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Anyone try modifying stock Mitsubishi oil pumps for higher oil pressure? Wondering if can modify presure relief valve spring tension to increase? Seen it done on small block Chevy's, but haven't on these.
 

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Interesting thought, but please read-on if you're seriously considering this modification. BTW - why is this done on small blocks? All engines I've dealt with (mostly Chrysler) releive pressure between 60 and 75 psi. As you know, a stiffer spring will raise the relief pressure, however care must be taken to use a spring that will not fatigue, weaken, and fail.

FYI to all with interest. . .
In general terms, oil pumps (gerotor and gear) raise oil pressure linearly with pump speed. Most of todays pumps run at crank speed. Pumps are sized by displacement per revolution (example .9 cubic inches per revolution). The relief circuit then holds pressure at a desired level, not allowing pressure to exceed a given value.

An oil pressure trace vs engine speed on a typical engine will show a curve that goes from 0psi at 0rpm to ~65psi (the relief pressure) at ~3,000rpm then holds at 65psi until redline.

This is very generalized, cavitation will cause pressure to drop off (most common at or near redline), and oil temp, viscosity, leak paths (bearing clearances) will greatly vary the engine speed at which the relief pressure is reached.

With this very brief and basic understanding of oil pumps, I would like to point out a dangerous side effect of raising the relief pressure. The higher the pressure, the greater the tendency of cavitation. Cavitation is very dangerous and can lead to pump failure if the implosions errode at the pump body or gerotor/gear lobes/teeth. The higher relief pressure will also rob the crank of a few more tenths of a horse power.

Oil pump design is quite specialized, with great detail paid to all aspects. I'm not an expert on the Mitsu pump, but would hesitate to modify something that seems to work quite well in stock form.

Has anyone torn down a high mileage oil pump and inspected it for cavitation wear?

my 2 cents,
Joe Gonsowski
'92 R/T TT
 

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Discussion Starter #3
Joe,
Thanks for the input. Have just read a lot of threads from people unhappy with factory oil pressure. The 3000's do tend to drop what appears a significant amount at idle after engine warms up- but don't know how much as I have never hooked up a pressure gauge.
I was going to tear down an old pump I have and see how it looks internally.
Once again thank for the info.
Steve
 

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I agree, our cars oil pressure does seem a bit low at idle. At idle, the first thing to suffer from low oil pressure are the lash adjusters which tend to get noisy at ~3 to 5 psi of unareated oil. As long as our heads receive that much pressure, all should be fine.

Changing the plunger (relief valve) spring will not change the idle oil pressure. Its only function is to allow oil an alternate path to flow once a desired oil pressure is reached. By bleeding off this excess oil, a fixed oil pressure is maintained. As I mentioned earlier, higher pressure oil can fail the pump due to cavitation and robs more horsepower than necessary.

To increase the idle oil pressure, you need a larger displacement pump. Each slug of oil (slug is the volume of oil pumped by each inner gerotor tooth) must have a larger volume. Or stated simply, it must displace more oil per revolution. I don't beleive there is a larger displacement pump available for our cars that we can just drop in. If so, I'm interested.

Joe Gonsowski
'92 R/T TT
 

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Yes it can be done.. Although the three times I have seen it done all had the pumps fail!!! I don't suggest it. Yes, it is just like doing a domestic pump where you shim the spring..My best advice, don't do it.. Just keep the oil clean, don't use "miracle in a bottle" from day one and you should not have a problem..
 
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