Specific Oil Viscosity Question...

[MidOHasp]

I know this topic is discussed in about 8 gazillion threads already, but I wanted to ask as specific of a question as possible rather than "what oil viscosity should I use?"

Application:
408W, built to considerably "loose" clearances
10.25:1 C/R
Run on mix of 94 and 110

Current Oil:
Mobil1 15W-50 Performance Driving Formula
Standard Canton Oil Pan (not race "T" pan)

Characteristics:
Cold Start-Up, 55-57 PSI, steady, every single time
Hot Idle (Water = 180, Oil = 180), 22-25 PSI
Hot, Crusing, 40-45 PSI

The cruising pressure does not seem to vary much with RPM (if at all). Once you get it up over 2000RPM, it holds rock steady at 40-45 PSI (depending on temps).

Some people tell me "as long as you have pressure, you're good," and some people say you need at least 10PSI for every 1000RPM. Just put the 6500 chip on, so that's 65 pounds minimum. I'm 20 short.

I just picked up a case of Valvoline SAE 50 Racing Oil and a new Mobil1 filter for the oil change I'm going to do this weekend. Is this a mistake at all? Should it solve the low pressure issue? Should I even be worried about that pressure with fairly loose clearances?

I've seen some posts where people had good luck with Castrol RS Synthetic 10W-60, but where in the hell can you buy that? Red-Line claims their straight-weight 50 is like a 15W-50 and their 60 is like a 20W-60 due to its cold pour characteristics.

Seems like there are 100 opinions on this matter. Should I be worried about my pressure? If so, what should my course of action be?

Thanks,
JP

[MidOHasp]

Oh yeah...

Melling M83 Std. Volume Oil Pump.

The shop who built our short-block recommended it along with several other builders, but now it seems the sentiment may be to go with the Hi-Vol unit.

Just wanted to make sure for you guys like Rick Dorman, Mr. Fixit, Bruce Edwards, et al, that all pieces of the equation were there.

And Rick, I wasn't including you in that company because I thought you were knowledgeable, it was only because you reply to every single thread at CC.

Just breaking your balls a little...

Thanks everyone, in advance, for your insight...

JP

[blykins]

How loose are the clearances? That would cause the low oil pressure right there....

I wouldn't use the straight weight oil. If it's not a multi-grade oil, it will get really thin when it gets warm. The multi-grade oils have additives that allow the oil to keep their viscosity when hot. The higher the second number, the thicker it is when hot...i.e. a 10W-30 would have thinner oil at temperature than a 10W-40.

If you're worried about low oil pressure, try a 20W-50....if you don't wanna run high viscosity oil, then you could swap your oil pump.

[blykins]

I'm running a Melling High Volume pump....it's about 60 psi at idle.....80 psi at rpm....never drops below 60. I use 10W-40 Mobil 1 dino oil.

[MidOHasp]

Will have to grab the original build sheet once I get home. Will let you know.

If the second number is supposedly the "hot" viscosity, would a 20W-50 hold up to heat any better than a 15W-50 (or a 5W-50 for that matter?) Just curious...

I see the point, then, that a straight 50 weight would give no gains to my 15W-50 and that I'd only have to be more careful on cold starts and with warming it up.

What I need is a 5W-100 I think.

[rdorman]

I really have nothing to add

Rick

[blykins]

hehehe...wonder what it would do with gear oil in it? hehehe

Actually I think the second number is just a relation. If you start out with 10 weight oil (low viscosity), then it doesn't make sense that it would thicken to 50 weight when hot.

So to answer your question, a 20W50 would be thicker at temp than a 5W50.

So it never gets over 45 psi even at wide open throttle? I really don't think the higher weight oils will help you. You may just wanna swap pumps....they're only $40....wouldn't take very long.

[rdorman]

Ahhhhhhh who am I kidding, I have an opinion on everything! Should have been a circus side show

Why the heck did you build it loose? I run 5-30 mobil 1. Water basically. 80 PSI when cold. 25 at HOT idle, 30 normally and it goes up about 10 psi per 1000.

