Savoy racers choose 30 grade because it gives the right flow at the normal engine operating
temperature of 212ºF and that would be the viscosity of 10 cSt at operating temps... so that
means for every 1000 rpms increase your oil pressure increases another 10 psi... a 30 grade
flows more oil at higher rpms which flows more oil between the critical bearings
which carries away more heat and you're not wasting HP just pumping oil through the blow
off valve...
30 grade psi
1000 10
2000 20
3000 30
4000 40
5000 50
6000 60
7000 70
8000 80
9000 90
10000 99
11000 99 blow off by the pressure relief valve
40 grade psi
1000 12
2000 24
3000 36
4000 48
5000 72
6000 84
7000 96
8000 99 blow off by the pressure relief valve
9000 99
10000 99
11000 99
50 grade psi
1000 15
2000 30
3000 45
4000 60
5000 75
6000 90
7000 99 blow off by the pressure relief valve
8000 99
9000 99
10000 99
11000 99
To know for sure I went to trouble to installed a digital oil
pressure gauge on my RC45 to verify 30 grade at 8000 rpms 82 Psi close
enough to perfect...
The same 30 grade at 203F Oil flowing 10 psi perfect...
The choice is yours, but choosing a 30 grade over a 40 grade is smarter because it will:
1)increase 1 to 2 HP at the rear wheel...
2)quicken the throttle response coming out of the corners...
3)decrease over all operating temps...
4)increase the oil flow at the critical bearings...
Any one of 30w 100% synthetic motorcycle specific or car oils will meet
and exceed both your racing and mileage expectations...
Quote 540Rat
SECTION 2 – MOTOR OIL VISCOSITY SELECTION
THE BENEFITS OF USING THINNER OIL:
• Thinner oil flows quicker at cold start-up to begin lubricating
critical engine components much more quickly than thicker oil can.
Most engine wear takes place during cold start-up before oil flow can
reach all the components. So, quicker flowing thinner oil will help
reduce start-up engine wear, which is actually reducing wear overall.
• The more free flowing thinner oil at cold start-up, is also much
less likely to cause the oil filter bypass to open up, compared to
thicker oil. Of course if the bypass opened up, that would allow
unfiltered oil to be pumped through the engine. The colder the ambient
temperature, and the more rpm used when the engine is cold, the more
important this becomes.
• Thinner oil also flows more at normal operating temperatures. And
oil FLOW is lubrication, but oil pressure is NOT lubrication. Oil
pressure is only a measurement of resistance to flow. Running thicker
oil just to up the oil pressure is the wrong thing to do, because that
only reduces oil flow/lubrication. Oil pressure in and of itself, is
NOT what we are after.
• The more free flowing thinner oil will also drain back to the oil
pan quicker than thicker oil. So, thinner oil can help maintain a
higher oil level in the oil pan during operation, which keeps the oil
pump pickup from possibly sucking air during braking and cornering.
• The old rule of thumb that we should have at least 10 psi for every
1,000 rpm is perfectly fine. Running thicker oil to achieve more
pressure than that, will simply reduce oil flow for no good reason. It
is best to run the thinnest oil we can, that will still maintain at
least the rule of thumb oil pressure. And one of the benefits of
running a high volume oil pump, is that it will allow us to enjoy all
the benefits of running thinner oil, while still maintaining
sufficient oil pressure. A high volume oil pump/thinner oil combo is
preferred over running a standard volume oil pump/thicker oil combo.
Because oil “flow” is our goal for ideal oiling, NOT simply high oil
pressure.
• Oil flow is what carries heat away from internal engine components.
Those engine components are DIRECTLY oil cooled, but only INdirectly
water cooled. And better flowing thinner oil will keep critical engine
components cooler because it carries heat away faster. If you run
thicker oil than needed, you will drive up engine component temps. For
example: Plain bearings, such as rod and main bearings are lubricated
by oil flow, not by oil pressure. Oil pressure is NOT what keeps these
parts separated. Oil pressure serves only to supply the oil to this
interface. The parts are kept apart by the incompressible hydrodynamic
liquid oil wedge that is formed as the liquid oil is pulled in between
the spinning parts. As long as sufficient oil is supplied, no wear can
occur. In addition to this, the flow of oil through the bearings is
what cools them.
Quote Gmtech94
When I raced we were sponsored by an oil company and helped with the
research of their product .The thought at the time was to run 20w50
race oil to provide for the best lubrication under racing conditions
hence no oil related failures . After many races and a lot of real
data research the conclusion was in this case to run a 10w30 oil as it
provided better lubrication and less engine wear over a long period of
time ,remember endurance racing in 24 and 30 hour races . Although we
never had an engine failure due to oil properties we did have a lot of
feedback on engine wear as well as transmission and clutch wear . I
have to say we did abuse these bikes on occasion with spinning the
back wheel to turn the bike as well as the occasional fall .The
ignition was a weak link but I could change out the pulsers in about
17 seconds once the bike was in the pits . In conclusion 10w30 ran
cooler and did not break down as much as the thicker oils did.
0.75 cP more HTHS can make a lot of difference in wear protection. Blackstone UOA is like looking for wear differences through a straw, a very narrow view of only measured particles around 5 microns and smaller. Basically a very insensitive method of determining wear. Especially when it's just all kinds of random data points.