200 rpm
Largest Gain: 54 ft-lbs @ 3,500 rpm
In terms of torque production, there really was no contest. Even though peak torque production differed by just 8 ft-lbs, the dual-plane offered gains that exceeded 50 ft-lbs down low. The additional torque offered by the dual-plane in the low- and mid-range is why it is usually chosen over the single-plane for most street applications. I even tested the dual-plane design under boost on a cathedral-port LS application with excellent results. If it’s better naturally aspirated (NA), then it’s better under boost!
Test 2: FAST LSXR vs Mast Carbureted Single-Plane
This test offered a comparison between a long- and short-runner intake design. In fact, I used nearly the same 468-stroker test engine to compare the Mast single-plane intake to the FAST LSXR LS3 manifold. The 468 featured a Darton-sleeved block stuffed with a Lunati crank and rods teamed with JE forged pistons. Unlike the previous test, the 468 was topped with Mast black-Label LS3 heads.
The combination also included factory LS3 rockers, Comp hardened pushrods, and Kooks 1⅞-inch stainless headers. Also present was a Milodon oil pan and windage tray, Meziere electric water pump, and FAST 75-pound injectors. The finishing touch was, of course, the FAST LSXR LS3 intake manifold and 102-mm Big Mouth throttle body. Equipped with the FAST LSXR intake, the 468 produced 732 hp at 6,400 rpm and 665 ft-lbs of torque at 5,200 rpm.
After running the FAST intake, I replaced the EFI system (FAST XFI/XIM) with the Mast single-plane intake. The Mast intake featured a two-piece construction, which allowed them to fully CNC port the internals. This thing was a work of art; the kind you hate to install and get dirty.
The Mast intake was flanged to accept a 4500-series Holley carburetor. To feed the 468, I installed a Holley 1050 Ultra Dominator. The Mast intake was also designed to run in injected form, so I plugged the injector holes with a set of 19-pound Ford injectors. Equipped with the Mast intake, the power output of the 468 increased to 761 hp and 645 ft-lbs of torque. Not that the peak power rose, but the peak torque dropped compared to the FAST intake. In fact, the long-runner FAST intake offered more power up to 5,900 rpm, but the Mast single-plane pulled away up to 6,700 rpm.
The two-piece Mast LSX intake was designed for high-RPM high-horsepower LS3 applications. (The company also offers cathedral-port and LS7 versions.)
Likely designed for slightly smaller and milder applications, the FAST LSXR intake performed well on this 468-inch stroker. It is hard to argue with more than 730 hp from any manifold.
FAST LSXR vs Mast Carbureted Single-Plane (Horsepower)
FAST LSXR LS3: 732 hp @ 6,400 rpm
Mast Carbureted Single-Plane: 761 hp @ 6,500 rpm
Largest Gain: 47 hp @ 6,700 rpm
The high-RPM nature of the single-plane intake was evident in this curve. The CNC-ported Mast intake was a work of art and boy, did it pull hard on the top end. Unfortunately, all the top-end power came with a trade-off lower in the rev range; in this case, below 5,900 rpm.
FAST LSXR vs Mast Carbureted Single-Plane (Torque)
FAST LSXR LS3: 614 ft-lbs @ 5,100 rpm
Mast Carbureted Single-Plane: 631 ft-lbs @ 5,300 rpm
Largest Gain: 37 ft-lbs @ 4,300 rpm
Much like the previous test run on the Holley Hi-Ram versus the stock LS3 intake, the long-runner FAST LSXR offered considerably more torque up to 5,850 rpm. The FAST offered torque gains as high as 37 ft-lbs lower in the rev range, but the high-RPM single-plane pulled away strong past 5,900 rpm.
Test 3: Stock LS7 vs MSD Atomic for LS7, Modified LS7
This was one of those instances where an intake manifold swap did not trade low-speed torque for top-end power. In fact, this intake improved power through the entire curve, so you know it was the right choice for the engine combination.
