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Guys after taking my truck in for several dyno pulls and seeing some others post their results something is starting to bother me. Dont get me wrong I love my truck and the power seems just fine, after all its not a sports car.
But, on the average Duramaxes pull about 240rwhp(rear wheel horse power), and from what I see PSD's pull about 210. Now you do the math, PSD is rated at what? 250hp! The 30 hp between the two at the wheels does not add up, seems like the Dmax is really only making about 280.
Then there is the most important number the torque. 520lb's is what the Dmax is rated at but the dyno results only show about 440 or so, and a PSD pulls about 470!!! How can this be? PSD is rated at less torque.
Just curious if anyone finds that my results are flawed please let me know.
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Then there is the most important number the torque.
Horsepower is much more important than torque. Anyone can make a mountain of torque by simply applying more gear reduction. Problem is, gear reduction reduces rpm. Horsepower is torque x rpm, so it reflects the importance of both. Ultimately, horsepower is a measure of how much torque can be made available for a given rpm, or ground speed.
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I dissagree, most people on here dont bother thinking about how to generate more torque, rather they want to know what the truck makes.
Besides you are completly off the topic, give me torque lessons at a latter date.
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ZFMAX,
Sorry I just read my post and realized that it sounds like I am being kind of a jerk. Just came out that way, didnt mean it too.
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You have to compare apples to apples. You are not doing that. Take a PSD and a Duramax and mount them in the same chassis, use the same tranny and rear axle and do the dyno. Your numbers would be more realistic then. The Allison eats up alot of torque and horsepower but...It takes much more horsepower and torque to thrash it than a F**D auto.
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RWHP, no problem, but I respectfully disagree, my post was both accurate and on topic. You have to understand the relationship between torque and hp to have a meaningful discussion about dyno results, no?
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The real test is out on the road where it counts. There was an article that reported on the Duramax, F--D PS, and D--GE/Cummins in a pulling test with trailers. I can't quite seem to located the url for the article right now, but it told the story quite well. I thing it might have been Trailer Life or one of those camping magazines.
That made me a believer and convinced me to purchase a Dmax over the PSD.
If anyone has the url for the article let us all know.
Jack Schultz, McKean, PA
jackschultz@adelphia.net
http://photos.yahoo.com/bc/jack_schultz2001
2001 Chevy Silverado, 4-WD, 2500HD, Crew Cab, Short Box
LT Trim, Black Onyx w/ Tan Leather
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Beltronics 980 Radar Detector
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Keep in mind that we have the mother of all automatic transmissions- The Allison. It takes 60 hp to turn the tranny. Other makes with different trannies take less HP away from the rear wheels. The 6 speed should have more RWHP. I haven't heard what that number is? So, you sacrifice HP for the features of the tranny.
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2001 Chevy 2500HD 4x4 D/A LS Regular Cab Una-Goose Hitch, Line-X, Westin CP/SS Nerf Bars, Lucerix Mirrors. Took delivery 12/8/00. Virginia DURAMAX plates.
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The real test is out on the road where it counts
Exactly. And the reason the Duramax can out pull the PSD is that it has more horsepower. Not a whole lot more, as RWHP points out, but more nonetheless, and horsepower is what matters, not engine torque. That's what I was getting at in my post, but I guess I wasn't clear.
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ZFMax,
I have always been taught that torque is more important than horsepower, because torque is what moves the vehicle, and hp is how fast it moves.
There are lots of engines that have enormous hp, but little torque. These are typically high-rpm motors. Diesels tend to have high torque, because they are lower-rpm motors.
Can you explain to me why hp is more important than torque?
Thanks.
Casey
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I have always been taught that torque is more important than horsepower, because torque is what moves the vehicle, and hp is how fast it moves.
You're right, torque is what moves the vehicle, and more is better. Torque is rotational force. 1 ft/lb of torque is 1 lb of force applied at a 1 foot radius.
