The Miller Cycle Engine: Is the Answer to My Search for a Decent Engine for the GEZROKET, a Supercharged Engine Tuned for 87 Octane Gasoline?

As is typical of most Hot Rodders, I want more power for the GEZROKET.  The car is geared WAY TO HIGH for performance, but it allows an EPA estimated 19 MPG city and 29 MPG highway.  The problem is that for this large, heavy (3450 lbs as built with 6 gallons of fuel in a 19 gallon tank), the engine needs to be rev happy to keep the car with a 2.00:1 final drive ratio in Overdrive, so it can accelerate in an acceptable manner.  The problem is, it is not rev happy, and the PCM doesn't bring in downshifts quickly enough to make the car comfortable to drive in traffic.  Yet the engine doesn't have the gut pulling torque to lug the car around either.

In speaking with my car buddy Michael, we've talked over engine swaps and upgrades.  Here were the choices:

• L-67 3800 Series II Supercharged V-6 Engine/4T-65E-HD Transaxle with HD Differential
• LS-4 5300 Displacement on Demand Transverse V-8/4T-65E-HD Transaxle with HD Differential
• Cadillac 4.5 Liter Digital (Port) Fuel Injection V-8/4T-60E Transaxle
• "Built” L-36 GM 3800 V-6, using ZZP Series D Heads, a short duration, high lift Comp Cams Hydraulic Roller Cam, designed for a Buick Grand National turbo V-6 (800-5200 rpm range), ZZP High Velocity Intake Manifold Insert, SLP FWD Headers for a GM 3800 Series II engine, Catalyst and Resonator "U-bend" Delete Pipe, Cold Air Intake Filter Kit, 180 degree thermostat and colder spark plugs
• Australian C.O.M.E. Stroker Kit for GM 3800 V-6s
• ZZP Supercharged 3800 V-6 Conversion for L-36 Normally Aspirated V-6

Each of these has their own advantages and disadvantages.  Believe it or not the ZZP Supercharged L-36 Conversion was actually the cheapest, requiring the least work.  However, ZZP's programmers did not think they'd be able to tune such a heavy car without perpetual Check Engine MIL Light events, and as this is an OBD-II emissions system and I live in a Consolidated Metropolitan Statistical Area for exhaust emissions inspection requirements and the fuel economy a large car such as this gets and the Premium Fuel Requirement at an additional $.50/gallon to safely run the Supercharger without detonation, I really didn't want to go there.

My gut feel has always been to swap the LS-4 Transverse V-8 from a Monte Carlo SS, Impala SS or Buick Lucerne Sport Super.  But that becomes more difficult, mating the LS-4/4T-65E-HD PCM to the digital dash in the GEZROKET and making the engine mounts and getting a Radiator to cool the engine correctly.

The Cadillac 4.5 digital V-8 is reliable and an easy, bolt-in swap as the 1995 and earlier Sedan de Ville's are the same chassis (both built at Lake Orion, Michigan) and had similar digital dashboards.  However, it's a brick (although a very reliable brick) with 175 HP as compared to the L-36's 205 HP at an admittedly high 6000 rpms.

The "Built GM 3800 Series II" would probably have the same "Peakiness" as the stock engine has now, even though the camshaft and heads would pass more air and have more torque.

The C.O.M.E. Racing Stroker, with a 3.7" crankshaft stroke, would give the added "oomph" the car needs at low RPMS, but it's expensive and needs better heads, a better camshaft, a cold air intake, the High Velocity insert, Headers and a low restriction exhaust of the "Built L-36 V-6 (basically everything listed)," if the engine were ever to see the high side of 4000 rpms.

Michael even suggested a turbocharged GM 3800 Series II V-6, as turbo boost can provide significant torque and these engines are well developed in both durability and electronics/tuning.  However, I always thought the reason GM went to Supercharging over Turbocharging was they could more easily control how much boost comes in and more importantly, when it comes in.  And we're probably back to a high octane fuel requirement and the Check Engine Light Scenario at best, or broken engine parts due to an over-enthusiastic tune at worst.

There seemed to be no easy solution, as every option had its significant downsides.

Then I read about the Atkinson Cycle and Miller Cycle Engines.

I am very drawn to build a Miller Cycle 3800 type engine for the GEZROKET.   From what I’m reading from Wikipedia about on the Miller Cycle engine:  

• I can drop the compression ratio by holding the intake valve open longer, releasing some cylinder pressure
• I can keep the quench, through tight piston to head clearance on the aluminum heads, which also reject more heat than the stock iron heads.  This would help prevent detonation. 
• I can use the factory blower and an a liquid to air intercooler to keep intake charge temperature down enough to use an aggressive timing tune and more boost, without detonation.  

This keeps the Horsepower and Torque up to at least the same level as the stock engine under boost, but allows a “smaller” volume of compressed air in the engine (as compared to the expansion size of 3.8 Liters volume).

Based on what I've read, I think it should be very turnable and very drivable.  This would use both stock and very available aftermarket pieces, helping with reliability.  My goal would be a supercharged engine that can still run on 87 octane fuel.

I need to find out more information about it, specifically from Cam grinders who actually understand the Miller Cycle (Crower) and some vendor like ZZP who does the specializes in V-6 performance for the 3800 Series 2 and 3 engines and see if they or some other shop would be willing to design a tune for it.  

Some questions arise about the tune:

• If the Compression displacement is say 3.3 liters, will the reduced air volume signal in the Mass Air Flow Sensor and the O2 sensor "chop" the injector pulses to a point where the amount of fuel delivered to the engine is just what is needed for the 3.3 liters of displacement during cruise events?
• Will the Vacuum motor on the blower “come in” when the engine needs the power, or will is be delayed to meet the 3.8 Liter ECM map?
• Can a “Miller Cycle 3800 Series II Supercharged L-67 use the stock L-67 PCM, without additional tuning

As I investigate building a Miller Cycle Engine, I’ll keep you informed.  It's doubtful that this won’t be another still born project, as I'd have to find someone who would understand just how to tune the PCM to take advantage of a less dense charge, but it is worth looking into.