pretty knarly [Archive] - Diesel Place : Chevrolet and GMC Diesel Truck Forums

southern2500

03-06-2007, 09:07 PM

I went and looked at one of those new 6.4's the other day and was loving the fact that Ford made the interior much better then before and the tailgate step is pretty freaken cool to but all was good till I looked under the hood. All I can say is I really feel sorry for the Ford mechanics that get those to work on. I couldnt even fit my hand down to touch the engine thats how clumped that was. As I see it the Ford's have always been nice trucks especially when they brought out the styling of the 05-07's and worked out alot of kinks of that garbage 6.0L. If it came to buying a new 08 though I would defitnetly try and buy the new LMM or the new 6.7L cummins. Ford ruined the styling of the exterior and the engine bay is way to much for me to even consider the thought of spending that much on it. Very nice inside though. I am a big Chevy/GMC fan but when it comes to diesels I try to give all of the three my fair points. If I were buying any of the new 08's it would honestly come to the point of which one I could get a better deal on as far as the Cummins or the DMAX and even then it would still be hard to go against the new GMC's. Saw all 3 at the rodeo in Houston this weekand (LMM, 6.4 and 6.7) and GMC is ahead of a close second Dodge and a very distant Ford. Just my .02

Kyle

WHISTLER.06

03-09-2007, 08:10 PM

i own both...the ford is the better truck.

http://www.ford-trucks.com/forums/587268-08-eye-candy.html
UGLY OH AN ALSO THE MOST UGLY TRUCK I'VE EVER SEEN.:eek: -:t :bawl: :bleah: :duh: :laugh_exp :lol2: :shake: :cookoo: :saluteusa: :chevy:

flyingphish

03-09-2007, 10:38 PM

bet that took a lot of thought...say something, interesting.

pofarmboy

03-09-2007, 11:57 PM

Congrats on the new ride Phish, hope ya have good luck with it. Personally after the 6.0 I had I will never buy another Ford anything again. The lack luster attitude from Ford soured it real quick. When you have people climbing down your azz cause your not working on their house cause the Focus (loner) isn't tool savy, and the woman on the phone from Ford is explaining the wonderful warranty, you tend to get a tad testy.
My dealership and I still compare notes about truck stuff, but last week when i saw my old truck sitting in the shop with the turbo tore apart I can honestly say I have no regrets dumping that thing.

jww2124

03-10-2007, 12:34 AM

Ford should just quit there warrenty program and offer lifetime roadside assitance.

bagofdimes

03-10-2007, 11:20 PM

bet that took a lot of thought...say something, interesting.

HEHEHE...Funny post.

Thats a nice looking truck. I hope the new engine works out better than the last one.

I am a truck fan in general and I like certain things about all three. The GMC was the best option for me, but I have considered all three.

I have seen really nice trucks from all three major companies, and my friends own a mixture of those trucks. If I had the finances to "collect trucks", I would own one of each...but I have to face reality:rolleyes:

Keep us up to date with how it runs.

Good luck and enjoy it.

flyingphish

03-11-2007, 01:51 AM

i agree with you. i like all cars, trucks, planes...anything that has a motor, wheels, or wings.

ive owned all three. dodge, chevy, ford. all three are awesome.

so far so good with this one.

floriduramax1

03-11-2007, 10:18 AM

No offense, but this does look a little Nissanish!

fordude

03-11-2007, 09:07 PM

http://www.dieselpowermag.com/videos/0702dp_2008_superduty_dyno/

wow 630 ft lbs what does a stock lbz do on a dyno?

Hey, that's pretty impressive! :rolleyes: :rolleyes:

fordude

03-11-2007, 09:07 PM

http://www.dieselpowermag.com/videos/0702dp_2008_superduty_dyno/

wow 630 ft lbs what does a stock lbz do on a dyno?

