oil viscosity for 67 300 hp in South

[Joe C.]

Re: oil viscosity for 67 300 hp in South

I too used to run 20w-20 practically year around in Wisconsin/Illinois back in the day, and later 10w-30. But, when the concern for ZDDP arose and I'm looking at my "never been apart" 63 L-76, I shopped around for the best source. That turned out to be Sam's club where they had cases upon cases of 15w-40 at a reasonable price - so I bought a few. I've been keeping my eyes open where I go and have yet to see any 10w-30 meeting CJ-I or CJ-4 API specs on the shelf. Granted, I have not looked hard as I have a lot of the Shell Rotella -T in 15w-40 in stock. I suppose some of our less commercial auto parts stores including NAPA may have some. I found a case of Wix spin on oil filters at one place near MCO a number of months back. Perhaps I will check with them to see what they have or can get.

Any other suggestions?

Stu Fox

Last month, I bought 2 cases of Rotella 10W-30 from a local distributor who was happy to supply it...............at a few cents less/bottle than I have seen the 15W-40 Rotella in any store, including Wally-Mart.

My greater concern is with "dry" starts, where it's better to have a lighter oil which can quickly get pumped thru the journals/gallerys and quickly coat the sliding surfaces after the engine has not been started in awhile. Sometimes I go further by removing the coil wire, cranking the engine over to help distribute the oil, then fire the engine.

The "CI/CJ" category oil is not popular, yet, in 10W-30 viscosity because most of the demand is from truckers who use it in their diesel engines which operate with extreme bearing pressures and very high shear stress. Once more vintage car owners become savvy of the benefits of concentrations of phosphorous such as those found in CI/CJ multi-vis lubricants, then the demand for 10W-30 will increase, and stores will stock it.

If you do not ROUTINELY RACE your vintage Corvette, have "normal" bearing-to-journal clearances, have an engine that is not excessively worn, are looking to maximize power and fuel economy while minimizing parastitic losses, then use the 10W-30.

If you occasionally use your Corvette for quarter mile blasts, then the oil temp shouldn't become high enough in that short 12-15 second interval to cause metal-to-metal contact and spun bearings with 10W-30 oil. If you road race or autocross your Corvette, then you might want the extra film strength provided by the 15W-40.

If you have a specially prepared race engine, built with wider than normal bearing-to-journal clearances and which usually requires a high volume oil pump, then you will definitely need the higher film strength developed by higher viscosity oils.

Joe

[Duke W.]

Re: oil viscosity for 67 300 hp in South

I don't know where people come up with some of their "theories" - most have no bearing on what's actually going on inside an engine, but the bottom line is that some of you are overly obsessive about slight differences in engine oil viscosity.

For typical vintage car use, which is usually confined to mild to hot weather any viscosity grade of C-category oil that you can find is probably okay.

Duke

[William F.]

Re: oil viscosity for 67 300 hp in South

Seems to be a lot of opinions on viscosity:Michael says too high a viscosity is what leads to shear while Joe seems to say if you experience high loads such as racing you need a higher viscosity to prevent metal to metal contact(same as shear?). Duke says"Forgitaboutit."Bound to be some reason manuals specify certain viscosities for certain engines and certain conditions. I understand about the cold weather part, but how about shear at relatively high temps and loads?
Help!

[Michael H.]

Re: oil viscosity for 67 300 hp in South

Seems to be a lot of opinions on viscosity:Michael says too high a viscosity is what leads to shear while Joe seems to say if you experience high loads such as racing you need a higher viscosity !

I've been digging through some info on lubrication oils and there's some pretty interesting stuff out there. Also, just chatted on the phone with a retired GM engineer and friend, Dave. Some of what he explained agrees completely with the info that I found and posted below.

The "heavy oil for high RPM" theory is actually just the opposite. The viscosity requirement increases as RPM decreases. Low shaft speeds require heavier lubricant than high speed.

