High rpms

I hear ya. I’m a Buick guy, at 510 lb/ft torque. It’s not a diesel, and doesn’t break driveline components like they do either. lol

 

Interestingly I prompted AI with a more pointed question regarding stress on bearings from high torque and high load at low RPM and it spit this out. This does match what I’ve seen others with more engine background knowledge than myself post in some other threads. Getting the right answers using AI definitely seems to require asking detailed and specific questions, otherwise you get broad generalizations.

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Yes — high torque at low RPM, especially under heavy load (like towing or hauling), can put significant stress on engine bearings, particularly main and rod bearings.


Let’s break down why:







Why Low-RPM, High-Torque Load Is Tough on Bearings

1. More Force Per Rotation:
   • Torque is a twisting force applied to the crankshaft.
   • At lower RPMs, each power stroke applies more force per cycle because the engine isn’t spinning as fast to spread the load across more revolutions.
   • That means the bearings absorb more energy per combustion event.
2. ⚖️ Hydrodynamic Oil Film Stress:
   • Bearings are protected by a thin hydrodynamic oil film.
   • At low RPM, oil pressure and flow are lower, reducing the film strength.
   • If torque is high (like peak torque at 2400 RPM), the film can thin, and metal-to-metal contact risk increases — especially on rod bearings, where peak cylinder pressure translates directly.
3. High Cylinder Pressure = High Bearing Load:
   • High torque typically comes from high cylinder pressures, whether via boost or combustion tuning.
   • That pressure translates into strong downward force on the piston, which is transferred to the rod bearing and crank journal.
4. Fewer Rotations = More Load Per Rotation:
   • Contrast this with high-RPM horsepower use — though the engine spins faster, the torque per cycle is lower, and the load is spread across more rotations, reducing peak stress per revolution.
   
   
   
   
   
   Common Issues from This Load Profile:
   
   
   
   • Rod bearing wear or failure (especially if lubrication is marginal)
   • Main bearing distortion
   • Crankshaft flex, especially in engines with fewer main bearings (e.g., Toyota’s V35A-FTS has 4 mains)
   • Oil starvation at low RPM, if pump volume doesn’t match load

 

ROFLMAO....

Just put this into Chat GPT

"Is high torque at low RPM harmful to an engine?"

It actually gave me two responses and asked which one I preferred. Of course one said bad and the other good. I would have pasted in the text but it wouldn't let me copy it until I made a choice.

Long live AI!!!

 

Guys have already done a good job of explaining but I'll throw in a couple thoughts, and maybe a couple repeats.

Just because it has a good quantity of low-rpm torque (a very good thing by the way) does not necessarily mean that it runs out of power early.
Definitely somewhat sooner than an engine built to rev higher, or a racing engine, but it doesn't magically hit a wall at 3K rpm like you were thinking.
The V35A engine has a relatively/comparatively low redline because it doesn't NEED to rev high to make power.
2 smaller turbos are great for making (relatively) low rpm torque. The flip side to that is they will "run out of breath" sooner/lower in the rev range.
But for a truck doing truck things, so what? Low rpm torque is what you want.

The unfortunate downside to the above strategy for making torque is what @Silver17 posted a couple posts above.

 

Its all and only a matter of what the engine was DESIGNED for. Some are screamers & some are grunters.

 

So Toyota designed a motor to generate low rpm torque but failed to design a bearing to withstand it?


Nevermind, that can't be the case or all our 3rd gens would be eating them.

 

No, not necessarily. Maybe partially.
But the bean counters and the EPA and CAFE appeasers within Toyota that very likely rate higher than the engine designers can get an oil spec in place that does not bode well for long term bearing life given the loads they're subjected to.

 

I’m not an engineer and surely there are different benefits to both designs, but it is interesting that the most similar engine in the competition’s truck being the ford 3.5 ecoboost uses a design incorporating 6 main bearings vs 4 in the V35.

 

I think you are confusing number of main bearing cap bolts versus number of main bearings.
I'm no EcoBoost expert, so I had to go look.
I'm seeing (reading, actually) 4 main bearings on an EcoBoost, no different than the V35A, but has 6 main bearing bolts, with 2 of the 6 being cross-bolted. (Similar to a LS engine.)

 

Since we are talking HP and torque, does anyone remember from high school physics why HP and torque always cross at 5252 RPM on a dyno chart?

I do.

Try to answer without using AI.

 

I just remember it's a mathemagical constant.
HP is a function of torque.

Doesn't really answer the question though.... Next!

 

Never once have I felt like this truck is “high” in RPMs. Turbos light at 2600 and come on strong and keep the torque curve flat to redline

I find this functional for a few reasons.

Area under the curve.
And it keeps the engine in a good spot to not stress on the low end.

There have been zero instances I’ve thought, you know what, this truck doesn’t have enough low end torque.

The tuning and sizing for turbos and displacement is solid on this thing.

 

Thank you all, I think i'm starting to grasp the idea. Much appreciated for all input.

 

You are asking the wrong question. We are not talking about high RPM, like 5-7K rpm. Question is 1.5k RPM high low-end torque / load vs 2.5K rpm same load and torque. Which one will have more bearing wear?

Not sure if you have any engineering background, but if you look at the Stribeck curve you can see that high load or torque with lower RPMs may cause the oil to shear with boundary lubrication. You can see from the graph that increasing speed, in this case RPMs, will increase oil film strength and lubrication.

 

Is that why diesel trucks spin bearings so often?

Now, I do question whether a 0-20 oil should be used. I really think a 5-30 or a 0-30 would be more beneficial for our torque abilities with this logic in mind.

 

That’s a reason I swapped to 0w-40.

Pennzoil ultra platinum has typically shown the best shear performance.

The 0w-20 is just an accident waiting to happen

 

I love the curve band the Stillen (if it's casuing it) has when you actually press heavy on the gas. 3-4k between gears

 

You are right about me confusing things. I believe the higher bearing count thought I was attempting to regurgitate poorly was actually in regards to the hurricane I6, not the ecoboost. The hurricane may even have 7 bearings from the googling I just attempted? I believe that’s partly why the inline 6s are often times very stout.

 

FIFY

 

Mighty fine man

 

That's correct. But, how the constant was derived is the real fascinating story to me.