full channel main rod bearings

[30psi 4agte]

The fact that the 3a has full channel bearings and the 4a supposedly being a "performance engine" was only given half channel from the factory raises some question as to why ?

[fixeruperer]

its could also be a small sump so its always got oil just there

[allencr]

Here's something (pages 14, 15 &16 of 88) that graphs a greater power loss for each degree of grooving in the lower main!

http://www.engineparts.com/publications/EB-40-06.pdf
Thanks Clevite!
************************************************** **********************

INFLUENCE OF GROOVING ON MAIN BEARING PERFORMANCE
Various forms of main bearing grooving have been used
over the years. We are frequently asked what difference
grooving makes.
First, it’s essential to understand that bearings depend on a
film of oil to keep them separated from the shaft surface.
This oil film is developed by shaft rotation. As the shaft
rotates it pulls oil into the loaded area of the bearing and
rides up on this film much like a tire hydroplaning on wet
pavement. Grooving in a bearing acts like tread in a tire to
break up the oil film. While you want your tires to grip the
road, you don’t want your bearings to grip the shaft.
The primary reason for having any grooving in a main
bearing is to provide oil to the connecting rods. Without rod
bearings to feed, a simple oil hole would be sufficient to
lubricate a main bearing. Many early engines used full
grooved bearings and some even used multiple grooves. As
engine and bearing technology developed, bearing grooving
was removed from modern lower main bearings. The result
is in a thicker film of oil for the shaft to ride on. This
provides a greater safety margin and improved bearing life.
Upper main shells, which see lower loads than the lowers,
have retained a groove to supply the connecting rods with
oil.
In an effort to develop the best possible main bearing
designs for performance engines, we’ve investigated the
effects of main bearing grooving on bearing performance.
The graphs on the next page illustrate that a simple 180°
groove in the upper main shell is still the best overall
design.
While a slightly shorter groove of 140° provides a marginal
gain, most of the benefit is to the upper shell, which doesn’t
need improvement. On the other hand, extending the
groove into the lower half, even as little as 20° at each
parting line (220° in total), takes away from upper bearing
performance without providing any benefit to the lower half.
It’s also interesting to note that as groove length increases
so do Horsepower Loss and Peak Oil Film Pressure which
is transmitted directly to the bearing.


15

[30psi 4agte]

good find mate!
+ rep

[DeftAnesthetik]

now THAT answers my question +rep

[Mr Revhead]

TRD mains are full grooved