Well We have cat diesels here where I am working putting out 20,000hp can a high spinning gasser do that???? I am gonna take a stab at the answer myself and say NO they can't You have made a statemant that it is hard to make big HP numbers with a Diesel and that is just not true.

 

What is the torque spec for that CAT engine?
If you take a large enough engine, any horsepower number should be within reach.

These are the specs from that "World's Largest Diesel" site that pops up here every few weeks.

Total engine weight: 2300 tons (The crankshaft alone weighs 300 tons.)
Length: 89 feet
Height: 44 feet
Maximum power: 108,920 hp at 102 rpm
Maximum torque: 5,608,312 lb/ft at 102rpm

 

Someone said the most rpm you can get from the 5.9 is 4000 i myself as hard as it is to believe have seen stock bottom ends turn 5100rpm in a diesel pulling truck. It is a 1994 block i believe running a close race on 900 hp, its really hard to tell as there are not many diesel dynoes rated for this around here that can hand torque in that excess either.

 

Actually, a semi has more tranny gears because of the relatively short rpm range. Imagine driving a semi with an engine rpm max of 2000 rpm and only having 6 speeds. You would need much higher rear end differential gearing in order to actually maintain a decent highway speed. Of course, higher differential gearing means you're putting less torque to the ground. They gear semis to keep the engines near peak torque, not hp. Imagine driving you're CTD around at 2800 rpm where the peak hp is. The engine definitely wouldn't like it and I doubt you would also.

I really like that howstuffworks.com site. I thought they did an excellent job explaining torque and hp. Notice the truck makes more torque than the car but less hp. Now which one would you want to tow with. Torque is far more important.

 

What I understand from that article is this: Horsepower will accelerate you. Torque will sustain your vehicle w/ a load. Torque doesn't care how fast it accelerates you...all it wants to do is turn a load. That's why big rigs have so many gears...they can't accelerate very fast because their horsepower to weight ratio is so low. But because they have so much torque that they can turn their wheels pretty easily. Start out in a gear, get moving, shift to the next gear.

Check out this website: http://www.cumminsracing.com/

They say their engine is around 500 HP w/ regular fuel, but their torque was so high that they were snapping tranny parts like nothing. Note: they were using tranny parts that are normally used in other dragsters and the HP is relatively low compared to other dragsters out there and they had parts breaking all over the place. That tells me that it's not HP that destroys trannys or makes your wheels spin...it's torque!

 

Oh yeah...I forgot...they can make diesels in excess of 1000 HP, but to make a diesel w/ that much power to put in your truck is pretty hard. I think that's what the original poster was thinking about.

 

I have two horse power but of course they ride in the back of the horse trialer being pulled by my Dodge!!!

 

I generally agree with you Alpine, I have driven all kinds of combination of trucks, especially with my wreckers of yesteryear. A gas engine of equal horsepower to a diesel, both running at peak hp/rpm will not stay anyway near the diesel. It's not the diesel function, it is the high torque design. One example, a 292 cubic inch chevy six cylinder with really low horsepower ratings, pulls a great load. A chevy 327 v8 in the same truck will do half the work. Been there, lost a good friend and job over it. Gas truck engines have the same charistics as the diesel truck engines, longer stroke, advanced cams, lot of torque and little power up high. Running 460 Ford gas engines in trucks, I used to advance the cam a whole tooth, amazing torque increase, much less horsepower. Pulling and high speed are two different setups and functions. A gas engine for high horsepower and speed will not duplicate an engine set up for torque and pulling with any gearing.

 

I think that I have oversimplified: I just wanted to state that the horsepower determines what speed you will pull your trailer up the grade. If you took two engines of the same hp output and gave them proper gearing for the job they would do the same.
The reason why you keep a diesel at peak torque or between peak torque and peak hp while towing is that the diesel usually has its best efficiency around the speed of max torque.
A gasser, especially a sports gasser has a smaller powerband. It will look wider rpm-wise, but the factor between max-torque and max hp rpm is the important part. A gasser (Nice big one) will have max hp at 5000 rpm. And max torque around 3900-4000 rpm. (Factor between 1.25-1.3) The diesel will have max torque @1600 and peak hp @ 2600. ( Factor 1.625)
The higher the factor the less gears you will need. In pulling a load you need all the horsepower you can get at the wheels when going up a mountain. You can't choose like in a racecar that you do set up that maximum acceleration will come on at 40mph and continue to 180 mph.
The great advantage of the diesel is that it will give you this hp with a reasonable noise level, and without drying up the fuel tank.

AlpineRAM

 

Great discussion I love it It sounds like a gasser can't make alot more torque without high HP but thats just the way things are done today. Take for example tractors from the 50's a 400 farmall gas made 52 HP and 412ft# torque 1475 rpms max.

 

Where's Hohn at, he's all over this stuff. That statement about the diesels not being able to make horsepower because of the RPM's being so low.... well maybe on the cummin's 5.9 that could SOMEWHAT be interpretted.... but a general statement that diesels cannot make high horsepower because they have lower rpm's is GENERALLY false. Different engine designs to different things. Take that monsterous 108 thousand hp engine... it runs at a RPM of 102... that's right 102 revolutions per minute.

So tell me again how that makes it difficult for diesels to make hp because of they're limited RPM?

HP is what sells cars and trucks in my opinion...people have become consumed with it.... the important figure is Torque. HP is simply the rate at which torque is force is applied...the force being torque.

Hohn has a great post on this over on the TDR.

A good example for some thinking is the difference in Dynojet and Mustang dynometers. Dynojets have a rep for being not as accurate....well they calculate how quickly an engine can accelerate a known load, which to me is very important. A mustang dyno is better suited for a static torque reading, which supports towing enthusiasts who what to maintain heavy loads efficiently. The Dynojet gives a true accelaration calculation which is what the engines ability to accelerate under load is like.

 

I wouldn't say we NEED them. The engines they're putting in these trucks will pull more than the truck can safely handle. Why would we NEED more?? Some folks might WANT more....but what we've got now works just fine for what we NEED.

Personally, I don't want an engine screaming at the kind of RPM's you're talking about.

 

I propose that we ban all discussions of horsepower on the DTR forums. Too irrelevant. Not ambitious enough. Lets talk about torque, instead.

Or British Thermal Units, maybe. BTU's are cool.

Currently, my truck develops 714 pounds of torque, and 995,095 BTU's. Like I said: cool.

Edit: scratch that -- nearly a million BTU's. . . .

 

That is what I was trying to get across. Horsepower is a mathamatical formula of torque-rpms. Raise the rpm's and you will have more horsepower with the same torque, run faster 0-60, but not pull a load any better. You can lower the horsepower, raising the torque with lower rpm's and pull a load much better but the 0-60 times are slower. Torque is what is measured, the rest is math.

 

Crap, I didn't mean to start a war. I just posted something on HP explained.