A zero cost oil pump upgrade saves money, bearings and parasitic losses.
We work hard to make power in the cylinders but parasitic losses counter our efforts all the way to the tire contact patch. Here’s just one little trick we can do to help that situation.
It’s not uncommon for a head porter to spend 50 hours porting a set of production heads. The result can be an increase of 50 to maybe as much as 75 hp. That works out at one to one and a half hp for every hour spent on the porting. It is not so obvious but the same deal, or there abouts, can be had by ‘porting’ your oil pump. By spending between 30 minutes to an hour reworking the oil pump about one and a half to two hp can be saved depending on the rpm you run your engine too.
To see how this works we need to be clear in our understanding of how the stock Chevy oil pump works.
Take a look at the photo below.
Oil enters from the pickup through the cap containing the pressure relief by-pass valve on the bottom of the pump and enters the cavity indicated by the lower arrow of the above photo. The gears rotate around in the direction of the two red arrows and in so doing carry oil by trapping it between the valleys between the teeth and the wall of the pump casing. When the oil reaches the discharge cavity of the pump body (upper arrow) it gets squeezed out from between the gear teeth as they come into mesh in the center. Now take a look at the little void formed by the valley of gear tooth #1 in the photo and the tooth below it of the mating gear. If, as the gears turn, there is nowhere for the oil in that formed cavity to go except by leakage, we can see that it is trying to compress the oil. That’s not going to happen but a considerable amount of extra torque will be applied to the gear pair just at the last moment before the pair pass an imaginary line drawn between the gear centers. In reality there is nowhere for that last drop of oil trapped at this point to go other than through forced leakage. Why – because the exhaust ditch in the body and the cap of almost every pump casting you see has not be carried quite far enough to allow an effective route for the oil to escape.
The photo below shows the situation that exists in most instances.
The smallest volume between the valley of one gear and the tooth of another occurs when the valley and tooth lie on the centerline between the two gears. The top edge of the yellow line in the photo above is the centerline between the two gears. Note how the exhaust ditch, which is supposed to carry the oil squeezed from the trapped volume between the two gears, falls short of the yellow line. A similar situation occurs on the cap. To rectify this and to carry the oil away in a more efficient manner to whole exit side of the pump needs to be ‘ported’ as shown below.
What you see here is the exhaust ditch cut to the centerline of the gears and widened. Also the radius along the edge of the exhaust depression at the 12 o’clock to 2.30 position of the left and 9.30 to 12 o’clock on the right is cut to coincide with the root of the gear teeth. Also the exhaust depression has been made deeper by about a mm and a generous radius applied to the area leading into the passage to the mains cap.
In a like manner the exit from the pump body can also be improved as shown below.
By grinding the exit passage like this we give the oil more room to maneuver around the shaft of the pump securing bolt. That same theme needs to be carried on to the mains cap as shown below.
With the pump body and mains cap done we need to turn our attention to the pump cap containing the pressure release valve. There are several details that need our attention here. First there is no exhaust ditch for the last of the oil trapped between the gears and secondly we have to try and smooth the flow from the bypass back into the pump body. Just in case you were unaware the bypassed oil is looped around back to the intake side of the pump rather than being dumped back into the pan. A pump with too much capacity (such as the high volume pump) means the oil gets heated up more as it goes through the pump time and time again rather than going through the bearings. The before and after shots of the pump body cap below should show the detail you need to modify yours similarly.
At this point the performance of the pump is noticeably enhanced. Firstly less loss of pressure within the pump means that a few extra psi is available at the main bearings. Secondly it appears the oil gets heated slightly less within the pump so a slightly thinner grade of oil can be used. Third the effective delivery volume of the pump is increased so you won’t need a high volume pump anyway. At GFN we are seeing the oil pressure, using a stock relief spring, at about 5 psi more than with a stock pump. (Melling color code on springs is – plain 40-45 psi, yellow 50-55 psi, pink 65-75 psi) In most instances the fear of not having enough oil pressure prompts the use of a higher poundage pressure relief spring. Judging by what is used in some of the most expensive and powerful race engines (and it’s thick with those in the Charlotte area) it seems that 50 or so PSI is more than enough for the job in engines turning to 7500 even 8000 rpm Remember the oil pumps job is to get the oil to the bearings not to support the bearing loads. The bearing loads are actually supported by the hydro-dynamic pressure developed during component rotation and, at high rpm, amounts to over 10,000 psi!
Of course some of the gains we have made here can be lost due to an overly restrictive oil filter. The filter we most often use on the dyno is the System One stainless mesh filter seen below right. This has about 800% greater flow than a typical quality conventional filter. There is however a new guy on the block here. Based on flow and filtration capabilities we are starting to use more and more of the Amsoil high flow micro filtration oil filters.
So what have we achieved up to this point? If you prime your freshly built Chevy motor by removing the distributor and running the pump with a dummy drive shaft and an electric drill you will be aware that when the oil fills everything up and pressure starts to build in the block components the drag on the drill goes up considerably. The first thing you will notice with a pump modified as shown here is, with a typical drill speed, that the drag on the drill is noticeably less for the same bearing pressure seen on the pressure gauge (if you have one hooked up that is).
If you have redone a pump that was used previously you will also see about 5 psi more pressure. This begs the question as to whether or not we could reduce the pump size and make a further cut in the power required to drive it since it is now acting as if it was bigger. The answer is yes. Seems DV shortens his pumps by about 0.06 to 0.10 inches. That’s about the limit allowed by the body before the securing screw threads are too short to do their job.
Dusty Kennett