"Z28" Oil Pump
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From: Charlestown, IN
Car: 1971 Camaro
Engine: 427
Transmission: TKO600
Axle/Gears: 3.73
"Z28" Oil Pump
What makes the old z28 style oil pump different, better than the standard pumps?
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From: Loveland, OH, US
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Right; same pump, different relief spring.
You can build the same thing yourself for about half the price, by buying a regular M55, and adding the Mr Gasket spring, part # 26.
You can build the same thing yourself for about half the price, by buying a regular M55, and adding the Mr Gasket spring, part # 26.
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From: So. Ohio
Car: 88 Camaro
Engine: L98 350
Transmission: 700r4
Just about everyone agrees that the higher pressure is not needed or wanted on a modern engine, especially with roller lifters. Pretty much a waste of horsepower to run the pump.
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From: Louisville, Ky
Car: 1991 Z28
Engine: 383
Transmission: T-5
Axle/Gears: 3.08 10 Bolt
Originally Posted by tom3
Just about everyone agrees that the higher pressure is not needed or wanted on a modern engine, especially with roller lifters. Pretty much a waste of horsepower to run the pump.
Why would that be? [I hate when info is thrown around with no reasoning]
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From: Saskatoon, SK, Canada
Car: '83 Z28, '07 Charger SRT8
Engine: 454ci, 6.1 Hemi
Transmission: TH350, A5
Axle/Gears: 2.73 posi, 3.06 posi
Because at a certain point, more pressure isn't going to help anything, but it takes up more power to run it.
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From: Overland Park in the Great State of KANSAS
Car: 91 Z28
Engine: 468 ci
Transmission: thm 350
It also puts more load on the cam, twisting, and can cause spark scatter and valve timing differences from front to back of the engine.
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From: Armpit state
Car: 71 Nova
Engine: Superramed 383, Topline heads
Transmission: 700r4
Axle/Gears: 8.2 posi 3.08
Originally Posted by katman
It also puts more load on the cam, twisting, and can cause spark scatter and valve timing differences from front to back of the engine.
Funny the manufacture of the most popular oil pumps seems to disagree.
Melling Engine Parts: Technical Bulletins
That is what a high volume pump will do. Now let Is consider what it will not do.
It will not replace a rebuild in a worn-out engine. It may increase pressure but the engine is still worn-out.
It will not pump the oil pan dry. Both solid and hydraulic lifters have metering valves to limit flow of the oil to the top of the engine. If a pan is pumped dry, it is because the holes that drain oil back to the pan are plugged. If the high volume pump is also higher pressure, there will be a slight increase in flow to the top.
It will not wear out distributor gears. The load on the gear is directly related to the resistance to flow. Oil pressure is the measure of resistance to flow. The Ford 427 FE "side oiler" used a pump with relief valve set at 125 psi and it used a standard distributor gear. Distributor gear failures are usually caused by a worn gear on a new cam gear and/or worn bearings allowing misalignment.
It will not cause foaming of the oil. With any oil pump, the excess oil not needed by the engine is recirculated within the pump. Any additional foaming is usually created by revving the engine higher. The oil thrown from the rod bearings is going faster and causes the foaming. This is why high performance engines use a windage tray.
It will not cause spark scatter. Because of the pump pressure there is a load on the distributor gear. The number of teeth on the oil pump gears determine the number of impulses per revolution of the pump. In a SB Chevy there are seven teeth on each gear giving 14 impulses per revolution. At 6000 RPM the oil pump is turning 3000 RPM or 50 revolutions per second. To have an effect on the distributor, these impulses would have to vibrate the distributor gear through an intermediate shaft that has loose connections at both ends. Spark scatter is usually caused by weak springs in the points or dust inside the distributor cap.
It will not replace a rebuild in a worn-out engine. It may increase pressure but the engine is still worn-out.
It will not pump the oil pan dry. Both solid and hydraulic lifters have metering valves to limit flow of the oil to the top of the engine. If a pan is pumped dry, it is because the holes that drain oil back to the pan are plugged. If the high volume pump is also higher pressure, there will be a slight increase in flow to the top.
It will not wear out distributor gears. The load on the gear is directly related to the resistance to flow. Oil pressure is the measure of resistance to flow. The Ford 427 FE "side oiler" used a pump with relief valve set at 125 psi and it used a standard distributor gear. Distributor gear failures are usually caused by a worn gear on a new cam gear and/or worn bearings allowing misalignment.
It will not cause foaming of the oil. With any oil pump, the excess oil not needed by the engine is recirculated within the pump. Any additional foaming is usually created by revving the engine higher. The oil thrown from the rod bearings is going faster and causes the foaming. This is why high performance engines use a windage tray.
