Q-talk 85 - Turbo Subaru Installation
- Category: Q-Talk Articles
- Published: Friday, 04 December 2009 16:13
- Written by Jon Finley
- Hits: 1171
(Part 2 of 3) Continued from Issue 84
I required a redundant ignition system. There are many variations of redundant systems and each has its own positives and negatives. I feel that the system I settled on meets my requirements for redundancy without adding complexity or expense.
The stock distributor is utilized. Within the distributor, there are two Subaru pickup modules. These modules are mounted 180 degrees apart to a new internal mounting plate. Each pickup is wired to a GM electronic control module (NAPA part #TP45) mounted on the firewall. Each control module is wired to a GM coil (NAPA part #IC107). The high-tension outputs from the coils are connected to an MSD “Dual Coil Selector”. The “Coil Selector” takes two high- tension inputs and supplies a single high-tension output.
The vacuum advance system was removed and the rotating plate within the distributor removed. The standard mechanical advance system was retained. It provides a total of 20 crankshaft degrees of advance. I initially selected 25 degrees BTDC as my full advance position. I have since changed to 28 degrees BTDC.
The primary ignition and fuel pump are powered from the main bus. The secondary ignition and fuel pump are powered directly off the alternator through a capacitor that is responsible for keeping the alternator excited should the battery/main bus fail.
A Nippondenso 45 amp alternator was selected due to its small size and weight (7 lbs.). It has an internal voltage regulator. Mounting brackets were fabricated using 3/8” aluminum angle. I machined the second (power steering) pulley off to reduce weight The alternator electrical connection plug is special so get the matching plug if you get one of these alternators from a wecking yard.
To add redundancy to the electrical system I installed a large capacitor connected across the field wire. Once the engine has been started and the alternator is generating power the battery can be removed and the alternator continues generating power. This system has been verified on the ground.
Due to the location of the carburetor, it is not possible to use a gravity feed fuel system. This being the case, I decided that it did not make much sense to pump fuel to the header tank and then pump fuel from the header to the engine. In my opinion, this was wnsted effort and a less than ideal situation. If the fuel pump to the header ever failed I would be left with only 3-4 gallons of fuel available while sitting on many unusable gallons. One possible solution would be to install dual fuel pumps to pump from the main to header and then dual pumps to pump from header to engine. This seemed silly to me. I finally decided to use the header as an auxiliary tank and pump fuel only from the main tank. Dual fuel pumps have been installed and fuel is gravity drained to the main tank when needed. The header tank is filled by changing the position of the fuel valve and turning on one of the fuel pumps. This can only be done on the ground with the engine stopped as the fuel flow is redirected from engine to header tank. The main fuel feed is from the largest source of fuel and the feed of fuel from the header is a very simple gravity feed system.
Currently I am running to Facet 3.Spsi pumps in series. At the time of installation I understood that the Facet pumps could not fail “closed” (shutting off fuel flow). I have since seen reports indicating that they can and plan to change to a parallel configuration with check valves. I plan to investigate installing a second pickup point in the main tank to have further redundancy.
A radiator from a 1979 VW Rabbit was used. It is mounted about five feet aft of the firewall on the bottom of the fuselage. The forward edge of the radiator is directly under the seatback bulkhead. It is mounted lengthwise using .050” aluminum. The forward edge is mounted 3.5” below the fuselage and the aft end is mounted flush with the fuselage forming a scoop. The coolant flows through 1” x .035 aluminum tubing along the bottom of the fuselage.
A swirl pot was fabricated using a length of 4” aluminum tubing. The ends capped and welded, a radiator cap fitting welded to the top, and inlet and outlet fittings welded to the sides. The idea of a swirl pot is to direct the inlet ports at an angle to induce a swirling action inside the pot The outlet is located at the bottom of the pot at an angle to encourage the coolant to flow out of the pot and into the port. The swirling action is supposed to cause air to separate and move to the top. This air is forced out of the system into a catch tank.
