Engine oil recommendation for Turbocharged Airboat

[Hohn]

That said, bearings are one of the few parts of the engine that really have a "too thick" penalty in terms of wear or life. The rest of the engine frankly doesn't mind if you run up a 50 or 60 grade at temps as low as 220-240. The thing is, the extra thick viscosity isn't doing anything helpful for you though. It's just robbing power and reducing the flow that cools many important parts of the engine. Once you have enough viscosity, adding more of it isn't lowering wear. You're just moving along the Stribeck in the same state of lubrication with less end less efficiency.

I think it's important to realize a unique aspect of the fan drive (which is shared with other prop drives): the peak load on the engine is always at peak RPM. Yes, on the dyno, the engine might show a torque peak well below rated power, but that's under a dyno load which is controlled independently of speed. With the fan/prop, the speed IS the load. If the fan was the dyno, you'd see peak HP and peak torque at the same RPM all the time.

So while the engine might be capable of 800hp or such, the actual power output is determined by the fan load (prop curve, drive ratio, etc). It's probably quite a bit less than the full dyno power the engine is capable of.

This means the engine will never see a high load at lower RPM. In my mind, that makes this application the textbook case of choosing viscosity by oil pressure at sustained high temp. If your oil is thick enough to keep the pump in regulation at peak temps in the application, then you have enough viscosity. Having more of it is doing nothing but reducing power.

I think a stout 30 grade is almost certainly sufficient here in terms of viscosity. IMO, the more important aspect of picking an oil here is the additive pack and base. I think a race oil (like HPLs BARO 5w30 or 5w40) would be warranted. I think an "optimal" peak oil temp would be in the 250F-270F range. With alcohol fuels, running too cold is a bigger problem than too hot. R4W is absolutely right, hotter oil is your friend here, and pick an oil that can handle the temp.

If the OP doesn't want to run a racing oil and wants perhaps a bit longer oxidation life, the other HPL oils I'd recommend would be
1) No VII 10w30 Euro
2) PCMO SAE30 or SAE40. (Straight grade is a real option for this case)
3) Supercar/Euro 5w40

The low key great option oil here is also VR1 10w30 synthetic. It's easy to find and it's proven. It just doesn't last long so you'll need to stay on top of oil changes.

 

[RDY4WAR]

The OP chose a recommendation a while back already.

While RPM is a factor in viscosity, it's not as much as one might think. In fact, higher rpm actually allows a lower viscosity for a given clearance, temperature, and load due to the crank journal becoming more centric. The load is more evenly distributed with less reliance on the oil wedge.

VR1 synthetic is a bit of a hidden gem. It's not common, but the AW/FM chemistry synergy is quite good.

 

[IndyIan]

No oil cooler. No one runs them, I've never seen one on anyone's boat. Like I said it runs pretty cool, and holds 8 quarts.

I guess all aluminum motor and oil pan too? Heat transfer and lots and lots of wind must take care of it! Also I guess E85 must take a bit of heat out of the motor too.

 

[Hohn]

I guess all aluminum motor and oil pan too? Heat transfer and lots and lots of wind must take care of it! Also I guess E85 must take a bit of heat out of the motor too.

Alcohol fuels can suck a ton of heat out of an engine. Talk to a sprint car driver who runs methanol— after an extended run in the feature, the intake can feel cold to the touch. They have a high “latent heat of vaporization” and absorb a lot of heat in the process of vaporizing.

Add to that the huge amount of airflow and it’s easy to imagine how an engine like this might even struggle to build heat.

 

[RDY4WAR]

Alcohol fuels can suck a ton of heat out of an engine. Talk to a sprint car driver who runs methanol— after an extended run in the feature, the intake can feel cold to the touch. They have a high “latent heat of vaporization” and absorb a lot of heat in the process of vaporizing.

Add to that the huge amount of airflow and it’s easy to imagine how an engine like this might even struggle to build heat.

This. The heat of vaporization of ethanol and methanol is much higher than gasoline. The higher the HoV, the more heat the fuel absorbs (or is required to be absorbed) as the fuel vaporizes.

These units are in BTU per pound of air at stoichiometric air/fuel ratio.

Gasoline - 9.7
Gasohol (E10) - 12.7 (+31%)
Gasohol (E85) - 35.0 (+361%)
Ethanol - 39.5 (+407%)
Methanol - 78.3 (+807%)

Another benefit of evaporative cooling is improved knock resistance. Knock (detonation or pre-ignition) is largely a factor of temperature and pressure. Since the temperature of the homogenous vaporized mixture in the cylinder is cooler, the risk of detonation/pre-ignition is lower. This is why E85, which has an equivalent octane (anti-knock index) of ~101, has equivalent knock resistance of 116 octane gasoline. Even though a given E10 premium and E-free premium pump gas may both be 93 octane, the E10 will have slightly better knock resistance than E-free because of the cooling effect.

