Oil temp, viscosity and pressure.

Ok, I am going to open a can of worms. I have a question for all you that have raced your cars. What viscosity of oil are you using, at what temps and rmp is your pressure adequate?

I have been driving my 40 for almost a year and put about 4500 miles on it, all but 118 miles at normal speeds with short burst up to 100+, my oil temp have always been 200-210 even in the dead of summer. My oil pressure has always been 50-55 on cold start up then 40-45 at idle warm so I haven't been concerned as I considered this good. Last winter I changed the oil to 5-20 Mobil 1 as I didn't didn't want to put a lot of unwanted stress on the distributor drive gear when real cold engine starts. I took my car to Texas for the Big Bend Open Road Race and just left the 5-20 in the engine. Well it was 95 down there in the shade and when I ran the race for 59 miles at 4200 rpm (110-120 mph) and 59 miles back the oil temp got up to 250 which is not bad but the accusump oil pressure switch started to open and close (pulsate) during the run. I have a light on the dash that tells me when its below 35 psi and accusump is open. I have a high volume high pressure pump. My question is what is low pressure at rpm, what viscosity oil should I have used? When the idiot light started to blink the idiot got nervous. I have a Dart aluminum 351W block bored to 427. Using the standard oil cooler provided by SPF. Engine holds 8 quarts and accusump another 3.

Jack,
I personally don't think your oil temps are anything to worry about. You were running some high revs in a pretty hot environment. Others will chime in who know more than I. I do have some suggestions.
With the Accusump your E P C valve may need a lower pressure setting for it to chime in. Why it was pulsating is up to speculation. Your oil volume seems about right. Canton makes several pressure setting for the Accusump, down to 20-25 psi, and as high as 55-60.
www.cantonracingproducts.com
What bothers me is the intermittent cycling of the valve. My guess is either your oil pressure is droping due to the increased temp, or the pickup is coming up out of the oil, or there is airating going on, causing some fluctuating of the pressure. I would think the second option would only happen in high G turns/accelerations in an unbaffled oil pan. The third if the oil pump volumn is high and not allowing the air to escape before pumping.
Having stated that, there ought to be some simple fixes. Does your cooler have a fan. If not then think of adding one. If you do, what is the turn on temp. May need to turn it on sooner with a lower thermostat. The hotter the oil the lower the viscosity, which seems it would drop the presssure a bit. So your warm pressure of 40-45 is probably dropping to the turn on pressure of the accusump. Easily fixed by dorpping the turn on pressure to 20-25. Or you could go the cheap route and just go back to the thicker oil in the summer.:idea:

Bill

Hi Jack,

Like Bill - I don't think your oil temps are a great concern.
Would be interested in knowing where you take your temps from.
Personally I prefer to take my oil temps on the output side of the oil cooler if possible as this tells me the temp of the oil that I'm feeding my bearings (really the only relevant temp).

I've concerns about Accusump systems in general that I've posted on elsewhere here.

That not withstanding, the key reason for drop in oil pressure at speed, when g-Forces are not a great factor, are oil pump / flow restriction, cavitation or starvation.
High Volume oil pumps, at speed, will move more oil than many oiling systems can pass.

Cavitation
This usually only happens with a very poorly designed oil pump inlet (like just a raw tube stuck into a pool of oil) - I sincerely doubt that's the case with your system.

Starvation
If you examine your pickup screen you'll likely see something like this from Canton;


Then there's something like these OEM ones (could not find the std FORD pickup, but these convey the message;


Notice how on the OEM pickups that there is a captive chamber for the pickup to draw from. This is to prevent starvation issues. However - they won't flow the volume you need to move.

What's the answer? Use the performance pickup that came with your pan, but finish the rest of the oiling package with proper sizing and application of components.

---Sizing and application (restriction)----

Of concern here is the Oil Filter itself, cooler and lines and their ability to pass the volume of oil you're trying to move..

I use -12 hose and full flow Aeroquip fittings on all my oiling systems. I like the larger Fram HP series oil filters for the reasons identified above as well. There are also double oil filter mounts out there that will allow you to run a pair of standard oil filters.

Full Flow Fittings vs Dog-legged Fittings

Dog-Legged


Full Flow


The later - far less restrictive and preferable in oiling, coolant and fuel systems.



Please note that I'm not telling you that your particular package was not well designed or executed. Any one of these things can be at fault for what you're seeing.

Your Motor is a 427w, that means you have a 4" stroke & therefore a lot of counterweight dia/area/mass in the crankshaft all in a pan that is really designed for a smaller crank.. I would suggest that your problem might be windage related, even though RPM is relatively low at 4200, it is continous & if you think back maybe the pressure fluctuations occured shortly after a dip/brow on the road where the car experienced a small negative G situation. This could have been enough to lift the oil up for the crank to wrap it up, if it was not already doing so, which I suspect from the lowered oil pressure. The 427 Fe's in the Mk2 went dry sump for a similar reason, big crank dia, low ground clearance.

BTW, If you 'need' an accusump, then you 'really' need a dry sump.