Hey, that's pretty impressive! :rolleyes: :rolleyes:

flyingphish

03-12-2007, 03:01 AM

No offense, but this does look a little Nissanish!

the new HD with its 'plastic' bumper corners painted to match body color look just like the front end of a Titan. Ford stole their interior.

if you cant beat em', join em'.

floriduramax1

03-12-2007, 11:27 AM

the new HD with its 'plastic' bumper corners painted to match body color look just like the front end of a Titan. Ford stole their interior.

if you cant beat em', join em'.
I agree totally, thats why I bought the "classic GMC" I cant stand the looks of the new Chevy bumper corners. Their interiors, however, look pretty sharp. I also dont like the wheel well extrusions on the Chevy, looks like Colorado on steroids. After a year or two their might be a new GMC hd in my driveway...:D

PADiesel

03-12-2007, 01:18 PM

If the numbers are true, that's great for Ferd but the 6.4L is going to have be pretty flawless for years to come before I'd go back. I also agree with the others I love the open space of the engine bay on the Chevy. I looked up close at the 6.4L jammed in cluster and was glad I didn't go there. For me personally it was time to make a change, I drive a lot so good fuel mileage is a definite plus for me and the D-max is smoking everything but 2002 in my sig but I believe it will only get better with some age.

Flyingphish keep us updated and good luck.

cwest

03-12-2007, 07:06 PM

The Ford was impresive, no smoke and quiet. If you want to be scared just look under the hood, hoses, lines, coolers . Iwill keep my GMC, wife loves it and so do I. Rides better than the car.

ZFMax

03-12-2007, 08:42 PM

PHXDiesel

03-13-2007, 06:00 PM

That ain't rear wheel torque. That's engine torque as measured at the rear wheels, and there's a huge difference.

Given equal drivetrain losses, the motor that's making the most horsepower will put the most torque to the rear wheels at any given rear wheel speed. That's a mathematical fact.

I fail to see how you can conclude that this is "engine torque". That would be a very very very sloppy calculation(read EXTREMELY innaccurate) and considering this was a huge event with ALL Makes and models included, I'd bet they were err'ing on the side of accuracy. Here is another link to the same dyno run with the computer screen showing.

http://www.youtube.com/watch?v=x3ma2I2-N6A

If the 2008 ford does in fact put out 630rwtq, that's pretty impressive.

And to be more correct, for any given engine _RPM_, more HP == more torque. But I fail to see how this relates to your point. Just because the Furd shows 274hp doesn't mean it can't have 630lb/ft of torque.

PHXDiesel

03-13-2007, 06:03 PM

Oh yeah.. just to add another post.. I'm new! Figured it's time to start posting. I'm a fan of everything diesel, and not particularly biased towards any one engine. The dmax is one serious powerhouse!

ZFMax

03-13-2007, 07:13 PM

You're failing to consider the gear reduction that sits between the engine and rear wheels. Every time you gear something down, you raise torque and reduce rpm.

Let's say your motor makes 630 lb-ft at 2000rpm. And let's say your transmission is in a gear that's 1:1 and your rear axle is 4.10:1. What do the wheels get?

630 x 1 x 4.10 = 2,583 lb-ft of torque

630 / 1 / 4.10 = 153.7 rpm

Note that in the above example, 630 lb-ft and 2000 rpm at the engine calculates out to 240 horsepower (horsepower is just torque times rpm, divided by 5252).

At the rear wheels, 2583 lb-ft and 153.7 rpm also calculates out to 240 horsepower.

Gearing doesn't increase or decrease horsepower, it simply changes the mixture of torque and rpm that makes up the horsepower.

My point here is that at the rear wheels, you have similar horsepower to what the engine has, but you have massively higher torque and massively lower rpm. That's true even in the highest gears. When you're in a low gear, it's even more so.

Want a mountain of torque at the rear wheels? Simple. Slip it into 4 low and put it in first. You'll have many thousands of lb-ft of torque available. But you won't go very fast.

Every time you upshift, you give up some rear wheel torque, and trade it for some rear wheel rpm. In top gear, you have much less rear wheel torque available, but a whole lot of rear wheel rpm. You can go pretty fast, but if you're pulling a big trailer and you come on a hill, you may not have enough rear wheel torque anymore to maintain your speed. Thus, you downshift, give up some rear wheel rpm, and gain some rear wheel torque.

