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[Mark_Kendrick]

Originally posted by cditrani





I respectfully disagree. hp is calculated from torque and rpm because that is the only practical way to measure it with a dyno. hp is a measure of how much work is being done. It's work that accelerates you.



Put a wrench on stuck bolt. Apply 10 #' of torque. It's till stuck, so it doesn't move. You are applying 10 #' of torque, but you aren't accelerating anything. You aren't doing any work.



I've read the article you cited, and it doesn't dispute anything I've said. This is subtle stuff, and it took me several years as a physics major before I really got it.

Well, I have ans associates in physics and mathematics and a BS in Comp Sci so suffice it to say that I have an understanding of the concepts.

You are right they are subtle concepts.



If you have 2 engines. . these are hypothetical but typical ratings

a chevy 350 245hp 350 ftlb

a dodge 383 'B' 236 hp 440ftlb



Which would you want to pull a trailer with??? assume the same gearing and identical manual trannies in similar vehicles.



well the chevy will make it's power at 5200rpm. the dodge will do it at 4500rpm. torque peaks will occur at 3500 and 3000rpm respectively.



the 383 will pull a heavier load better but will not achieve the same top speed.



ina 1/4 mi race the 383 will launch much better and have a much better 1/8mi time but the 350 will beat it to the finish line.





later,

Mark

 

[DiTrani]

Originally posted by Mark_Kendrick





Most bog rigs have crank hp ratings of under 450hp yet they pull 80,000+lbs.



they do it by making 450hp at 1500rpm



(450/1500)5252=1575 ftlbs!!!

I think you're confusing cause and effect, so to speak. The 1575 #' at 1500 rpm isn't what makes the rig move, it the fact that 1575 #' at 1500 rpm means he's making 450 hp at that rpm. Way more than an engine that isn't making that torque that low.



This is sort of degenerating to semantics. Of course these long stroke I6 engine are great haulers, that why I bought one, but there are people saying that one with less hp than a V8 (and BTW, the diesel V8s are pretty long-stroked too) can out pull the V8. Not if the V8 has the gearing to let it use it's power. Now, this is NOT to say that the I6 with a more linear torque curve (DMAX looks pretty linear too guys) isn't more pleasant to haul with, doesn't get the load moving more easily, requires fewer gear changes, etc.



Give me a stock DMAX 6-spd and you take a stock HO 6-spd and let's race for pink slips, up a hill, loaded any way you like ;-) I just hope the Chevy doesn't break!

 

[Mark_Kendrick]

The problem is that the Dmax's are using allisons for the most part and we use 5/6 spds.



I ot a better one... bomb a Dmax any way you can and I'll take my HO and race you from Tulsa to LA and back pulling a 15k goosneck.



when you get back I'll have more money (that i didn't spend on fuel or $2500 injectors) and be well rested after the full day of rest i've had

 

[DiTrani]

Originally posted by Mark_Kendrick



I ot a better one... bomb a Dmax any way you can and I'll take my HO and race you from Tulsa to LA and back pulling a 15k goosneck.



when you get back I'll have more money (that i didn't spend on fuel or $2500 injectors) and be well rested after the full day of rest i've had

No way!

 

[Mark_Kendrick]

Aw, come on I've been needin a new truck for my wife. A Dmax should be able to bring home some groceries and a few bags of feed shouldn' t it???



she'll love it. . nice, quiet, and fast between stoplights

 

[SLightfoot]

Originally posted by Shawn. L. Turbo

Remember that torque is ONLY a calculated figure from torque and RPM.

Sorry, I meant to write "HP is only calculated from Torque and RPM". My fingers didn't do what my brain was thinking... .



And still, torque accelerates you.



I also work in the engineering field, and understand physics.



Take, for example that you have a high horsepower engine, however let's say that the torque at the first 75% of the RPM range is almost nothing (unlikely, but for sake of making the point). Let's say at the top 20% where you have a peak torque, you also have high RPM, which will of course calculate out to be a large HP number.



How fast do you think you will accelerate?



Very slowly, because the torque curve at the first 75% of the RPM range is going to be so low, you won't have the twisting force to accelerate quickly, until you reach the high end of the RPM and torque curve.



Add that to a gearing ratio that is imperfect for the torque curve (which IS realistic, since we only have a few to choose from) and now you have a recipe for a very slow acceleration.



