Re: New Crank Scraper Patern (Stroked Engine)

["James J." <m1garand@speakeasy.net>]

Barrie and company,
 The theory is simply that within the sump, there is a cloud of 
atomized oil, called a "windage cloud".  This oil cloud is a physical 
barrier and produces drag against the crank.  This oil is usualy from 
the drainback from the heads and lifter gallery.  In addition, all the 
oil that is pushed out of the bearings and journals as part of regular 
operation runs down the counterweights of the crank.  This is a 
quantifiable increase in rotating mass that possesses inertia and 
therefore requires work to accelerate and keep at speed.  It can also 
through the rotating assembly out of ballance.  Keep in mind that the 
crank is rotating at several thousand RPM and small masses can have huge 
effects at that speed (look at the tiny weights we use to ballance the 
wheels on our cars, or driveshafts, and the problems if we lose those 
weights).  Again keep in mind that racers also remove as much of the 
ballance pads as they can from their connecting rods to gain a few HP.  
This mass is of the same order of magnitude as the oil.
   The scraper follows the profile of the crank with a gap of about 40 
thou (0.040") and provides a brick wall that the windage cloud slams 
into.  It also can remove big drops of oil along the side of the 
counterweights.  By eliminating the windage cloud, aeration of the oil 
in the sump is also minimized.
   Some engine designs benefit more from a scraper than others.  The 
Buick/Rover comes equipped with a windage tray that accomplishes many of 
the same benefits to a lesser degree, and the block/sump design of the 
B.O.P.R also keeps the oil marginaly farther away from the crank than 
with other designs.
 My personal reason for using it is the reduced aeration.  BOPR's have 
weak oiling systems to begin with, and any little thing I can do to  
give the oiling system a hand I will do.  A handfull of HP isn't going 
to help an engine built for midrange torque (vs. a high-rpm race block)
 Hope this helps.
James J.

p.s.  I built this template on a 3.9 rover block, with the old-style 
(distributor) front covers.  It should fit all pre-95 Rover blocks w/out 
a problem.  To use it on a Buick/Olds block (and perhaps a Gen-I Rover 
block) , two of the holes near the flywheel will have to be ovaled to 
fit the older sump pattern.  I have both a rover sump and a Buick sump.  
All but two of the holes line up, and the two in question are close 
enough to fix with a Dremel tool.



Barrie Robinson wrote:

> James,
>
> Does this fit an SD1 Rover 3.5L engine?  I am a bit puzzled by the 
> 3-5hp increase.   I like engineering explanations so can anyone give 
> me the factual evidence that the scraper helps out?
>
> At 05:44 PM 2/12/2004, James J. wrote:
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