Okay, I am building a motor for my son's truck and the stock vortec motor had an oil pump with a .75 pickup tube. My machinist just got me a rering kit to go along with his machine work, but he also included a Melling M55HV pump. That is the high volume oil pump that has a 5/8" pickup tube. I am sure it would work, but there must be some reason that GM went to a 3/4" pickup tube in the 90's. This is a factory roller cam engine. My concern is that because of the roller lifters, it may consume more oil volume than the traditional flat tappet engines, thus justifying the larger pickup tube. A high volume pump is already supposed to deliver 25% more volume than a stock pump. The M55HV is apparently able to do that with a 5/8" tube. Taking it back to the machinist is not an option, but should I go buy a modern version of this pump that supports a 3/4" pickup tube or is it unanimous that it doesn't matter?
I agree. The easy answer is to get a stock replacement or better, which would dictate a 3/4" pickup tube. I am hoping someone has some inside info/understanding of the oil flow requirements of the Vortec motor over a staditional Chevy Small Block. The only difference seems to be the roller cam setup, which is what they started using by default around the same time they increased the size of the pickup tube. The change over to 5W-30 oil came along with slightly tighter tolerances on the bearings (.001-.003), which would reduce oil volume requirements.
When GM went to the 3/4" pump inlet it also started some problems on a long term basis. The engines started to show bearing wear on the front most crank throws. I'm told that this is because the large tube pump creates an air pocket in the oil system on initial fire up. This in turn starves the forthest bearings for just that first instant. This is a very real problem on the 4.3 engine that uses the same pump. The only reason to use the 3/4" inlet pump is if a correct pump pickup can't be found. Such as in 4.3 4wd. apps. Personally I have been makin a living building engines since the mid sixties. Small block chevies in general don't need the M55HV pump. The pump ends up byp***ing a great deal of the oil picked up. Also wears the distrib/cam drive. I have always used the M55A pump. This std volume High pressure (aka Z/28 pump). Tho last year Melling has changed the pump casting to a weaker design (two broken ones on my OOPS! desk)) and I have to scrounge the older warehouses to get the good pump.
That's the same pump I run I'm going to say that you don't have anything to worry about. I've got @ 100K on my motor at this point. Those would be hard miles. I still hold 30 PSI at idle and over 60 cruising once the oil gets warmed up. When its cold out I have to go to winter oil.
Excellent info. Much appreciated. I have a 5/8" pickup tube to go with the new pump and feel more comfortable using it now.
I build a motor about every three years, and my 16 year old son is funding this one, so I just need to do everything right the first time. I appreciate all the comments.
I ran into that problem. I was in a pinch so I did this... http://www.jalopyjournal.com/forum/showthread.php?t=345737
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