Increased Boost vs Viscosity?

[Skips]

Hello everyone! Using my first post to pose a question I've been pondering for a while.

I have a turbocharged petrol vehicle that is running more boost than stock, giving roughly 30% additional peak torque. Will this higher torque load require a higher viscosity oil? If so, what's the relationship between increased load and viscosity requirements?

My thinking is that this increased torque would put additional load on bearings and reduce the MOFT, therefore requiring an oil with a higher HTHS. I have no idea if this is correct, or if the oft-given advice to 'go up a grade' for a modified vehicle is simply to compensate for the increased temps you will likely see.

 

[facility1]

Everyone here is going to recommend Mobil 1 ESP.

 

[GI_GRIFF]

My thinking is that this increased torque would put additional load on bearings

You are definitely correct about this. What Is the vehicle and engine and what does the owner's manual recommend for oil with the stock engine, before you modified it?

 

[edyvw]

Hello everyone! Using my first post to pose a question I've been pondering for a while.

I have a turbocharged petrol vehicle that is running more boost than stock, giving roughly 30% additional peak torque. Will this higher torque load require a higher viscosity oil? If so, what's the relationship between increased load and viscosity requirements?

My thinking is that this increased torque would put additional load on bearings and reduce the MOFT, therefore requiring an oil with a higher HTHS. I have no idea if this is correct, or if the oft-given advice to 'go up a grade' for a modified vehicle is simply to compensate for the increased temps you will likely see.

What vehicle is that? What is original hp? What is hp now? Is alcohol involved?

 

[Skips]

What vehicle is that? What is original hp? What is hp now? Is alcohol involved?

Apologies for not including this in original post but didn't want this to turn into an oil recommendation thread - I figured the discussion would apply to any vehicle that's been modified in this way.

For reference, the vehicle is a 2003 Ford Falcon XR6 Turbo, originally producing 320hp and now producing 415hp. OEM recommendation is 15w-40. Using petrol (gasoline, you might say) with 0% ethanol.

 

[ka9mnx]

You are on the right track. Forget grade and look for HTHS >3.5. Your 15w-40 probably covers that.

 

[Cujet]

Higher loads require higher viscosity. How this is achieved is up to you. Managing oil temps down to belo 180F is one way racers successfully use low viscosity oils in high output engines. For the rest of us, we can typically use a HP per cylinder point of view. With a stable 40 viscosity oil being a very good idea when near the 80HP per cyl point.

The reason this works is that rod bearings really don't vary that much in size. But the load they are asked to carry does.

In my case, the AJ126 Jaguar V6 makes 79HP per cyl with the increased boost and tune. That is clearly enough to overwhelm the OEM 0W-20, and even the upgraded 5W-30, in my case, M1 15W-50 is the right choice. It is not a particularly viscous oil and is well proven to protect. Much more along the lines of a 10W-40 from other sources.

 

[JavierH19]

Everyone here is going to recommend Mobil 1 ESP.

Wow I didn't know you were a psychic, how'd you know? What're the next powerball numbers gonna be?

I had to look up the spelling to make sure and it says ESP in there. Doesn't get more prophetic than that.

 

[RDY4WAR]

This is more of a complex equation with a lot of "it depends" factors. Generally speaking, if BMEP increases >25% above OEM figures, then I like to go up one grade. If oil temperature increases >20°F from typical, I like to go up one grade. Let's say you have an MK6 GTI EA888 that made 207 lb-ft (BMEP = 258 psi) stock, then I would considering going up one grade when that BMEP exceeds 323 psi (259 lb-ft). I don't think much of this with a second jump in grade because usually, by the time you get to that point, you're tearing the engine down to build for that kind of power anyway and thus you're dictating the viscosity from scratch.