Bill, the switch is set at 35 psi. No fan on the oil cooler, I think I will change the oil to higher weight oil for summer. Randy I use all the full flow fittings you have in your second picture. I am not sure of the oil pump pick up. Jac Mac your right, and if I could figure out room for an external pump I would at least do that, but dry sump is the the way to go. I have always had worries about distributor drive gears going out. One of my friends DNF one of the open road race because it got eaten up. My plan to change next time engine out to either external or dry sump. Thank you all for your advise this is what I really enjoy about this forum.
Jack

All makes sense to me and JacMac - great thoughts re the enlarged counterweights/volume, I'd never considered that line before and it pretty much is spot on with our own experiences on Roy Smarts alloy bored and stroked Clevor GTD. (RIP)

Interestingly enough he also went down the Accusump route which helped initially although was not so good once the engine was hot. (good for pre-start oiling though)

The data logging would clearly show dropping oil pressure, especially once hot and cornering hard. The fitment of an Aviad drysump system completely eliminated this problem. Pressure would sit at selected pressure all day long once at working revs and would only drop to a low level when both HOT and idling. At any driving level of rpm - oil pressure was good.

Once Bjorn's exhaust is complete on his Roush 427IR powered GTD we'll see how that does as it also has a dry sump system.

jac mac said:

Your Motor is a 427w, that means you have a 4" stroke & therefore a lot of counterweight dia/area/mass in the crankshaft all in a pan that is really designed for a smaller crank.. I would suggest that your problem might be windage related, even though RPM is relatively low at 4200, it is continous & if you think back maybe the pressure fluctuations occured shortly after a dip/brow on the road where the car experienced a small negative G situation. This could have been enough to lift the oil up for the crank to wrap it up, if it was not already doing so, which I suspect from the lowered oil pressure. The 427 Fe's in the Mk2 went dry sump for a similar reason, big crank dia, low ground clearance.

BTW, If you 'need' an accusump, then you 'really' need a dry sump.

Click to expand...

What would you recommend Jac Mac? Boat tailing or knife edging the crank??

What about a simple windage tray or has that already been done?

Hope you guys can follow these 'mental' pics in regard to this.
1. While reworking counterweights & fitting windage trays, scraper rails ,etc help there are a couple of 'unseen' factors working against you as well.

2. The speed of the counterweight outer dia along with rod bigend bolts etc- lets say for example that we are using the same pan on a std stroke 302[3"]-351[3.5"]-427[4.0"] and for the purpose of the discussion they all use a 2.100" chevy crankpin dia [ the effective radius from rod journal center to bolt head of which is approx 2"].
So on the swing radius of the rod bolt [1/2 stroke + rod big end dimension] is:302[3.5"],351[3.75"],427[4.00"] .
Now to put this in perspective the speed of the head of the bolt on the rod at 5000rpm is around 104 mph [302],112mph[351],119mph[427], also lets assume that the oil level in our pan is at the same height, so the 427 crank is going to be 1/2" closer to that oil & travelling faster, thereby tending to pull that oil into its low pressure area or wake.

3. If this isnt bad enough we also have a large amount of air being shuffled back and forth thru the length of the crankcase during each rotation- the amount being directly proportional to the capacity of the motor. In the case of the 427 approx 1 liter gets displaced by pistons #1/5 that -should- go to the space occupied by #4/8 [ this is due to the throws for the conventional V8 being displaced at 90° on front/rear halves of crank---- the throw with #2/6 is @ 180° to #3/7 and these cancel each other out, but leave the two end cavities to fend for themselves].

4. So as well as a crank assy that is detemined to whip the oil into a frenzy, we also have a small windstorm back and forth that plays havoc with any oil that might be suspended in mid air.. Makes you wonder how the damn things last as long as they do.

5. Based on the above & allowing for a couple of fairly well accepted numbers your wet sump in a GT40 has to be fairly clever to accomodate the following.
Your running oil level needs to be a minimum of 2" above the pickup at all times[I would prefer 3"], the distance from oil level to crank or rod end needs to be at least 1"[more would be better]. This leaves you with a minimum pan depth in the order of 8.5" for the 427[4" stroke] motor.

Jac Mac,
You are the man! Great explaination and I get it. The big displacement motors have a lot to overcome. What about the 289/302 motors? Do you feel that dry sump is the way to go for high speed applications? I seem to remember that Shelby tried both dry and wet sump applications in the early cars, but I don't remember if one was better than the other. If anyone else can weigh in on this it would be appreciated.
Garry

If your racing & with the extra lateral grip available from modern tires then the dry sump is a 'must have' regardless of crankshaft stroke and or RPM etc.

I ran wet sump on my Boss 302 saloon & watched the 30psi light like a hawk, mainly because any failure was going to come out of my pocket. However since building motors for 'other' people I have realised that not everyone is as careful or frugal as I 'was' and to them a warning light is only an indicator that their race might end prematurely. If I had my way the oil pressure warning light switch should be hooked up to an electric fence unit hard wired into the scrotal area of the drivers seat.

Jac-Mac......I love your thoughts on driver warning systems, I had a boss when I was driving that thought Speed limiters on trucks should be a huge fist that came out of the dash and smacked the driver in the head, Same but different. And this has been a very enlightening thread, I have learded more in the last 6 months watching this forum that in my entire life around cars. Thanks everybody. Leonmac