|
RPM |
Fuel Economy |
|
| Stock 4.09 at 70 MPH |
4150 |
~ 17 MPG |
| Custom 3.27 at 70 MPH |
3350 |
~ 21 MPG |
Note: MPG based on test using tire size 215/60 R16 or 26″ diameter wheel
Super Flier R&P Product Testing
Testing was done with Subaru EJ25 converted van first using the stock 4.09 R&P and then the custom 3.27 R&P.
Because of the nature of the automatic with its torque converter, it was not feasible to generate exact RPM vs speed data since it depends on engine load. At the same speed it’s easily possible to have 500 rpm difference depending on the terrain. We ran multipe tests to accurately determine engine speed values at 70 MPH on flat terrain (to get a steady-load engine speed). We collected OBD engine data with special software and determined speed from a GPS unit.
At 70 MPH engine speed with the stock 4.09 R&P we measured 4150 RPM and with the 3.27 R&P ratio gearing it is approximately 3350 RPM. This results in approximately 800 RPM drop at 70 MPH. At 60 MPH we estimate 2900 RPM using the custom 3.27 R&P.
Super Flier R&P Fuel Economy Test
Testing was done with Subaru EJ25 converted van first using the stock 4.09 R&P and then the custom 3.27 R&P.
Super Flier R&P Test Statistics
Primary Test Vehicle
87 Westy Vanagon
Engine: 2010 EJ25 engine
Ambient temperature 70 F
Wind speed: minimal
Terrain: mostly country highway with several villages on route (several slower speed intervals)
Maximum speed: 60 MPH
Gas Consumption:
4.09 R&P gearing: 4.0 gallons of gas used, for a fuel economy of 17 miles per gallon US.
3.27 R&P gearing (same van and engine) same route, similar conditions. Gas consumption dropped to 3.2 gallons, for a fuel economy of 21 miles per gallon US.
Increase in fuel economy: 23%.
Tires: 215/60 R16 tires with stock vanagon diameter of about 26″
Transmission governor modified to adjust the shift points higher to take advantage of the subaru 2.5 liter engine’s much higher power (172hp/165 ft-lb) than the stock engine.
Acceleration from a stop with the stock 4.09 R&P gearing is very strong with more than adequate torque. Acceleration with the 3.27 R&P gearing still feels more than adequate – it still accelerates with full authority even on a steep incline.
Driving noise : significantly diminished since the engine is turning much slower.
With the 4.09 gearing, you have to push the accelerator down abnormally to get to 60 mph just to get the engine RPM high enough, much more acceleration than it should take based on the engine’s power. The 3.27 removes that effect and the acceleration to full speed is much more natural. On a mountain highway the van could accelerate up grades effortlessly. Going 70mph and want to go 75? Just push the pedal down a little bit and voila!
An interesting side effect is that the 2nd gear actually becomes usable at highway speeds with the power of the 2.5 liter Subaru. Approaching a car traveling around 50 to 55 mph and wanting to pass on a straight section, I pushed the accelerator down and was surprised by a downshift to second gear at around 55 mph, something impossible with the 4.09 R&P gearing.
Additional Test Vehicle
California-compliant EJ22 Multivan (passenger van with pop top) and stock sized tires.
Owner is extremely satisfied with driveability and overall performance.
On highway such as toward Tahoe, when the EJ22 cannot keep up on heavy inclines, the 3.27 allows him to shift down to second gear and climb the hill at 60+ mph still.
The 3.27 gear set is ideal for high-power conversion engines such as:
- Subaru 4-cylinder EJ25
- Subaru 6-cylinder EZ30
- Subaru 6-cylinder EG33
- Higher torque diesels such as VW 4-cylinder TDI
- VW 4-cylinder 1.8L Turbo
- Other engine conversions in that range
The 3.27 gear set is also usable for engines such as:
- Smaller 4-cylinder Subaru EJ22
- Worked VW Waterboxer engine
- Zetec
- Tiico
- Other inline engines
Note: vans should not be overly heavy. Tire diameter should be around stock size. Not advised for very high altitude usage.
Table I
4.09 vs 3.27 Super Flier Ring and Pinion Comparison: Heat (Temperature in Celsius) and mean RPM
Our tests to determine transmission heat changes gave us the following results. They show that there is minimal difference in transmission temperature between the two R&Ps.
