Does size matter? (1 Viewer)

[MiniPigg]

Ok I wanted to ask something that has been on my mind for some time now.

If you have two diesel engines that produce the exact same horse power and torque. Lets say 150hp and 300ft-lbs. One is a 2.0 liter and the other is a 6.0 liter. Lets say the 2.0 weighs in at 350 lbs and the 6.0 is something like 1100 lbs. They are both install into different FJ62's. Arent they still pretty much the same when used in a diesel conversion. If they both have the same power band then I couldnt see why the smaller one would not work any differently then the larger engine. If not then using some math, etc... why ?

Maybe the mass of the flywheel used?

 

[inkpot]

Howdy! May be the difference in the total rpm range which delivers most of the power. Also, the smaller engine must be "pushed" a lot to be even close to the power of the larger one. The smaller one may have extras like twin turbos, huge exhaust, fancy computer, etc. There is no substitute for cubic displacement. John

 

[Towpack]

Turbocharging theoretically increases the displacement of an engine by ramming more air into the combustion chambers. Not sure how the maths is worked out but depending on the boost you could effectively 'increase' the size of your engine by 2 or even 3 times maybe. What will be different is the delivery.

2 Litre + turbo = power & torque high up the rev range + turbo lag.

6 Litre NA = similar power & torque from tickover with a lower rev cieling.

The power may be the same but the power band most definately will not be.
Obviously gearing will play a major factor in determining an alternative engine option unless you want to play around with different FD ratios or gearboxes.

 

[MiniPigg]

A couple of the small turbo diesels that are around 2.0 liters started and maxed torque out very similar to a diesel twice their size. The powerband was very close with both horsepower and torque. But the larger diesels horsepower dropped off between 3K and 3.5K and the smaller turbo diesel continued to go till about 4K till it started to drop. Same with torque.. the smaller diesel went another 500rpm before dropping off.

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[Gold Boy]

size is less important when off-roading when you are going slow using 4low. for highway hill climbing and towing, cubes and a turbo is important.

.000000 2 cents.

 

[rchalmers3]

Ok I wanted to ask something that has been on my mind for some time now.

If you have two diesel engines that produce the exact same horse power and torque. Lets say 150hp and 300ft-lbs. One is a 2.0 liter and the other is a 6.0 liter. Lets say the 2.0 weighs in at 350 lbs and the 6.0 is something like 1100 lbs. They are both install into different FJ62's. Arent they still pretty much the same when used in a diesel conversion. If they both have the same power band then I couldnt see why the smaller one would not work any differently then the larger engine. If not then using some math, etc... why ?

Maybe the mass of the flywheel used?

Hey there,

My answer is that the difference between a 2.0L and 6.0L motor is their ability to move air. The more air you move, the more fuel you can mix in and burn. The more fuel you burn, the more heat and pressure you make to push pistons.

The 6.0L would have a x3 potential to produce power over the 2.0L. The fact it is not producing more power in your example is only because of your chosen comparison constraints. In the real world you could bet the engineers wouldn't give you such a 1100lb slug.

An important comparison of motors to consider is what I think you call the "power band". When you have 2 motors making 150hp and 300ft/lbs, the very next comparison is where they make those numbers.

For two disparate motors like your example, it would be likely that the 2.0L would have to wind very fast, in order to move large amounts of air through to make the numbers. That means the motor would have to be revved to produce enough power to pull the car along.

Meanwhile your 6.0L lumbering beast is probably not going to have to turn very fast or be very efficient to make those under-achieving numbers! Just getting it off idle would give you the power to pull the car.

Now, which would you rather drive? A motor that needs to be revved to get you around, or a tractor motor that will let you make second gear starts and gives you crawling control? I know what I like, but what are your driving needs and preference?

Rick

 

[MiniPigg]

so then maybe the rotating mass of the larger engine allows it to continue to rotate without slowing it down as much as the smaller engine would.

 

[crushers]

so post up the 2 engines you are comparing. which 2L vs which 6L?

 

[rockcrawler]

If you had two hypothetical engines like that or real, the smaller one would be the one working the hardest to produce the power whether through higher revs, turbocharging etc. They may produce more or less the same result power wise but they are not the same when it comes to reliability or longevity. Those sports rice burners with their high revving engines will crap themselves out way before a V8 does.
"Does size matter" is a question of application.

