[Supras] Oil accumulator vs. pumping air

Sat Dec 8 18:57:50 CST 2007

Jeff, Pat:

    Thanks for the responses.  My first cars were Ford Y-block V8s from 
the 50's which had front sumps.  The first was a '54 which wound up with 
a '57 312 CID block and heads, Crane cam, 3-2's (3 bolt Holleys).  I 
also had a directly connected aircraft surplus oil pressure gauge which 
read fast.  It went to zero when making uphill left turns.  Had to 
change con rod bearings, down to the brass.  OK, that is understandable 
due to the sump design.  A '70 Firebird Formula 400 bought new developed 
noisy lifters when exploring the cornering limits of newly designed 
Michelin XWX tires (South Orange Avenue on the west side of second 
Watchung mountain if anyone here in NJ knows where it is).  It did not 
take long to figure out that the pickup was sucking air.  And that was 
going slightly uphill with a rear sump.  On the other hand that car 
handled like a go-kart (tires lasted only 8K miles or so).  Still have 
the car but it is in storage and needs restoration (not driven for 10 
years).  Put a BB Chevy in it in 1974. 

    We can discount starvation in early OHV Fords due to the front 
sump.  But the Firebird?  The pan appeared to be bulletproof and was 
regarding straight line acceleration (about the same push in the arse as 
the '91 Supra is now, over 3000 RPM with mods made to date).  That was 
one reason I moved the pickup back by one main bearing spacing.  No, 
XWXs are not made any more.  Besides they were harsh riding due to very 
stiff sidewalls.  For that and other reasons I'm not going to get the 
same lateral force with the Supra as with the Firebird.  Nonetheless, 
the old adage of "once burned, twice careful" kicked in here. 

    Although I'm beyond the age where I should know better I sometimes 
drive on back roads at the very edge of controllability.  When the first 
oil analysis showed 43 PPM of lead after 400 miles with re-used 
bearings, and the stock gage with a new sender read zero at hot idle, 
oil starvation was the first thing that came to mind.  I did make some 
WOT runs to the top of 4th gear once the engine had about 100 miles on 
it (JDM rebuild, 550cc. Lex, Cometic, ARP, 57 trim CT26, 3" turbo back 
exhaust, '98 mounts, Walbro, 15-17 PSI boost).  The stock bearings were 
in fine shape and were re-used.  Hence the anguish over the lead report 
at first. 

    Since that time the following has been uncovered:

    1.  I've begun to suspect wearing away of the soft cam journal 
coating on the intake cam as the source of lead.  I refinished the caps 
for .002" to .003" clearance.  But the intakes are now somewhat noisy.  
The exhausts are not, presumably because the soft coating was just about 
gone when I put the engine together.  The JDM came from a an automatic 
(still had the flex plate on it when I got it), and judging from 
cylinder bore condition (essentially no ridge, maybe .001" max barrel 
shaping, cross hatching still evident) it was treated gently, so the 
intake cam still had the soft coating on most of the journals.  Yet the 
caps were worn, in some cases to .006", a chronic problem affecting 
others I've spoken with, especially at the rear.  This may have 
something to do with the soft mystery coating, and the TSRM allowing 
.005" service clearance for a journal less than 1.5" in diameter.  7M 
cams are hollow and are oiled by feeding oil in the front journal, which 
is grooved.  All others are cross drilled, so the rear caps wear the 
most, especially on the hotter exhaust side.  Moreover, the head is fed 
oil by only a small bore from the front main bearing feed hole.  The 
MkIV J series cams are fed at the center journal. 

    2.  There is no audible indication of con rod bearing wear, using a 
stethoscope at the crankcase flange and teasing the throttle with the 
5W-40 break-in oil hot enough to cycle the electric fans.  Some noise 
during warmup appears strongly due to piston slap, somewhat surprising 
with stock steel strut autothermic pistons.  Then again, the '90 I had 
before (all stock) had some diesel-like piston slap when cold after 
about 100K miles, 60K of which were with synthetic oil.

    3.  Some time ago I made up a quick oil pressure tester by center 
punching a hole in the bottom of a new oil filter (no chips by 
punching), soldering in a piece of 1/4" copper tubing, and connecting to 
a precision pressure gauge.  I used it for 20 minutes on the '90 and was 
pleasantly surprised at the high oil pressure.  One of the many items I 
bought during the JDM freshening for the '91 was a new sender.  But 
guess what:  It reads zero at a hot idle with the 5W-40 oil.  So, out 
came the modified filter last night, only to find that pressure at a hot 
idle with the electric fans cycling on and off was 20 PSI.  Granted, 
there is pressure drop in the filter element, but it cannot be that much 
at 600 RPM with the oil as thin as water (or so it seemed at the first 
change after 400 miles, done hot for sampling).  I'll either check the 
filter pressure drop, install a real gauge in the car, or check pressure 
with a temporary connection to the side oil gallery. 

