torque low is it the dyno or the truck

revolutiondsl

revolutiondsl

Cat buys my Cummins parts
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Jun 3, 2007
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So I dynoed at TS on friday and i was really happy with the hp but it seems the torque was low i have the dyno sheet somewhere i cant find it now to post but the 1st 2 runs the torque was reading like 2000+ lb ft but the 3rd I made 540hp and 986lb ft i made 536 the 1st and 538 the 2nd ive been told by more then a couple peole that dunbars dyno is sometimes low on torque. I figured with that kind of hp id be well over 1000 lb ft. ant input im going to dyno again soon and was curious
 
i just did 708 and 1229

i think it was because it took a while to get it spooled and by the time it did i was over the peak torque rpm
 
Look at my sig....well past 2:1.

Every truck and every dyno is different. Nature of the beast.
 
I dont really trust the TQ numbers from any dyno... I remember the first time I dyno'd my dodge,, 348,, and it showed over 900ft lbs,, aint going to happen. The last time I dyno'd it, 1013 hp, and only 1600 ft lbs of tq... the tq readings rely on too many things, if they dont have the sticker on right on the damper, or if the sensor moves... all makes a difference... I really would caution reading too much into your tq readings... I would have to say that it is highly unlikely that you really have over 1500 ft lbs on 650hp,, not to be rude,, and please dont take it that way. but really ,, a really good ratio is 1.8 to 1 ish,, not allmost 3 to 1..


just my 2 cents
 
smoke machines numbers are much more realistic. that is a normal ratio for a diesel engine
 
forrest,, exactly my point,, the readings on most dyno's are skewed... if you have hp, you will have lots of tq
 
I would have to say that it is highly unlikely that you really have over 1500 ft lbs on 650hp,, not to be rude,, and please dont take it that way. but really ,, a really good ratio is 1.8 to 1 ish,, not allmost 3 to 1..


just my 2 cents[/QUOTE]

where did u get 650 and 1500 i made 540 and 986 unless im missing something
 
post a graph, i find it interesting to see what rpm the power was made, what the curve looks like. higher hp usually takes higher rpm, old 1st gen ve pumps often made 2.2-1 or 2.3-1 torque due to pumps mechanical timing advance ,good low end fueling. ive only dynoed twice, both at shops with lots of diesel experience. put down approx. 300 hp @2600 rpm,800 ftlbs tq @1950 rpm, on the other dyno 400 hp 1050 tq at same rpms the old 12v, p-pumped or ve do put down more torque down low it seems. i prefer torque myself, when i beat 400 hp 6.0 powerstrokes i suspect its the low end torque. just my observation in my limited experience.
 
has a lot to do with how hard you load the truck.

torque is all about making hp at lower rpms -- If you start the run with a lot of boost, your torque numbers will be higher than if you roll into the throttle without brake loading.

Take tq #'s for what they are -- they can easily be manipulated.

There isn't much you can do to manipulate hp readings.
 
jlibert said:
has a lot to do with how hard you load the truck.

torque is all about making hp at lower rpms -- If you start the run with a lot of boost, your torque numbers will be higher than if you roll into the throttle without brake loading.

Take tq #'s for what they are -- they can easily be manipulated.

There isn't much you can do to manipulate hp readings.
Click to expand...



Very good point, I agree with you. The lower in the rpm band that you load it up, and the harder you load it sooner makes a world of difference on the torque number readings...
 
crewcabxlt said:
post a graph, i find it interesting to see what rpm the power was made, what the curve looks like. higher hp usually takes higher rpm, old 1st gen ve pumps often made 2.2-1 or 2.3-1 torque due to pumps mechanical timing advance ,good low end fueling. ive only dynoed twice, both at shops with lots of diesel experience. put down approx. 300 hp @2600 rpm,800 ftlbs tq @1950 rpm, on the other dyno 400 hp 1050 tq at same rpms the old 12v, p-pumped or ve do put down more torque down low it seems. i prefer torque myself, when i beat 400 hp 6.0 powerstrokes i suspect its the low end torque. just my observation in my limited experience.
Click to expand...

Here is a link to the vids that JP posted after I made my runs at Brown's...

650/1509 CR vids - Competition Diesel.Com - Bringing The BEST Together
 
jlibert said:
has a lot to do with how hard you load the truck.

torque is all about making hp at lower rpms -- If you start the run with a lot of boost, your torque numbers will be higher than if you roll into the throttle without brake loading.

Take tq #'s for what they are -- they can easily be manipulated.

There isn't much you can do to manipulate hp readings.
Click to expand...

I do agree JP. :rules::rules:
 
Crewcab is on to something there with where its made. EDIT: and others it would seem.


The quicker you are able to light the charger, the more torque you see. Other factors as Mork mentioned should also be considered. But, the bottom line is the earlier the engine begins generating force in its RPM range, the more torque you have.

In a turbo diesel, this requires being on the charger earlier.

Go back to the equation: (Torque*RPM)/5252=Horsepower

To obtain a larger numerator in the HP equation there are two elements that must be considered: Torque and RPM. To affect torque and it's ratio to horsepower, you must generate more force at a lower RPM. To do that on a diesel you must light the charger early.

Hens, the disparity in ratio we see with different setups at similar HP levels.

Slower spooling setups rely more on the RPM portion of the numerator in the above equation. They generate their force at a higher RPM and achieve more of a balance with the two multipliers.

It all gets divided by 5252 to make HP, but setup, more specifically the point in the RPM range force is generated can drastically affect TQ. (Edit, used HP initially and meant TQ. )

Let's take your numbers and plug them into that equation to validate their accuracy instead of opinion on typical ratios and guessing possibility.

I'll restate: (TQ*RPM)/5252=HP

You said your first two runs showed 2000+ torque readings. Lets pick the best one and round the torque to an even 2000.

(2000*RPM)/5252=538

Dusting off my Algebra skills I get roughly 1413 RPM to make everything jive.

Assuming the typical broad and relatively flat torque curve diesels are famous for, I ask you: Can you light and peg boost on your 62MM charger (thereby generating near peak force) by 1400 RPM? Your answer to that question should tie closely with your perception of that 2000 torque number being valid.

Lets do the third run:

(986*RPM)/5252=540

I get 2876 RPM with my dusty math skills.

I wasn't there, but I'm guessing you were pretty well up on the charger by then with a 62mm. LOL If that was your reported peak torque, I would guess it could be possibly catching a shift spike at the end of the curve. Without seeing the graphs, it's hard to tell.

Why was the peak so late in the RPM range? Could be many reasons. The operator could have started the run at a higher rpm or rolled into the throttle a bit more slowly are two possibilities.

For torque to be big with respect to HP, you've got to make it early in the RPM range.
 
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well i have the dyno sheet just have to scan it which is at my parents so give me a day and ill post in a day or so
 
just to clarify, im not downplaying anyones big hp numbers,its all good. my operating rpm is usually 1500 to 2500 rpm, especially towing. i like good fuel to 3200,3300 rpm on occasion,so thats how i set up my truck. torque to hp ratio will usually drop the higher the rpm peak hp is made,as others have stated. the graph would be interesting to see.
 
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