Camshaft Housing Oil Pressure Restrictors

Richard Burns · Richard Burns's Garage

Has anybody fitted these restrictors to an early 911? and what was the result?
I am thinking of fitting them to my 77 3litre carrera as I have very low oil pressure at idle when hot. I am told that the low oil pressure is normal as long as I have normal pressure under driving conditions.I have 3 to 4 bar of pressure at 3000RPM.
Any advise would be helpfull.
Thanks in advance,
Richard.

GIBSON · GIBSON's Garage

Richard, I've been using them on my '73 for a couple years now, no down side I'm aware of, nice boost in oil pressure, especially when fully warm. I really like seeing that oil pressure gauge up a bit higher when I'm running over 180 degrees. I've pulled off the cam covers and had a look checking for any increased cam lobe wear and all looks good. I'd assume with those restrictors that the spray bar for the cams would be seeing a bit less oil but there is plenty of oil in the area so I think lubrication does not suffer. That's my experience anyway.

RoninLB · 02-03-2006, 02:53 PM

some nice for me reading in the current BA section of Excellence's current delivery about spray and center cam etc oiling. Just a bit more background concerning low & mid rpm cam, rocker, valve oil cooling.

That said my oil psi is plenty good at idle and all rpms so I didn't see a need for restrictors. Maybe if I was doing light to light street action in desert heat it would be a different story for idle oil psi?

That said an oil psi dash ga may not be very accurate for idle psi which is fine at 10psi imo. I'd hook a mechanical analog ga to read before I did the restrictors based on low dash ga psi.

Elombard · 02-03-2006, 05:12 PM

I was just thinking about these again today. I had them on my last motor and they were fine. I am going to post and ask if some one with Cyl. head temp gauges will try a set and see if they see any diff. I think they are great - that is the one concern I have heard is that you might lose some cooling in that critical area.

cmonref · 02-03-2006, 05:35 PM

Richard Burns,

3-4 bar at 3,000 rpm is really good oil pressure. The spec for my 1980 SC at 90C oil temp is 4 bar at 5,000 rpm.

RoninLB · 02-03-2006, 06:03 PM

Quote:

Originally posted by Elombard
I am going to post and ask if some one with Cyl. head temp gauges will try a set and see if they see any diff. I think they are great - that is the one concern I have heard is that you might lose some cooling in that critical area.

Good thinking imo.

unless it's a track example I don't think you'll learn much. Once the head temps are set to engine configuration the head temps are pretty stable between ambient temps of 40F-80F for example. Also maybe 15F-20F head differential between a steady 5th gear 3k-4.5k rpm at fixed ambient.

that's all the info I'm good for. BTW, I run 6 CHT probes and a digital ga.

I bet Grady might have track info ?

Alan Cottrill · Alan Cottrill's Garage

I've always wondered how effective they can be. the hole in the end of the cam spray bar is smaller than the hole in the restrictor. it seems to me like it shouldn't matter how big the hole in the oil line adapter is because it's going to neck down when it hits the spray bar.

am I missing something here?

KTL · 02-03-2006, 06:57 PM

Do a search on this topic with Souk as your Pelican member search. He's commented on this issue before and he's pretty well versed in pressure & flow stuff.

Elombard · 02-03-2006, 07:18 PM

Ronin I was thinking watch your head temps during normal driving for a few days (sounds like you have done this). Install the restrictors and see if you see a few degrees higher temps with the same routine. I am thinking (hoping) you wont but some pretty smart folks here think you will. Obviously the temp diff would be more extreme on the track. My thinking is if the temps go up on your car for instance in normal use you better avoid on the track.

FWIW another benefit is that (I think) it keeps more oil in the tank and out of the motor sump. Less foaming and less chance for starvation under hard braking because it cant slosh far enough to expose the oil PU in the tank.

So Ronin you up to try it???