Assembled by Cool Performance Machine, the 427 LS7 test engine was created by sleeving an LS3 block. The 4.130-inch bore received a complete Manley stroker assembly that included flat-top pistons, H-beam rods, and a Platinum-series (4.0-inch) stroker crank. Also included in the mix were Total Seal rings, a custom CMP cam (.644 lift and a 246/254-degree duration split), and an adjustable cam sprocket. In true LS7 fashion, the stroker featured an Aviad dry-sump oiling system. Feeding the over-bore LS7 was a set of CNC-ported CMP Brodix SI LS7 heads (395-cfm). Lucas 5W-20 synthetic oil, a Holley Dominator management system and Kooks long-tube headers were included in the mix. The build list also featured an ATI dampener, Meziere electric water pump, and FAST 102-mm throttle body.
It was easy and fast to swap intakes on the LS7. The factory LS7 intake offered good power but nothing compared to the MSD Atomic.
This test involved running the stock LS7 composite intake against the MSD Atomic AirForce LS7 intake, which is also available for cathedral-port heads. Equipped with the stock LS7 intake, the modified LS7 produced 642 hp at 6,800 rpm and 554 ft-lbs of torque at 5,400 rpm. Torque production exceeded 540 ft-lbs for a 1,100-rpm spread (from 4,750 to 5,850 rpm). Since both intakes offered long(ish) runners, I was eager to see how well the MSD compared to the stock LS7.
After installation of the Atomic intake, I was immediately rewarded with both extra torque and horsepower. The peak numbers jumped to 684 hp and 586 ft-lbs of torque. The MSD intake offered nearly 20 ft-lbs below 3,500 rpm but as much as 40 ft-lbs elsewhere. The gains became serious after the tach passed 4,500 rpm. As much as I liked the extra 42 hp (peak-to-peak gain), I also liked the fact that the MSD improved the power output everywhere on this modified LS7.
Equipped with the stock LS7 intake, the CMP-modified LS7 produced 642 hp and 554 ft-lbs of torque. Both intakes were run with a FAST throttle body.
Stock LS7 vs MSD Atomic for LS7, Modified LS7 (Horsepower)
Stock LS7 Intake: 642 hp @ 6,800 rpm
MSD Atomic LS7 Intake: 684 hp @ 6,900 rpm
Largest Gain: 52 hp @ 6,000 rpm
The MSD Atomic intake started well and then became excellent as the tach zoomed past 4,500 rpm. Even down low, the Atomic offered improved power, but the intake really came alive after passing 4,500 rpm. Compared to the stock LS7 intake, the MSD increased the peak output by 42 hp but offered as much as 52 hp elsewhere in the curve.
Stock LS7 vs MSD Atomic for LS7, Modified LS7 (Torque)
Stock LS7 Intake: 554 ft-lbs @ 5,400 rpm
MSD Atomic LS7 Intake: 586 ft-lbs @ 5,100 rpm
Largest Gain: 40 ft-lbs @ 5,000 rpm
As much as I love an extra 42 hp, I love extra torque through the entire rev range even more. As this chapter illustrates, top-end gains are often accompanied by losses in low-speed (and mid-range) torque. This was not the case on the Atomic intake test. The MSD AirForce intake improved torque production through the tested rev range and improved torque output by as much as 54 ft-lbs.
Test 4: Stock LS3 vs Speedmaster IR on a Modified LS3
More than just a change in runner length, this test involved a comparison between a conventional long-runner factory intake and an individual-runner (IR) intake from Speedmaster. The IR intake differed from the factory not only in the length of the runners (although they were different), but also in the lack of a common plenum. Each of the runners on the stock LS3 intake was connected to a common plenum fed by a single throttle body. By comparison, the Speedmaster intake featured no common plenum and eight individual throttle bodies, which measured 50 mm.
Some might be quick to point out that the IR system offered better airflow from the increased surface area of the eight throttle blades. However, the change in runner length, combined with the lack of a common plenum and, therefore, the absence of Helmholtz resonance are what really produced the power differences. (You know this because of the lack of vacuum present in the stock intake at wide-open throttle, or WOT.)
