Oil weight for high rpm's?

[Bigsyke]

On my Nissan 240sx with the Ka24de engine, the reccomended weight is 5w30. However the FSM states if 5/10w30 is not available, I can use a higher weight. I was thinking maybe for higher rpm protection maybe a 0w40 or 5w40? Currently using amsoil 5w30, but havent been racing the engine on that oil yet.

Thanks.

 

[aquariuscsm]

If it were mine,I`d start out with a 10W40.

 

[tomcat27]

once we get out of winter, I'm a big fan of 4w-40 in german and japanese engines. amsoil, of course

 

[ThirdeYe]

fwiw I used to have a KA24DE and I used to drive that car hard. It saw its share of redlines. I used only bulk Valvoline 5W-30 or 10W-30 and it still ran great when I sold it with 128k miles. I didn't treat that car very well, I'm afraid to admit. I only had the oil changed when it hit 3,000 miles which was usually 6-9 months of hard, short trip driving in all 4 seasons.

 

[Bigsyke]

Im going to be road racing in the summer, does thicker weight matter much?

 

[Jim Allen]

Look around for posts from Dr. Haas. Also Doug Hillary. Both have lubricant-related experience with high performance sports cars. Plan on spending some time, as the BITOG search engine sucks. Still, it wil be a fun search because you will see so many other interesting things

Anyway, from my limited knowledge of the topic, the main consideration is oil temp. You want the lowest viscosity possible that will keep the engine safe at whatever oil temp the engine will run. High viscosity costs HP. Plus, high RPM with a thick oil can get the oil pressure up super high and send the pump into relief, maybe even bypass the filter. If the engine oil runs super hot, like 250F, yeah, you'd want that grade 40 because at that oil temp it's a grade 20 (or thereabouts). If you are serious, you'll hook up an oil temp gauge.

Finally, as I understand it, high rpms do not require a thick oil. You have plenty of oil volume for a good hydrodynamic wedge, plus the parts are turning so fast and the power stroke is happening so fast that it doesn't have time to push the oil out of the bearings. It's low-speed grunting where the engine needs the thick oil. The power stroke takes longer, so it has more time to push the oil out of the bearings. Plus oil volume is lower.

 

[jorton]

Originally Posted By: Bigsyke
Im going to be road racing in the summer, does thicker weight matter much?


Not much for passenger car engines. How many miles are on your engine. Look in the UOA forum. Oils that retain viscosity and tbn have the best anti-wear film.

Race engine builders can can build looser bearing clearances, and use low tension rings in a very high rpm engine. Those engines use thicker oil.

 

[JAG]

I'd use a XW-40 oil that is shear stable enough to remain an XW-40 oil.

High rpms require good film strength because of inertial effects of the quickly accelerating engine parts. Mid rpms are the generally the best for maximum oil film thicknesses. That's because the inertial effects are moderate and because of the benefit of moderately high relative velocities between parts. Low rpms with high loads give thin oil films because of the low relative velocity between parts.

 

[mechtech2]

Jim Allen has a good post.

Thicker oil at high RPM usually makes the oil temp HOTTER.
It increases internal drag and makes a thicker boundary layer on parts that take away heat.

Remember that Nascar cars often qualify with 5W.

 

[crazyoildude]

yes thicker oil weight means you will get slightly less horse power, your engine will run slightly hotter and you will get worse fuel mileage (maybe not noticable but it's real)
In the 70s and early 80s you needed thick now you dont unless your engine is making noise or you are burning oil

 

[jorton]

Originally Posted By: mechtech2
Jim Allen has a good post.

Thicker oil at high RPM usually makes the oil temp HOTTER.
It increases internal drag and makes a thicker boundary layer on parts that take away heat.

Remember that Nascar cars often qualify with 5W.



For races, Hendrick engines use 0w-30 in restrictor plate or 20w-50 in open engines. Open runs higher rpm.