If I was going to build loose, I would put in a high volume pump.

Of course, you could try gear oil. There is a some good 80W-140 weights out there.

Rick

[MidOHasp]

Rick, you're a basturd.

I didn't build the short block. This brings me to another question, but I've ALWAYS been too afraid to ask because heck, if I get bad news, then what do I do?

Wynne Speed out of Mississippi built the Short Block. Any one have good or bad experiences with them? I haven't seen any "RED ALERTS" on here, thank God. Seems to run like a champion...

It was built loose I guess because it was their "competition model". They had like 3 different 408's available, each one had different crank, pistons, compression, and recommended head choices.

Why in the heck they recommended the M83 pump? GOT ME! Oh yeah, something about wear on the distributor and cam gear...

But it's a steel hydraulic roller cam and a steel gear on the distributor, so would that really be an issue? Seems like when I was researching specs for the motor, everyone was saying "NO don't use a Hi-Vol pump" and now that it's in there, everyone's saying "Why the heck do you have a std. vol pump???"

I'm not under the car right now and won't be until Friday night or Saturday morning. Any SPF owners out there tell me if dropping the pan is simple like it should be? I'm having trouble visualizing if there is some piece of car that would make it tough.

Maybe I'll just get the hi-vol pump...

Or maybe I can dump some corn starch in the oil. Seem's to have worked for years in Mom's gravy.....Mobil1 may taste better.

Rick, I use that oil you use in my ACCORD. Doesn't seem right!!!

[Mr.Fixit]

25 psi at idle and 45 psi cruising, is enough pressure.

[flipper35]

Mine is a little on the loose side for clearances and it is about 25psi at idle and about 60psi at 5500. I use synthetic 20w-50 and a high volume pump. I was told to be careful with the hv pump pumping too much oil to the top end starving the bottom if there are no restrictions.

[rdorman]

Originally posted by MidOHasp


Rick, you're a basturd.

Yup! You nailed it!

You ordered the competition model and that is what you got! Loose clearences generally equal lower internal friction and higher HP plus with the standard pump there is less work being done there as well. Fixit hit it though. You have enough pressure. Nothing wrong with the numbers. Just remember, when it comes time to rebuild that short block at what may seem like a relatively short interval, it is what you ordered!

Give you an example. We used to order our road race motors tight. Because we had no money. Motor would run a full season without being overhauled. The really fast guys would have to have theirs overhauled every two or three races. So expect the motor to last 20%-30% as long as the same built tight. Of course this depends on just how loose they built it!

Run what the builder recommends and realize that the life span before the motor requires a fresh'ning will not be as long as that Honda! The additional oil pressure will probably not buy you a thing. Although I would run the best stuff I could put in it. Amsoil, Red Line, Mobil 1 all synthetic. Change the oil once a year and filter often.

Rick "the bastard" Dorman

[MidOHasp]

Rick, you know I'm just screwin' with you, right? You're not a bastard. You're a bastard of the highest order! And I've only even shared a couple beers w/ you...

Wow, 20-30% as long? Crap. When I find the clearance numbers I'm going to post them. Then people who have forgotten more than I will ever know can tell me just "how loose" it is and how soon I'm going to need to pull it apart.

[blykins]

If it's over .0025" or .003" it's loose.

[MidOHasp]

Haven't found the build sheet yet, but let's assume the worst. It's loose. Now, I'm assuming that driving behavior helps to determine engine life, too, right? If most driving is spirited, occasionally "hard" but limited to nearly no track time, etc... am I really going to be rebuilding in 2 years?

Well, I guess I'll leave that question open for a couple years, hopefully. Hoping for <.0025" ... LOL

[blykins]

JP, .0025" is about right. .003" is probably good....but when you get past that, the clearances are gonna be big.

I wouldn't worry about it....I'd say a race engine running at high revs for lap after lap would have a shorter life span. A street car is a different story in my eyes.