It will not cause spark scatter. Because of the pump pressure there is a load on the distributor gear. The number of teeth on the oil pump gears determine the number of impulses per revolution of the pump. In a SB Chevy there are seven teeth on each gear giving 14 impulses per revolution. At 6000 RPM the oil pump is turning 3000 RPM or 50 revolutions per second. To have an effect on the distributor, these impulses would have to vibrate the distributor gear through an intermediate shaft that has loose connections at both ends. Spark scatter is usually caused by weak springs in the points or dust inside the distributor cap.
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From: So. Ohio
Car: 88 Camaro
Engine: L98 350
Transmission: 700r4
Let's look at it from a different angle. Why would 60 psi be better than 40 psi? Consider that most friction in an engine is sliding friction, an oil film is the required lubrication. The high pressure Z28 pump may have some benefit at very high rpm, which might be why GM used it in only this engine? Or maybe the higher pressure prevents foaming? But the high volume and high pressure pumps are not recommend by any engine guys I know or articles that I've read for the modern engines. It would be interesting to see an engineering report on one or the other.
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From: Yellowknife, NWT, Canada
Car: 84 Z28
Engine: 357
Transmission: TH-350C
Axle/Gears: 3.43
of course melling is only going to say good things.
Their the ones trying to sell it!
Whether what they say is true or not i dont really care. A regular old stock replacement pump is all im putting in...
Their the ones trying to sell it!
Whether what they say is true or not i dont really care. A regular old stock replacement pump is all im putting in...
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From: Armpit state
Car: 71 Nova
Engine: Superramed 383, Topline heads
Transmission: 700r4
Axle/Gears: 8.2 posi 3.08
Originally Posted by 84z28350
of course melling is only going to say good things.
Their the ones trying to sell it!
Their the ones trying to sell it!
Last edited by shaggy56; Jul 12, 2006 at 08:06 PM.
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From: Armpit state
Car: 71 Nova
Engine: Superramed 383, Topline heads
Transmission: 700r4
Axle/Gears: 8.2 posi 3.08
I found some interesting info from another site. This information is not coming from a manufacturer or trying to sell you anything.
High-pressure oil pumps are another option. A high-pressure pump contains a stiffer relief valve spring that doesn't open until a higher pressure is reached (75 psi or higher). The actual flow rate of a high-pressure pump may be no different than a stock pump, or it may be higher if longer gears are used. Either way, the pump will increase the system oil pressure reading at high rpm when the pump is working hard, but it won't have any effect on idle pressure when the pump is turning slowly
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Their the ones trying to sell it!
There's a time and a place for a high volume pump. When you get there, Melling will sell you one. There's a time and a place for a totally stock replacement pump. They sell that too. And of course, there's a time and a place for a pump that delivers stock volume, but has a higher pressure relief spring, to oil the journals properly at the higher RPMs that a more "performance"-oriented street engine will see, and they make that one TOO.
I also use the regular Melling M55 with the Mr. G spring for street motors. That's basically identical to the "Z28" or "Corvette" pump (Melling M55-A), but for less money. I don't use the high-volume pump (M55-HV) or the REALLY-high-everything pump (M99-HVS) in typical street motors because they're unnecessary. Those are for race motors with significantly modified oil systems.
Also keep in mind, the Melling write-up that was quoted, applies to STOCK REPLACEMENT situations; NOT performance or racing build-ups.
Roller lifters vs. flat-tappet lifters has absolutely nothing to do with the choice of oil pressure.
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Joined: Oct 2001
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From: Louisville, Ky
Car: 1991 Z28
Engine: 383
Transmission: T-5
Axle/Gears: 3.08 10 Bolt
Plugging Oil Filter Bypass
Would the high pressure spring possibly be more likely to blow out a filter because I have my high pressure bypass plugged on the oil filter adapter.
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more likely to blow out a filter
high pressure bypass ... on the oil filter adapter
No such thing...The only "bypass" on the filter adapter, is a valve that opens when there gets to be about 5 psi or so of pressure drop in the filter. This is not connected in any way with the system pressure; only, whether the filter is stopped up or not. I don't plug those, myself; seems kind of unnecessary to me, if the filter gets changed on a more or less regular basis. All that the bypass does, is to allow dirty oil to get to the motor, rather than NO OIL AT ALL, in the case of a stopped-up filter. IMO dirty oil is better than running dry. On the other hand, keeping a functional filter installed is better than either.
