I had low oil pressure (under 20 psi at idle) after my rebuild last year with stock oil pump. So after a few recommendations, I put in a Melling 55A high pressure (standard volume) pump. I believe it's the Z28 pump.

Now my oil pressure is at 80 psi (max gauge reading) at start up. Drops down to 60 after warming up, but stays within 60-80 psi range depending on rpm.

Are there any negative points here? I know I don't have any oil leaks...

 

no, not really, just that everything is well oiled, i wouldnt worry about it, i'll take lots of oil pressure over too little oil pressure every day of the week and twice on sunday.

-alex

 

While too much may be better than too little, this isn't one of those "if some is good, more is even better" things. All your engine needs is about 10psi per 1K rpm for adequate oiling, even if it's a highly stressed racing lump, so unless your idle was north of 2000 rpm you had plenty of idle pressure, assuming your gauge is accurate. That 60-80psi is good for 6-8000 rpm, which means if your engine never sees those kind of revs it's too much pressure, which is just unnecessarily heating up the oil, wasting power, adding wear to the oil pump and related drive, and causing the filter's bypass to open even more than normal (not a good thing).

Fortunately, should you decide to address this issue, a C3's pan is relatively easy to drop so you can adjust/change that relief spring, if not the pump outright, as with that much pressure it's unlikely a thinner viscosity will make enough difference to take care of this. I'd do it, but then I'm picky about this mechanical stuff being right. Short of that, at least try to run a thinner oil and high flowing filter (that last one being something you should do anyway).

You ought to make whoever advised you to install that HP pump to do the nasty work of pulling the pan, scrapping the gasket and cleaning everything up, and then ban them from your garage.

 

That pump is indeed listed for the 1971 z28 camero, it is also listed for the 1974 corvette as the high performance pump. I run the same pump and have the same pressure 80 psi. I have faith in the person that recommended this pump, I"ll keep mine

 

Dropping the pan is easy. I have the FelPro reuseable gasket. But I don't want to change the pump if there are no major side effects of high pressure.

I use 10W30 with AC Delco filters. Car never runs over 195 degrees. I think I will things as they are.

 

I'm running a high volumn/high pressure pump in my 74 and I get the same pressure as you. I like it and would rather have it over the 3 lb./idle and 20 lb/running pressure I had before my rebuild.

 

Are you saying it NEVER drops below 60 psi or is that a normal cruise range?

I would expect it to drop lower than that with a stock pump/big spring combo at low rpms.

I'd double check with another gauge to make sure.

I'd rather see you run some 5-10/30 oil (if you aren't already) than to change the pump. Obviously your motor has some nice tight clearances.

It's possible the bypass piston in pump is sticking and will need to be cleaned up by removing pump....but before I recommended that I'd want info on above questions. To me...60-80psi at WOT is no problem.

JIM

 

Jim, that's what I understand he's saying here, and that's the reason for my post. I'm just not one of those guys who accepts something like this when it's that far out of spec. Apparently, that puts me in the minority here, but the company that shares my opnion includes David Vizard and the late Smokey Yunick, so I'm OK with that.

 

I haven't driven it yet. Just fired it up for the first time yesterday, since changing the pump last year. I will drive tonight and pay close attension to it. I always use 10W30 reg oil.

As far as motor goes, yes it's a tight one. Compression of 205 - 210 on a COLD motor Changed all gaskets and torqued the bolts properly, so not too worried about leakage.

stay tuned....

 

Before you change anything, I would get it really warmed up. It takes a while to get oil temp up...good bit longer than water.

Skunkworks- I'm with you there.....when things are way out from what you expect....you need to investigate why. That seems like a lot of pressure for a Z-28 pump....they usually don't hit 80+...especially when warmed up. That's what's worrying me about the oil temp first then the gauge and then the relief valve in pump.

I would also change the oil/filter because a bunch of assy lube can plug up a filter. Might as well get that out of the way while we're at it.

JIM

 

I"ve got about 7000 miles on my engine now. it idles at 700 holds 80 psi cold or at cruise, oils got to be pretty warm to see 60 psi (like a hour drive and stop and idle on a 95 degree day) i run 15w-40 rotella. I had the exact same kind of pump in the engine before rebuild, did the same thing on pressure. Guess i"m old school but i like the high pressure, so i give up a couple pony"s, it sure beats sitting at a stop light staring at a guage that only says 10 psi.

 

The thing that worried me the most when I had a high pressure oil pump was that the gauge was pegged most of the time, I wasn't sure that the gauge was working properly at start up. I put in a standard relief spring just so the gauge always reads somewhere in the middle, easier to tell at a glance that somethings going wrong. Maybe you could find a different pressure sensor to do the same thing so 80psi actually reads 40 on the meter (Didn't think of that at the time)

 

Your high pressure/hi flow oil pump is doing just what it should do. The standard GM pump is designed to properly lube a stock engine; and the design allows for the pressure to drop to about 10-20psi at idle which saves fuel and has less wear and tear on the pump. But you wanted a "jazzy" pump which puts out lots of flow and lots of pressure. It also does lots of WORK and doesn't really improve engine reliability....unless you have a high performance engine and use it regularly.

 

A std volume pump with the high pressure spring won't really put out any more pressure at low speeds. A stock pump can put out incredible pressure with a stout enough spring. The spring really just increases the upper limits and to some degree "when" it comes in. The pump still has to spin *X* rpm to build the pressure. The spring just lets it build more before bypass starts to open.



