68Formula

I believe this is true for the LS6 vs. LS2 manifolds (an LS6 modified by TPIS with 90mm actually outperforms a factory LS2 with stock 87mm). But in HR's testing, the TBSS/NBSS intakes outperformed the GENIII all the way from 3000rpm up.
https://www.motortrend.com/news/20-l...ifolds-tested/
That to me would mean there's additional advantages of the later style truck manifold (plenum size, runner length, etc.) beyond just the throttle body. Otherwise, I would expect the low end to be pretty similar. In other words, with the bigger TB, they might be closer on the high end of the rpm, but the low/mid range will still not be as good.

shakenfake

LSXRT was just the first aftermarket intake to come to my mind. I like it just because it looks nice, call me gay if you want. Holley is nicer though, the FAST ones seem cheap and chinesey

Yeah if I remember correctly the runner length and plenum size is much different than the NBS. I think someone here or on LS1Tech cut one open?

Mattt

Thanks for all the replies guys. Sounds like the common thought is that the 2005 4 bolt manifold would still rank under the later NNBS/TBSS as far as flow, even though it has the same throttle body as the latter. I wonder if it would rank higher, improve performance over the truck manifold with the smaller 3 bolt 78mm throttle body. I'm only considering factory option manifolds at this point in time. While the aftermarket manifold options would be great, it's not part of the plan for this vehicle(daily driver). Since I'd seen this rare bird, 4 bolt TB truck manifold, multiple times recently I gave it a second thought, and it allowed for an easier swap without having to re-jigger fuel lines/return lines.

Shakenfake, if you run across the thread here or on LS1tech where the differences are explored and dissected, please post a link. I'll go on the look out for it too. Thanks again.

RedXray

What are the mods on the LQ9 like cam and exhaust choice? I've seen a thread on here where the TBSS lost rwhp on a 5.3 after swapping from the Gen3 intake. If you're not twisting past 6000 RPM my guess is the oddball intake with a 90mm will be close in numbers to a TBSS.

Mattt

LQ9 with small-ish Summit truck cam & and a little bowl blend head work ~10.4:1 CR, going into a 2004 daily driver, road trip Tahoe, occasional tow rig Tahoe with factory exhaust for now. I would not see this rig anywhere near 6000rpm, more like 5000rpm and below.

I may have to be the guinea pig on this 2005 hybrid manifold. Wondering if the old truck style intake kills the flow of the larger 4 bolt throttle body or if the intake can support more flow from the larger 4 bolt throttle body. I have a NNBS intake in the parts pile, but if the difference would be negligible from the NNBS to the 05 hybrid 05 manifold, I may go that route for it's simpler install(not having to re-do fuel lines & return).

RedXray

We know the Gen3 6.0L benefits with the TBSS/NBSS intake swap but most the power gains are after 5000 RPM . My guess is the GM engineers designed that one off GEN3 intake with the larger TB for more power or torque or possibly both compared to the old 3 bolt truck intake. If it didn't check either of those boxes I don't think it would have made it into production. I'm sure it wasn't designed to meet CAFE standards (fuel mileage) with the larger TB. I wouldn't think you'd see much gains with your 5000 RPM limit with the TBSS and stock exhaust manifolds.

If you come across the C5 Corvette fuel tank line... it allows the use of the C5 fuel filter making the TBSS swap plug & play. You'll need to adjust the static "Injector flow rate" in the tune to a progressive flow rate because you will be eliminating the vacuum referenced fuel pressure regulator to the non vacuum C5 Corvette regulator. If you don't have HP Tuners this is another reason (cost wise) with staying with the GEN3 style intake. (If you don't have the vacuum regulator on the gen3 fuel rail disregard changing the IFR in the tune)

Photo of the Corvette regulator and Corvette tank (loop) hose I bought from a member here so I could use my return system with the TBSS.

68Formula

From what i can piece together, this would have been the LH6 and probably it's aluminium block counterpart the LY5.
https://www.onallcylinders.com/2019/...ads-cam-specs/
These also had the better 799/243 heads and an AFM version of the L33 cam: https://www.bishopenginereplacementp...25_p_2243.html but without VVT.
So it likely benefited from the 87mm, and was probably a matter of changing an insert in the mold tooling, rather than a whole new mold tool. Meanwhile, not having to change the fuel system.

But when they introduced the VVT, they stepped up the camshaft durations even more; therefore changing to the TBSS style could net an extra few hp. Plus the original GENIII intake mold tool was probably showing it's age by then, so it was worth retooling, and replacing the fuel rails, injectors, etc.

RedXray

My guess... with the introduction of the gen4 with rectangular port heads that have really good flow numbers... GM had to design a flow matching square port intake (LY6 L79 L92 etc). With the better designed intake it probably took very little tooling to design the cathedral port version (TBSS/NBSS) intakes from the same square port casting.

The only difference between the cathedral and the square port truck intakes (besides the port shape) is the cathedral head fuel rail (bolts) mounts are on the inside of the rails whereas the square port heads fuel rail bolt to the outside of the rails. (It's a quick way to ID square port heads in salvage yards or donor trucks)

arthursc2

iTrader: (5)

Wow I did not know that! Thanks for that tidbit, now I have to look

Mattt

What you are saying makes logical sense. If there was no difference or gain, why would the factory have bothered to make the changes to the intake manifold incorporating a larger TB. I may take a swing at this one year old, odd bird manifold on this 6.0. I had been planning to do a TBSS manifold, which I already have, but it wasn't going to happen for a while until I worked out the differences in the fuel system and return line. My Tahoe does have a return line and a vacuum ref regulator. It is a "Z" 5.3 L59 flex fuel 5.3 in it's original life. Hopefully the Gen3 truck intake does not choke down all the flow that the larger 4 bolt TB will take in.

I really don't know what RPM range this thing will push to, but I'm just picturing on the gauge cluster tach where 5000+ is and I rarely ever saw the original 5.3 operating in that range or above, guess I'm just not into hot-rodding the daily. Is there much to be gained by dumping the factory exhaust? Thought I'd read it flows pretty decent for a factory setup?