Back to the original point: An inertia dyno measures horsepower at the rear wheels. It will then plot horsepower vs. speed.

IF you also hooked up the tach pickup, it's able to see the engine rpm, and therefore it's able to calculate the engine torque. It'll then let you plot torque vs. engine rpm. That's because it's engine torque, i.e. before the gear reduction.

Bottom line, the same formula that relates horsepower to torque and rpm works just as well at the rear wheels as it does at the engine. At a given rear wheel speed, the wheels with the most horsepower also have the most torque. It's a mathematical fact.

PHXDiesel

03-13-2007, 08:00 PM

vettelovralexand

03-13-2007, 08:50 PM

I fail to see how you can conclude that this is "engine torque". That would be a very very very sloppy calculation(read EXTREMELY innaccurate) and considering this was a huge event with ALL Makes and models included, I'd bet they were err'ing on the side of accuracy. Here is another link to the same dyno run with the computer screen showing.

http://www.youtube.com/watch?v=x3ma2I2-N6A

If the 2008 ford does in fact put out 630rwtq, that's pretty impressive.

And to be more correct, for any given engine _RPM_, more HP == more torque. But I fail to see how this relates to your point. Just because the Furd shows 274hp doesn't mean it can't have 630lb/ft of torque.

Something is up with that dyno. Looks like the board shows an 04 Dmax with 339 rwhp and 740 rwtq. That is nearly 100 more than I would expect to see for that horsepower figure. Something very fishy...

flyingphish

03-14-2007, 01:37 AM

its a conspiracy!

ZFMax

03-14-2007, 10:58 AM

Your mathematical fact is only true because Horsepower is a function of RPM and Torque

Absolutely! Horsepower is a term that's used to describe the total combination of torque and rpm, without specifying the makeup. It could be very high rpm and very low torque, or very low rpm and very high torque. The horsepower figure doesn't tell you that part, only the total combination.

But for evaluating performance, the makeup of torque and rpm at the engine isn't important. At the engine, it's not made of the correct combination that we want. The rpm is too high and the torque is too low. We run it through a transmission and a rear axle to turn it into the combination we want. After we do that, we end up with MUCH higher torque and MUCH lower rpm at the rear wheels than we had at the engine. The horsepower is the same, it's just made of a different combination of torque and rpm.

You can have a higher RPM, a lower torque #, and higher Horsepower.

Absolutely!

Just because the dyno says you make 630tq, doesn't mean that the HP number comes from that same RPM, it may be 750 rpm up in the powerband, where the torque is lower.

That's right. You can have higiher horsepower even with lower torque, if the rpm is higher. Horsepower = (torque x rpm) / 5252. Which also means they'll cross at 5252 rpm. Which we don't ever see on our diesel engines.

So an "inertia" Dyno is different than what everyone else uses?

No, almost everyone uses inertia dynos anymore.

So there is a different type of Dyno that gives rear wheel numbers?

Well, like I said, rear wheel horsepower and engine horsepower are the same. They're made of a different combination of torque and rpm in each place, but the horsepower is the same in both places.

Now before someone pipes up and talks about 15% losses through the drivetrain, keep in mind that the crankshaft in the engine sees those losses too, if it's hooked up to the drivetrain. The only way you'll get a bigger figure at the crank is if you disconnect it from the transmission and remove the losses. But my point is that as installed in the truck, the power at the crank is the same as the power at the rear wheels, as both places are subject to drivetrain losses.

Torque and rpm are massively different at the crank versus the rear wheels though. The rear wheels have higher torque and lower rpm. That's because of the gear reduction in the transmission and the rear axle.

The dyno shows engine torque and rpm. Yeah, it makes the measurement at the rear wheels, but it corrects it back to the engine. That's why it needs the tach pickup to show torque and rpm.

I've never seen a dyno that shows rer wheel torque. I don't think it'd be very useful, because it would vary wildly depending on the gear you're in.

