Oil Pressure Control

paulydee

paulydee

New member
I am in need of some clarification. I want to run slightly higher oil pressure (80-90PSI) and wanted to get a second opinion on how to do it. I am under the impression that I just have to add a washer or two under the oil pressure control valve spring. Is this rigt or do I have to do something with the regulator located in the bottom part of the rear housing?

Pauly D
 
Originally posted by paulydee:
...I want to run slightly higher oil pressure (80-90PSI) and wanted to get a second opinion on how to do it...
Pauly D
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I would be really interested to know why you want to.

(Please don't misunderstand. I'm not implying you are wrong. Just interested in learning something new.)

Everything I've read/learned over the years says that you need enough oil pressure to adequately lubricate the parts farthest from the pump. Do you feel that's not happening?

Higher pressure can be achieved by simplying running a heavier oil. That doesn't do what you probably want, but the gauge goes up. Modifying the spring (properly, and no I don't know how to do that) sounds like it would move more oil in a given amount of time. At some point, you will empty the pan before enough gets down through the engine and back to the pump (which is probably why you said "slightly").

Anyway, I was just curious.

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Mike Spencer
NC Region
ITA/7 RX-7 (almost)
ITS RX-7 (just started)
1990 RX-7 Convertible (street car)
 
Well I am going off a recommendation of another racer. He mentioned higher pressure promotes better cooling. My car makes about 75PSI of oil pressure at high RPM. I have heard of race engines making over 100. I though 80-85 would be a happy medium.
 
Originally posted by paulydee:
...He mentioned higher pressure promotes better cooling...
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I hadn't thought about that. It makes sense. Unfortunately, in IT you're stuck with the stock pump. However, "Oil pans, pan baffles, scrapers, windage trays, oil pickups, lines, and filters are unrestricted."

I don't know what you drive, but there are probably higher volume pans available, as well as some that (at least claim to) promote better oil cooling.

That would be in addition to increasing your pressure. Good luck!

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Mike Spencer
NC Region
ITA/7 RX-7 (almost)
ITS RX-7 (just started)
1990 RX-7 Convertible (street car)
 
I assume we're talking about 1st gen RX-7's... ?

My understanding is that you also need the higher pressure to get the oil to work its way fully into the rotor bearings at high RPM.

The stock pump on the 84-85 engine has exactly the same impeller size as the Mazda comp pump (I have personally measured this). The only difference is that the comp pump has hardened gears.

Shimming the front regulator will not be enough to raise your oil pressure. You also need to replace the rear with either the comp unit for 115 PSI or with a third gen RX-7 part for 85 PSI.

If you're building the engine, you also need high flow eccentric shaft jets and ideally competition main bearings (but the latter are expensive).

3rd gen regulator is about $30, e-shaft jets are a couple of bucks each, and yes shim the front spring 1/8".

I know that these parts aren't specifically named in the ITCS, but I think that section is generally interpreted as "oiling system is free, no dry sumps". You make the call on that.

Steven
 
Oh yeah, it is possible, though a bit difficult, to replace both regulators without tearing the engine down (just drop the oil pan). While you're in there, add a baffle, $20, and if you can afford it Mazdacomp also sells a beautiful heavy duty racing oil pan for $200 or so.

Steven

[This message has been edited by sburkett (edited June 24, 2004).]
 
Steven has said it very completely. I have a 3rd gen regulator for cheap if you want it. I would really recommend going with the comp unit though and the 115psi. I don't see the oil pressure as being something you can have too much of.

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Chris Ludwig
08 ITS RX7 CenDiv
 
By the way, cooling your oil is not a function of oil pressure. It is a function of heat transfer rate and flow through the heat transfer unit. If you need to get better cooling either clean your oil cooler, relocate it for better air flow or get a better (larger) unit. Keep in mind that too much oil pressure can damage seals in the pump and elsewhere. A little higher than originally designed might not be a problem, but if you go a lot higher than the parts were designed for and you might have problems you didn't expect.
Have fun & be safe.
 
