Engine Masters (MotorTrend) Tests Oil Viscosity (Thickies Rejoice!)
- Thread starter RDY4WAR
- Start date
But, what about their shirt pockets?
Wrong Show.
They said the cam was probably a Comp 276HR. The short block is a Mercury Marine engine with very low compression (7.5-8.0:1)
They say in the wrap up they think the result of the 20/50 making more HP is atypical and a result of it improving a poor ring seal.
That's painting with a pretty broad brush. What if I had data that showed when I pour water on things they get wetter? Would that be worth sharing?
If that thing is hydrophobic sand or polyester.... yes!
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- Jun 24, 2023
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I saw that episode too. The part that confused me the most was in both cases, the hot (thin) oil resulted in more power than the cold (thick) oil, yet the 20W50 ultimately made more power than the 5W20.
I'd be curious to know if the difference in power between the hot and cold oil was just as a result of the viscosity changing or other factors like less friction at higher temperatures because the oil's additive package worked better, varying clearances, etc. If the engine just wanted a thicker oil, I'd think the cold 5W20 and hot 20W50 results would have been more similar.
I'd be curious to know if the difference in power between the hot and cold oil was just as a result of the viscosity changing or other factors like less friction at higher temperatures because the oil's additive package worked better, varying clearances, etc. If the engine just wanted a thicker oil, I'd think the cold 5W20 and hot 20W50 results would have been more similar.
Loaded for bear!But, what about their shirt pockets?
The higher viscosity at cold temperature and reduced additive reactivity are the reasons for the power loss when the oil was cold. The 5W-20 is likely ~50 cSt @ 100°F which is 2.5x (+30 cSt) more viscous than a 20W-50 at 212°F which contributes the viscous drag. (hydrodynamic friction) Friction modifier, anti-wear, and extreme pressure additives become more reactive with heat. When the oil is 100°F, there's not a lot of additive activity. The higher viscosity also reduces additive response. That's another reason for the power loss. When the oil is nice an hot, that viscosity is thinned down to reduce that viscous drag, the friction modifier additives are working better, you see an increase in power. The key to making good power is a cold engine and hot oil.
I believe this is why Dave w/HPL has described why teams (running HPL of course!) heat the oil before drag runs...and why they run thin oils vs. thick. Interesting article:
Why the Heavy Weights of Drag Racing Choose Light Weight Oils - Engine Builder Magazine
Long before the oil ever enters the equation, the process to facilitate use of power-enhancing, low-viscosity oils begins with the engine builder.
www.enginebuildermag.com
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I believe this is why Dave w/HPL has described why teams (running HPL of course!) heat the oil before drag runs...and why they run thin oils vs. thick. Interesting article:
Why the Heavy Weights of Drag Racing Choose Light Weight Oils - Engine Builder Magazine
Long before the oil ever enters the equation, the process to facilitate use of power-enhancing, low-viscosity oils begins with the engine builder.
Pan/sump heaters and water chillers are great. You start the car right before pulling into the burnout box, with coolant temp below ambient, and the oil temp at 160-180°F.
And I'd bet that thinner oil at only 160F has around the same KV100 (or even higher) as a much thicker KV100 oil at 250F. If they would run that Redline "5WT Racing Oil" or similar with 2400 ppm of zinc and 3350 ppm phosphorus for antiwear, they probably wouldn't have to heat it much (if at all) for a 6 second run down a drag strip.
Also watch the video in the link.
People read this stuff about drag cars running thin oils thinking thin oils give the same engine protection, but most don't understand that the oil temperature is way lower, and the AF/AW add pack is insanely higher than most cars cruising around on the roads, and at a much lower temperature than cars on a race track running near redline RPM for 20-30 minutes.
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The oil temp in those cars can still hit 200+°F by the end of the run. The oil on the cylinder walls is still 400+°F like a street car would see. It's just not for nearly as long.
The KV40 for a Pro Stock oil is 11-13 cSt or about a 30 grade at 100°F. At 160°F, it's 5.2-5.6 cSt with a KV100 of ~3.2 cSt.
The KV40 for a Pro Stock oil is 11-13 cSt or about a 30 grade at 100°F. At 160°F, it's 5.2-5.6 cSt with a KV100 of ~3.2 cSt.
How many quarts of oil are in the oiling system of those cars? I can't see running the engine at redline for 6-7 seconds is going to raise the oil bulk temperature from 160 to 200+ F. Too much thermal mass for it to change that fast. Also, if the sump was around 7 qts and the pump output 15 GPM, only one sump worth of oil volume would go through the engine in 7 seconds ... so a "one time sump" cycle of constant starting temperature sump oil.
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160°F when they fire it up. Then there's the burnout, idle (~1600 rpm) for upwards of a minute or so, stage, 2-step, make the pass running between 8500-10500 rpm for the 6.5 seconds, and then back to idle and shutoff at the top end. The oil is close to 200°F when they shut it off. It's a 10 qt dry sump. These blocks also don't have coolant passages through the block, only through the heads, and there's no drainback from the cam valley.
I thought that in bracket racing, consistency and repeatability were more important than trying to wring the last horsepower out of an engine.
In bracket racing, yes, but Pro Stock cars aren't bracket racing. Every 0.1 HP matters.