 

[MiniPigg]

The two engines are hypothetical. I wanted to see if you had two diesels that produced the same powerband but one was more then twice the size and weight of the other, would there really be any difference being they both produce the same hp and torque with the same powerband over the rpm range. I forgot to add before but let them both be placed in identical trucks with same tire, gearing, etc...

I know many of us often see our rigs as weighing a certain amount. Like one of my old FJ55's. It was something around 4200 pounds. So with that in mind one would just think, well the engine must move 4200 pounds. Without an engine the truck would be somewhere around.... I am guessing maybe 3400 pounds? So then with the base of 3500 and then adding the different diesel engines... one at 400lbs and the other at 800 lbs... they are both moving different weights with the same gearings, tire size, and such. The smaller diesel would not need to work nearly as hard to move the same truck... ?

 

[canucksafari]

And if you want to tinker even more in your study, then compare a straight 6 to say a V 6 or even a V8 I'd take a straight 6 any day (gas or diesel) in tems of dependability. My money is on the straight 6 lasting longer and being easier to repair - if needed.

 

[rchalmers3]

so then maybe the rotating mass of the larger engine allows it to continue to rotate without slowing it down as much as the smaller engine would.

The two engines are hypothetical. I wanted to see if you had two diesels that produced the same powerband but one was more then twice the size and weight of the other, would there really be any difference being they both produce the same hp and torque with the same powerband over the rpm range. I forgot to add before but let them both be placed in identical trucks with same tire, gearing, etc...

I know many of us often see our rigs as weighing a certain amount. Like one of my old FJ55's. It was something around 4200 pounds. So with that in mind one would just think, well the engine must move 4200 pounds. Without an engine the truck would be somewhere around.... I am guessing maybe 3400 pounds? So then with the base of 3500 and then adding the different diesel engines... one at 400lbs and the other at 800 lbs... they are both moving different weights with the same gearings, tire size, and such. The smaller diesel would not need to work nearly as hard to move the same truck... ?

Your hypothesis dosen't work and it's leading you astray. There is no reason to hypothisize that:

A) A 2.0L and a 6.0L would produce the same torque and HP at the same "power band"

B) If there was such an opportunity to fit such an unlikely pair of motors, I doubt the enginers would use the same gearing

If there was a truck engineered and manufactured for the small motor and you swapped in the big motor, it would probably not work very well.

If there was a truck made with the big motor and you swapped in the small motor, it also would not work very well.

If you want to compare how the relative weights of two similar out put motors affects accelleration, great, we can do that.

If you want to compare the differences in how a large displacement and small displacement motor makes power, great, we can do that.

I believe crushers requested specific examples of your hypothetical motors was actually a challenge to your hypothesis.

I believe there's no such animals.

Respectfully,

Rick

 

[amaurer]

Your hypothesis dosen't work and it's leading you astray. There is no reason to hypothisize that:

A) A 2.0L and a 6.0L would produce the same torque and HP at the same "power band"

I disagree... sure, its contrived, but not impossible. I'm pretty sure that there are teeny tiny engines out there nowadays with similar performance as a big old 2F, ignoring of course any additional performance at higher RPMs.

B) If there was such an opportunity to fit such an unlikely pair of motors, I doubt the enginers would use the same gearing

If there was a truck engineered and manufactured for the small motor and you swapped in the big motor, it would probably not work very well.

If there was a truck made with the big motor and you swapped in the small motor, it also would not work very well.

Why not? The only parameters that come "out" of the engine are the size and shape of the torque curve, nothing else. The gearing could, and probably would be, identical.

Down low, as was mentioned, the inertia of the rotating mass might be important, but that wouldn't be part of the torque curve. Since this question already has BS stacked on top of BS, there is really no reason to assume the rotating masses aren't identical as well - there could be a huge flywheel on the 2L... we just don't know

But thats the point of why this isn't an interesting question - if everything is hypothetical then indeed you can say things like:
-Identical torque curve (peak, shape, etc)
-Identical engine mass (perhaps the 2L is over built)
-Identical rotating mass (perhaps the 2L has a huge flywheel)
...
and in the end so many things will be stated to be identical that, in fact, the two cases ARE identical!!!