Let’s face it: Nothing is sexier than an individual-runner (IR) intake on an LS engine. This unit from Speedmaster offered impressive power gains to go along with its good looks.
This test was a comparison between the stock LS3 intake and the Speedmaster IR manifold. The test engine was a crate LS3 upgraded with a Comp (PN 281LRRHR13) cam (.617/.624 lift split, 231/247 duration split, 113 LSA) and CNC-ported, TFS Gen X 255 heads. The LS3 crate engine from Gandrud Chevrolet was run with Kooks headers, a Holley HP management system, and Meziere electric water pump. Run on the dyno with the stock LS3 intake, the modified LS3 produced 575 hp at 6,500 rpm and 517 ft-lbs of torque at 5,500 rpm. As always, the long-runner, factory intake offered an impressive torque curve.
After installation of the Speedmaster IR intake, the peak power numbers jumped to 605 hp at 6,800 rpm and 533 ft-lbs of torque at 5,000 rpm. I liked the fact that both peak horsepower and torque were up, but also that the peak torque occurred lower in the rev range with the IR intake. With the exception of a small area near 4,500 rpm, the IR intake equaled or bettered the factory intake through the entire rev range.
The Speedmaster IR intake offered anodized fuel rails, full-radiused air horns, and individual ports to combine the MAP sensor readings.
Stock LS3 vs Speedmaster IR on a Modified LS3 (Horsepower)
Stock LS3 Intake: 575 hp @ 6,500 rpm
Speedmaster IR LS3 Intake: 605 hp @ 6,800 rpm
Largest Gain: 36 hp @ 6,800 rpm
With the exception of a slight dip in power near 4,500 rpm, the Speedmaster IR induction system improved the power output through the RPM range. There was a bump in power near 5,000 rpm and then a serious jump past 5,500 rpm. This intake would show even greater power gains on a larger or wilder application.
Stock LS3 vs Speedmaster IR on a Modified LS3 (Torque)
Stock LS3 Intake: 517 ft-lbs @ 5,500 rpm
Speedmaster IR LS3 Intake: 533 ft-lbs @ 5,000 rpm
Largest Gain: 22 ft-lbs @ 5,000 rpm
The torque curve shows the sign wave in power created by the IR intake from Speedmaster. The new induction system lost out in torque from 4,200 to 4,700 rpm, but bettered the stock LS3 intake everywhere else. A resonance wave at 5,000 rpm really bolstered torque production.
Test 5: Stock LS3 vs Speedmaster Fabricated Intake on a Mild LS3
A number of sources offer these fabricated intakes, but Speedmaster supplied this particular test piece for the LS3 application. Once again I was looking at a substantial change in runner length, to say nothing of plenum volume and throttle opening. Where the stock LS3 intake was designed to accept a 90-mm throttle body, the Speedmaster fabricated intake featured a 102-mm opening.
Various sources offer fabricated intake in different configurations, both with and without radiused air horns for the runners. If you plan to run one, make sure you select the one with air horns because the smooth air entry is worth 10 to 12 hp over the non-radiused version (at this power level).
The overall look of the intake combined with the cost make it a desirable commodity, but look over the dyno results before making your choice, especially for a mild street application. The intake certainly has its place, but like other short-runner intakes, there is a trade-off in low-speed (and mid-range) torque on all but the largest and wildest combos, which includes turbo and blower applications.
This test was run on an engine that clearly favored the long-runner, factory intake. The Gandrud LS3 crate engine was simply augmented with a mild 224 Crane cam (.624/.590 lift, 224/232 duration, 113 LSA), a set of long-tube 1¾-inch Quick Time Performance (QTP) headers with extensions, and mufflers. The test mule also featured a Holley 90-mm throttle body (stock intake), stock LS3 injectors (raised fuel pressure), and Holley HP management system. Run with the stock LS3 intake, the mild LS3 produced 538 hp at 6,300 rpm, and 504 ft-lbs of torque at 4,800 rpm.
