Duratothe max it has to do with dmaxes make there power high in the rpm which is great for drag racing . But if hp is truely equal a duramax will not maintain speed on a given hill with out screaming the engine where the cummins will hold it or have the power to leave the other one, with the torque. Just ride beside a dmax while in a car and set the cruise if they are loaded and see if they stay there it doenst take but a slight hill for there speed to fall off. Same reason big trucks use in line 6 engines. Dont get me wrong it is a good combo for a drag race though and with a 6spd he will really be handicapped from a standing start.

 

Thats what I just said.

So what if it has to rev higher to make power?? If you are maintaining speed who cares? Its the job of the transmission to keep the engine loaded in its power band when towing a heavy load up a hill....be it 1200rpm, 1400rpm, 2000 rpm, or 2500rpm.

There are MANY other reasons tractor trailers use inline 6's. Inframe rebuilds, easy to work on, take up less space than a V engine, less parts, etc.

There are plenty of bad inline engines and plenty of good V engines; If I recall correctly detroit made a couple of them V engines, as did mack, MB, etc..

as I said just my oppinion...anyway I dont want to take this off topic...do what I said (race from a roll, smarty, etc) and you will smoke him

ben

 

I'd say do a trifecta....50mph till 110mph closed course race.

Tow rope bumper to bumper....you are LSDiff on the rear right?

Sledpull

1/4 mile G56 to Allison will be tough...Smarty, TST built 48re and fuel and lotsa boost...say good bye

Durotothemax, Glad we have you around to give fair air on the D'max. KS

 

Tell them to come back when their trucks grow up, like around 250,000 miles.

 

Duratothemax:

Thanks for the great post. It's nice to see SOMEONE show a little reason with this stuff.

If a truck is faster to 100mph, weight doesn' t matter. The only way weight could matter is to the extent it changes shift points or highlights poor tranny performance.

Don't apologize D-max for your post. If people have a gripe with the truth, the problem is theirs, not yours.

Justin

 

First you were comparing trucks with similar setups and gearing. Now you've shifted (pun intended) to talking about the gearing differences between the two.

I agree a 360hp DMax/Allison will probably pull a load to the top first when compared to a 360hp CTD/48RE. The extra two gears will help it stay in the powerband, especially if they were to start from a dead stop. However, I would also bet that a 360hp (5.9) CTD/68RE would reach the top before the DMax/Allison...simply because the CTD has more torque.

I'm not sure how the DMax dyno charts look, but the CTD's typically carry a very wide powerband. As long as we're over 2k RPM when towing it will rip to the top of just about any hill without losing speed. The wide powerband let's us get away with only having 4 gears. I think most heavy haulers usually choose manuals for the added reliability, reduced maintenance, and longer lifespan. They're generally used to driving manuals anyway.

Justin, I know you're a knowledgeable poster and I usually agree with the things you post, but I have to say not in this case. There are plenty of little V8 gasser race trucks that are faster to 100mph, but does that mean they will also be faster hauling a 10k load up a hill? I'm sure we've all towed with a 250-300hp V8 gasser before and noticed how they bog down when going up a hill. What's the difference there....torque.

You guys are ignoring the fact that CTD's put out more torque for a given HP when compared to DMax's. All else being equal, that extra torque will get you to the top faster with a load hooked up.

 

Wells there is some good info in this post but...

The bottom line is your going to lose this race. Unless you got several mods, clutch, smarty, etc. Your not gonna keep up with them. The 6spd just wasn't meant for drag racing.

Good luck.

 

There are MANY other reasons tractor trailers use inline 6's. Inframe rebuilds, easy to work on, take up less space than a V engine, less parts, etc.

There are plenty of bad inline engines and plenty of good V engines; If I recall correctly detroit made a couple of them V engines, as did mack, MB, etc..


ben[/QUOTE]

Have you ever driven a Marmon v-12?? I have...and
That is an older engine... older technology.. but for its day, wow. Take a cummins 350 and leave it in the dust.

Wasn't gonna argue with you Ben, still not, but you have to realize a difference between theory and reality. You can talk power/weight ratios all day long hp/torque and etc. But how that power arrives and how it gets to the ground is ultimately what counts. That is what the drag strip is good for. Puts all the talk to rest. In the gasser world, why would a BMW with 20hp less and 200lb more weight beat a similarly equipped Cadi with a Northstar? For (what most of us regardless of preferences agree to be a flawed and objective comparison) these purposes I ask you simply to consider that last truck shootout. Empty 1/4 mile, the Duromax beat the Cummins by a small margin. Towing 10k, the Cummins beat the Duromax... Same trucks, same power, different results... reality, not theory.

 

Ive seen that happen with my own eyes from a rolling start
I had a 6spd before and would run my buddy rolling. his big bad allison would go into limp mode everytime. they do that on the dyno also with 3 or 400 hp.