JIM

 

My engine is not stock by any means. On dyno it made 250 rwhp before the carb swap which was running pig rich. I think I am at 270 rwhp now. With TH400 loss, the motor should be pretty close to 350 fwhp.

I took the car out yesterday for a good run (120 miles, mixed city-highway driving) and here's what I jotted down:

cold (under 160 degree) - 80 psi regardless of RPM
warm (190+ degree) -
35-40 psi at idle in load (under 1000 rpm)
60 psi at 1500 rpm
75 psi at 2000 rpm
80 psi at 2200 or more rpm

Honestly, I'd rather see this pressure curve than watch the needle go below 20 at idle with stock pump

 

From what I see from your numbers is after 2200 rpm the pressure causes the bypass to kick in and more oil is not getting filtered I would not like to see them numbers myself and agree with skunk on this one. my engine has race clearance and hv pump and I get

cold start idle below 160 + 60psi
Hot idle + 20 psi
Hot 5000 rpm + 60psi
bypass doesnt kick in till 80 psi therefore oil always gets filtered like its intended to be. Thats way engines dont run the psi like yours. So to much of a good thing can be bad like was stated earlier. You might want to try 0w 20 but not sure it will help you that much.

 

The pump were talking about is a standard volume, high pressure. I never could comperhend how it has high pressure and standard volume, Jim just answered that when he said : The spring just lets it build more before bypass starts to open. (still learning here, thanks Jim)

Allthough it"s a good idea, i"m not to excited about changing out sending unit to only read half of actuall pressure. I"d be more interested in a device that went from sending unit to ignition so if oil pressure ever dropped to zero it would kill the engine.

My 355 sounds like it"s making 500 hp allthough it only made 276 rwhp, and 7000 miles in 6 months it gets driven, i like my "jazzy" pump, but i love driving this car !!!!!!!!!!!
david

 

I don't think filteration should be an issue in my case. I change the oil every 3 months and that's usually between 500-1000 miles. It's very clean when it comes out.

 

I think there is confusion on the two *bypasses*.

There is a filter bypass located in the oil filter adapter. It's a simple spring/disc affair that is opened by a difference in oil pressure above and below the filter.Depending on adapter it could be from 4-15 psi or so difference. It's designed to allow oil flow if the filter gets plugged by people not changing their oil. It also opens often with thick cold oil trying to get through a stock type filter. In fact...it's actually open a pretty good bit of the time. That's why you see many builders block it off, and specify the largest possible filter you can fit and tell you to make sure it's warmed up before you go out and smack it around some.

Then in the oil pump there is the bypass valve. Again it's a simple spring/plunger device that regulates max oil pressure. If you block off the bypass completely a stock pump can put out a couple of hundred pounds of pressure in less than a second or so before something breaks. Usually the oil filter blows off. All they did on the Z-28 hi pressure pumps was to install a stiffer spring. It allows higher oil pressure before the plunger moves to open the oil pump bypass internally. The oil actually returns to the inlet side of pump internally..it doesn't dump to the pan. So this bypass has no effect on oil filtering. It's just sending the oil within the pump right back into pickup area.

Now if you have a pump that is operating at max pressure against bypass all the time..that's not perfect. All that oil that is bypassing back into the pickup creates some havoc. It's actually can mess up the flow INTO the pickup by creating some pressure in the pickup tube when you would really prefer some suction. It can make oil foam more etc.

The idea is to have a pump that can stay off the bypass until you are at higher rpm ranges. That's why a Z-28 type pump, works well for motors with normal clearances. It will idle with stock type pressure...maybe 20-35 psi or so...and as you rev it it will continue to climb past the 45-50 psi that a stock spring allows. This way at 7000 rpm you get the 70+ psi oil pressure.

But it's all about internal engine clearances. When clearances are opened up in main and rod bearings, or just adding solid roller lifters..or adding the rollers or flat tappets with extra EDM oiling..you get internal leaks. That causes poor low speed oil pressure. A stock pump can get the pressure up there...but it takes more RPM to outrun the leaks. This is where a HV comes in. The gears are larger and they will be able to move more oil at lower speeds. This allows race type guys to run thinner oils too if they want to and it can also keep up with the amount of oil required to outrun all those leaks at high RPM...where a stock one might have trouble.

It's pretty common for folks to juggle pumps and springs. There are 3 springs that are common for big blocks. People use the mid pressure one in stock pumps (usually comes in the box) to make it act like a Z-28 pump. Then there is a higher pressure one that comes with the HV pumps..it can really crank it out. I've seen HV pumps with stock springs in them for old loose motors that don't need a lot of high rpm pressure.

My pump actually has a few shims behind the spring..I like oil pressure! Just makes me feel good. But it keeps me from having the bypass open as much as I approach high RPM.

Anyway, hope this helps some.

JIM

PS- And if you really want to get depressed...look up the oiling system flow charts in a stock small block. Rear main pretty much gets unfiltered oil all the time!

 

Jim, thanks for that information about bypass valves.

As far as my motor is concerned, I have stock bottom end with stock rods and pistons with 53,000 original miles on them. I have only done cam/head/intake swap. It is a 'normal' motor.

Is there a spring that you can recommend that I can use with this pump that'll give me pressure in between stock and Z-28 pump?

My stock was below 20 at idle even when cold.