After installation of the fabricated intake, the peak power jumped to 556 hp at (a higher) 6,800 rpm, but peak torque dropped to 485 ft-lbs of torque at 5,200 rpm. The stock intake offered improved power up to 6,050 rpm, where the fabricated began to pull away. This intake works much better on high-RPM or larger (and wilder) applications than on this mild LS3.
The factory LS3 intake is impressive, offering a good combination of power and torque production on most mild and modified LS3 applications.
Run with a mild cam, headers, and the stock intake, the LS3 produced peak numbers of 538 hp and 504 ft-lbs of torque.
Stock LS3 vs Speedmaster Fabricated Intake on a Mild LS3 (Horsepower)
Stock LS3 Intake: 538 hp @ 6,300 rpm
Speedmaster Fabricated Intake: 556 hp @ 6,800 rpm
Largest Gain: 32 hp @ 6,800 rpm
The Speedmaster fabricated intake offered impressive peak power gains, increasing the power output of the mild LS3 from 538 to 556 hp. It is important to note that the peak power occurred 500 rpm higher (from 6,300 to 6,800 rpm). This was a surefire indication of the high-RPM nature of the intake design.
Stock LS3 vs Speedmaster Fabricated Intake on a Mild LS3 (Torque)
Stock LS3 Intake: 504 ft-lbs @ 4,800 rpm
Speedmaster Fabricated Intake: 485 ft-lbs @ 5,200 rpm
Largest Gain: 40 ft-lbs @ 4,500 rpm
The torque curve is even more telling because the long-runner, stock LS3 intake offered considerably more torque up to 6,000 rpm. As trick as they look, the short-runner intake designs are best left to high-RPM and/or large-displacement applications. The shorter runners lost as much as 40 ft-lbs of torque at 4,500 rpm.
Test 6: FAST Adjustable LSXR Intake on a Mild LS3
Perhaps the best illustration of the effect of runner length comes from this test on the (then new) FAST LSXR adjustable intake. Recognizing that changes in runner length alter the effective operating range of the intake manifold, FAST designed the new intake to allow installation of different runner configurations. Using bolt-in runs, users can swap out runner lengths to tune the intake to different engine combinations and/or applications (think street/strip).
One thing I also tested but did not show in this book was to combine different lengths (four short and four long or four medium), not unlike a single-plane, carbureted intake. For this test, I simply ran the intake on a cam-only LS3 with the different available runner lengths. As should be evident by now from the results of the previous tests in this chapter, shorter runner lengths increased peak power but traded low-speed torque.
The test engine was a crate LS3 from Gandrud Chevrolet augmented with a cam from Brian Tooley Racing (BTR). The grind featured a .615/.595 lift split, a 229/244-degree duration split, and 113-degree (+4) LSA. The cam was combined with a dual-spring upgrade to replace the factory LS3 springs. Other components used on the test engine included a FAST management system and injectors, Hooker long-tube headers, and a Meziere electric water pump.
Running 5 quarts of Lucas oil and the longest of the three runner configurations, the LS3 produced 562 hp at 6,400 rpm and 512 ft-lbs of torque at 5,200 rpm. Installation of the medium-length runners increased peak power to 568 hp at 6,800 rpm, but torque dropped to 490 ft-lbs at 5,300 rpm. The final test involved installation of the shortest runners that resulted in 577 hp at 7,100 rpm, but torque dropped further still to 478 ft-lbs at 5,300 rpm. Each successive decrease in runner length resulted in increase peak power but a drop in torque (in this case, below 6,500 rpm).
The adjustable intake offered three bolt-in runner lengths to dial in the power curve to a specific combination.
The LSXR adjustable intake looked just like the original, but under the lid was a surprise.
FAST Adjustable LSXR Intake on a Mild LS3 (Horsepower)
FAST LSXR Long Runner: 562 hp @ 6,400 rpm
FAST LSXR Medium Runner: 568 hp @ 7,000 rpm
FAST LSXR Short Runner: 577 hp @ 7,100 rpm
Largest Gain: 20 hp @ 6,700 rpm
Looking at the numbers, you might be tempted to pick the intake combination that offered the highest peak power. Unfortunately, we do not live by peak power alone. While the middle and shorter runner offered higher peak power numbers, there was a trade-off in power elsewhere in the curve. Only above 6,500 rpm and below 3,400 rpm did the middle or shorter runners offer more power.
