The compressor is a Majestic...
The compressor is a Majestic T-76, capable of 90 lb/min of air-that's 900 hp. The compound-system turbine A/R was a .81, which worked well with the blower, but was sub-optimal in turbo-only configuration.
The location placed the compressor conveniently close to the rear firewall, intercooler and throttlebody. Later, we would reinforce critical areas of the header-to-turbo plumbing with gussets and TIG welding for maximum strength.
After mocking up and tack-welding the basic turbo plumbing, we pulled the 1MZ-FE V6 engine for final turbo system welding and for machining operations on the block to install fittings to supply pressurized oil to the turbo center section and drain oil back to the sump.
In the final mock-up and installation of the turbo system, Alamo techs welded a V-band discharge fitting to the T-76's turbine, and carefully constructed a mandrel-bent exhaust system with Borla stainless tubing and super-high-flow muffler. With the exhaust system in place, we then bolted the Majestic Deltagate to a flange welded onto the side of the collector-to-turbine inlet pipe.
Dyno 1: Compound-supercharged...
Dyno 1: Compound-supercharged MR6 made 330-rwhp at 5700 rpm on the Norwood Autocraft dynamometer, and 300 lb-ft torque from 4000 rpm on up with the wastegate open.
While dyno testing the supercharged-only MR6, we had pushed the stock injectors to their fuel-delivery limit and beyond. With the stock 288cc injectors operating at 100 percent of duty-cycle under MoTeC control, the only option to deliver more fuel had been to increase fuel pressure using a Bell Engineering variable-rate-of-gain fuel pressure regulator. We had finally achieved nearly 260 rwhp on the Norwood Dynojet with the stock injectors.
Now, with bigger power in mind, we obtained a set of giant 630cc peak-and-hold injectors from Bosch. These injectors are low-resistance 6-amp units with a form-factor similar enough to the stock 1MZ's 288s that-with O-ring changes-they're usable with the stock 1MZ fuel rail and lower-manifold injector bosses. At rated fuel pressure, these injectors can deliver sufficient fuel for as much as 750 hp.
The stock MR2 Turbo fuel pump runs out of capacity at roughly 60 psi, just above 400 flywheel horsepower, and requires boosted voltage (for example, from a Kenne-Bell Boost-A-Pump) to deliver additional fuel. In lieu of boosting the OE pump, an auxiliary in-line fuel pump could be added or a high-capacity in-tank unit could be substituted.
Dyno 2: Blower only, turbo...
Dyno 2: Blower only, turbo only, and compounded dyno runs. The blower's torque curve is almost flat, while the turbo-only run is hump shaped. The Compound dyno run pushed torque up another 50 to 100 lb-ft above the blower and hung on to 6500 rpm. The big T-76 turbo was optimized well with the blower, but for turbo-only operation, Majestic later changed to a lower-inertia assembly and smaller A/R turbine housing.
Compound-Supercharging Test and Analysis
Compounded behavior was simple: With the wastegate referenced directly from the compressor section of the turbo, the turbo began making additional boost and torque above and beyond that of the supercharger as low as 2300 rpm. From this point, torque and boost increased in a smooth, linear fashion until the wastegate opened at 4000 rpm and stopped the boost increase at 5-psi turbo boost, 5 to 10 psi total boost (depending on wastegate setting).
If we kept the wastegate closed, boost and torque headed directly for the top of the dyno chart. In one memorable early runaway dyno pull, the MR6 managed to hit 300 lb-ft rear-wheel torque at 4000 rpm before Bob Norwood backed off the throttle.
It became apparent the forced-induction and fuel-delivery systems vastly exceeded the mechanical capacity of the 1MZ V6 powerplant. And when a 15-psi dyno run lifted the rear head just enough to produce a slight, brief outbreath of coolant steam, we realized that further gains demanded better head fasteners and wire O-ringed cylinders with copper head gaskets to prevent catastrophic head gasket failure. We also knew the stock pistons and connecting rods would not be long in this world at 15 psi boost..
We contacted Wiseco to order custom super-duty pistons built with the stock 10.4:1 compression ratio, but designed such that the piston crowns could be machined to reduce compression while maintaining sufficient thickness. We also began looking for a set of custom 1MZ rods or possibly some super-duty performance rods that could be modified to fit the 1MZ crankshaft.