Project FD RX7 Restomod: Part 31 – Re-designing the Oil Cooling System

To improve crankcase venting from the block, we ran a relatively massive -12AN stainless steel vent line to a -8AN ORB to -12AN fitting on the Raceonly Billet Oil Filler Neck.

The -12AN hose attaches to a fitting we welded onto an OMP block off plate, which now vents crankcase pressure from the gutted oil metering pump (OMP) port on the front cover.

An important disclaimer: If you are going to consider this, you MUST remove the front cover and block the oil passage from the front iron to the front cover.  You can’t simply remove the OMP shaft and call it a day or you will have significant oil pressure and flow issues that can damage your engine.

PROBLEM:

When tracking FD RX-7s on road courses in the 350-400whp+ range with an experienced driver, there is a common problem of filling catch cans with oil from the crankcase.  While beginners and intermediate drivers may not run into this issue, running sticky tires or adding aero increase lateral grip, cornering speeds, and makes this problem worse.  Many veteran drivers who regularly track single turbo FDs often install a -8AN or -10AN vent line from the factory turbo oil drain port on the rear iron to a catch can or oil filler neck only to continue to struggle with filling their catch cans with oil during 15-minute sessions.

The problem here is more than just excessive crankcase pressure.  The real issue is likely caused by oil from the pan sloshing up and covering the vent hole during sustained, high-G right-hand corners, creating a buildup of pressure (especially on-throttle) which pushes slugs of oil up the oil fill neck and quickly fills the catch can.  This pressure can be so great that it can eject the dipstick out of its tube!

Adding a vent line in the turbo drain port of the rear iron helps, but during sustained left-hand corners, oil can also cover this port.  Crankcase venting through the oil fill neck has been reported as insufficient at preventing oil from being forced up the vent and into the catch can.

SOLUTION: VENT FROM THE OMP PORT

Having known many of these experienced drivers who regularly track their FDs for years and understanding the problems that they face, I have contemplated a solution for a while on how to improve the venting of the block when tracking the car.  During the assembly of our 13B RE in Part-19, I noticed that the diameter of the OMP shaft is much larger than the oil drain port in the rear iron that is commonly used for venting.  A larger vent hole means less pressure buildup in the block and a lower chance of forcing oil into the catch can.  More importantly, the front cover has a massive opening to the oil pan that is ~2” x 12” in size on the front side of the engine that cannot be covered by oil sloshing around during cornering or acceleration.  This is the game-changer that will ensure significant crankcase venting under all conditions and should prevent oil from being forced into the catch can.  I am eager to test this theory out on track.

IMPORTANT FACTORS TO CONSIDER:

This solution only works if the OMP shaft and gear are removed from the front cover, AND THE OIL PASSAGE TO THE FRONT COVER IS BLOCKED OFF FROM THE FRONT IRON with a set screw.  This is necessary because the OMP shaft acts as a flow restrictor maintaining pressure in the engine while feeding the OMP.  Removing the shaft and gear fully exposes this port which will bleed a significant amount of pressure and flow from the engine, which can cause damage at idle or at high RPM and load.

To make serviceability and turbo removal and installation easier, we drew up and 3D printed a couple of custom AN fittings for the turbo oil drain from our Borg Warner EFR 8374 EWG turbo.  One custom fitting bolts to the turbo center cartridge, clearing the T4 exhaust flange and strategically locating the AN fitting in an easy to access location.  The other fitting bolts to the turbo oil drain on the front cover.

After test fitting the 3D printed fittings, we had them machined out of 6061 aluminum.

We designed these fittings to use an O-ring to further improve serviceability without having to rely on gaskets.  We made the -10AN oil drain line with Earls SuperPro PTFE Stainless Steel Hose and now had a turbo drain solution that was much easier to work with than the original drain line, rubber flex joint, and hose clamps.

We bolted the new turbo oil drain fitting to the front cover, which is angled to clear the lower front cover bolt.  Then we tightened the new AN line which made for an easy installation that was worth the effort.

For the turbo oil drain port in the rear iron, we initially use an off-the-shelf -8AN fitting that we originally intended to vent the block with before going down the path of our OMP vent solution.  While we were designing the turbo drain fittings, we went ahead and designed a custom block-off plate for the rear iron turbo drain port.

We started with the capped-off -8AN fitting and designed a simple block-off plate with an integrated O-ring.  We then 3D printed the block-off plate and test fit it.  Once everything was verified, we had the block-off plate machined.  Compared to the bulky AN fitting, our new block-off plate is a very clean design that fits the spacing of the RX-7’s turbo oil drain mounting studs.

Quick Reference:

Page 1 – Stock FD RX-7 Oil Coolers

Page 2 – Hayden HD Cool 778 Oil Coolers

Page 3 – Oil Cooler Ducting

Page 4 – Improved Racing Remote Engine Oil Filter Mount & Thermostat

Page 5 – How to Make Earl’s Performance Stainless Steel Hose

Page 6 – Oil Plumbing Series vs Parallel & Radium Low Profile Swivel Fittings

Page 7 – Raceonly Billet Remote Oil Filter Pedestal & Front Iron Oiling

Page 8 – Raceonly Billet Oil Filler Neck & Improved Racing Catch Can

Page 9 – Crank Venting from Gutted OMP Port & Turbo Drain Fittings

Page 10 – Raceonly Billet Power Steering Reservoir