As I said earlier, your point of higher HP pulling a load faster than a higher torque, lower HP engine is TRUE, IF and only IF you have enough gears to take advantage of the HP. If not, then you will be placing some reliance on low end torque.



Just as a standard 350 CID (which can run over 240 HP) cannot outpull a 230 HP Diesel. Mainly due to the fact that the 350 won't have enough gears to take advantage of the HP.



I like this sort of discussion - it's a lot of fun. Gets the grey matter going.



Shawn

 

[SLightfoot]

Originally posted by Mark_Kendrick



ina 1/4 mi race the 383 will launch much better and have a much better 1/8mi time but the 350 will beat it to the finish line.

Yes, this is a true concept. The only thing is that the 1/8 and "finsih line" are really undefined without serious calculation.



Given a stretch long enough enough, yes, in your comparison of the 350 and 383, the 350 (because it's higher HP) will EVENTUALLY be pulling ahead of the 383 at some distance from the start point. This distance will be how long it takes the 350 to get UP to it's peak torque and HP, and out of the low torque end. Unless of course the 350 has a ton more gears, then it will pull ahead much sooner.



It may be semantics, but it's fun just the same, dontcha think?







Shawn

 

[Mark_Kendrick]

Originally posted by Shawn. L. Turbo



It may be semantics, but it's fun just the same, dontcha think?

yep

 

[Gary - K7GLD]

Reminds me very much of how Yamaha 350cc bikes dominated the much larger displacement Harleys in Daytona 40 years or more ago - LOTS of *peak* HP, and fast, as LONG AS you kept the revs up - not much down low in the rpm band. The Harleys could easily pull away from the Yamahas down at lower speeds - but once speeds increased, the Yamahas were GONE!



BUT, if used in pulling some sort of appropriate load - up a grade - which do you think would get to the top first? and which engine do you think would be most likely to last longer in that sort of service - the low speed torqer - or the high speed rever?



Same with the 383 vs 350 example - no one will argue against the drag racing scenario presented - but we've ALREADY pretty much agreed that the V8's WILL accellerate better EMPTY from stoplite to stoplite than our I-6's - but in the 383 vs 350 example, WHICH, all things being equal, would you rather bet on towing a load up a grade?



Bottom line, if higher reving V8s were REALLY the sensible, durable and economical way to get loads from point "A" to point "B", WHY aren't the 18 wheelers using them today and WHY did the quickly discard the idea when they DID try it for a while?



After all, their economical survival DEPENDS on power sources that will function with the BEST combination of economy and power - do any here REALLY suggest they would avoid a V8 diesel in their rigs IF they provided better bottom line possibilities?



*I*, for one, use the same sort of parameters THEY do when it comes to a choice of power to tow MY load - and for all the same reasons!

 

[kchristopher]

Originally posted by Shawn. L. Turbo

Just as a standard 350 CID (which can run over 240 HP) cannot outpull a 230 HP Diesel. Mainly due to the fact that the 350 won't have enough gears to take advantage of the HP.



Shawn

I still think that people around hear are forgetting that more low-end torque = more low end hp. Torque doesn't take time in to account and hp does. How can you accelerate without time?



When you say the 350 doesn't have enough gears to take advantage of the hp, you are correct. It isn't the fact that it has no low end torque (and thus no low end hp), it is the fact that it needs some sort of multiplier to assist its lack of low end hp.

 

[rob10858]

so the verdict is....

of course there is none. our duramax may be able to outrun our injector inhanced 2001. 5 ho's and our powerstrokes. it may even pull a load faster up a grade, but which engine pulls the grade easier? and what's the long term deduction in power as the engine and drivetrain get some miles on them? that's what we want to see in the isuzu. since these are the first "powerstrokes" [ we started with the old non turbo fords] , time will tell for them also. our gassers all have held their power to about 125000, then gradually lost their original pulling speed and back to the seat performance. our duramax has a grand total of 5000 miles pulling, and already some of our guys with trade ins coming up are looking seriously at this truck. i'll tell ya'll what i tell them. think of a tractor pull, now think about a truck pull with sleds. one truck may win the pull, but in our case, that truck has to take that sled home for the next two years and take it to work with it, and if it breaks, we're going to dock you for downtime. so what would you pick if your livelyhood depended on it? :-{}

 

[HoleshotHolset]

I'll take my 150# crankshaft, 7 main bearings, and connecting rods designed so that the forces acting against them are not parallel to the rod bolts (very ingenious design... resists rod bolt stretch, etc. ) and big enough to support any reasonable HP level I choose.



