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.)

So, same number of main bearings between the two, but different methods and number of bolts holding those main bearings in place.
EcoBoost has individual, 6 bolt main caps.
V35A has a one piece ladder style bearing retainer, with each bearing secured by 4 bolts.

 

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.

 

There may be some connection there, but may not be so simple. I think thicker oil will protect main bearings more: look what GM recommended in their recent recall for the 6.2 V8- increase in oil thickness. IMO, main cause is stratospheric torque below 2k rpm, which lots of trucks and newer direct injection engines have. Even LSPI happens because of this same issue.

However, looking at the oil lubrication curve, one can increase the oil film strength by either oil thickness or speed/rpm. Increasing rpm may be more simple than increasing oil thickness to achieve the same oil strength.

I have 35s on my truck that are about 12-15 lbs heavier per corner and have wider diameter. Some 35” LT tires people run are 70lbs per tire. That is about 30-32 lbs heavier per corner, in addition to the increased diameter. This will further put more strain and load on the engine at low rpm’s, below 2k.

These rigs have 10-speed auto, and with Tow/haul mode activated, they act like old rigs re-geared. In tow/haul mode, my truck runs at least 1 gear lower compared to normal mode, and keeps RPMs above 2k.

I recommend running these Tundras in tow/haul mode if you have a lead foot, bigger tires or more sprung or unsprung weight. Add 5w30 grade, old v8 longevity is in sights.

 

Forced induction like the twin turbo setup of the Gen 3 tundra is all about forcing extra air in to the cylinder to make power when power is needed, but letting the smaller displacement and cylinder count of the motor be more fuel efficient when power is not needed.

Looking at a naturally aspirated gas motor the like venerable 5.7 in Gen 2 trucks, it has the ability to make 'X' amount of torque by flowing 'Y' amount of air in a specified amount of time to make some amount of power 'Z'. Power is made by combining air with fuel to create thermal expansion (an explosion as we view it) that forces the piston to move. That movement is translated via the rods and bearing into a rotational force at the crankshaft, which we call torque, since torque is a twisting force. How much torque we can create in a given amount of time is called power - more specifically horsepower as that's the metric that we decided to use, derived from the mining days when horses and pulleys were used to draw loads of rumble up a mineshaft. Since we measure motor speed in RPM or Rotations per Minute, the time element is used to derive the number of horse powers a motor has. Yes, horsepower is a derived number and isn't measured directly. More RPM means more combustion events in a certain time, which yields more torque output, which creates more HP.

The air coming in to the motor is limited by the blade of the throttle body; this allows use to modulate the amount of power output by the motor instead of simply running the motor wide open all the time. (as a side note, diesel motors have no throttle blade, but instead, modulate RPM and power by how much fuel is injected into a cylinder). At idle, we are choking the motor almost to the point that no air is flowing in to it. This keeps RPM low, fuel consumption low, and torque low - barely enough torque to turn the crankshaft and move the pistons without creating an excess of torque that can be transmitted to the wheels. This creates a vacuum in the system that is read literally as vacuum. It's what allows us to have power brake boosters that are vacuum operated. At full throttle, we are allowing as much air in to the motor as it can possibly flow, and injecting as much fuel as can possibly be burned, and creating an excess amount of torque and power than is needed to overcome the friction and inefficiencies of spinning the motor itself, which can be used to do useful work - like moving the car down the road. But the air is not scooped in to the motor, nor does it fall in to the motor, but the ambient atmospheric pressure is what is pushing the air in to the motor. Thus, motors make more power at sea level than at high elevations.

The amount of power a motor can make depends on the amount of torque a motor can make in a specific time. The amount of torque a motor can make depends on the amount of air that it can flow since your air to fuel ratio has a small window in which it operates efficiently; you need to have enough oxygen molecules to combine with the hydrocarbon molecules in gasoline in order for it to ignite and create that thermal expansion (explosion). Simply adding more fuel without more air doesn't gain any horsepower and can actually cost you horsepower. So really horsepower is simply limited to the amount of air pumped through the motor. Increasing the displacement of the motor or the RPM of the motor will yield more HP, with a few caveats which we'll get to... but for simplicity sake, that holds true:

HP = Air Flow through a motor via displacement or RPM.

So what does this have to do with your original question? And why is it desirable for a truck to have lots of low-end torque? And furthermore, why are small displacement turbo motors becoming standard, like the Gen3 3.4TT?

Simply put - the more torque a motor makes at any RPM, the more HP it also makes at that RPM. If you can make more torque at lower RPM, you can also make more power at lower RPM. You need both to move a big heavy vehicle.

Since full size trucks are big and heavy with poor aerodynamics, they require lots of torque to start moving. We (some of us) use trucks to do truck things like haul cargo and pull trailers, adding to the weight and making aerodynamics even worse. Moving big heavy objects requires a large motivating force, or Torque. Via the magic of gear reduction in a transmission and final gear (differential gears in the axle) we create a torque advantage in lower gears, multiplying the torque needed to move the truck, cargo, trailer, etc. Some vehicles actually create more torque in lower gears than the engineers deemed allowable or tolerable by some components of the vehicle, so the motor is electronically limited to make less torque in first or second gear.