To answer your question about other dynos, though, Stuska water brake dynos with instrumentation from Depac and others are common in engine shops. The water brake loads down the engine and a strain gauge is used to measure torque. The instrumentation measures rpm, measures torque, and therefore can calculate horsepower. Kind of the reverse of an inertia dyno, which measures horsepower and engine rpm and calculates engine torque.

One huge difference between the results ofa water brake dyno and an inertia dyno comes from flywheel effect. Since a water brake dyno makes it's measurements in a steady state, additional flywheel weight doesn't affect the reading. On an inertia dyno, however, flywheel weight affects spin up time and therefore affects the measurement (an inertia dyno works by just timing how long it takes to spin up a drum of a known mass, or more correctly, a known mass moment of inertia).

How does this inertia dyno account for driveline loss that is a variable between _all_ vehicles?

It doesn't. But I submit you don't really want it to. You want it to show how much is getting to the wheels.

PHXDiesel

03-14-2007, 01:02 PM

Absolutely! Horsepower is a term that's used to describe the total combination of torque and rpm, without specifying the makeup. It could be very high rpm and very low torque, or very low rpm and very high torque. The horsepower figure doesn't tell you that part, only the total combination.

But for evaluating performance, the makeup of torque and rpm at the engine isn't important. At the engine, it's not made of the correct combination that we want. The rpm is too high and the torque is too low. We run it through a transmission and a rear axle to turn it into the combination we want. After we do that, we end up with MUCH higher torque and MUCH lower rpm at the rear wheels than we had at the engine. The horsepower is the same, it's just made of a different combination of torque and rpm.

Absolutely!

That's right. You can have higiher horsepower even with lower torque, if the rpm is higher. Horsepower = (torque x rpm) / 5252. Which also means they'll cross at 5252 rpm. Which we don't ever see on our diesel engines.

No, almost everyone uses inertia dynos anymore.

Well, like I said, rear wheel horsepower and engine horsepower are the same. They're made of a different combination of torque and rpm in each place, but the horsepower is the same in both places.

Now before someone pipes up and talks about 15% losses through the drivetrain, keep in mind that the crankshaft in the engine sees those losses too, if it's hooked up to the drivetrain. The only way you'll get a bigger figure at the crank is if you disconnect it from the transmission and remove the losses. But my point is that as installed in the truck, the power at the crank is the same as the power at the rear wheels, as both places are subject to drivetrain losses.

Torque and rpm are massively different at the crank versus the rear wheels though. The rear wheels have higher torque and lower rpm. That's because of the gear reduction in the transmission and the rear axle.

The dyno shows engine torque and rpm. Yeah, it makes the measurement at the rear wheels, but it corrects it back to the engine. That's why it needs the tach pickup to show torque and rpm.

I've never seen a dyno that shows rer wheel torque. I don't think it'd be very useful, because it would vary wildly depending on the gear you're in.

To answer your question about other dynos, though, Stuska water brake dynos with instrumentation from Depac and others are common in engine shops. The water brake loads down the engine and a strain gauge is used to measure torque. The instrumentation measures rpm, measures torque, and therefore can calculate horsepower. Kind of the reverse of an inertia dyno, which measures horsepower and engine rpm and calculates engine torque.

One huge difference between the results ofa water brake dyno and an inertia dyno comes from flywheel effect. Since a water brake dyno makes it's measurements in a steady state, additional flywheel weight doesn't affect the reading. On an inertia dyno, however, flywheel weight affects spin up time and therefore affects the measurement (an inertia dyno works by just timing how long it takes to spin up a drum of a known mass, or more correctly, a known mass moment of inertia).

It doesn't. But I submit you don't really want it to. You want it to show how much is getting to the wheels.

I think we are going around in circles here. My original argument was that the number ouput by the dyno is NOT engine power, it is rear wheel power. Horsepower figures will NOT be the same at the rear wheels as it is at the crank. The dyno measures torque, which is affected by the driveline loss (transmission, driveshafts, rear gear, tires, weights of all previous items, etc),and therefore your statement that the power figures indicated are at the ENGINE is not true. They are rear wheel numbers which are the only numbers a dyno can measure, and these numbers, be it horsepower or torque will be significantly lower than Engine/crank power.

