I had this debate with a guy back years ago on this site and he was saying that because on paper a gas motor makes just as much and more HP that if you keep it in the right RPM range a gas will pull as well as a diesel if correctly setup and I was saying I do not care what paper was telling you a diesel was much better for towing because it was making hundreds of HP just above idle and you were always in the power band so it was always applying hundreds of HP to moving the load at a constant so it just hooked up better and went better pulling no matter what the paper specs lead you to believe.

I told him with a 30 or 40 speed gearbox a gas may be able to pull it off but that was just not feasible in standard shift to apply the power, a automatic tranny maybe but much power would be wasted shifting in such a tranny and trans would be to complex?

Just out of curiosity am I right or can a gas motor compete with a diesel pulling all things being equal but are not as good because of fuel use and the fact they generate to much heat because they turn many more rpm and will burn up loaded like that at a constant.

Any input to educate would be nice and thanks.

 

The only reason I am posting this is because I am considering getting a gas engine truck and if I ever want to like pull like 15 or 20 grand can a gas do it near as well as a diesel?

 

No a gas cant pull as much as a diesel, not cause im a diesel fan but diesel make there HP and torque way down low, gas you would need a 3500 stall converter to pull anything. that would wind up over heating the trans or blowing something up. A diesel makes 500lbs just off idle which is what you need to tow, thats why you dont see a Mack or Peterbuilt with a gas engine. You need that low end power and torque to get that load moving

 

Thanksssssssss

 

The guy you were arguing with is right, a gas can pull as well as a diesel if properly setup and driven. BUT it will use considerably more fuel and wear faster to do it.

Pulling ability is about driveline torque, cause a gas spins faster it stays in a lower gear longer making overall the same driveline torque. But again cause it stays on a lower gear longer it uses more fuel and wears out faster.

 

X2. I used to drive a F 750 with the little 200 hp cummins in it hauling rock. I now have a f-800 with the 235 hp gas 429 in it. Both trucks grossed 34k loaded. The gas engine will actually pull the same hills faster than the little cummins, as long as I keep the rpm above 3000. But the cummins averaged 9 mpg and the gas gets 6 mpg, largely due to the fact that the cummins never got above 2500 rpm. So yes a gas will pull just fine, but you got to let it rev.

 

I have read here where guys had like the V10 and went PS and said the PS was a major improvement pulling on hills maintaining speed but maybe a V10 lacks the torque of a BB v8?

So basically the laws physics do not lie. If you are pushing a load and maintaining 500 HP pushing power it does not matter weather you are doing it at 2000 RPM or 5000 RPM 500 HP is 500 HP but the diesel does it much earlier and because it does not turn as many RPM the fuel mileage is a lot better and the engine will last twice as long.

On thing for sure in a automatic or manual the diesel will get the load going much easier off idle over a gas and in a manual it seams like the gas would eat a lot more clutches because you would need to ride it to keep the engine RPM up to stay in the meat of the power band?

 

So basically it pulls faster up the hill because in the meat of the power band it is making 35 more HP and it shows on the hill because it moves the load a little faster up the hill? So essentially a dyno does not lie but most people cannot read them and understand what the RPM curve is telling them.

We know torque is also very important when trying to maintain HP under load because if it were not a 1.5 HP RC model airplane motor would be able to run a moped which it cannot.

Just like a Mack I was looking at had a 238HP Maxidyne with a 5 speed that made 1100 FT pounds of torque and I bet it could stay in the power band and would be way easier to pull a load like 50,000 plus pounds over the 429 gasser? The 429 could do it but would need like I said earlier a 25 or 30 speed gearbox to keep the RPM's up to make the power so it would lose pulling ability applying the power to moving the load at a constant because all the shifting?

 

You have it down pat. In laymens terms hp is how fast you can move a load up a hill, TQ determine how much you are going to have to rev the engine to get that hp. That is the example my physics professor in college gave when we asked him how hp is related to TQ.

 

So a ocean liner only turns a 100 RPM but makes like milllions of FT pounds of torque but dose not make millions of HP because it does not turn many RPM.

 

This is backwards, in general you'll need more gears with a diesel the a gas. A gas engine typically has a much wider power band, this of course has a lot of variation. The diesel in my Freightliner has about 600PRM range where it makes peak power, and about 1000RPM usable RPM. Behind it is a 10 speed and it needs all 10 with very little gear overlap, x speed = y gear, I'd much prefer a 18 or 13. Putting that same 10 speed behind a gas engine would be ridiculous, a good gas engine has a much wider power band thus has more speed change in the same gear and rarely needs more then 6 gears. That said I'd take a super 10 type tranny behind anything light to medium duty.

On the flip side my IDI will pull to 3800 RPM and has a good 2000 RPM usable power band, a 5 speed behind it is plenty. Same for a typical big block, spins to say 5000 RPM and makes good power for a good 3000 RPM range, a 5 speed is plenty. However you hop up a gas engine with a radical cam and all of sudden it makes great power in just one narrow range, this is why you'll see 7 speeds in race cars.

It all depends.

 

Yaa but even though a diesel has a narrow power band it makes a ton of power early to get things going and makes max HP just above idle so you are always applying max power to move the load, a gasser has a much wider power band but not necessarily the torque you need with a heavy load to spin up to max HP and stay spun up to max HP when heavily loaded?

This is the thing about HP, a RC model airplane motor will make like 1.5 HP at 40 grand but if you put it in a moped there is no way from a dead stop to get it spinning up to 40 grand and make the HP to get the load going to 30MPH because it does not have the torque to do it.

If you were to jump pull it up to 30MPH on flat land so it could spin up to 40 grand it could hold the 30MPH because it would be making the 1.5HP but the first gust of wind or hill it would fall off the pipe and never be able to spin up again to make the power required to get the moped and rider up to speed again because it lacks the torque to be able to spin up to make the max power necessary to move that heavy a load back up to 30MPH, you would have to give it another shove or hill. Where as in a model RC plane because it weighs 1/100 the weight of a Moped n rider it can spin up to make the power because little torque is required to do so with that little weight. That is why a diesel of the same HP rating should always be able to pull a good bit more weight? Shifting and clutching to keep RPM up to get at the power also robs a good bit of power in the process? Just curious


The extra torque allows the engine to spin up with a load on it to the max HP rating with less effort.

Thanks for straightening me out on the big gear box, the Maxidyne 238 Mack was supposed to have a wide torque curve so it only needed a 5 speed but only had a top speed of 67MPH.

 

IDK where you're getting that, it's not true at all. Yeah the power ban is lower, but so is redline, and in almost all vehicle diesel engines there is an area just above idle that doesn't make good power at all. If what your saying is true a truck wouldn't have to downshift for hills.

 

the maxidyne 238 only got a 5 speed because it was built before the rat race started. back then you did not need to get where you were going yesterday.

the guys pulling heavy loads in hill country got the duplex (10 speed), triplex (15 speed), or quadraplex (20 speed) transmissions.

 

You know a lot about this but doesn't torque in the lower RPM range make it much easier for the a machine to make max HP much easier with a heavy load applied and stay in the max HP groove much more effortlessly no matter how you do the gearing all things being equal ?.

I am just saying a machine that makes 1000 HP at 3000 RPM vs 1000 HP at 6000 RPM no matter what gearing is applied to both the lower RPM motor will be much easier to access the power as needed to move the load?

When I was saying above Idle I was referring to a engine that does not spin more than like 2500 or 3000 RPM because to me that is not much above idle when compared to a gas engine at like 6 or 8.

So the Maxidyne was in relax mode because those were the day's ?