However, there's a lot of factors like RPM, fuel choice, climate, driving style/usage, oil brand/series, etc... that create deviations from those general rules. Thus, this is often a case-by-case thing for me. For example, if BMEP has increased by 30-40% but the torque curve has been pushed to a higher rpm range, then I may not increase viscosity. The higher piston speed will promote earlier transitions into EHD and HD lubrication regimes which reduces the MOFT. Higher crank journal speed promotes greater centricity within the bearings which reduces the MOFT. In such a case, higher viscosity could just hurt power (by way of increased hydrodynamic friction) for no positive trade-off. The quality of the oil is a significant variable. I may like HPL No VII 5W-30 in a given application but if someone wants something they can get off the Walmart shelf, knowing the oil won't be nearly as shear stable and tolerant of fuel dilution, I may recommend a 5W-40.

 

[edyvw]

Apologies for not including this in original post but didn't want this to turn into an oil recommendation thread - I figured the discussion would apply to any vehicle that's been modified in this way.

For reference, the vehicle is a 2003 Ford Falcon XR6 Turbo, originally producing 320hp and now producing 415hp. OEM recommendation is 15w-40. Using petrol (gasoline, you might say) with 0% ethanol.

I am with @RDY4WAR.
5W40. 15W40 might not be of the same quality as it is just cheaper to make.
I don't think you have HPL in Australia, or it would be expensive to ship it. Nulon has good 5W40 high-performance oils, Maybe Motul power 5W40. There are always the usual suspects here: Mobil 1 0W40, Shell Helix 5W40, Castrol 0W40.

 

[Skips]

Some great answers and appreciate some of the real-world experience shared.

In my case, the AJ126 Jaguar V6 makes 79HP per cyl with the increased boost and tune. That is clearly enough to overwhelm the OEM 0W-20, and even the upgraded 5W-30, in my case, M1 15W-50 is the right choice. It is not a particularly viscous oil and is well proven to protect. Much more along the lines of a 10W-40 from other sources.

In my case the HP per cylinder is less than yours at around 70hp/cyl, however my baseline OEM viscosity is higher so I'd probably target something similar in the end.

This is more of a complex equation with a lot of "it depends" factors. Generally speaking, if BMEP increases >25% above OEM figures, then I like to go up one grade. If oil temperature increases >20°F from typical, I like to go up one grade. Let's say you have an MK6 GTI EA888 that made 207 lb-ft (BMEP = 258 psi) stock, then I would considering going up one grade when that BMEP exceeds 323 psi (259 lb-ft). I don't think much of this with a second jump in grade because usually, by the time you get to that point, you're tearing the engine down to build for that kind of power anyway and thus you're dictating the viscosity from scratch.

However, there's a lot of factors like RPM, fuel choice, climate, driving style/usage, oil brand/series, etc... that create deviations from those general rules. Thus, this is often a case-by-case thing for me. For example, if BMEP has increased by 30-40% but the torque curve has been pushed to a higher rpm range, then I may not increase viscosity. The higher piston speed will promote earlier transitions into EHD and HD lubrication regimes which reduces the MOFT. Higher crank journal speed promotes greater centricity within the bearings which reduces the MOFT. In such a case, higher viscosity could just hurt power (by way of increased hydrodynamic friction) for no positive trade-off. The quality of the oil is a significant variable. I may like HPL No VII 5W-30 in a given application but if someone wants something they can get off the Walmart shelf, knowing the oil won't be nearly as shear stable and tolerant of fuel dilution, I may recommend a 5W-40.

Interesting! Regarding your point about the transition into EHD and HD regimes, when do you typically see the EHD regime in a crank bearing? Does it transition from EHD into HD at higher rpms?

For those wondering I'm currently using Penrite 10 Tenths Racing oil, a local PAO/Ester blend which despite the name can be used on the street. Currently in the 15w-50 grade which has a HTHS of 5.3 but thinking of stepping down to the 10w-40 which has a HTHS of 4.5. My thinking was OEM required HTHS≥3.7, multiply by 130% giving 4.8 and then round up!

 

[RDY4WAR]

The bearings will ideally never see EHD. If they do, it will be at low rpm when the crank journal is more eccentric in the bearing and more reliant on an oil wedge.

Penrite oils are quite good. I think you'd be fine with their 10W-40, but their 15W-50 is great oil too.

 

[YZJB]

I would stick with the 15W-50 you’re using. Sounds perfect for your application and the Barra won’t mind having a thick oil in the sump.