The chart shows pressures far less than those in a typical engine but the curve definitely shows a decrease in viscosity requirement as RPM increases.

This is something that "ol Dave" tried to explain to me 40 years ago. (but I wasn't especially interested then)

[John H.]

Re: oil viscosity for 67 300 hp in South

Relative surface velocity is another factor - I remember from my Pontiac days that the guys who raced 389's and 421's regularly had a hard time with main bearings - they were 3" journals. The NASCAR guys turned them down to 2-1/2" and used bearing spacers to keep them alive.

[Michael H.]

Re: oil viscosity for 67 300 hp in South

Relative surface velocity is another factor - I remember from my Pontiac days that the guys who raced 389's and 421's regularly had a hard time with main bearings - they were 3" journals. The NASCAR guys turned them down to 2-1/2" and used bearing spacers to keep them alive.

Yup, I forgot about the old Pontiacs with their huge main bearings.

In our discussion last night, Dave refered to this as angular velocity. (same thing, I guess)
The larger the journal/bearing, the higher the surface speed @ RPM.

[Stuart F.]

Re: oil viscosity for 67 300 hp in South

I can concur on the Pontiac 389 bearing problem. The friend that I bought my 58 Fuelie engine in 1958 out of his Vette, replaced it with a new 59 Pontiac 389 and he ran it regularly at the dragstrip. He continued to knock the rod bearings out of it, specially when he warmed it up with a solid lifter cam and more carburetion. Each time he had it apart due to the rods, he tried something to solve the problem, i.e. the journals were ground smaller, then chromed, and different brand/material bearings were used until he finally gave up on the stock crank. He learned a big and expensive lesson, but had a lot of fun along the way - like a fuelie dragster, i.e. one run = one rebuild (sort of).

Stu Fox

[Duke W.]

Re: oil viscosity for 67 300 hp in South

Relative surface velocity is another factor - I remember from my Pontiac days that the guys who raced 389's and 421's regularly had a hard time with main bearings - they were 3" journals. The NASCAR guys turned them down to 2-1/2" and used bearing spacers to keep them alive.

That is often referred to as "tangential velocity", which is the product of radial velocity (of which "RPM" is representative) and journal radius. Above a certain level (I don't remember off hand.) pressure lubricated plain bearings should be replaced by oil lubricated ball or roller bearings. (Grease lubricated ball or roller bearings are okay for low velocity applications like wheel bearings.), which is why turbine engines have roller bearings.

Ball and roller bearings have traditionally been called "anti-friction bearings", but within the speed range that journal bearings are acceptable ball or roller bearings provide little if any advantage. Spin a freshly installed crankshaft in the block, and you'll see what I mean.

Ball or roller bearings are also necessary in very low speed applications where the hydrodyanmic pressure generated in a plain bearing, which is a function of tangential velocity, is not sufficient to support the load resulting in metal to metal contact.

The bottom line regarding Chevrolet small blocks is that the OE bearings and oiling system are virtually free of any issues other than oil starvation under high dynamic loading conditions, which is usually caused by letting the oil level get low - an operator/maintenance issue, NOT a design or oil viscosity issue.

That's why I apply the classic aphorism: If it works, don't fix it!... i.e. use OE replacment parts for all engine restorations.

A 3" journal yields the same tangential velocity at 6000 revs as a 2.3" "small" journal SB main generates at 7800, which is beyond the practical maximum of about 7200 for a decent 327 broad torque bandwidth road engine configuration.

Duke

[Michael H.]

Re: oil viscosity for 67 300 hp in South

I can concur on the Pontiac 389 bearing problem. The friend that I bought my 58 Fuelie engine in 1958 out of his Vette, replaced it with a new 59 Pontiac 389 and he ran it regularly at the dragstrip. He continued to knock the rod bearings out of it,

I remember a guy that had the same problem with Pontiac engines in his 56 Chevy. He spun several rod and main bearings in quite a few almost new Pontiac engines. (not exactly sure where he was getting the "almost new Pontiac engines" though)

I've heard that it was difficult to pump oil INTO the main journal at high RPM because of the high amount of centrifugal force created by the large radius of the Pontiac mains. If it won't go in, it isn't going to go througgh and feed the connecting rod.