Lower gears lets you move more weight, but at the disadvantage of reducing the speed at which it is moved. First gear tops out at 30-something miles an hour while spinning the motor to 6k RPM, ya? So shift in to another gear, but that reduces the torque applied to the wheels and the tops out again around 60 MPH. So shift another gear for even less torque to the wheels. Eventually, you want to find that happy medium where the motor can spin fast enough to create enough torque to move the weight, and enough horsepower to move it at whatever speed you desire. Once you reach about 55 MPH, the wind resistance of the vehicle starts to become the dominating factor in power output requirements to keep a vehicle moving; below that, it's rolling resistant of the tires plus the weight of the vehicle. Then you need more HP to keep the vehicle moving.

So more torque down low allows you to move a big heavy truck with ease at high speeds without spinning the motor too fast. It also allows you to achieve that speed with haste.

Since HP and torque are all about airflow, you can either spin a bigger motor slower or a smaller motor faster to move the same amount of air, creating the same amount of power. This is where small-displacement forced inductions motors show up to throw their hat in to the ring. By forcing excess air in to the motor via a turbocharger or supercharger, you are no longer limited to the atmospheric pressure limits flowing air through the motor. This allows you to inject more fuel and make more power at the same RPM as a naturally aspirated motor. We can measure boost in PSI, ATM, inHG, etc, but generally we use PSI. I atmosphere = 14.7 PSI. When a turbo motor makes boost, it is creating additional pressure beyond the atmospheric 14.7 lbs per square inch. A supercharger in stock trim makes about 6 or 7 PSI; a turbo makes 14-21 PSI, or more! From an airflow perspective, we can view that additional boost pressure as additional motor displacement - simply divide the boost pressure by atmospheric pressure and multiply by your motor displacement.

A 5.7L motor on 7 psi = 5.7 * (1+ (7/14.7)) = 5.7 * (1+.476) = 8.41L.

A 3.4L motor on 14.7 psi =3.4 * (1+(14.7/14.7) = 3.4 *2 = 6.8L.

A 3.4L motor on 21 psi = 3.4 * (1+(21/14.7) = 3.4 * 2.429 = 8.26L.

Turbochargers are interesting in how the make boost compared to blowers, but I'll save that for another discussion. Suffice to say, turbos need exhaust pressure to spool up, then make full boost that has to be limited by a wastegate to a specific amount of boost. You can make full boost down low, but it requires a preceding amount of full throttle in order to build boost. This is called turbo lag. It is much less of an issue with modern vehicles but is still there. Blowers are run mechanically off the motor, so can make full boost instantly, at the cost of using engine power to make the boost. But the end result is the same: boost = more air in the motor = more power out.

If you are driving around town or at light load on the highway, the small displacement motor doesn't require an extra air (or boost) to make the requisite amount of power to maintain speed. Thus they can be more efficient by reducing parasitic losses of a larger motor. HOWEVER, power = power, so you need the same power to move the same vehicle at the same speed, regardless of the motor displacement. You simply get mileage gains from reducing parasitic losses due to displacement and increased weight of a bigger motor. And when you need MORE power to pull a trailer with a head wind, for example, you are going to consume the same amount of fuel (or in some cases more) to make the same power regardless of whether or not you have a naturally aspirated V8 or a TTV6 with the only difference being parasitic losses.

Now, as mentioned by @Silver17, the smaller V6 with few main bearings that is asked to make the same or more torque and power as its larger V8 counterpart sees higher loads on each individual bearing. Fewer cylinders to spread the load and heat, fewer connecting arms and bearings to disperse the load, and fewer main caps and bearings to keep the torque in line. So long as those bearings are overbuilt, it's not a problem. If they are equally sized, you are over stressing the V6 compared to the V8.

Since a TTV6 is capable of making max boost down low as soon as the turbo spools, and peak torque at 2400 RPM, that's puts quite the load on the motor. The torque is then limited or tapered off after some certain RPM, creating a torque curve along with a HP curve. There are mechanical limits as well as flame propagation limits in the fuel that prevent a motor from making 100% torque all through the RPM band, but mostly airflow limits. Those airflow limits can be either on the pump (turbo or supercharger), software limits, or simply the system components or system as a whole. But as RPM increases, so will HP until you run out of air, fuel, or mechanical capacity. Compressor maps are a rabbit hole to fall down if you want to look in to how and when turbo makes power or doesn't. Designing a system to work well inside those limits is the job of the engineers that built the vehicle, so they dictate how and when power is made. To project the vehicle and keep the vehicle "streetable" we are given good midrange power and torque that tails off at higher RPM.

In comparison to turbos, a blower makes very linear power. It compresses a fixed amount of air to feed in to the motor with ever rotation of the motor, so torque is instant and basically flat from off-idle to about 5k, then runs in to airflow limits. This means HP increases linearly with RPM. This also means that parasitic losses are linear with a system in boost, so they are generally less efficient than turbo system. Not saying one is better, just illustrating some differences. Both make lots of torque down low to move a heavy truck.

 

Wow!

Well done.

 

Is octanes relationship to power the next chapter?

Well done, Benton.