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)