What are the pros and cons of using a standard volume vs a high volume oil pump on a moderately modified big inch (383-421) small block that will rarely see over 6000 rpm?

 

If your clearances are put up on the loose side (0.0025-0.0030") to free up some power, the high-volume pump will be better able to keep up with demands on the lubricating system.

But, watch your pressures. According to Smokey Yunick, you shouldn't need more than about 10 psi per 1000 rpm to supply adequate oiling. Anything much more is going to unnecessarily heat up the oil, waste power, cause extra wear in the pump and its related drive components, and open up the filter bypass more often.

If you have high pressures which changing oil viscosity won't remedy, you'll need to adjust the pump's high-pressure relief spring.

 

All things being equal there is no advantage for the HV pump...if you build the motor with looser clearances the HV will help hold a higher pressure, something a High Pressure pump wont do.

So long as you arent seeing High rpms for prolonged periods you dont have to worry about a HV pump pumping too much oil up top...

Go read This and This from the Melling Website.

ultimately the RoT of 10 psi/1000rpm is what everyone goes by...if you plan up to 6000 rpm then I would suggest a Z28 oil pump which is a standard Melling M55 with a 60psi oil pressure relief spring pressure...

That should give you 60 psi @ 6000 rpm, clearances allowing of course.

 

Are we talking high volume or pressure?
I have heard a high volume is good for for loose engines, but I would think a high pressure would hurt the cam and distributar gears?

 

Racers that are going to run at high rpm, especially for long periods
of time run more clearance in the bearings, the extra clearance
slings off more oil, they run a high volume pump. you don't need
extra clearance in bearings for low rpm street engines. You can
put the high volume pump in your low rpm street engine, but
pumping the extra volume of oil costs a small bit of HP makes it
harder on the pump shaft the distributor gear. The racer needs
the extra volume and higher pressure, he just puts up with the slight HP loss.
If you were going to run regular clearance on the bearings and high
rpm for a little bit then you would want a high pressure pump, but
the high volume is only needed for loose bearing clearance. the
longer gears of the high volume pump trying to pump more volume
of oil puts more stress on the shaft and dist. gear.

Newer thin dino oils and synthetics are very easy on the oil pump,
its not as thick heavy to pump.

 

As noted above, the "Z28" pump is all most will need on this forum, that's the one I have

 

ok, how do I know what kind of pump I just purchased?

I am replacing the pump on a tight engine, are there any markings on the box that will tell me I have a Z28 pump?

I specifically said I didn't want a HV pump!

now comes the QA/QC portion, did I get what I asked for?

 

It takes more to turn a high volume pump, longer gears trying to move a lot more oil. High pressure,not so much

 

M55A - SB-Chevy Z28 H.O. Oil Pump

 

Thanks,

it's a clevite pump, box marking says M-55, I am assuming it is a close match, canadian vs american box markings!

Thanks

 

If it's a M55, then it's a Melling OEM replacement pump. Std volume, std pressure.

http://store.summitracing.com/partde...5&autoview=sku

 

Another pitfall of using an HV pump is that you'll very quickly flood the valve covers with oil unless you go to the trouble of tearing the engine down and having crank-to-cam oil restrictors installed to prevent that from happening. Try it and see.....

 

I have run the high pressure Z/28 pump on every small block I
ever built, far as I'm concerned all small blocks should have one
low rpm or higher, pull the bottom off the pump, braze the pickup
tube, pressed in pickup tubes can be an accident waiting to happen.
When I was 17 late one night out on the freeway I was running as
fast as my little 302 screamer would run, the oil pressure gauge was
down on the console, I failed to notice my oil pressure gauge, the
pressed in pickup tube fell into the pan, the car was still under
warranty, Cliff Peck chevy put a new crank in it two new rods.
The car had 18,000 miles on it, when it happened.

 

I have - never happened to me.