The only way a dyno can give an ENGINE power rating, is by hooking the ENGINE up to a dyno and eliminating drivetrain.

So in this case a rear wheel tq rating of 630lb/ft would indicate a significantly higher amount of torque at the engine than what the manufacturer is advertising. The 630lb/ft is not at the engine as you originally claimed.

BARRA6706

03-14-2007, 01:14 PM

vettelovralexand

03-14-2007, 01:14 PM

its a conspiracy!

Didn't say that. Just pointing out that these numbers do not seem to be on the level with other dynos that I have seen.

PHXDiesel

03-14-2007, 02:13 PM

Its a load of BS, Ford states that the 08 has 350hp and 650tq, Chevy states that the 07 make 360hp and 650tq. Numbers are similar, I think the dyno operator was calculating flywheel TQ,and HP. Thats what I think.

Yeah the number definitely seems on the high side, but making flywheel calculations would be extremely inaccurate.

porterz

03-14-2007, 02:34 PM

gregw

03-14-2007, 02:53 PM

i was serious!! he has a crazy sense of humor, im going to tell him still...sorry to put it to you with such guilt though...just wasnt feeling the love for the ferd.

On this site?? Slumming with us looking for daily affirmation on buying a Ford??):h

What kind of mileage are you getting so far?

PHXDiesel

03-14-2007, 03:16 PM

I'll put in my bit. If GM comes out with a twin turbo set up.. you can bet it will stomp the crap out of ford. As it sits now the LBZ's single turbo is just as good if not better than fords twins. Numbers from GM are 360 and 650. Ford are as stated 350 and 650. So yes close.. but ours is much less complicated, already has variable veins for the turbo... Now tuning for the ford.. here we might see a GIANT difference... It could be like the LB7s... tons of untapped power.. Even if so.. will it be reliable?

I think a lot of people are missing the point of the dual turbo's. They are used to make more boost yes, but this does not mean you have to inject MORE fuel just because you have more airflow. The sequential turbo's are there to aid in a smoother power delivery(getting rid of the massive kick you get when the boost hits all at once), and higher boost levels (more airflow) which help the fuel burn more cleanly. If Ford were to use previous years calculations to inject fuel based on air density, their power output numbers would be _tremendously_ higher than 350/650. But due to the amount of soot that is released when they have too much fuel for a given air density, they don't.

They want the fuel to burn completely, so they give it a TON of air. They avoid at all costs, creating extra soot. This is just an emissions strategy. I don't know how chevy/GM or Cummins does it. But soot is bad news for DPF's. The more you have, the more it has to regenerate, and the faster you will come up on your DPF manual cleaning/replacement interval.

And about tuning... I will bet large amounts of money on the fact that getting large gains by tuning is going to be severely detrimental to your DPF/emissions system. The days of adding a chip and gaining 200hp are gone. I'm sure it's possible for a short period of time, but at the cost of your emissions systems which are _very_ far from cheap to fix or replace.

Occitiger

03-14-2007, 04:37 PM

I think a lot of people are missing the point of the dual turbo's. They are used to make more boost yes, but this does not mean you have to inject MORE fuel just because you have more airflow. The sequential turbo's are there to aid in a smoother power delivery(getting rid of the massive kick you get when the boost hits all at once), and higher boost levels (more airflow) which help the fuel burn more cleanly. If Ford were to use previous years calculations to inject fuel based on air density, their power output numbers would be _tremendously_ higher than 350/650. But due to the amount of soot that is released when they have too much fuel for a given air density, they don't.

They want the fuel to burn completely, so they give it a TON of air. They avoid at all costs, creating extra soot. This is just an emissions strategy. I don't know how chevy/GM or Cummins does it. But soot is bad news for DPF's. The more you have, the more it has to regenerate, and the faster you will come up on your DPF manual cleaning/replacement interval.