[Duke W.]

Re: oil viscosity for 67 300 hp in South

There are a limited number of crank angles that the pressure system can feed oil into a journal bearing, and as revs increase the range of acceptable locations usually narrows.

I have a buddy who spun bearings on a Bonneville Lakester (5.0L 9000 RPM SB) - twice - before even completing a one-way pass. It turned out that the "budget" crank he bought had poorly located oil feed holes. He bought a cross-drilled Crower crank, and has been running ever since without problems.

Oil feed hole location was a primary reason why the Olds Indycar engines were blowing like clockwork in the early days of the IRL. The OE oil feed holes worked fine at up to 7000 on the production engine, but not at over 10,000 on the racing version!

One solution is to "cross drill" the crank so oil feed holes are at two angular positions, but regardless of the number of feed holes, it takes a good bearing engineer to analyze the loads and hydrodynamic pressure distribution at all crank angles to determine the optimum location(s) for the oil feed holes.

It's a testament to the GM engineers who designed and tested the SB 55 years ago that their oil system design was near perfect from the get-go (or at least by 1957), including racing engines that made far more power and revs than the original design specifications ever called for!

At some point as tire grip increased, dynamic loading became so high that in order to ensure a continuous supply of oil at the pump pick-up, a dry sump system was required, but the internal design of the oiling system from 1957 was, and is, virtually flawless.

Duke

[Stuart F.]

Re: oil viscosity for 67 300 hp in South

Michael;

As a side note about your friend's ability to come up with near new Pontiac engines; if he lived near Chicago back in the late 50's early 60's, there was a very thriving market in performance parts back then (probably not unique to Chicago or that time frame). It was not uncommon to place an order one night at the "Pie Pan" off the Edens and take delivery in the parking lot the next evening - rear end posi's - name the ratio (still dripping gear lube), Fuelie Corvette engine - w/ or w/o accessories (still warm), Pontiac 389's - cheap!

I left the country in 62 - did they ever solve the drive belt system on the Ponchos? The 59 -61's were always tossing their belts which was a disaster with that reverse cooling system. Seems the Pontiac engineers had some real good ideas (ahead of their time), but failed in execution. Not sure when Chevy adopted the two belt w/idler pulley system, but they at least used larger and deeper pulley's to limit the problems early on. Then too, we could always loosen or remove the drive belt for more HP at the track and still get normal convection cooling.

Stu Fox

[Michael H.]

Re: oil viscosity for 67 300 hp in South

Michael;

As a side note about your friend's ability to come up with near new Pontiac engines; if he lived near Chicago back in the late 50's early 60's, there was a very thriving market in performance parts back then

I think the guy with the 56, Bruce, did a lot of his own "shopping" around the La Grange/Brookfield area in around 62-64.
Seemed there was a different near new Pontiac engine in that Chevy every week.
He used to "find a lotta good deals" on 4-speeds too.

He finally gave up on Pontiac. Most people didn't know about the issue with the huge main bearings at that time. Only knew about the results.
I'm sure it was a good system for what it was designed for but it failed at high RPM for the exact reason that we discussed.

[Jerry G.]

Re: oil viscosity for 67 300 hp in South

i've been using 0-5W in my small block race engine for many years. I use full syntetic. I recently shifted from a dry sump system to a wet sump system and after discussing with one the experts on the board i went with Chevron Delo 0W-30W. I have run my small block over 9000 RPM and never had an oil related problem. We get into pretty high oil temperatures so we need a sythetic to handle the heat withour breaking down. With the wet sump system i also think the lower viscosities help in quicker drain down from the cylinder heads and less problems with windage in the oil pan. just a thought.