However, this will have little impact on oil temperature at sustained rpm and load. In that state, the majority of oil temperature comes from internal friction, not combustion heat or coolant temperature. Using the Sprint car example, while the intake can be cool to the touch after a race, the oil is still reaching >300°F. This isn't a bad thing though, so long as the oil is up to the task. Most additives become more reactive the hotter the oil gets. The ones that don't are solid particle additives like MoS2, ceramic particles, solid borates, etc... which is why oils and oil supplements containing these are largely worthless. They'll show good friction reduction at room temperature, but once the oil is heated to >200°F, the 80 ppm of tri-nuclear MoDTC already in most engine oils will far surpass it.

Hot oil is happy oil. If the oil you're using can't take the heat, you don't need a cooler, you need a better oil.

 

[Hohn]

Another benefit of evaporative cooling is improved knock resistance. Knock (detonation or pre-ignition) is largely a factor of temperature and pressure. Since the temperature of the homogenous vaporized mixture in the cylinder is cooler, the risk of detonation/pre-ignition is lower. This is why E85, which has an equivalent octane (anti-knock index) of ~101, has equivalent knock resistance of 116 octane gasoline. Even though a given E10 premium and E-free premium pump gas may both be 93 octane, the E10 will have slightly better knock resistance than E-free because of the cooling effect.

This is a major contributor to why direct injection engines can have so much higher static compression. Instead of the evaporative cooling happening in the manifold (where it's less useful), direct injection moves this into the chamber where it can harness the heat from the piston crown and valve bridge area to both more effectively atomize fuel and cool these critical hot zones.

There's still part of me that struggles to grasp how Honda made my K20c4 capable of 9.8:1 while pushing nearly 20psi of boost as low as 1500rpm on 87 octane. My brain knows it's with DI and fancy VTEC massaging of cam timing, but as kid reading hot rod magazines where 9:1 was the "pump gas" compression limit for 93 octane with no boost, it's just mind-boggling that tech makes it possible for this combination of compression, octane and boost to coexist and do so in mass production.

 

[RDY4WAR]

This is a major contributor to why direct injection engines can have so much higher static compression. Instead of the evaporative cooling happening in the manifold (where it's less useful), direct injection moves this into the chamber where it can harness the heat from the piston crown and valve bridge area to both more effectively atomize fuel and cool these critical hot zones.

There's still part of me that struggles to grasp how Honda made my K20c4 capable of 9.8:1 while pushing nearly 20psi of boost as low as 1500rpm on 87 octane. My brain knows it's with DI and fancy VTEC massaging of cam timing, but as kid reading hot rod magazines where 9:1 was the "pump gas" compression limit for 93 octane with no boost, it's just mind-boggling that tech makes it possible for this combination of compression, octane and boost to coexist and do so in mass production.

Chamber design is a big part of that as well. A 4v pentroof chamber with a flat piston, with no obstructions to the flame front, will have smooth and even flame propagation. I was looking at the chambers of a late 70s 454 smog head the other day and thinking about just how inefficient it is with an awkward shape and offset plug. We've definitely come a long way since then.

 

[factorytuned2012]

Posting a potential unique situation, and looking for insight from the experts here. I've been researched and have a few ideas. I have built a forged bottom end, pretty aggressive cam/valve train LS (V8) with a turbo running on e85. It is making about 750-800 hp but I plan to turn it up to ~900 soon. This is on an airboat running in Florida so it never gets run below ~40°F but run consistently over 85-90F. It gets run for long amounts of time and we beat on them pretty hard. It sees boost constantly. I have been previously using Driven racing oils 10w40 but was looking for a more economical or potentially better oil to use. One other thing to add is the boat will sit for a few weeks at a time, so something with some corrosion protection would be nice.

I had two schools of thought. A cheaper oil but still quality that is easily available that I can change more frequent. Such as Penzoil Platinum Euro 5w40, or one of the other 5w40 that maybe meets the A40 spec. For a little more I can go with Amsoil Signature Max Duty 5w40 or their Premium Protection 10w40 (I already have a membership so it's ~$44ish a gallon). I need 8 quarts.

Or finally go all out with a top tier oil that is more expensive such as Redline, HPL, even stick with Driven it would just come at an extended oil change interval.

I am open to ideas and opinions I would like to keep 5w40 or 10w40.

Thank you all!

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