The stock intake manifold, that I did not use, incorporates the coolant thermostat. I elected to use an in-line coolant thermostat from a 1978-1980 Subaru Justy. A BMW unit was initially used. This unit was ideal as it positively shut off the by-pass line when the thermostat was open. However; I was only able to get this unit with a 210- degree thermostat, which is quite high for the Subaru. The current unit contains a 180-degree thermostat
Standard automotive radiator hoses were used. The clerks thought I was crazy when I asked if I could dig through their hoses until I found the shapes that I was looking for!
I studied all of radiator/cooling theory documentation that I could fmd. The obvious problem with applying the principles from these articles is the lack of physical space. They all call for a substantial length to slow the airflow and recover pressure before the radiator and an equally long distance to accelerate the heated air. The Q2 cowling simpiy does not have enough space for an ideal arrangement I initially installed a Saturn auto radiator in the cowling using a large NACA duct on the cowling bottom for air. This approach worked in the cool fall/winter temperatures but I was sure that it would not be acceptable during hot outside temps. I modified the cowling in an attempt to get more air to the radiator before admitting defeat and locating the VW radiator on the belly. There are much more ideal radiator installation practices that will be explored as time permits. The current location cools very well but is obviously quite draggy. As time permits, I plan to research installing the radiator in the fuselage, aft of the split line, pulling air in from the bottom of the fuselage and exiting on the top. This is the only arrangement that I can image that may come close to following the pressure recovery theories. For now, I am happy to fly. Two additional approaches that I plan to research include a custom radiator fit in the cowl and a custom radiator fit on the belly with a nice tunnel/scoop arrangement. I believe a very thick (four inches or so) radiator appropriately sized could work in the cowl. The limiting factor to trying either of these approaches is the cost of the radiator.
The following engine instrumentation was installed:
- Oil Pressure
- Oil Temperature
- Low Oil Pressure Warning Light Water Pressure
- Water Temperature
- Tachometer Manifold Pressure/Boost
- Exhaust Gas Temperature
- High/Low Voltage Warning Circuit
A Valeo starter from a Saturn automobile was utilized due to its small size and weight (7 lbs.). The starter was mounted to a 1/4” aluminum plate which was bolted through the bellhousing into the block. Currently the starter is oriented such that a small bump is required on the top of the cowling. I have modified another Valeo starter to mount such that the bump will not be required. This was done by removing the mounting tabs from the starter and welding on new tabs at the “correct” location. I plan to install this modified starter sometime this winter.
Flyweheel & Prop Hub
The flywheel was machined from a 10.5” x 1” square hunk of aluminum. The flywheel bolts to the crankshaft using the eight bolts that normally attach the stock flywheel. The crankshaft is drilled and tapped and a large bolt inserted through the flywheel and into the crankshaft. A starter ring was liberated from a 1988 Ford Taurus. The ring gear machined off and shrunk fit onto the flywheel. The flywheel is solid aluminum. I now wish now that I drilled lightening holes in the flywheel. It is a relatively heavy part, the next time it is off for maintenance I plan to drill five or six very large holes (2” possibly) to reduce the total weight.
The prop hub was machined from a 6” x 4” hunk of aluminum. The hub has a diameter of 6” at the flywheel end and 5.5” at the prop end. The hub bolts to the flywheel and prop using six 3/8” bolts. The standard Continental prop flange bolt pattern is used.
My Q2 weighed 640 lbs. empty with the Revmaster. With the Subarn, it weighs 672 lbs. including oil and coolant This includes the addition of an auxiliary fuel pump, additional gauges, electrical system changes, 45 amp alternator, turbocharger, three-bladed Warp Drive carbon fiber propeller (replacing the kit two-bladed Cowley wood propeller), and extensive cowling modifications (which have resulted in a very heavy cowling).
To be continued in Issue 86.
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