And about tuning... I will bet large amounts of money on the fact that getting large gains by tuning is going to be severely detrimental to your DPF/emissions system. The days of adding a chip and gaining 200hp are gone. I'm sure it's possible for a short period of time, but at the cost of your emissions systems which are _very_ far from cheap to fix or replace.

Well the most valuable addition to these things, will be the removal of all the DPF crap...
I know its impossible to remove...
Know will be able to make anything for that...
We'll never land on the moon...
GM will never put out a diesel worth having...
If you drive over 40mph your face will rip off...

vettelovralexand

03-14-2007, 04:38 PM

They want the fuel to burn completely, so they give it a TON of air. They avoid at all costs, creating extra soot. This is just an emissions strategy. I don't know how chevy/GM or Cummins does it. But soot is bad news for DPF's. The more you have, the more it has to regenerate, and the faster you will come up on your DPF manual cleaning/replacement interval.

Not entirely correct...Soot may cause you to have to regenerate more, but it does not alter at all the cleaning/replacement interval. The only thing needed to be cleaned from the filter manually is ash that actually comes from the oil.

A_T_Ver

03-14-2007, 04:51 PM

I thought the average loss through the drivetrain was around 12%, and the ford rated at 650 at the crank, that would be like around 575-580 maybe, at the wheels.

porterz

03-14-2007, 04:56 PM

Emissions are great in states that have requirements.. in MO I can run nothing.. we don't have tests here. In AR I believe you get one when you first purchase, then never again. Emissions are going to go out the window fast. So saying something like 200hp gains are out the window.. I don't believe it for a second.

I understand the theory behind twins.. but if done properly you get the best of both worlds.. run a small enough one that you never have the lag.. and at the other end a big enough one that you keep power all the way. Turbos in my opinion are the way to go with anything. I love the idea. I planned a rebuild on my stealth 3 yrs ago and am just now getting to it.. I kicked around the HUGE turbos in replacement for my tiny ones. but instead I am going medium boring, destroking and running MUCH higher RPMS.. In the end it all comes down to driver style in that. This is similar all in application.. if you want smoke.. go bigger turbos so you have lag.. if you want tons of power.. you need more air.
twins make sense was all I was really trying to say. For performance anyway.

PHXDiesel

03-14-2007, 05:59 PM

Not entirely correct...Soot may cause you to have to regenerate more, but it does not alter at all the cleaning/replacement interval. The only thing needed to be cleaned from the filter manually is ash that actually comes from the oil.

Some ash does come from the oil, but the soot also does not burn completely away.

ZFMax

03-14-2007, 06:28 PM

I think we are going around in circles here. My original argument was that the number ouput by the dyno is NOT engine power, it is rear wheel power.

I agree. An inertia dyno directly measures how much power reaches the rear wheels.

Horsepower figures will NOT be the same at the rear wheels as it is at the crank.

If both are subject to the same drivetrain losses it will.

The dyno measures torque, which is affected by the driveline loss (transmission, driveshafts, rear gear, tires, weights of all previous items, etc),and therefore your statement that the power figures indicated are at the ENGINE is not true.

No, an inertia dyno measures horsepower directly by timing how long it takes to spin up a drum of a known mass moment of inertia. It doesn't measure torque directly.

In fact, if you've ever used an inertia dyno, you'd know that it will not even give you a torque reading unless you use the tach pickup. Without the tach pickup, you can only plot horsepower vs. speed.

If you use the tach pickup, however, it will let you plot horsepower and/or torque against speed or rpm. That's because knowing engine rpm, and horsepower after drivetrain losses, it can calculate engine torque after drivetrain losses. And that's what it displays.

If it was showing rear wheel torque, the number would be a WHOLE BUNCH bigger. The gear reduction of the transmission and rear axle multiply the torque. Even in top gear, you have literally thousands of lb-ft of torque at the rear wheels. In a low gear, you have more. Ever notice that you can lay rubber in first gear a whole lot easier than you can in top gear? The reason is that you have a whole lot more torque at the rear wheels in first gear than you have in top gear.

