By now it should come as no surprise to anyone that the very best factory intake manifold for a cathedral-port LS application is the Trailblazer SS, often referred to simply as the TBSS.

The revised intake design, compared to the original unit used on all the early truck motors (shared by 4.8L, 5.3L and 6.0L engines) offered improved power. Testing has shown the TBSS to be better than the factory LS1, LS2, LS4, early truck and even the mighty LS6—though the LS6 is very close in performance. The limiting factory on the LS6 intake would eventually be the smaller throttle opening, as the LS6 was designed for the smaller (75 to 78mm) LS1-style throttle body, where the TBSS was designed for the later (86 to 90mm) drive-by-wire throttle body.

At higher power levels, the larger throttle opening offered by the TBSS intake would come into play, though it must be stated that the power gains offered by the TBSS intake over the other factory designs is not simply a matter of throttle body sizing. The intake design elements (runner length, diameter, taper, plenum volume, etc.) all come into play when determining the effectiveness (and power production) of the intake manifold.

comparing 2 throttle bodies side by side
When you upgrade your LS from an early truck intake to the better TBSS, do you need to run the TBSS with a larger 90mm throttle body? (Image/Richard Holdener)

We know the TBSS intake is a desirable intake manifold, and it is much more readably available and affordable than the LS6. As a side note, the Dorman LS6 and LS2 style manifolds make a nice alternative, especially for vehicles with hood clearance issues—I’m taking to you Camaro, Corvette, and GTO owners. The problem with the Dorman versions is cost and availability. Time was when the Dorman intakes were dirt cheap and readily available, but after some positive testing by you-know-who, the price on them skyrocketed, placing them near (in cost) to the FAST LSXR intake manifolds (which are superior in power to all of these), but will also set you back a cool $1,200 or more.

If you have the hood clearance, the TBSS intake is tough to beat for performance and price, at least among the factory intakes.

The Role of Throttle Body Size

The question here is not whether the TBSS intake adds power over the stock truck intake (it does), but do you have to also upgrade to a larger throttle body when upgrading your truck intake? The extra expense of the larger throttle body (unless your TBSS came equipped with one) makes the intake swap less affordable, but how much would you be restricting the gains offered by the TBSS if you installed smaller throttle body with an adapter rather than upgrade to a 90mm throttle body?

One of the things that determines the answer to our intake/throttle body question is the test motor. We know from testing that if we add a TBSS to a stock 4.8L or 5.3L, the gains would be less than if we perform the same swap on a 6.0L. The same goes for modified versions of each, as the higher the power output of the test motor, the more power you get from swapping the intake. On a 300 hp motor, the gains are less than on a 400 or 500 hp motor. The same goes for our throttle body question, as the stock 75-78mm throttle body can easily support the flow needs of a stock 4.8L, but the smaller throttle body becomes more of a restriction on a modified 6.0L (or bigger).

For our test, we selected a mild 5.3L equipped with a cam. The choice was more one of convenience, rather than design, as the junkyard, aluminum 5.3L L33 has become a mainstay for testing to the tune of over 700 dyno pulls! It has been used to test all manner of intakes, cams, heads, nitrous and boost, but for this test, the L33 was returned back to near stock trim. This configuration included the stock short block, stock 799 heads (with a BTR valve spring upgrade) and stock early truck intake and manual throttle body. The non-stock modifications included a .552/.552 lift cam upgrade, 1-7/8 long-tube headers and 1,000cc injectors. Tuning was via a Holley HP management system.


To test itself involved first running the 5.3L with the TBSS intake (the L33 came factory equipped with the early truck intake) and manual 75-78mm early truck throttle body using an ICT billet throttle body adapter. The adapter was necessary to convert the larger 90mm, 4-hole throttle body flange on the TBSS intake to the 3-hole, 75-78mm throttle body used on the early truck intake.

Run with the smaller throttle body on the TBSS intake, the 5.3L produced 427 hp and 411 lb.-ft. of torque. After installation of the larger 92mm FAST Big Mouth throttle body (which better matched the opening on the TBSS intake), the power output increased to 434 hp and 416 lb.-ft. of torque.

Since airflow requirements increase with engine speed, it is not surprising that gains offered by the larger throttle body came past 4,500 rpm. Using the Holley HP system, we also logged the kpa during the run and the larger throttle body showed a peak of 96 kpa to the slightly more restrictive 95 kpa offered by the smaller throttle body.

