First a little info: My motors bottom end is bone stock factory 73 350 with 80k mi. I did change to a high volume pump not long after I got the car. My pressure readings were always good with the high volume pump. IE; 25 to 35 at hot idle and 65 to 70 at 2500rpm.

Today during my 4th run I glanced down at the oil gauge just before the end of the run and was shocked to see it reading 35psi at 5000rpm. As soon as I let of the gas at the end of the run the pressure shot back up to its normal 65 to 70. Always in the past the pressure would maintain 65 to 70 anywhere above 2500rpm. So I did a little test while comming back down the return road. I slowed down enough to put it in 1st gear. I nailed the gas and watched the pressure gauge. As the r's went up the pressure was reading 65+ untill, about a slpit second after the engine reaches 4500rpm the pressure suddenly drops off to 35 and below. As soon as I let off the gas, back up to 65. I know that 35psi is not bad in and of itself. But shouldnt my presure be maintaining the higher reading throughout the higher revs?

Now for some info leading up to this:

1.Before leaving for the track I accedentally put about a 1/2 qt too much oil in. Could this cause this problem with pressure dropping off at high rpm. I figure maybe the crank sweeping the higher level migh cause aireation and starve the sump.

2. During the burnout for that 4th run, my rpms shot far above where I usually go. For a split second it reved up to 6500rpm. But the run was good at 13.40. Could I have damaged something with the over rev and if so what? The car still runs great with no noise or any kind of knocking.

3. So I have the high volume pump. Ive heard that, and believe that high volume pumps can starve the sump by pumping oil into the engine faster than it can return to the pan. But the thing is, Ive had this pump on the car for a couple of years and never had this problem before. So if its a matter of the pump starving the pan, why would it start doing this all of the sudden?

Any help or other ideas are greatly appreciated

 

maybe your frothing from to much oil and at the higher rpm your oil is more like a cappucino and therfore has trouble in the pick up.
smokey yunick said as little as 1/2 qt could cause this in his power secrets book.

 

I was reading a lot of people say you need 7 quart pan when doing track like accelerations or RPM over 5000 cause you will run dry. Not sure, I have high V pump and I'm fighting low pressure at hot idle. Less than 20.

 

Sounds as if the high volume pump is pumping all the oil out of pan to the top end before it can run back down. That extra oil could be causing frothing from to much oil like was mentioned above. Thus nothing of the pickup to get ahold of.

One note about oil pumps. Chevy never used a high volume pump on any of its production engines. They only used a high pressure pump on a hand full of solid lifter engines. Think the Chevy engine engineers knew something that we don't :)

tom...


[Modified by Tom73, 8:46 AM 9/8/2003]

 

Well, the HV pump never caused it to run out of oil before yesterday and ive played hard with it many times. I guess the first thing ill do is drain that extra 1/2 qt out and go for a test drive. Thats simple enough. But I also like the idea of a 7 qt pan. I could add a windage tray while im at it. But ill correct the oil level first and test, then report back with results. Thank you all for the help so far. :yesnod:

 

what weight oil?

 

Mobil1 10w-30

 

1st get the right amount of oil, or up to 1/2 qt low.
retest!
10w30 was awful in my cars; same problem right at 4500
much improved with 20w50 :yesnod:

 

Matt, Are you running high volume pump? I drained 3/4 qt which brought the level 1/2 way between the "full" and "add" mark and took it for a drive. Same thing. Cruisin along at 2000rpm reading 65psi. Punch it and drop to 2nd gear and watch the pressure as the rpm's raise. Right at about 5k the pressure rapidly drops off to 35psi. So you think maybe its a combination of high volume pump and thinner oil causing cavitation of oil from the pickup? I think the next move is to change the oil to 15w-50 and test again. Its funny how I never noticed this problem untill I over revved during that burnout at the track. Momentarily had it to 6500rpm. Still runs great though. Knock on wood.

 

I would replace the pump. I don't know how exactly, but maybe it was damaged by the high revs and it goes into the damaged mode above 4500 rpm now. You don't have safe supply with only 35 pounds at 5000 rpm - you need 50#. My 2c.

 

standard pump.
if yours is the same as mine, you can test it stopped in neutral. right at 4500 it will drop.
on my 61 i also added an oil cooler. i found that when the oil temp is 150-220 it does NOT drop. the hotter it gets, the more it drops.
so i have my fun below 220. it has 65 then. I should note that i am too cheap/stubborn/lazy to get the correct oil pan, studs, and windage tray. since i am not racing, i just haven't bothered.
My 72 does seem OK, ever since the oil pan got smashed against the screen, it works great! :crazy: :lol: shifts at 5700 steady 65psi
Both now have a special red oil light, 50psi on the 61, 30 psi on the 72. :cheers:

 

Is the pickup welded in place or pinned?
If not, and it's moved down to closer than 3/8" ,you maybe starving the pump. LOL
Bob

 

Thanks for the suggestion Bob. Its a Melling high volume pump with pickup welded on. I got one this way since ive had the problem you mention on other motors. On the 350 in my Blazer the pickup totally fell off the pump. I was tipped off to that by a strange moaning sound.

 

update: Changed out the 10w-30 for 15w-50. Didnt notice anything unusual in the way of metal filings in the old oil, filter or on the magnetic drain plug. The pressure is about 5lbs higher across the board but it still drops off above 4500rpm. 65psi at cruise....punch it....pressure drops to 35psi above 4500rpm. Let off the gas, comes right back up to 65psi.

 

what oil pan?
chevy
or corvette wih trap door?

 

Its the original pan for a 73 Corvette. Im pretty sure I remember it having some sort of baffle in it. Is that what yo mean when you say "trap door"?

 

No. some options like L82, LT-1 come with the trap door pan and windage tray that bolts to the mains. (i forget the details, maybe someone will chime in)
it may be needed for higher power(maybe not for us).
There are dozens of aftermarket pans, but nobody agrees on what works best.
.

But the question still remains, why is one good, and not the other!(my 72 is fine, 61 NOT) both use the same base pan.


[Modified by Matt Gruber, 10:03 AM 9/19/2003]

 

No it doesnt have a windage tray/trap door that bolts to the mains. Just a welded in baffle in the sump area of the pan.

How about the pressure relief valve in the pump? Could that be releasing at a certian point dropping pressure to the top of the motor where the gauge line hooks up?

 

No. it's whipped oil.
Get this, i get the most steady PSI with 3 to 3.5 qts in the pan :eek:
Smokey sasy in his book, the less oil, the more power.
One guy here said it was .2 sec. faster in the 1/4, 1 qt. low.
But don't listen to me, try Pete79L82, he builds loads of motors and has given generally very good advice. :cheers:

 

OK..if the crank is whipping the oil away from the pickup then there has to be a fix. I dont like the pressure dropping off like that and really want to correct the situation. Running low on oil might stop the whipping at high rpm but somehow I dont think thats the best idea for the engine overall. What about a bolt in windage tray? would that solve the problem? Are there any of those available for my 73 350 that will work with the stock 5qt pan?