[Supras] more 7M oiling considerations

[berniek at technicaldevelop.com]

Before flames or disagreements begin, what is stated here is fact, 
without embellishment.

 Most who are into engine building are under the impression that the oil 
pressure required is only enough to get oil to the main bearings.  That 
is a misconception of the first order.  The oil must be FORCED inward 
into the connecting rod drillings in the main bearings against 
centrifugal force, which IT RESISTS.  It wants to be thrown out or not 
enter the main bearing instead.  The situation is the same as whirling a 
bucket of water over your head, and none spilling out at the top if he 
speed is high enough.   In that regard the main journals are about the 
same diameter as for the big block Chevy I went through the same 
consideration with some time ago. For reliable connecting rod oiling, 
feed pressure needed to be 60-65 PSI  at 6300 RPM.  That is one reason 
(power is the other) that I switched over to a bb Cheby for my 
Firebird.  It was VERY  common for Pontiac engines to spin rod bearings 
before they would float valves.  Pontiac was the last to trust nodular 
iron crankshafts, to the point where the main journal size grew to 3-1/4 
inches for the perceived sake of strength.  Bear in mind that the 
centrifugal force needed to supply oil to the connecting rod bearings 
increases as the SQUARE of the main journal diameter.  So if you rev the 
engine 10% higher, you need 21% more oil pressure to make up the 
difference.  The same SQUARING considerations also holds for main 
bearing diameter as evidenced by the Pontiac failures. 
   
    More to the point with 7M Supras:  The TSRM stock oil pressure is 36 
to 71 PSI at 3000 RPM, the bottom end being scary, although I did 
measure 60 PSI with my '90T some time ago.  However, on the JDM engine I 
shimmed the oil pump spring by about .180" which results in a nominal 
pressure of 76 PSI (cold oil, cooler hose blocked off, testing done on 
stand with 11mm socket on the oil pump sprocket driven with high speed 
drill ).  This is only about 5% higher than the maximum stated in the 
TSRM, and hopefully will not cause drive gear wear.  If anyone has done 
this and had had gear wear I'd like to hear about it.  .  

The bypass through  the oil cooler really sets the system pressure to a 
major extent. However, the spring constant and rate at which the 
pressure grows is much faster than for the main pump.  I found that on 
compressed air that mine cracked open at about 32 PSI.  The spring 
constant and initial preload is high engough that the pressure will grow 
at higher RPM.  Nonetheless I shiimmed my bypass to crack open at 55 PSI 
which required a stack of about .100" washers.  Fortunately this 
adjustment is accessible from outside the engine, at the oil filter 
bypass (the smaller of the two bolts). 

    Please bear in mind here that while may on the list have had 
catastropic oiling related failures, others had none.  I'm not taking 
any chances, moving the pickup to the rear of the pan tilt, and relief 
valve modifications mentioned above.  Another consideration is that the 
top end never gets enough oil, which is part of the reason why it wears 
rearmost bearing caps, as I've covered . 

    These modifications amount to no more than common sense in the 
'60's.  The only concern I have is wear of the oil pump driving gears. 
GM used to sell a hardended  Ram Air 4 distributor drive gear for 70-75 
PSI oil pumps.  Please let me know if oil pump grear wear has ever been 
a 7M problem.  They look pretty small to be carrying the required torque.

    As always comments would be appreciated.  But please, consider the 
physics involved in forcing oil into the connecting rod drillings, 
rather than repeating the (low pressure high volume) verbiage so often 
heard.  Bearing clearances clearances are about .001" per inch of 
journal diameter, a defacto standard,  True, the turbo takes a lot of 
oil, but that is the only real difference between our engines and a well 
built Chevy inline 6.

    Looking forward to comments, hopefully without flames.

          BernieK