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Old 02-05-2013, 03:46 PM
ap72 ap72 is offline
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Originally Posted by View Post
Yes, they improved the pump. But, there are thousands of the bad pumps out there as old stock in the parts warehouses. Of course the price went higher.
Luckily I bought all the original design pumps my warehouse could get back when the problem started. My left turn guys insist on them.
NEVER run a hi-vol pump in a street engine. The pump will cause excessive dist gear/cam drive wear in many applications. I have been seeing a lot of this since the oils we are forced to use came about. Plus most of that hi-volume oil just blows by the pressure by pass and is wasted.
My left turn customers are known for using an engine up. Amazes me how much a rules built engine can put out, and they all use std volume pumps with a spring replaced. Or M55-A
The bypass will open up once your operating pressure is reached, most of the time in the mid RPM range (2-3k RPM) when that happens the only additional stress it can put on the cam drive gear is the force it takes to pump oil through the bypass (not much). In fact a high pressure spring will cause a lot more stress than a high volume pump.

There really is little to no truth about additional stress at high RPM, BUT it will put more load on the cam gear at low RPM, while also providing more oil pressure and flow throughout the engine (hence why I recommend it for the street and not racing).

One draw back it will have at high RPM is circulating a lot of oil through the bypass, causing cavitation and foaming. Porting the pumps passageways will help, as will using a good oil, as will increasing the bypass pressure (though that adds more stress to the cam gear again).

On the street where you'll see low rpms fairly often it can help a lot (if you run an OD, low gears, big tires, etc), BUT if you are almost always over about 2500 RPM or so (where the bypass opens up) then you won't see any advantage and actually create problems at high RPM.

SO for a street car that is usually at 2500 RPM or less its a good idea, if you're over that then it starts becoming unnecessary and if you're at HIGH RPM (5,000+) then it can become a problem.

Also, if you can always run the largest diameter pickup you can and port all the oil passageways you can to reduce dynamic pressure loss and cavitation- improving flow and quality of oil.

There are also pumps that are designed to deliver better pressure, volume, and quality of oil, but they're more expensive- these are the typical pumps that you'll get for $50 or less and are common to rebuild kits.
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