Chrysler/Mopar

Copyright 2002-2024 © All rights are reserved on our product designs.

Upstroke scraper with trap doors: trap doors have been added to help prevent migrating oil in the sump from being blasted up the side of the block and churned during hard left turns.  This is a problem that is inherent in the engine design and can be seen in BMW and Porsche engines with the same sort of slant.  $174.95 standard steel version; $304.95 with a Teflon blade.  This scraper comes with an updated downstroke scraper (seen below).  These updates are based on our very successful BMW M20 and M30 patterns.

~~~~~~~~~~~~~~~~~~~

Updated 5-24-2011

Please note the important consequences of the Kibort Effect on where oil will end up in the pan during hard turns.  A great deal will depend on how the suspension is setup as well as how the car is driven.

Updated 7-01-2010

The Leaning Tower of Power

Mopar Slant six:

170, 198, 225

The scraper for this engine has gone through several generations of design over the last six years.  I am fond of the slant six because I owned a 1966 Plymouth Valiant and extensively modified it and the engine.  I will expand more than I normally do in descriptions because of this.  Please feel free to copy this information if you feel it is useful.

The slant six has a well deserved reputation for durability under normal operating conditions.  However, there are some very real issues with the oil system that should be considered if you really "push" your engine or race it.

In most automotive applications the slant six pan design (and there are numerous pans) has a very shallow sump that allows the sump oil to migrate backwards and/or collect there if the car is under steady acceleration forward -- at even fairly modest levels.  This can happen under braking as well in the front of the pan.  The oil is then struck by the rotating assembly and whipped full of air.  This "entrainment of air" is different from simple oil foaming.  It takes much longer for this air to be released than for foam to be dispersed and broken.

This air entrainment can also happen in competition when the car enters high speed left turns and the oil collects in the rear corner of the pan.  The clockwise moving rotating assembly tries to push the oil up the side of the block and in the process churns it full of air.  This is simply an inherent issue when using an engine tilted to its side.  BMW racers are very familiar with this issue and have dealt with it for at least 50 years now.

Above: typical pan (1973 Dart pan shown)

If enough air is entrained into the oil this can lead to rod bearing failure and other issues.  When highly aerated and pressurized oil passes through the lubrication circuit any abrupt changes in the flow path can cause localized pressure drops.  The localized pressure drops allow air that is dissolved in the oil to come out of solution and collect into bubbles.  Yes, air really does dissolve into your oil - it is a normal thing. The higher the oil pressure, the more air that can be dissolved.

It is extremely important to realize that this high aeration or entrainment can occur at relatively low to medium engine rpms.  Try to imagine the big end of a rod whipping through a puddle of oil at ten times a second -- that is merely idling speed (600 rpms).  People testing engines alone on stands or in cars on roller dynos can sometimes forget what happens when significant movement of the engine/car is introduced.

These entrained bubbles can cause damage in the bearing shells.  In fact, the slant six has been known over its production history for losing the number 5 rod bearing and now you know why.  There are fixes to the oil circuit that have been developed by very talented tuners and engineers, notably Doug Dutra. 

When the slant six had its crankshaft redesigned for lighter weight and higher efficiency one of the major changes was to dramatically reduce the swept path of the counterweights.  At the same time, this helped to reduce the amount of air churned into the oil.  Why? 

Hydraulic lifter circuits were being developed for the engine.  Hydraulic lifters will not tolerate extremely aerated oil: by the time oil reaches the lifters in a dynamic hydraulic circuit the pressure has lowered and air that was dissolved under higher pressure at the pump would be coming out of solution.  A fluid with air bubbles in it is compressible and will cause erratic lifter operation.

Another more esoteric problem that emerges at high engine speeds (approximately 6000 rpms or that neighborhood) is vibration from cavitation at the oil pump -- from the aerated oil.  This chaotic vibration and shock loading was not contemplated when the small "point contact" oil pump pinion drive gear was designed.  Racers have reported loosing pumps in this rpm range.  Then too, six cylinder inline crankshafts have a third order harmonic that emerges around this rpm.  Overall, a difficult situation.  Click here for a possible partial solution -- performance oil pump modifications.

All in all, the best solution to the entrainment problem is to try to prevent the excess air from being churned into the oil in the first place and this is why crank scrapers are offered. 

Note: if you are running a reverse rotation marine engine there are scraper designs for this available.

These parts should all be compatible with the windage tray designed by Larry Shepherd during the Direct Connection days -- many thanks to Slant Six guru, Doug Dutra for that information.  Here is a picture of an earlier generation of the scraper with the tray installed:

Several years ago we were asked to design an exhaust manifold flange for the Slant Six community.  This design is shareware; please double check to ensure that the measurements are accurate.  You can have this pattern cut out at a local water jet jobshop. Please click here.

Here is a jpg:

We were recently asked to design a halo type girdle for a dedicated slant six engine.  A custom pan was to be made by the customer with scavenge pumps.  Please note the design will probably NOT fit into any OEM slant six pan and will probably have frame clearance issues.  It also does not have a provision for a stock pickup tube.  Please double check all measurements and clearances.  It is designed to come very close on the pressure or downstroke side of a stock 225 rotating assembly.  You may have to make small notches for rod bolt/nut clearance there. It is suggested that the part be cut by water abrasive jet from cold rolled plate steel.  Any warp in the plate will be bad for main bearing alignment.

Here is a jpeg: