This is info from the old site, I’m sure most have read it before.
credit=patooyee
I spoke to an engineer who worked for Saginaw today and he gave me some VERY enlightening information. I'll try to summarize it ...
First, the P-Pump displacement calcs I had given above are wrong because I was ASSuming that the “idle” speed they were specifying was around 800 rpm. In fact it is 465 pump shaft rpm. Thus:
P132 = .66 CID
P185 = .92 CID
P235 = 1.17 CID
Also, it has been stated that the P185 and 235 have the same internals, which is only partially correct. The 235 has a larger egg-shape machined into its ring. This is how it gets its larger displacement figure.
The P235 and the TC pumps are the only two automotive pumps in our consideration that use bearings to support the shafts. All the rest use bushings. This is an aspect that I believe ALL of the aftermarket is not taking into consideration.
The the bushings start out as a flat piece of bronze. That piece is then rolled into a round shape, pressed into the bore of the snout of the pump and honed for exact fit. Where the two ends of the flat piece meet is left open as a seam for oil to travel through and at the factory this seam is precisely clocked to match the orientation of how the pump is to be mounted on the specific engine it is to go on. IE, if the pump is to be mounted at about 3 o’clock as you look at the front of the engine, the groove on that bushing will also be mounted at 3 o’clock in the bore so that the tension of the belt does not pull the shaft toward the seam and cause it to wear excessively. The engineer I spoke to speculated that misorientation of the bushing is what leads to most pump failures. There are a few reasons for this. One is that people will move their PS pumps around or use pumps from other applications. Another is that the mass rebuilders whom most of the pumps come from at the parts houses don’t take bushing orientation into consideration. IE, they see a p-pump, they rebuild it not knowing or caring what it came off of or what it goes onto. It then becomes just a generic p-pump for any vehicle that needs one. Even if the bushing doesn’t cause the front pump seal to leak, it can cause the vane rotor to run out of true which would then cause hp fluid to leak past the vanes into the low pressure areas and cause tons of cavitation. I now believe that this may be the cause of all my failures as I always ran very high belt tension on my pumps to prevent belt slippage. Wear bad enough to destroy a pump could be invisible to the human eye.
TC pumps are what most NASCAR rigs are running. This is for a few different reasons. The bearings allow the pump to be spun fast … VERY fast. The engineer did not recommend it but said that some NASCAR teams are spinning the pumps up to 10,000 rpm and they are surviving. In addition, TC pumps are more durable when upping the pressure due to the thick cast back plate / cover. This doesn’t mean you can push them to 3000psi. They were designed to be run in the 1200 – 1300 range and some people are pushing them as high as 1600. In addition, their smaller displacement sucks less hp out of the engine. Something I didn’t know about TC pumps is that they have 3 displacements, .4 gpm @ 465 rpm, .6 gpm @ 465 rpm, and .88 gpm @ 465 rpm. The difference in them is larger bored cam rings. Obviously the .88 is going to be what we all want despite its parasitic draw. You can tell what you have though by looking at the cam ring. 4 cast diamonds = .2, 3 diamonds = .3, 2 diamonds = .44. The one in the pics above has two diamonds and it came out of a 1997 Jeep Wrangler 4.0L. Other common applications are ’06 Corvette, ’02 Wrangler and Corvette. He said lots of Jeeps have the higher displacement TC pumps because Jeep knew they would be going offroad a lot. HOWEVER, just because you go to a part store and ask for that application doesn’t guarantee you will get a double diamond pump. This is for the same reasons you may not get the correct clocked bushing in a p-pump. Many reman houses will just see a TC pump, rebuild it, and send it out. They don’t know or care what it came off of or what it goes on.