    All of the foregoing makes me less suspicious that oil starvation 
will be a problem.  Nonetheless, during the heat of next summer, the 
present Bridgestone RE750's will stick to the pavement better than now 
(the '91 has wide '98 wheels).  What had concerned me more was straight 
line performance due to the gentle fore and aft slopes in the pan, 
particularly the baffle at the rear.  That is the primary reason I moved 
the pickup back by one main bearing spacing, to the rearmost kickup in 
the pan.  That could leave open the possibility of starvation under very 
hard braking, pulling down from 120+ MPH on I-80 when the cops are not 
around.   No doubt I'll be back to Jeff at some point, probably next 
summer regarding brakes, unless I wind up in the graybar hotel first 
(really not likely, but the way the '91 now performs, I'm always in the 
pedal to the metal mood). 

    I do wish to thank both of you for the reassurances.  Take care.

       BernieK

Patrick Golder wrote:
> Hi Bernie,
>  
> I'll second what Jeff says.  I've driven my 88 Supra in dozens of 
> track days at Watkins Glen, which has lots of turns with elevation 
> changes, and have never experienced any oil starvation.  I really 
> don't think you need to worry about it.  Aside from the head gasket, 
> these cars are pretty bulletproof.  Drive it and enjoy it!
>  
> Patrick
>  
>  
>
>     ------------------------------
>
>     Message: 2
>     Date: Fri, 7 Dec 2007 16:25:31 -1000
>     From: "Jeff Mohler"
>     Subject: Re: [Supras] Oil accumulator vs. pumping air
>     To: berniek at technicaldevelop.com
>     Cc: "Supras at supras.com"
>     Message-ID:
>
>     Content-Type: text/plain; charset=ISO-8859-1
>
>     Bernie..whats the facination with adding Detroit style fixes to
>     problems that do not exist?
>
>     I _race_ cars, and short of my Super Unlimited TransAm that is burning
>     580 ground HP on 12" wide goodyear slickes around the tracks, ive
>     -never- seen or heard of any "deceleration, acceleration, or
>     cornering" oil control issues on anything short of my class, other
>     than 3000GT's. Which..are chronic with hard enough track use.
>
>     You do -not-, and will -not- have enough braking or rubber in a MK3
>     without significant upgrades on both of those (including R compound
>     rubber) to decelerate that fast, or..corner a supra that fast.
>
>     I _applaud_ you for wanting to throw money at it, but..youre adding
>     complexity, a mess, and..well, headache to what will be a VERY clean
>     and fun, reliable, car..if you just drive it as is.
>
>     Serious..if youre going to visually determine that in "from all
>     appearances" there is a problem, then youre doing a hell of a lot more
>     gassing, braking, and cornering than anyone has ever been able to get
>     out of any supra...anywhere. And on hundreds of HP less.
>
>
>     Id be more worried about the lead in your oil, than a starvation issue
>     that people on 2-3x your HP range have never experienced.
>
>
>
>     On Dec 7, 2007 4:19 PM, berniek at technicaldevelop.com
>     wrote:
>     > Thinking of adding an oil accumulator (1-1/2 to 3 qt.) to protect
>     > against starvation during high speed stops and cornering at the
>     limit.
>     > I've already relocated the pickup as far back in the pan as it
>     will fit,
>     > necessitating cutting back the baffle. The baffle angle was so
>     shallow
>     > that from all appearances, oil would not flow back to the pickup
>     under
>     > hard acceleration. So under acceleration, I should be OK. Its
>     pulling
>     > the speed down from over 3 figures in MPH and cornering that I'm
>     trying
>     > to address. I've had instances in the past where cornering with
>     another
>     > car ran the oil up the side of the pan, evidenced by hydraulic
>     lifters
>     > getting noisy suddenly.
>     >
>     >
>     > The question is this: Since, the oil pump is in good condition
>     and will
>     > have oil wetted gears, what is to keep it from pumping air at
>     60-70 PSI
>     > during conditions at high engine speed when it becomes
>     uncovered? Under
>     > those conditions, the accumulator will not be of any value. Yes,
>     air is
>     > compressible, but it can also be pumped by a positive
>     displacement pump
>     > in good condition (i.e., the sump oil pump).
>     >
>     >
>     > Really looking forward to answers to this one. Thanks.
>     >
>     >
>     > Bernie
>
>     End of Supras Digest, Vol 48, Issue 11
>     **************************************
>
>
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