Re: Jon H...Chev 350 oil pres

Posted by Jon H on February 25, 2005 at 09:26:42 from (69.26.17.242):

In Reply to: Jon H...Chev 350 oil pres posted by txblu on February 25, 2005 at 06:21:58:

The 10 psi per 1000 rpm rule of thumb comes from engine building advice of several big name race engine builders,A fellow Texan named smokey Y being one of them. In my 20 years of building dirt track race engines,those numbers have proven reliable. I have been told that the reason chevy's oil pressure varies more is that a chevy gear pump has more internal leakage than a Ford gear rotor type,so it maintains less pressure at low rpm. My comment about not using a high pressure or high volume pump on a chevy is from experience and comments from other engine builders. Chevy engines do not seem to gain any reliability from a high volume or high pressure pump,,but the extra power required to turn one of these pumps causes much faster wear of the distributor drive gears,especially in a cammed up race engine that idles at 2000 rpm with cold 50 wt in the pan and the oil guage at 80 psi.
The exception is engines like the Ford 351M and 400. Ford built that engine family on the same bore spacing as the little 289-302 engines so they could use the same tooling to build them. The increased HP and torque from these larger engines required larger than 289-302 size bearings to carry the load. With the narrow "smallblock"bore spacing,Ford had no room to make the bearings wider,so they had to go to larger diameter. I believe the 400 has huge 4 inch diameter main bearings. A bearing journal that large spinning at up to 5000 rom has tremendous surface speed and needs a lot of oilflow to keep it cool. Also a bearing that is large diameter and narrow tends to leak a lot of oil in the gap between the crank journal and bearing sides. For these reasons Ford insists that you should have 70-100 psi of oil pressure on those engines for race or even heavy towing use,that takes a high volume/pressure pump.
I hope this sheds a little light on my comments.

Follow Ups:

• Re: Jon H...Chev 350 oil pres Jon H 09:51:53 02/25/05 (1)
  • Re: Jon H...Chev 350 oil pres txblu 06:15:00 02/26/05 (0)

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