RoninLB · 02-03-2006, 09:11 PM

[QUOTE]Originally posted by Elombard

Ronin I was thinking watch your head temps during normal driving for a few days (sounds like you have done this).
------------ yep.. big time.
What was interesting concerned 3.5k-4k in 5th drives thru the south west deserts during summer when daytimes hit around 100-110F. Lets say oil temps and CHT temps were baseline at dawn.. as the daytime heat came on I'd watch oil temps rise maybe 30F which put the envelope on top driving rpms. I was Not at all worried as CHT temps only rose about half that. That led me to figure the high ambiant desert heat wasn't all bad to my engine. [ different engines should all react differently]

Install the restrictors and see if you see a few degrees higher temps with the same routine.
--------- If I had oil psi issues I'd probably do it. It's not a track engine so I don't currently have the motivation to experminent.

I am thinking (hoping) you wont but some pretty smart folks here think you will.

---------

Obviously the temp diff would be more extreme on the track. My thinking is if the temps go up on your car for instance in normal use you better avoid on the track.
--------- that's a kinda yes but but no motivation to start.
If I was suggesting something to someone wanting to pull 3rd and 4th thru red line at the track and be somewhat safe I'd say to install at least one EGT gauge in #5 exhaust tube and use a digital read out gauge. That EGT gauge would be like looking inside the universe imo.

FWIW another benefit is that (I think) it keeps more oil in the tank and out of the motor sump. Less foaming and less chance for starvation under hard braking because it cant slosh far enough to expose the oil PU in the tank.
---------- I've read that in a few different respected places.

So Ronin you up to try it???
--------- So E are you ready to spend maybe $150 and 4-8hrs to install a single EGT for great combustion info ?

Also it's difficult to compare two different engines of the same configuration concerning CHTs & EGTs. Kinda like every install and reading is specific to the said engine, driver, and conditions.

For entertainment this is what my tubes look like..

RoninLB · 02-03-2006, 09:23 PM

Quote:

Originally posted by KTL
Do a search on this topic with Souk as your Pelican member search. He's commented on this issue before and he's pretty well versed in pressure & flow stuff.

Souk's comments seem to read like text imo.

Lubemaster77 is another encyclopedia in waiting.

RoninLB · 02-03-2006, 09:34 PM

[QUOTE]Originally posted by Alan Cottrill

I've always wondered how effective they can be.
-------- we'll know eventually after these restrictor engines rack up 50-100k miles of usage and get rebuilt.

the hole in the end of the cam spray bar is smaller than the hole in the restrictor. it seems to me like it shouldn't matter how big the hole in the oil line adapter is because it's going to neck down when it hits the spray bar.
---------- Only speculating.. but the restricted hole should lower oil volume available.. which would/might limit the spray bar psi if the restriction is small enough?

am I missing something here?
----------- the same as me.
What are the hard answers to hard questions for street and track usage ?

Chuck Moreland · 02-04-2006, 08:59 AM

My understanding of why oil level is affected by the restrictors goes like this:

When the car is going straight, oil level will not be affected by the presence of the restrictors. The volume of oil that needs to be scavenged is the same with both configurations. With restrictors more oil is diverted to the bottom end, but the total volume remains constant.

When the car is turning (high G) oil will accumulate in the cam housing. Consider that a 1 G turn is like operating the engine while leaning at a 45 degree angle! Oil in the lowside cam housing will NOT flow back to the sump. The accumulated oil in the housing is not scavenged, and therefore the oil level in the tank is reduced until the car straightens out. Eventually, the tank oil level gets too low and the tank pickup can suck air.

With oil restrictors in place this still happens, but it takes longer due to reduced oil flow.

For street cars, the above is not relevent. They never corner hard and long enough for the pickup to be uncovered.

The article in the new Excellence by Bruce A. said the 935s used both center feed AND spray bar lubrication on the heads. So they had even more oil flowing to the head. Grady has also recommended this dual configuration for race motors.

Maybe Grady or someone familiar with the 935s can add to this, but I think the 935s had some special provisions for scavenging from the cam housings. So the oil accumulation issue may have been addressed.

Certainly the oil tank level issue can be addressed in other ways such as deepening the tank and/or adding baffles.

My concern with the restrictor is reduced head oil flow is likely to mean hotter running heads. For now, I'm sticking with the larger restrictors.

Wil Ferch · 06:15 PM

I think Chuck and others are coming close to the core two issues...

- how are head temps affected?.... and..
- do the restrictors act in a way to make oil starvation less likely with deep-braking ( cornering too?)...like for DE or other tack events?