FYI: Tuners, he scaling on the MAP sensor meant 96 kpa was zero vacuum (not 100 kpa).

The upshot of this test shows that the early truck throttle body can be run on the TBSS, but it will cost you some power at the top of the rev range. Remember too, the greater the power output of your test motor, the more you will benefit from the larger throttle body.

dyno chart screengrab
The question on the table was can you run a TBSS intake with the smaller (early truck) throttle body and 3-hole to 4-hole adapter? The answer is obviously yes, but the follow up question was how much does it hurt power? The dyno results show that the near 90mm opening in the TBSS intake works best (meaning makes the most power) with a comparable 92mm throttle body. In this test, we compared a stock early truck throttle body and ICT Billet adapter to a FAST 92mm throttle body. On this cammed L33 5.3L, the larger throttle body was worth 6 to 7 hp, with gains coming past 4,500 rpm. Since airflow increases with engine speed, we expect the larger throttle body to add power where airflow demands are greatest. The gains would also increase with a more powerful test motor. (Dyno Chart/Richard Holdener)
piston getting removed form an engine
The all-aluminum L33 5.3L junkyard test motor now had over 700 dyno pulls on it, but was still going strong. We had long ago added extra ring gap to the stock rings for turbo testing, though it would not be needed on this throttle body test. (Image/Richard Holdener)
man holding camshaft
Wanting something more power than stock, we equipped the test motor with an .552/.552-inch lift truck cam. (Image/Richard Holdener)
799 number mark on a ls cylinder head
From the factory, the L33 5.3L was equipped with a set of 799 heads. The stock heads were treated to a set of .560 lift springs from Brian Tooley Racing. (Image/Richard Holdener)
ls engine on a dyno test pull
Rather than run stock truck coils, we equipped the L33 with a set of LS3 coils mounted to the BTR aluminum valve covers. The LS3 coils offered no power over the stock truck coils at this power level, the BTR valve covers were already set up and used on most of our test motors. (Image/Richard Holdener)
ls engine dyno headers
The throttle body test was run with these 1-7/8 inch, long-tube dyno headers featuring collector extensions, no mufflers. (Image/Richard Holdener)
electric water pump on an ls engine
Nearly all of the LS test motors run on the engine dyno are equipped with the same Meziere electric water pump, with no other accessories. (Image/Richard Holdener)
man at laptop adjusting engine tuning software
To dial in the 1,000cc injectors (for when we add boost), we employed a Holley HP management system. (Image/Richard Holdener)
tbss intake manifold on an ls engine
For this test, the motor was run with a Trailblazer SS intake and two different throttle body systems. (Image/Richard Holdener)
throttle body intake port for an ls manifold
The near 90mm opening in the TBSS intake was designed to accept a factory 87mm (we call it a 90mm) DBW throttle body. (Image/Richard Holdener)
ict billet throttle body adapter spacer
In order to run the smaller 78mm throttle body from the early truck (ours was a manual unit), we employed this ICT Billet 3-bolt to 4-bolt adapter plate. (Image/Richard Holdener)
ls engine on dyno run
The adapter allowed us to run the TBSS on the dyno with the smaller 78mm (3-bolt) throttle body. Equipped with the adapter and smaller throttle body, the cammed 5.3L produced 427 hp and 411 lb.-ft. of torque. (Image/Richard Holdener)
ls engine intake manifold resting on floor
The TBSS intake is a common upgrade for this early truck intake. Note the 3-bolt throttle body pattern on the early truck intake. (Image/Richard Holdener)
man holding throttle body adapter
After our dyno session had ended, we found this tapered 4-bolt to 3-bolt adapter. Do you think it would have done better? (Image/Richard Holdener)
man holding throttle body for an ls engine
If you are upgrading an early truck intake with a DBW throttle body, then just run the stock 87mm throttle body that comes with the TBSS. (Image/Richard Holdener)
fast engraving on an ls engine throttle body
For our test, we ran this mechanical FAST 92mm Big Mouth throttle body. (Image/Richard Holdener)
ls engine doing a dyno test
Run on the dyno with the larger FAST throttle body, the TBSS-equipped 5.3L produced 434 hp and 414 lb.-ft. of torque. The gains offered by the larger TB came past 4,500 rpm. (Image/Richard Holdener)


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Keywords
dyno test , TBSS , throttle body
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Author: 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.