For base 350 is it OK to use high volume 70 psi oil pump or should I stick with lower 35 psi? Is there any concerns I should have?

 

Typical automotive oil pumps are called "constant volume pumps". If you were to dump the output into a bucket they would deliver volume flow approximately linearly proportional to speed.

In an engine the oil is pumped against a restriction, which is the sum of the restriction of the bearings and other internal restrictions. This causes pressure to build up as volume increases. Once the pressure opens the relief valve, oil delivery to the engine is regulated by the pressure and the excess volume is bypassed back to the sump. If the engine achieves full oil pressure by about 2000 RPM you do not need a "higher volume" pump.

You do not need a "high volume" pump or high pressure on a street engine. For a medium performance engine that won't usually be revved over 5000 RPM a typical OEM pump and 35-45 psi relief spring is more than adequate. For a high performance engine that will see over 6000 RPM a 50-60 psi relief spring is optional, but plenty of mechanical lifter SHP small blocks were built with 40-45 psi springs and they rarely suffered oiling problems.

Higher pressure means more power is required to drive the pump, which reduces brake horsepower, and a "high volume" pump will just short the excess oil back to the sump, but that will take some power, too.

Duke

 

I am a fan of high volume pumps. I tend to add a few extra oiling holes to the block and distributor and I like the old rule of 10 psi per 1000 rpm. I also like to see my idle hot idle pressure around 40-50 psi and cruising around 60. It might take extra horsepower, not really needed but it makes me feel good and once the revs climb it is a good feeling to see the pressure around 80.
Alot recommend not going this route but for piece of mind I do it.

 

As stated above you don't need a high volume pump you gain nothing from it.
You shouldl have 10psi for every 1000rpms
I used a standard melling pump and changed the spring pressure is 63lbs hot I shift at 6500 max.

 

I agree with norval - I have a high volume and I happy with it. I use 10w40 year round.
The idle oil pressure is what I was looking for. Lots of idling in Los Angeles traffic. The only way to increase oil pressure at idle is to move more oil or use thicker oil.

 

Bearing load increases with the square of engine speed, so at a 750 RPM idle speed, the bearing loads are less than 2 percent of what they are at 6000!

Idle oil pressure of 5-10 psi is perfectly adequate. OEMs began reducing oil pressure back in the seventies to reduce parasitic loss, which improves power and fuel consumption and this trend continues today.

Duke

 

SWCDuke - Are you really ok with having 5 to 10 psi at idle? When do you start to worry? (when it gets in the 3-4 psi range - right?) :crazy:

 

I've never owned a car that was less than 15-20 at idle with a very hot engine, but some engines may be 5-10. As long as the pressure is up close full spec by about 2000 I wouldn't worry. There just isn't any bearing loading at idle.

Ever seen one of the displays for some snake oil additive, and they have an old Dodge slant six operating on a stand with no oil pan, and it's chugging at about 300-400 RPM. They'll run like that all day, snake oil supplement or not!

The prewar stovebolt six had splash lubricated rod bearings.

Duke

 

Now with new high vol I get almost 70 cold, 45 hot on hiway but goes down low like you guys are saying at 750 rpm to around 5-8. I have heard that for every 1000 rpm you should have 10 psi pressure, or something like that? So at 750, 8 psi is about right? Using 10W-40

 

You installed a high volume pump and you are only getting 8 psi at idle?
A high volume would give you at least 20 psi at idle. I have a HV in my 355 and I get 35-40 psi idle pressure when hot.

Is this a new motor?

 

Yes, new rebuilt motor. And the 8 psi is after coming off the hiway. Cold or other idle situations are much higher.

 

while 8psi is enough at idle to keep it from blowing a bearing if you have a new engine with a high volume pump and it idles at 8psi you have a serious problem with your engine. To give you something to compare to I do not have a high volume pump and mine runs 63lbs. on the road and 43lbs at idle this is hot.

 

There is a plug that is easily missed during an engine overhaul. If left out, you will end up with very low oil pressure. I believe it's near the oil pump area, but not sure. I will try to dig up some info on this.

I would contact the company that rebuilt the motor (if that's the case) & not drive it until you locate the problem :(

 

would that be loss of pressure at all rpms or just at idle?

I'm getting mixed responses. Some say gauge could be faulty. Engine place says use 20w-50 instead of 10w-40. Friend with small block hi-perf says his is around 20 psi at idle hot with high flow pump.

I think first step is get gauge that plugs into block directly and check. Someone did mention missing plug thing but said it would be in timing chain area.

 

I'll need to check my books when I get home tonight & I'll get back with you.
The small plug I'm talking about will give the same problems (low at idle and almost normal at higher rpm)
Can you give us more info on the motor? (piston info: cast/forged, bearing info, etc) Thanks.

 

Are you talking about the plug at the rear main.
They may have left that out. I can't believe that they recommended 50w instead of the 10-40 if you have low pressure with 10w-40 you have a problem that 50w is not going to cure.

 

I believe in the theory of high volume pumps combined with thinner oil grades. The thinner oil will flow faster which will create more oil circulating past the bearing surfaces. This will keep the bearings cooler and provide better protection. Good oiling is more about volume than it is pressure. I recomend the high volume pump along with Mobil1 synth 10w/30. If engine is new then break in with dino straight 30 weight, then switch to Mobil1 10w/30. The high volume pumps usually require a steel sleeve between the dist and pump shaft. The stock coupler sleeves are nylon and prone to failure.


[Modified by Jvette73, 9:44 PM 8/15/2003]

 

Black Bart - I think that's the one. The book I'm looking at references a plug above the rear main cap. It says: "If this plug is missing, oil will not be routed to the filter and the engine will not have satisfactory oil pressure. This plug is not installed on any new GM small block Chevy bare blocks from the factory"

It has a diagram but it's too small to see the plug location.

Hope this helps.

 

OK, on the plug, I believe there would be more symptoms at all rpms than just low hot rpms, so i'm pretty confident the plug arent missing. This all started when I spun a #1 rod bearing driving at 3500 rpms on hiway. Unfortunately I wasnt paying attention to gauge (nightime) so dont know if there was oil failure until engine tried to seize then no oil pressure. Anyway, engine was rebuilt, 040 over, new crank 010, crank holes bored/lined?,heads redone new everything, bearings, new cam,pistons,rings etc..but now with high vol pump.
I have special steel sleeve shaft made for mallory? pumps.

The thing is I had this behavior with old pump also. And engine builder said when inspecting broken engine it looked like there was no oil in there, but there was the perfect amount when I took it apart. So reason for failure is still unkown which makes me nervious about this problem. I do see big differences in basic pressures where I was 35 max before and now 70.

Just wanted to add shop asks if I removed air from plasic line to gauge which I havent. They said that could effect accuracy. I dont think I buy that one. To me pressure is pressure.

I'de like to know more about the plug at rear main cap. Exactly where would I find it to check. Could I see by taking pan off? THX


[Modified by Surfer69, 8:41 AM 8/16/2003]

 

Air in the line could possibly cause a low reading because the air is compressible. You are on the right track about confirming the gauge w/ a mechanical gauge directly connected. IMHO that shop is way F.O.S. to tell you to use 20W-50 on a street motor. Maybe they know that the main bearing clearances are high and want to use a band aid ?

p.s. I've read the same thing about the missing plug but I can't remember exactly where it is either.......surely someone does. What about Clem?


[Modified by need-for-speed, 4:38 PM 8/16/2003]