Adding the restrictors is less involved than opening up the oil tank and adding baffles, ...so I would like to know this.....although people on this board have done the tank mod with good results.

BTW.. Chuck..the engine would have to lean over 90 degrees ( right?) for it to equal a 1 g side load ???....force applied equal to the force of gravity?....

- Wil

Chuck Moreland · 02-04-2006, 09:47 AM

Wil, we have two force vectors acting on the oil; gravity which is pulling the oil straight down at 1G, and centripetal force induced by cornering action acting laterally at 1G. The combined force vector is equal to 1G acting at 45 degrees.

Elombard · 02-04-2006, 10:45 AM

Yah I think its 45 deg.

Good point about the oil level, PV= NRT will mean same oil volume moving wont it, that is why you see higher pressures. Doh I should have payed more attention in school. So does this mean that the idea of less foaming is debunked? same amount of oil in the crank case to get frothed??

As I mentioned above I was thinking even a small average increase in head temp for a street driven car adding the restrictors would mean a bad idea for a DE/street car. Are the CHT sensors that some have installed sensitive enough to tell us this or am I missing something?

RoninLB · 02-04-2006, 12:01 PM

Quote:

Originally posted by Elombard

Are the CHT sensors that some have installed sensitive enough to tell us this or am I missing something?

the routine is the replacement for the spark plug gasket. The gasket is also a plug heat dissipater. When accelerating and deecelerating the plug temps change. It's a kinda art to find temp numbers. The restrictor head temp difference would have to be very noticable and the testing would take a log time to figure out to the artty driver.

HarryD · 02-04-2006, 01:46 PM

Quote:

Originally posted by Elombard
Yah I think its 45 deg.

Good point about the oil level, PV= NRT will mean same oil volume moving wont it, that is why you see higher pressures. Doh I should have payed more attention in school. So does this mean that the idea of less foaming is debunked? same amount of oil in the crank case to get frothed??

As I mentioned above I was thinking even a small average increase in head temp for a street driven car adding the restrictors would mean a bad idea for a DE/street car. Are the CHT sensors that some have installed sensitive enough to tell us this or am I missing something?

PV=nRT is the Ideal Gas law requation to show the relation of a gases temperature, pressure and volume. For liquids this eqaution is meaningless since a liquid is incompressible.

Liquid volume is a physical property that is temerpaure dependent. For most common liquids, higher temperature = higher volume and lower density.

System pressure for a pumped liquid system is a function of the pump used, restrictions in the suction and discharge piping, and heights of fluid columns. An oil pump is a positive displacement type of device. As such, for each turn it will move a fixed amount of fluid. The outlet pressure can rise and fall based on the factors above.

But back to the restrictors. For ordinary applications, I am not sure of the true benefits since reducing flow to the hottest part of the engine (the heads) seems to be a bad idea. Since only the oil pump can control the total system pressure, the restrictors appear to rasie oil pressure only because the car's pressure transmitter is on the upstream side of the restrictors. If it was on the downstream side, it would appear to lower the pressures yet in both cases, the same thing is happening.

A long time ago I asked if the change in the restrictor design coincided with an increase in oil pump capacity. If so, the use of the restrictors would then reduce the oil flow to the heads back to their original design point not some higher level. Never got an answer.

For me, bottom line, I will maintain full flow to my heads. No restrictors here.

Chuck Moreland · 02-04-2006, 02:15 PM

Harry you make a good point about pump volume. The 964s and turbos that had the restrictors had high volume pumps.

Also the twin plug heads on the 964s run cooler to start with.

Tyson Schmidt · 02-04-2006, 02:44 PM

You must remember that the pressure relief valve on '76 and later cars dumps the excess into the inlet side of the pressure pump. (The earlier engines dumped it into the case.)

This has the same effect as dumping it directly back into the tank, but just at the shortest possible path. This relieves the scavenge pump of much of it's duty.

The point of what I said above is that if you reduce the volume of oil going to the cam towers, you are reducing the volume of oil going into the engine, period. So no matter what, the level in the tank will remain higher using these restrictors. ( on engines with the late-style bypass)

So keeping more oil in the tank means less likelihood of oil starvation at the track.