If we're going to be reasonable about it, however, and fix ONLY the torque curve and make reasonable guesses about everything else, I'd come up with:

-The 2L is lighter, so overall the acceleration will be better.
-The 2L probably has lower rotating mass, again assisting acceleration, but also hurting your ability to bump it over rocks at idle.
-If the 6L is a 6 or 8 cylinder then its very likely smoother.

Even more reasonable still would be to fix only the peak torque or power values, and let th shape of the curves be variable as well. Then I'd add to the above:

-The 2L probably revs much higher, so the gears would need to be much lower for the same crawl ratio. Highway maximum speed would probably be better, or the 6L would need an overdrive.

etc etc etc...

 

[rchalmers3]

The only way to get a 2.0L to make power like a 6.0L is to turn it at higher revs. The little motor has got a lot of spinning to do to move the same amount of air.

There is no way the "power band" (whatever that is) will be the same. They can't be.

If the little motor makes it's nM and/or kW at 7,000 rpm and the big dude at 3500 rpm, we are talking apples and oranges.

I'm with crushers. Get me some real motors and we can talk. Otherwise the hypothesis gets things all jammed up.

Rick

 

[amaurer]

The only way to get a 2.0L to make power like a 6.0L is to turn it at higher revs. The little motor has got a lot of spinning to do to move the same amount of air.

There is no way the "power band" (whatever that is) will be the same. They can't be.

If the little motor makes it's nM and/or kW at 7,000 rpm and the big dude at 3500 rpm, we are talking apples and oranges.

I'm with crushers. Get me some real motors and we can talk. Otherwise the hypothesis gets things all jammed up.

Rick

That is often true, but rpm is not "ONLY" way of anything. If the 2L had some forced induction it could have exactly the same amount of air and fuel in each cylinder as the 6L. Or the 6L might just be particularly inefficient with the fuel its got, and be fuel-lean...

Its very possible.

 

[rchalmers3]

Just saw you edited your reply.

Discussing this issue is useless unless you come up with something other than hypothetical 2.0L and 6.0L motors that are magically compatible.

Rick

 

[crushers]

grab 2 engines out of the air and lets talk... otherwise this thread is useless.

 

[Tapage]

Some comparisions come to my mind .. .

Lets see a 80 series stock brand new from factory one with the NA 1HZ and other with the TDI 1HD-T

You need to rev the 1HZ higger to " try " reach the same speed ( at same time ) compared to the HDJ80 ..

Other comparision ..

The 60 series come with 3B - 2H - 12H-T from 3.5 NA to 4.0 TDI ..

Other more new comparision ..

The new prado 120 - 125 series, are fitted with

3RZ - 5L - 1KZ-T - 1GR

The smaller 3RZ ( 2.7 ) need to rev it up ( lot more ) to move the prado at the same speed than the 1KZ-T ( sure gasser vs diesel )

Other example come from the Hi Luz .. those with the 2.5 engine and no intercooler ( 2KD-FTV ) come with 3.91 R&P and the others with the 1KD-FTV come with 3.54

 

[crushers]

Tapage,
i hate to break it to you but the 1HZ and the HDT have to rev the same RPMs to move the same geared 81 down the road at the same speed... it is mechanical math buddy.

a better comparision is the LJ78 and the HZJ77, both are similar vehicles but with a 2L engine and a HZ 4L engine.
to allow the smaller engine to move the (close to) same weight vehicle down the road Toyota had to install 4.90 diff gears in the LJ78 vs the 4.11 gears in the HZJ77. even then the 2L enigne struggles with the challenge and surprisingly both return close to the same fuel milage.

 

[Tapage]

Tapage,
i hate to break it to you but the 1HZ and the HDT have to rev the same RPMs to move the same geared 81 down the road at the same speed... it is mechanical math buddy.

no problem dude ..

But that's the reason why I talk ( write ) about speed in time .. to reach the same speed in the same time you need to make more strees on the 1HZ ( more fuel ) compared to the 1HD-T engine ..