 

I could just as easily make the case that the difference isn’t tq, it’s gearing. In reality, they are one and the same. This is because power has two components: force and time. The more force in the less time, the more power. The formula tells us this: HP= tq (force) x RPM (time). Since RPM is the inverse of time (i.e. more RPM means less time for each revolution), we could just as easily say HP= Force/Time.

The relationship of these three variables is fixed. If I know two of them, I can always calculate the 3rd.

So, with the physics covered we can approach the question of towing power or acceleration power (which are the same). If I have identical loads and identical power available, it will take the same amount of time.

So when one vehicle does the same work in less time, it has more power—by definition. Same for any variation of the same: the relationship of the three variables is fixed and has no elasticity.

My earlier post made different assumptions than others in here, thus a different result. I had assumed we were talking about IDENTICAL trucks. If two trucks of the same weight have difference rates of acceleration, then adding equal amounts of weight to those trucks will not change the outcome—the faster truck is still the faster truck.

But there IS a scenario where a faster truck can become the slower truck when identical amounts of weight are added—ONLY If the truck were of different weight to begin with.

Acceleration is a function of power to weight. This ie because our derived formula tells us this: HP= force/time, thus Time=force/hp. Force in this case is weight, so it’s Time=weight/HP. Thus, we can see that as HP goes up OR as weight goes down, TIME will go down as well.

So depending on the power and weight of the two vehicles, the addition of identical weights to drastically change the power/weight ratio.

Let’s say I have a 300hp Honda weighing 3000lb and a 300hp CTD weighing 6000lb. In this scenario, the Honda will accelerate twice as fast as the CTD. The power to weight ratio tells us this: the Honda is 1/10 while the CTD is 1/20.

But if we add 18K pounds to each, the ratio of the Honda goes to 1/70 (300/21000) and the CTD goes to 1/80 (300/24000). So while the Honda was once twice as fast as the CTD, it is now just 14.3% faster accelerating (compared to 100% faster before!).

Now this starts with two vehicles of identical HP and radically different weights. If you have vehicles of similar weights and different hp levels, the addition of weight can have similarly drastic effects on outcome.

Anyway, since we start our “race” at idle RPM and accelerate from there, we can see that low-rpm HP matters most, and gives a “hi torque” engine a huge advantage because it has more HP available in a given amount of time.

This is why more informed folks talk about “area under the curve” because THAT is what determines acceleration rate. The “area under the curve” from launch RPM to shift RPM will determine the winner for a given weight each and every time all else equal.

JH

 

wow......................

 

That whole post could be complete BS I'm not going to argue with him. Anyone who takes that kind of time to argue his point must be right. I tried to read it and my head hurts now. I think it's the severe A-D-D......Oooh look a quarter!

 

Ok, I think I understand the theory behind it, but what about the following scenario?

Let's say we have 2 Dodge Ram 2500's that weigh exactly the same. One has a CTD with 300hp/600ft-lbs and the other a V8 gasser with 300hp/300ft-lbs. Which one do you think would win a race?

 

I ran 13.86 et at 98mph with just a turbo, smarty, and a dual disc clutch at 16psi at the light in third gear. That will eat a d-max with a edge hot juice.

 

There's no way to know because it's more complicated than that.

The problem is that you are giving me PEAK hp numbers. These occur only at one engine speed. How long can you hold an engine at one rpm while accelerating??

Now, by deductive reasoning we can assume that the CTD would have more HP lower in the RPM band because of the relationship of hp/tq. This means it will pull out to a lead early on over the gasser truck.

But if the gasser can rev higher, it might close the gap when the CTD has to shift (there's the gearing again). The CTD will lose a lot of tq to the rear tires when it has to shift, while the gasser winding out will be holding the lower gear.

Now, if we said something like we had two identical Ram 2500s and were more precise in describing their power outputs, then we could actually say who wins the race.

For example, if we had one CTD truck with 300hp average from 2000-3000 rpm, the other a gasser with 300hp average from 4000-6000 rpm, then we could say who might win. In this particular case, I could gear the gasser twice as low (say 7:1 axle vs the 3.5 for the CTD) and I'd have IDENTICAL acceleration; yes, an exact tie.

But notice two things: the crazy axle ratio of 7:1 required to let the gasser accelerate equally, and the high rpm the gasser will require: 4000-6000 rpm.

In a towing scenario, the gasser COULD tow just as well as the CTD setup like this. But that engine isn't going to be very durable or efficient at 6000rpm and full load.

That's why large diesel engines are used for towing, and small-high revving engines are used in racing. Where efficiency and durability matter, the large diesels are used and you live with the high weight penalty.

But in racing, light weight for the hp matters very much, and you live with the reduced durability and efficiency.

That's why the idea of racing a CTD seems to odd to me. It's as odd to me as using a Formula 1 engine at 17000 rpm to pull at boat


Justin