There are advantages and disadvantages of EVERYTHING in life. Choose what you believe is the best solution to your problems, and to heck with what everyone else thinks. I bought my engine (the truck just sorta comes with the Cummins... . ) with the understanding that it will stand up to the test of time and outperform even the most demanding loads I'll ever put on it.



DMAX, PSD, Cummins ISB/6BT/KTTA/6CT, Cat 3208/3416/etc, DD 8V-92/6V-71/ad-infinitum, yadda-yadda-yadda... . all have their fine points/not-so-fine points and do their jobs very well, but try to compare apples and apples.



Just be happy that you bought a diesel, and try not to blow too much soot at those gassers... ... they get jealous easily!



Matt - diesel soot forever... . or as long as there is still fuel to burn.

 

[Mark_Kendrick]

HoleShot. . I'll second that. . But I want to turn that soot to power!!!!!

 

[HDH]

Re: Well....

Originally posted by Shawn. L. Turbo

I've talked to a few DMax owners.



Ya wanna know why GM is selling so many?



It's quiet. I know, I know, realy diesels aren't quiet, and I wouldn't want my Cummins to be quiet. BUT, that fact is that many, many average consumers are sold on the quietness of the Dmax.



Last weekend, I pulled our fiver out to the campsite, and a DMax pulled in after towing with his Dmax for the first time.



The very first thing he does - before even unhitching- he looks under the hood, because "something must have broke". Truck runs so strong empty, but pulling his trailer for the first time it seemed "too slow"... .



Frankly, I hope GM sells thousands of DMax's - gives me more vehicles to PASS on the hills!!!



Shawn

Shawn,

Those GM Customers want a Diesel to run like a gasser, Why? I dont know. I think most of it is Blind Brand loyalty and Blind faith.

Like Most of the US populous, I too was a GM Fanatic, But GM Lost me in the Late 80's when they went to a IFS 4x4 set up.

The DuraMax,(Like Most Vehicles) is really Quiet when they along the side of the Road with their hoods up.



Yep on the hills,

Its No Contest. Low end grunt is where its at.



Most of the DuraMax'es I see around here are empty and not pulling. Citified trucks for the family.

Most of the Ford and Dodges i see around here, Are pulling Oil,Farming and or Construction equip and are realy Torn up...

To sum it up, If I were going to pay $45k for a tow rig, It would be for a Medium Duty Rig, Not for a Lightduty Light truck.

Doug.

 

[SmokinJoe]

Re: Little Reality

Originally posted by cditrani

Guys, while I agree that the long-stroke I6 design is inherently a better motor for pulling heavy, numbers don' t lie. If you have a DMax pulling a n0,000 # trailer and a CTD pulling the same up the same hill, if the DMax is rated at 300 hp and the CTD is rated at 245 hp, the only way the CTD is going to out pull the DMax is if the DMax doesn't have an gear available to let it use the power, which might be the reason some DMax truck _reportedly_ don't pull well. Any engine spinning up 300 hp can out pull an engine only spinning up 245, regardless of design or torque curves.

Why are stroker motors VERY popular a drag races? Because the race is won/lost at the 60 foot mark. The reaction time and the tourque to get the x,000 lbs of metal moving are what wins races. Why have the Honda racers taken years to get into the 9's and the first two Neons used for drag racing are in the 9's? Because of Tourque.



Automatic trannies are porgrammed so they last as long as the warranty, not to pull a load up a hill...

 

[Royal]

My friend attended a diesel seminar in the Midwest and was told about Duramax fuel system component cost. Evidently these are the list price,s. New Gm injectors $960. 00 ea. High pressure fuel pump $2200. 00. If these are accurate prices,maintenance will be very costly. He was also told replacement of a set of injectors and pump would be eight (8) hours labor. If anyone has a way to verfy these numbers it sure would be of intrest to anyone buying a Durawax.

 

[Mark_Kendrick]

Royal,

OUCH!!! I hope you're wron for all the DuraDud Owner's sakes!!

 

[JoeyD]

Is this the same fuel injection set-up that the new Cummins will use?

 

[LarryB]

It's a shame smog requirements have made it nessasary to add all this complexity just to "try" to keep up with our dinky little old 12 valve.

 

[Royal]

The new Cummins system will be about the same,as both will be the common rail system, made by BOSCH. Keep your hands on your wallet.