But it also makes sense to me that you would need a little more pressure in an engine with larger bearing clearances. If you can picture the film of oil the rotating assemblies ride on, if you have a bigger clearance, there's more chance of the assemblies "wobbling" back and forth in the journals if there's insufficient oil pressure to keep them in their place.

[Bob In Ct]

Just for the record, multi-viscosity oils (like 15w-50) do not get thicker as they heat up. A 15w-50 oil has the viscosity of a 15 weight at cold temps and the viscosity of a 50 weight oil at hot temps. They thin down, but not as much as straight weight oils. The synthetics are better at this trick than are the paraffin oils.

My own opinion on the oil pressure is that much of the pressure of thick oils is lost going through the long lengths of tubing, the filter and the oil cooler on Cobras. When I switched from Castrol 20w-50 to Mobil1 5w-30 my pressure went up! Remember the pressure sensor is at the end of all of that plumbing I just mentioned.

Bob

[blykins]

Bob, I'm showing my ignorance here...but how could that be? You're saying a 15W50 has a viscosity of a 15W oil when cold, and the viscosity of a 50W oil when hot? Wouldn't that be a lot thicker once hot? I can't imagine a oil getting thicker and thicker as heat increases.

I thought the relation between the numbers is just that....the second number is not a "weight" figure, but just a relation of how much it does thin once hot. As stated earlier, a 10W40 would not be as thin at temp as a 10W30 oil would be.

Once again, I could very much be wrong...

[ItBites]

Let me clarify the viscosity thing:

When it is said a 15W-50 behaves as a 15 weight when "cold" and a 50 weight when "hot" - that is correct.

This does not mean it flows easier when cold or thickens when hot. It means that when cold its viscosity matches that of a straight 15 weight oil - WHEN COLD. When hot its viscosity matches that of a 50 weight oil - WHEN HOT. A hot 50 weight oil will still flow easier than a 15 weight oil when cold.

The idea here is to not have the oil be so thick as to have poor flow properties when cold.

Maybe the best way to look at this is to look at only the second number. This is a measure of viscosity when the engine is up to temperature. All oils with a 50 second number will flow about the same (have about the same viscosity) when the engine is warm.

When the engine is cold you would like the oil to flow easily also. So then you wish instead of 50 weight, you had 10 weight oil. But if you put in 10 weight oil, it will be too thin when the engine gets hot... catch 22!

So now we get multi-viscosity oil. the oil is thin enough to flow cold (10W-...) and also thin enough to flow, but thick enough to maintain the hydrodynamic layer or wedge, when hot (-50).

Therefore 5W-50 or 20W-50 will flow similarly when hot, the 5W will flow better cold and in very cold regions may be advantageous. The 20W-50 might be better if you live in Phoenix.

Remember when you compare viscosity you must reference to the same temperature. 5W-50 does not get thicker (higher absolute viscosity) when hot, it just doesn't thin out as much as a straight 5W oil would when hot.


Hope this is clear as mud.


BTW 45 psi is just fine at cruise speed.

I would however suggest to most folks to build the motor tighter and run thinner oil. the thinner oil will take less power to turn the oil pump and the tighter clearances allow for less dynamic events to cause crankshaft deflection even when used with a thinner oil. Windage losses are also reduced. High viscosity numbers are kinda old-school or for full-blown racecars (2000 hp Blown alcohol can put a pretty big load into the bearings and can use some thick oil "cushion" but these engines are way shy of those type of loads). These days a properly built engine will work just fine with 10w-30 synthetic.

[RallySnake]

Hey Guys,

All these questions about oil are answered here: http://www.micapeak.com/info/oiled.html

MidoHasp,

The question that has not been asked is, what is your oil pressure at 5000 or 6000 rpm. You see, it generally goes up the more an engine is revved. It could be 50 to 60 psi. But usually, when we're pushing it that hard, we're too busy to look at the gauge.

Paul