I have the maz comp full pump/reg/jets setup with the comp bearings, cold 125 psi, hot 100 to 120 changing with rpm, higher rpm = 100, lower rpm = 120. not sure why
 
For an IT engine 85 psi is plenty. Higher pressure just uses more of the engine's power. As the other writer said, use the 3rd gen regulator or get one from ISC. Shim the front regulator by 1/8 inch and add a baffle plate. It is possible to do it all with the engine in the car. I did mine that way. You'll need 2 pan gaskets.
 
Originally posted by Mike Guenther:
By the way, cooling your oil is not a function of oil pressure. It is a function of heat transfer rate and flow through the heat transfer unit. If you need to get better cooling either clean your oil cooler, relocate it for better air flow or get a better (larger) unit. Keep in mind that too much oil pressure can damage seals in the pump and elsewhere. A little higher than originally designed might not be a problem, but if you go a lot higher than the parts were designed for and you might have problems you didn't expect.
Have fun & be safe.
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There are no seals in the pump. Higher pressure may cause the pump to wear faster and will take a fraction of a horsepower out of the motor. It's good insurance in my book.



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Chris Ludwig
08 ITS RX7 CenDiv
 
Higher pressure DOES cool better for some very simple reasons. Higher pressure means higher velocity, which means the oil travels through the cooler more times in a given interval. Same reason that fuel pressure regulators work - if all other factors are equal, higher pressure means higher velocity and higher GPM. There are a whole list of other factors involving things like heat exchange coefficients, surface area, and pressure related temperature increase, but none are the controlling factor.
 
"Higher pressure DOES cool better for some very simple reasons. Higher pressure means higher velocity, which means the oil travels through the cooler more times in a given interval."

I admit up front I don't know alot about this but it would seem that if the above premise is correct, we should not be slowing our water pumps (cavitation aside) but speeding them up. The converse premise is that you want the fluid, be it water or oil, to spend more time in the radiator/cooler; too fast and it does not have time to transfer its heat.
 
Originally posted by sburkett:
... I know that these parts aren't specifically named in the ITCS, but I think that section is generally interpreted as "oiling system is free, no dry sumps". You make the call on that.

Steven
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I know *I* am not going to be protesting anyone over it, but the oil pump is SPECIFICALLY mentioned (as in "any oil pump") for Production, GT, American Sedan, Spec Racer, and some Formula cars. So, I wouldn't want to BE protested, either.

On a different note, in the June 2004 GRM there is an article about the 2nd Gen RX-7. In a sidebar, they get "tips" from Sylvain Tremblay and David Haskell of SpeedSource on prepping an IT car. At the very end it says, "A good rule of thumb for rotaries is to have 10 psi for every 1000 rpm run."

As always, your mileage may vary.

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Mike Spencer
NC Region
ITA/7 RX-7 (almost)
ITS RX-7 (just started)
1990 RX-7 Convertible (street car)
 
"Higher pressure DOES cool better for some very simple reasons. Higher pressure means higher velocity, which means the oil travels through the cooler more times in a given interval."

My experience with the water cooling system on Mustang AS cars would not support this theory. Many times when we encountered overheating problems the solution was to install a restrictor with a smaller orifice not a larger one. This slowed the water's movement through the radiator and lowered water temps. While moving a quantity of fluid through a cooler is important it is equally important to allow the cooling medium - air- to have enough time to do it's work.

As far as how much pressure is enough...on a rotary I don't personnaly know. The car I bought in 2003 has a Prather Racing 12A that idles at 20-40 and tops out at 80-85 when I rev the motor off idle. Oil temps are around 230-240 and water (with a 19"x21" double pass radiator) are 180-200. So far so good for this three year old motor.

Scott



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Scott Peterson
KC Region
IT7 #17
 
Originally posted by mustanghammer:
"Higher pressure DOES cool better...

My experience with the water cooling system on Mustang AS cars would not support this theory....
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I've seen this argument come up over oil temps and coolant temps in a number of places in the past. My personal $0.02 is that we are dealing with your basic sine wave situation. Too slow won't work and too fast won't work (for various reasons). Somewhere in the middle is "just right".