I found out about a new type of pump called a “CBR.” Externally it looks like a CB pump but it is designed for higher pressure operation. It has the same bolt pattern as a CB and TC. It uses a bushing like a CB does. It runs at 1700 – 1800 psi in factory form. Applications for it include newer GM trucks, the new Camaro, and the Buick Lacerne (sp?). He referred to this pump as a “hybrid” but I’m not sure what it is a hybrid of. I’d be willing to bet that it has a cast back plate similar to a TC to withstand those higher pressures though.
We also spoke a little about the pressure control valves and output orifices. I think there is a little misconception about those here on Pirate that was cleared up for me. The going theory is that drilling the orifice in the output fitting results in more flow at idle. That is wrong. The size of that orifice determines bypass pump shaft rpm. Pumps come stock set to bypass at 1500rpm. That means that, while you can do the math to figure out how much a pump will flow at say, 6000 rpm, it doesn’t matter because everything above 1500 rpm is bypassed back to the low pressure side of the pump. Drilling that hole increases the rpm at which the pump bypasses and therefore gives you more rpm to work with. That is why some people report no improvement with this modification, some report a lot, and others just report cavitation. It depends on your setup and what rpm your pulley is spinning the pump at during engine idle. IE, if your pulley ratio is idling your pump around 1500 rpm, you may see improvement with that modification because you are now able to use the additional flow at higher rpms. But if your pulley ratio is spinning your pump below 1500 rpm at engine idle you may see no improvement at all because you are idling below the bypass rpm limit that you have raised. Some people experience cavitation because they have restrictions in their systems that don’t allow the pump to pull enough fluid through at the new higher rpm range. Like Jstarnes pointed out in a previous thread of mine, the pump relies on that bypass volume at higher rpm’s and is not designed to take enough fluid in at the inlet without it. This leads me to my next point …
Finally, something that has bugged me is these crazy numbers that the aftermarket is claiming that their pumps put out. The reason it bugged me so bad is that I now know that they are using the same internals as stock pumps. Fluid is not air, it does not compress. Porting a pump is not like porting an engine intake. There is only a certain volume between vanes on a pump and nothing you can do will fit any more fluid in there than there is physical space to fit. The factory has to be using all of this space or cavitation would occur. Thus, at any rpm there is nothing you can do to a pump to increase its displacement. Displacement is a factor of rpms and volume. Since I know volume isn’t changing, all that can be changing is rpm. Thus, while the aftermarket can specify that they start with the largest internals available, the numbers they are quoting MUST be at different rpms than the factory quotes. IE, higher than 465. This makes sense to me though because I have yet to find a factory setup that actually idles the pump at 465 rpm. Virtually all of them idle much higher than that, normally around 1000 or so. In addition, much of the time the aftermarket will include a smaller pump pulley with their “matched” kits that would increase pump idle speed even more. And don’t think that I am implying that the aftermarket is being dishonest about their output because I don’t think they are. I think it wouldn’t make any sense to specify an output at 465 rpm because I personally guarantee you that NONE of the pumps on our rigs ever see rpm as low as 465. The factory does it there because they are building a pump to sell to many different manufacturers so they just pick a standard and stay there. (I’m sure there is a bit more logic to it than that, but the point is that once they pick a standard they have to remain there for all potential customers.)
There are further conclusions that can be drawn from here. I think at this point though I will just sit back to see what happens as I do not want to make any more ASSumptions. I will leave it for now with this chart and graph of the various stock pump outputs. Remember, in stock form nothing above 1500 rpm matters because it will all bypass at that point. BUT, if you modify a pump to bypass at a higher rpm than it is designed you must also be prepared to do something to replace that lost volume that the bypass valve would have otherwise supplied.
Thank you patooyee for the written post!
at 800 rpm idle, a cb pump with 5.5” pulley should net you 3.11gpm (assuming 100% efficiency) at still at 5200 engine rpm, be at 7040 pump rpm. Cb’s are ‘rated’ at max 7000.
even at a 6” pulley at idle you get 2.85, more then the tc can put out. With such a low redline, I think a cb pump would suit you well
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