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From: Louisville, Ky
Car: 1991 Z28
Engine: 383
Transmission: T-5
Axle/Gears: 3.08 10 Bolt
Originally Posted by sofakingdom
keeping a functional filter installed is better than either.
I thought the bypass on the filter adapter was setup to open when the oil pressure is very high to prevent the filter from blowing out (such as on cold starts).
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No, that's not what it does.
All it does, is bypass the filter: it opens when there's more than about 5 psi of pressure drop across the filter. In other words, if the pump puts out 150 psi, and there's 2 psi of pressure drop in the filter (new free-flowing filter) it will not bypass; but if the pump puts out 20 psi and there's 5 psi of drop in the filter (old dirty stopped-up filter) it opens and lets the oil through.
It has nothing whatsoever to do with "blowing out" the filter.
Messing with the spring in the pump is what does that. That spring, and the valve that it controls, regulates the pressure. The way an oil pump works is, it's "positive-displacement", which means, every time it turns, it moves exactly the same amount of oil. Then the regulator "bleeds off" enough of that volume, to keep the pressure below whatever it takes to push the valve open against the spring tension. Used to be, people would plug up the bypass IN THE PUMP, that the little regulator valve lives in; if you do that, then the oil pressure WILL go sky-high on a cold startup, especially with the candle wax that these same people used to run for oil. THAT'S what blows out filters, not anything to do with the one in the filter adapter.
All it does, is bypass the filter: it opens when there's more than about 5 psi of pressure drop across the filter. In other words, if the pump puts out 150 psi, and there's 2 psi of pressure drop in the filter (new free-flowing filter) it will not bypass; but if the pump puts out 20 psi and there's 5 psi of drop in the filter (old dirty stopped-up filter) it opens and lets the oil through.
It has nothing whatsoever to do with "blowing out" the filter.
Messing with the spring in the pump is what does that. That spring, and the valve that it controls, regulates the pressure. The way an oil pump works is, it's "positive-displacement", which means, every time it turns, it moves exactly the same amount of oil. Then the regulator "bleeds off" enough of that volume, to keep the pressure below whatever it takes to push the valve open against the spring tension. Used to be, people would plug up the bypass IN THE PUMP, that the little regulator valve lives in; if you do that, then the oil pressure WILL go sky-high on a cold startup, especially with the candle wax that these same people used to run for oil. THAT'S what blows out filters, not anything to do with the one in the filter adapter.
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From: Louisville, Ky
Car: 1991 Z28
Engine: 383
Transmission: T-5
Axle/Gears: 3.08 10 Bolt
Very good to know. I don't like the idea of unfiltered oil getting back into my motor, especially after this latest attempt at building one, so I plugged it.
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Well: what's worse?
Dirty oil?
Or, NO OIL AT ALL?
Hmmmmmm........
That's why I leave that filter bypass alone. Now that's just me, of course; everybody has his own personal comfort level about taking risk, and which risks they want the most to avoid. Me, personally, I'd rather have dirty oil than have my bearings run dry. Or in fact, I'd rather just keep a clean filter installed. But others may see that tradeoff differently. It's better to make an informed decision on the basis of knowing what the parts actually do, rather than "the guy in the McDonalds parking lot last Friday night said....." or even "I saw it in a magazine" (not too far from the same thing IMHO). Learn, and make an intelligent decision.
Dirty oil?
Or, NO OIL AT ALL?
Hmmmmmm........
That's why I leave that filter bypass alone. Now that's just me, of course; everybody has his own personal comfort level about taking risk, and which risks they want the most to avoid. Me, personally, I'd rather have dirty oil than have my bearings run dry. Or in fact, I'd rather just keep a clean filter installed. But others may see that tradeoff differently. It's better to make an informed decision on the basis of knowing what the parts actually do, rather than "the guy in the McDonalds parking lot last Friday night said....." or even "I saw it in a magazine" (not too far from the same thing IMHO). Learn, and make an intelligent decision.
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Joined: Oct 2001
Posts: 3,155
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From: Louisville, Ky
Car: 1991 Z28
Engine: 383
Transmission: T-5
Axle/Gears: 3.08 10 Bolt
I'm defenitly one to keep clean filters on my cars.
Heck, I changed the oil 6 times the very short time I had it running. This motor should never see anything close to a clog.
Heck, I changed the oil 6 times the very short time I had it running. This motor should never see anything close to a clog.
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From: Cypress, California
Car: 1989 GTA
Engine: 369 TPI
Transmission: 4L60E
Axle/Gears: 3.70 Nine Bolt
If GM thought the Z28 needed the "high pressure" pump that is good enough for me. I will have one in my next rebuild.
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