The oil (or coolant) has to stay in the engine long enough to efficiently absorb a certain amount of heat. Then, it has to stay in the radiator/pan long enough to efficiently dissipate a certain amount of heat. How long is "ideal" in each case probably won't be the same, so the "weak link" will determine what works best for you.

So, what's the "magic formula". There isn't one. It's called trial-and-error. And when you finally find what works best for you, don't expect that it will work best for everyone else.

(Sorry, that was probably closer to a nickel
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Mike Spencer
NC Region
ITA/7 RX-7 (almost)
ITS RX-7 (just started)
1990 RX-7 Convertible (street car)
 
Pressure and velocity are not inter related. Just think of a pump fighting a close orifice, when the volume and the velocity are zero. All the pressure in the world will not creat any flow.

Velocity and volume are related to the tube size. Admittedly the volume has to be "pushed" by something, but ultimately the limitations are the Interior Diameter, not the pressure. At its limit of flow, increasing pressure simply builds a boundry layer on the inside of the vessel restricting the flow regardless of the ultimate pressure achieved.

The only solution at this limit of flow thru a given size orifice is to go to a larger orifice size. Not greater pressure.

Summation: It works for a while, but ther is a limit determined by the actual orifice size.

I think!

Good racing.

Bill
 
Originally posted by bill f:
Pressure and velocity are not inter related.

<snip>

Summation: It works for a while, but there is a limit determined by the actual orifice size.

I think!

Good racing.

Bill
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Bill -

I agree with the theory (and ESPECIALLY the "I think" part!
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In our world there are only a couple of things that change. The viscosity of the fluid and the pressure from the pump (mostly by RPM, but can be changed in other ways).

Changing to a higher viscosity oil SHOULD increase oil pressure, but at the same time decrease flow. That is true for the same reason that you can drink soda through a straw, but if you try to drink pancake syrup through the same straw it will take more effort (pressure) but you will still get less fluid.

If all other things remain the same, a higher pressure SHOULD move more of the same oil through the same openings and to the top of the same motor.

Now, whether that additional flow cools the engine better brings us back to where we started.
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(EDITED for good grammar!
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Mike Spencer
NC Region
ITA/7 RX-7 (almost)
ITS RX-7 (just started)
1990 RX-7 Convertible (street car)

[This message has been edited by Mike Spencer (edited June 28, 2004).]
 
The control of flow, level, pressure and temperature can be very interesting and has been making a good living for me for over 25 years. Some writers here are on the right track, but I would like to briefly explain a few concepts so that any confusion is not propagated on this thread.
First, flow is related to pressure, but more specifically it is related to pressure drop. If there is no pressure drop, there is no flow, period, as Bill F pointed out in his example.
Flow is measured in units like gallons per minute, but the capacity of a valve, regulator, orifice or any opening, for the amount it can flow, is measured in units called Cv, (liquid), Cs, (steam), or Cg, (gas). The Cv is equal to the number of gallons of water that can pass through an opening in one minute at a 1 psig pressure drop, (psid). For the flow to increase either the opening must be enlarged or the pressure drop must be increased. In a closed system, simply increasing the pressure does not necessarily increase the rate of flow. You have to increase the pressure drop or open up some restriction. As Mike Spencer pointed out there is a limit to how much flow can be achieved through any given opening no matter how much higher you make the pressure drop. That point is called chocked flow. Once you reach that point no matter how much you increase the pressure upstream or decrease the pressure downstream, or both, you just won’t get any more flow through that restriction.
Secondly, increasing the flow of oil through a heat exchanger will help some in transferring the heat out of the oil, but not nearly as much as increasing the efficiency of the heat exchanger. To increase the efficiency of the heat exchanger you can use the most efficient materials, increase surface contact area, remove any barriers to the heat transfer, (clean the surfaces which also increases the contact area), or increase the volume and temperature differential of the transfer fluid, (air or liquid). In our applications, liquid to air heat exchangers are more frequently used than liquid to liquid heat exchangers.

There are some other factors but the bottom line is, to get a better cooling of your oil, you will have better results from cleaning your oil cooler and increasing the air flow through it rather than simply increasing the oil pressure. Mike Spencer and Mustanghammer were onto this.

Be safe and have fun.
 
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