But you're wrong, hp is not how fast it moves. RPM is how fast it moves.
These two things, torque and rpm, are interrelated and both are equally important. Gear reduction multiplies torque but divides rpm. So when you gear something down, you have more torque at the output, but you slow down. This is what happens when you downshift. Likewise, you gear something up and you lose torque at the output but you gain speed.
Obviously, downshifting to get more torque to the rear wheels is not the most desireable solution, since it slows you down. What you really want is as much torque as possible to the rear wheels for a given ground speed. So instead of torque or rpm, you need a metric that reflects both. That's what horsepower is. It's literally torque x rpm (divided by 5252, but that's a nit). Horsepower describes the combination of how much torque you're making and how fast you're making it. You can make less torque with one engine than another, but if you make it faster it allows you to apply more gear reduction and go the same speed, and that gear reduction multiplies the torque. It's the combination of torque and rpm that matters, and that's the definition of horsepower.
In a nutshell, the engine with the most horsepower will put MORE TORQUE to the rear wheels for a given ground speed, because horsepower reflects both torque and rpm.
So how can a PSD out-torque a Duramax on the dyno and yet have less power?
Well, that's because the dyno is showing engine torque as measured at the rear wheels, not rear wheel torque. Read my post here, I think it'll clear up a lot of this:
http://www.62-65-dieselpage.com/ubb/...ML/002094.html
[This message has been edited by ZFMax (edited 01-09-2002).]
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The mfg states the hp and torque values in accordance with a very specific set of conditions given in the SAE standard. It is also measured at the flywheel so the rating is independent of the vehicle. That is why chassis dynos do not repeat the mfgs numbers.
The mfgs us the corrected horsepower and torque standard SAE J1349. SAE J1349 specifies the brake horsepower and torque be corrected to 29.23" mercury barometric pressure, 77
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Does the PS have a longer stroke then the Dmax? The Dmax is "over square" isn't it?
In a nut shell (not all encompassing):
For "pulling" you want TORQUE, example, "Big Trucks", tractors, etc., relatively low HP compared to torque. Long stroke, low RPM's
For cruising (racing) around on the Blvd.s you want HP, example; motorcycles, sports cars. High HP relatively low torque. Short stroke, high RPM's.
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Man O Man,
All this HP/Torque is making me real anxiuos to go out and Race my car...
I must say...Numbers are for Ph'd's and statisticians.....because the projected potential is more fun to debate then actually do.
It all matters if goes and does what you want it to do..
Hey here is some numbers for all you number crunching people.....at 4800 rpm with 11 lbs boost my little ol SBC makes appx 851ft lb tq and 780HP, hit 6800rpm and 12.9 boost, It makes 1081ft lbs tq and 1311 hp ...Bring on them PSD's...HAHAHAHAHAHAHAHA I got some stump pulling power for them......Hey I wonder if an Allison would work in my car and be legal for the class. Kind of neat to have a tranny think for me while I am going down the track...1 less thing for to me do..... http://www.62-65-dieselpage.com/ubb/biggrin.gif...What do you think Big Al.......
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2001 Chevrolet K3500 4x4 LS
Duramax/Allison
Crew Cab
Long Bed
Victory Red
Light Grey Leather with Bench front
G80 Rearend
E-mail: cii@onebox.com
Homepage. www.j-line-racing.cityslide.com
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The powerstroke has a longer stroke than the Dmax, but- it has a smaller bore.
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2002 3500 Duramax/ZF6 speed/4x4
LS Interior
Summit white
2001 2500HD Alli-Max 4x4
LT Interior
Extended cab short box
Onyx Black
Graphite leather
295 BFG's
Eagle Alloys
MX7000 lightbar
DeeZee Gold series Toolbox
DeeZee Aluminum Tread Mud Guards
DeeZee Aluminum Tread Bed rail protectors
BOSS 9' snowplow
Straight piped
EGT/Boost guage (Pillar mount)
1994 Chevrolet 2500 Silverado
4x4
454
9" Lift
35X12.50 BFG's
15X10 American Racings
REAL men drive trucks....