FAST Adjustable LSXR Intake on a Mild LS3 (Torque)
FAST LSXR Long Runner: 512 ft-lbs @ 5,200 rpm
FAST LSXR Medium Runner: 490 ft-lbs @ 5,300 rpm
FAST LSXR Short Runner: 478 ft-lbs @ 5,300 rpm
Largest Gain: 45 ft-lbs 4,400 rpm
The results of this test on the mild (cam-only) LS3 clearly show the effects of changes in runner length. The trick LSXR adjustable intake allowed me to show the drop (or increase) in torque at lower engine speeds offered by shortening or lengthening the runners. The shortest runner offered the lowest peak torque, followed by the middle runners. The longest runners offered the highest peak (and average) torque production.
Test 7: Stock vs Kenne Bell 102-mm Throttle Body on a KB SC LS3
About the only thing better than a modified LS engine is a supercharged one. Nothing adds zing to an LS like some boost from a Kenne Bell twin-screw supercharger. While twin-screw kits are efficient and powerful, boost is only the beginning. The reality is that superchargers are only as good as their induction system.
Nothing chokes off the power potential of a supercharger faster than a restrictive throttle body or associated inlet components. Knowing this, the question is, How much power is a throttle body upgrade really worth? As an airflow device, the modified power output determines the amount of power hindered by the flow restriction inherent in the stock inlet system. This means that the more powerful the engine, the more restrictive the stock components become. This should not come as a big surprise, since the factory inlet system and throttle body were never designed for the elevated power levels offered by a Kenne Bell supercharger. The inlet system that General Motors designed to support 425 hp has no business on a supercharged engine making 600 or more horsepower.
It is important to stress here that power gains offered by the throttle body are entirely dependent on the engine combination. As a simple airflow device, the higher the power output of the test engine, the larger the throttle body required.
As an example, installation of a larger throttle body capable of supporting 1,000 hp is of little use on a 425-hp engine equipped with an (already oversized) throttle body capable of supporting 750 hp. The 750-hp throttle body is already oversized for the application, so there is no need to upgrade on the NA engine. Things change on (draw-through) supercharged applications, where elevated power levels are more commonplace. Although 600-hp NA Camaro engines are less common, supercharged LS3s exceeding 600, 700, or even 800 hp are everywhere.
This round of testing on a Kenne Bell supercharged (2010 LS3) Camaro illustrated that a throttle body upgrade on a 600-hp application (9.3 psi on stock engine) was worth 8 hp. Performing the same test at 13 psi (678 hp) was worth 26 hp (up to 702 hp) and an amazing 34 hp at 17 psi (from 755 hp to 789 hp). The higher the boost (and power) run on the test engine, the greater the losses associated with a restrictive throttle body. It is important to note that testing the same throttle body upgrade on the NA LS3 was worth 0 extra hp.
Airflow increases dramatically when you install a Kenne Bell twin-screw supercharger.
This round of testing was performed on a 2010 LS3 Camaro equipped with a 2.8L, twin-screw supercharger kit from Kenne Bell.
Stock vs Kenne Bell 102-mm Throttle Body (13psi) (Horsepower)
Stock 90-mm LS3 TB: 678 hp @ 4,300 rpm
KB 102-mm TB: 702 hp @ 4,400 rpm
Largest Gain: 26 hp @ 4,700 rpm
A throttle-body upgrade offers power gains that are in relation to the power output of the test engine. Tested on the stock NA, the larger throttle body was worth nothing. Tested at 13 psi, the upgrade was worth 26 hp.