 

Only difference between a m55a and a m55 is the pressure relief spring - you can buy the spring seperate if you need to

 

A stock pump can put out ungodly pressure if you install a stiff enough spring and spin it fast enough. They can easily blow the filter right off the motor and make way over 100 psi without breaking a sweat.

The only difference in a Z-28 pump and a stock pump is the spring. An M55A is a M55 with a different spring. BTW- it's a great setup overall.

First I suggest you do a little search just about anywhere on the net and look for Melling oil pump cracking issues the last few years and evaluate what you have and what you will do with it.

Next, way too many wives tales out there on HV vs Stock pumps. Most just repeat over and over what someone said once. Yes it takes power to build oil pressure...whether you do it with a stock pump and a big spring, or you do it with a HV pump. 60psi is pretty much 60 psi regardless of how you get it. If it's a HV pump..it's just going to get to 60 psi at a lot lower rpm. But when the spring allows bypass to open..it's just going to bypass oil at 60 psi just like the stock one will if it has a 60 psi spring. Now, you don't necessarily want to run around with the oil pressure gauge pegged all the time. In that case the pump is bypassing constantly. It returns oil to pickup tube area and it does disrupt flow somewhat. You want oil pressure to continuously rise as RPM goes up and hopefully it gets to the max area sometime around when you are at max RPM and power. If you have pressure fed roller lifters, EDM drilled flat tappet lifters, looser clearances etc etc..you will have a lot more internal leakage that will all add up to less oil pressure at low speed as well as more RPM required to get to *X* oil pressure.
A HV pump is a great advantage in those cases. They also help greatly when you want to run thinner oils. Sometimes the thin stuff ends up with pretty low pressure when it heats up. Some big block guys use a HV pump with a medium spring to get oil pressure in a reasonable area at high rpm, and still have good low speed pressure.

I personally *like* a lot of low speed pressure. It's funny, but even some of the newest high tech badboy stuff out there from the OEM's is seriously cranking the oil pressure up to go along with the super thin oils they use for mileage. They had to to keep them alive.

I've yet to wear out a dist gear with a HV pump. And I've done lots of road trips with them including lots of regular street miles.

As said, most folks are fine with a std pump and a good spring, but it sure is depressing to have to pull a pan back off because it only hold 5 psi at idle. I always sand the housings to tighten the end clearances to .0005-.001. That helps low speed pressure too.


JIM

 

A HV isnt a good solution for a motor with standard or tight clearances.. a HV/HP pump is a rediculous choice for the same...a HV pump makes perfect sense in a motor running super thin oils or running looser clearances.

As it often is, some people get caught up in the "bigger is better" conundrum and when they select that HV/HP pump for their stock clearance motor and they start pumping too much up top or do other sorts of damage...they never blame themselves for selecting the wrong pump for their application, its always "this pos Hv pump is.. blah blah.."

If your motor has std clearances, you shouldnt need anything more than a std pump...if you plan on running at higher RPM then a std pump with a higher pressure relief spring...if your clearances are on the loose side you can consider a HV pump without any concerns about flooding your valve covers or damaging your distributor gear.

 

Most HV are stock + 25%

Nice compromise is Melling P/N 10552 ... it's stock + 10% and it's the heavier competition casting. Unlike OE, it uses a bolt-on screen-pickup ... P/N 12557 is correct bolt-on screen for 7" deep stock pan ... 12558 for 7 1/2" ... 12559 for 8".

 

This is the pump I now have lying around, I don't really want the
10% more flow, I have not pulled it apart, but I believe the gears
are supported both at the top and the bottom, not just at the
top like the factory pump, bigger dia pickup tube,
bolt on screen, billet gears, super strong housing, its $30.00 bucks more, needs a
bigger pan. Probably massive overkill for anyone other then a
high rpm freak like me. did not mention it, afraid someone
would throw it into a stock five quart system, 10% more flow might
work in a stock pan might not.

 

if you are going to run solid roller lifters, you may want to run the HV pump to ensure lubrication to the rollers