REAL trucks are diesels....
www.picturetrail.com/gallery/view?username=dslpowr
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NorCalDmax,
How does that blown SBC pull a 6% grade with a 10,000 load? Think it will do it for 200,000 miles http://www.62-65-dieselpage.com/ubb/wink.gif
Like you said, all that matters is it goes and does what you want it to.
When was the last time anyone drove/raced a dyno graph?
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Very interesting reading! I bought my DMAX to out pull the competion with my 5th wheel on the long steep hills here in the Rockies. At least on paper this engine make 500+ ft. lbs. from 1500 to 3000 RPMs. That should keep a smile on my face from April through Oct. Later! Lone Eagle
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Allot of people get hung up on dyno numbers, and will immediately declare a winner on who produces highest dyno numbers. Unfortunately those dyno numbers only state what peak power was produced, they tell you nothing about application performance. Dyno numbers are just that..... numbers. Now looking at dyno horsepower and torque curves tells you much more about the application power output then just peak dyno numbers. What exactly is this dyno number? Well it's the "peak" production of horsepower and or torque. Key word is peak. This peak number doesn't tell you squat about the rest of the rpm range before peak and after peak. When accelerating, that peak moment only lasts a very short time when considering the entire rpm range. That means if your not at peak your somewhere else in the rpm range. You'll spend far greater time when driving towing at other than your "peak". That's why the rest of the rpm range is so important.
Your can have an application that produces more peak power than another, but just because it produces more peak power doesn't necessarily mean that's it's the best performer.
Torque is force performed. A unit of measure for force is Torque. Horsepower is a derivative of torque. Horsepower is basically torque over time. The more horsepower the greater amount of torque is available over a wider range.
Application A is 300hp/550tq compared to application B 300hp/600tq. Application is A is more efficient in using it's torque cause its at or closer to it's peak throughout more of the rpm range than application B. Application B produces more peak but is only at or close to peak for a shorter amount of time in the rpm range when compared to A.
Again, horsepower is derived from torque. Horsepower and Torque are both your friends. Horsepower just give you another perspective on how the torque curve your application behaves. Little horsepower means your application isn't at or close to it's torque peak for long through the rpm range. Lots of horsepower means your application is at or closer to it's torque peak for a longer period throughout the rpm range.
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Derek M
02 Chevy 2500HD D/A CC LB
95 Z28 11.077@132.120
88 Mustang LX
http://home.attbi.com/~z28sc
[This message has been edited by Derek M (edited 01-10-2002).]
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How does rotational mass fit into the picture, such as adding wieght to the flywheel - will that increase torque ?
Why does a Cat or Cummins in heavy equipment produce gobs of torque and very little HP in comparison ? rough numbers - 1200 ft.lbs of torque and only 275 hp.
On a dirt bike I had, I added a flywheel weight to increase the torque (or so I thought) to facilitate trail riding.
Any thoughts on my comments ?
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PROUD AMERICAN If you don't LOVE this country - LEAVE
2001 2500HD LS Ext.Cab,short bed,D-max,Allison, Onyx black w/graphite int.Leer 700 hard tonneau,16X8 Eagle Alloys w/265-75-16 Coopers, Powerplay from Kennedy diesel
1988 K1500 shortbed stepside Paxton supercharged 4" Trailmaster lift w/33" tires
2001 Polaris Sportsman 500 HO
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Here's a link to one of the more interesting (and in-depth) descriptions of the hp/torque relationship I've read. Taking time to read it may help answer some of the questions in this thread (but not the one about how much hp/torque the DMax really makes...sorry http://www.62-65-dieselpage.com/ubb/smile.gif )
http://www.zhome.com/ZCMnL/tech/torqueHP.htm
