[LS3] Induction Variability - VLIM

[monstar]

G'Day monstar, I'll try and find the article I was reading but was refering to LS3. In fact I found it by seaching for info on variable tract inlet manifolds for the LS3. As you're no doubt aware the main challenge in improving efficency in NA engines is overcoming manifold vacum as engine speed increases and efficency decreases. One effective way of helping overcome this (and every bit helps with NA engines) whilst maintaining flexibility is using variable length inlet manifolds. Long tracts improve low RPM torque, partially through the inertia supercharger effect. The only way to reduce intake manifold vacum at high RPM is to shorten the inlet tract as much as possible. This technology has been used on many HP engines over the last 30-40 odd years, its relavitly cheap to manufacture so I don't understand why chevrolet hasn't utilised it. Do you know whether there are aftermarket variable length manifolds for the LS3?. From what I've read re variable cam timing its all about the inlet valve timing, ICE's are very effective at pumping out exhaust gas.

Simple answer is not enough room for simple cheap system, plus it's the power density that puts our 200kg 340kW donk in the all time legend league (not the old school mechanical nostalgia like people toss off to).
TL;DR Variable Length Intake Manifold (VLIM) on LS is too bulky and all variability aims are more effectivey achieved using ECU controlled VVT modes. Also today's energy and emissions challenges mean the goal is not just optimum torque over time but low BSFC and high ITE as well.
Sure variable length intake tracts (VLIM) has some impact broadening or varying the powerband, but cost and complexity aside there's really not so much need with our design, practically zero benefit with ECU programmed VVT. Just like the similar theory for exhausts, how variable lengths broaden the powerband, but VLIM is only one clever means (not the best) nor is it a critical for a wide, variable powerband. Is why BMW and Alfa and Jag been there done that but don't lose sleep over it today.
It’s the art and science of choosing valve, spark, injector timing and somewhat integrate the natural resonance tuning of the engine powerband together surpasses trombone contraptions alone. VVT and lift are used in preference on the lower end of the car price range over variable length manifolds - better in terms of both power and fuel economy for the buck. All small cars have VVT some grocery getter even have licenced Moto GP race designs straight outta Honda and Yamaha etc., all hybrids are Atkinson Cycle, and 99% of cars are drive by wire throttle coz cost, complexity vs results.
However I love Mopar's results with Dodge brothers attitude in the active intake trickery. Was semi-seriously thinking that with a suitable port adaptor or plastic manifold "husbandry" it might be possible to utilise the BMW programmable DIVA helix plenum thing to do VLIM on an LS. The M62 DIVA intake is almost like an LS variant, plus being an old euro lux part likely be cheap from wreckers. The 4.0 V8 donor may be adapted to fit the physical dimension and is possible to integrate actuation into our e38 OS using the intake manifold tuning port PID to control the PWM.

The port integration is a challenge but not impossible

Active intake manifold tuning is less common than VVT and lift, I think coz cost and diminishing returns and all that, so it’s limited to more expensive engines. As mentioned the e38 OS does provide for intake manifold tuning valve (IMTV) programming though.
As opposed to the complication of an active variable length intake and exhaust I used PC software to calculate pressure wave resonance of the first, second, third and fourth order harmonic lengths based on engine RPM - resonance tuning. It works well.
I ported the induction to spec incl custom MAF tube, throttle body and plate, plenum and installed radius bars to induce tumble through the runners. BTW e85 also increases VE by 5%. But the thing I found to have the biggest impact on manifold vacuum is, not surprisingly, the throttle plate . See with huge combustion timing authority enabled in the tune simply by flash programming VVT in the ECU, means more than pressure wave tuning the perfect mechanical symphony for intake charge:
The basic need to close the throttle blade on our 6.x litre V8 CO2 generator is greatly reduced under light and partial load conditions by switching combustion phasing to over expansion (Atkinson Cycle). This near throttle-less operation increases Volumetric Efficiency by reducing the impact of the main obstruction that causes pumping losses - the actual blade.
This WOT "diesel like" power control is all ECU and a bit of DBW, the paradigm shift is that "throttling back" is done by entering extremely efficient, low power modes hardly thought viable in a street car. This is the foundation principle behind the of-maligned AFM cylinder deactivation as well.
These two anti pumping-loss devices work more effectively under high compression to deliver efficient power downscaling.
Old mate with a good overview:

 

[monstar]

As opposed to continuously variable runner length, GM and MOPAR use two-mode runner length modes, essentially like a power valve or bi-modal exhaust. GM uses it on some i4 and sixes, MOPAR on SRT 6.4:
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