Stock vs Kenne Bell 102-MM Throttle Body (17psi) (Horsepower)
Stock 90-mm LS3 TB: 755 hp @ 6,300 rpm
KB 102-mm TB: 789 hp @ 6,400 rpm
Largest Gain: 34 hp 6,400 rpm
Running the throttle-body test at a higher boost level (17.3) resulted in a significant rise in power. Run at this elevated power level, the throttle-body upgrade was worth 34 hp and increased boost by 1 psi.
Test 8: Custom Dual-Plenum Adjustable-Runner Intake on a 468 Stroker
Long before the introduction of the FAST Adjustable LS3 or Edelbrock Cross-Ram intake, enthusiasts were tinkering with custom intake designs. I designed this adjustable intake for LS3-headed applications in 2008 to illustrate changes in the power curve. In addition to the dual-plenum design (with removable plenum connection), I was able to quickly adjust the runner lengths to optimize power production at different engine speeds.
The runner length acts as a tuning device to tailor the shape of the power curve. Longer runners optimize power production lower in the rev range than shorter runners. The downside to any given length is that there are trade-offs at the other end of the rev range. The additional low- and mid-range torque offered by longer runners is offset by a loss in high-RPM power. The opposite is true of short runners because they give up low- and mid-range torque for optimization at high RPM. The idea is to tune the combination for the desired use.
The test engine was a 468 stroker that was made possible by combining an LS6 block with Darton sleeves to allow for a 4.185-inch bore.
To test the custom intake, I needed an engine capable of using the massive flow capability of the 2.25-inch runners. In short, I needed something more than either a stock LS3 or LS7. Knowing this, I assembled a big-bore, LS stroker engine by combining a Darton-sleeved LS6 block with a Lunati stroker crank and K1 connecting rods. The Darton MID sleeve system provided the necessary room to allow me to bore the block out to 4.185 inches.
I then combined the big bore with a 4.25-inch Lunati forged-steel stroker crank. The result was a stroker displacing a massive 468 ci, or more than enough to properly test the merits of the custom intake system. The 468 also featured a static compression ratio of 12.25:1, a healthy 305LRR HR15 Comp cam (.624 lift, a 255/271 duration split, and 115 LSA), and Speedmaster CNC LS3 heads.
Run with the short (7.25-inch) runners, the 468 produced 723 hp and 620 ft-lbs of torque, but these numbers changed to 704 hp and 638 ft-lbs with 10.5-inch runners, then to 688 hp and 648 ft-lbs with the longest 16.5-inch runners tested. As length increased so did torque production, but the peak power fell off. Such is the trade-off inherent in runner length.
The sleeved block was then treated to a Lunati 4.25-inch stroker crank and K1 rods, along with a set of Wiseco forged pistons.
Custom Dual-Plenum Adjustable-Runner Intake on a 468 Stroker (Horsepower)
16.5-inch Runners: 688 hp @ 6,500 rpm
10.5-inch Runners: 704 hp @ 6,400 rpm
7.25-inch Runners: 723 hp @ 6,900 rpm
Largest Gain: 36 hp @ 6,800 rpm
As I saw with the FAST Adjustable LS3 intake, adjusting the runner length on this custom, dual-plenum intake on the 468 stroker had a similar effect on power production. Shorter runners push power production higher in the rev range; longer runners optimize power at lower engine speeds. The 16½-inch runners offered the most power up to 5,400 rpm, but lost out to the shorter 10½ and 7¼-inch runners thereafter.
Custom Dual-Plenum Adjustable-Runner Intake on a 468 Stroker (Torque)
16.5-inch Runners: 648 ft-lbs @ 5,100 rpm
10.5-inch Runners: 638 ft-lbs @ 5,400 rpm
7.25-inch Runners: 620 ft-lbs @ 5,400 rpm
Largest Gain: 62 ft-lbs @ 3,900 rpm
The 16½-inch runners were the clear winner in torque production up to the crossover point of 5,400 rpm. The torque gains were as high as 62 ft-lbs at 3,600 rpm over the shortest runner length. The 10⅕-inch runners offered more torque than the 7¼-inch runners all the way up to 6,500 rpm. Only above that did the short-runner combination excel.