They are rear wheel numbers which are the only numbers a dyno can measure, and these numbers, be it horsepower or torque will be significantly lower than Engine/crank power. The only way a dyno can give an ENGINE power rating, is by hooking the ENGINE up to a dyno and eliminating drivetrain.

You're defining engine power as power produced by the engine without any drivetrain losses. And that's fine, you can define it that way, most people do. But your definition then makes it impossible to describe the torque figure the dyno is showing.

I was really just trying to illustrate how gearing is used to raise torque and lower rpm, and how the act of gearing something deeper does not change horsepower because the definition of horsepower is a combination of torque and rpm without regard for the makeup. 600 lb-ft and 3000 rpm at the engine can be run through a 4.10 axle, after which it becomes 2460 lb-ft and 731 rpm, but on both sides of that axle it's still 343hp, and both sides see any drivetrain losses that may exist.

So in this case a rear wheel tq rating of 630lb/ft would indicate a significantly higher amount of torque at the engine than what the manufacturer is advertising. The 630lb/ft is not at the engine as you originally claimed.

If that Ford really only has 630 lb-ft at the rear wheels, then a VW Beetle will out tow it any day of the week.

630 lb-ft after running through a 4.10 axle means it only had 154 lb-ft coming out of the transmission. Assuming they did the dyno pull in the 1:1 gear (whichever gear that is on a Ford), that means a whopping 154 lb-ft at the engine. Somehow I don't think so ;)

No, what their dyno is doing is exactly what my Dynojet does. It measures rear wheel horsepower, and then if it also knows engine rpm, it calculates torque at the crank. And yes, you're right, the torque figure it gives will reflect drivetrain losses, of course. But it's still torque at the crank. If it was torque at the rear wheels, the number would be 4.10 times bigger.

You don't have to believe all that, but if you don't, then explain something to me. I'm sure you agree that horsepower = (torque x rpm) / 5252, right? Common, well known formula. Okay, now look at any dyno sheet that shows horsepower and/or torque versus rpm. Is it plotted against engine rpm or rear wheel rpm?

It's plotted against engine rpm, right? And yet the formula relating the horsepower and the torque are still valid, right? I mean, you can pick any point on the torque curve, multiply the torque at that point by the rpm, divide by 5252, and come up with the horsepower at that rpm, right?

So if it's rear wheel torque, howcome you can multiply it by engine rpm and divide by 5252 and get the horsepower? Shouldn't you have to do the calculation with rear wheel rpm?

The answer is obvious: it's crank torque, i.e. on the upstream side of the gearing. So engine rpm is the right number to combine it with.

vettelovralexand

03-14-2007, 08:13 PM

Some ash does come from the oil, but the soot also does not burn completely away.

Ash comes completely from oil that is part of "blowby" into the cylinders. It may be mixed in the "soot" when it goes to the DPF, but all the ash is from the oil.

PHXDiesel

03-14-2007, 09:56 PM

I agree. An inertia dyno directly measures how much power reaches the rear wheels.

If both are subject to the same drivetrain losses it will.

No, an inertia dyno measures horsepower directly by timing how long it takes to spin up a drum of a known mass moment of inertia. It doesn't measure torque directly.

In fact, if you've ever used an inertia dyno, you'd know that it will not even give you a torque reading unless you use the tach pickup. Without the tach pickup, you can only plot horsepower vs. speed.

If you use the tach pickup, however, it will let you plot horsepower and/or torque against speed or rpm. That's because knowing engine rpm, and horsepower after drivetrain losses, it can calculate engine torque after drivetrain losses. And that's what it displays.

If it was showing rear wheel torque, the number would be a WHOLE BUNCH bigger. The gear reduction of the transmission and rear axle multiply the torque. Even in top gear, you have literally thousands of lb-ft of torque at the rear wheels. In a low gear, you have more. Ever notice that you can lay rubber in first gear a whole lot easier than you can in top gear? The reason is that you have a whole lot more torque at the rear wheels in first gear than you have in top gear.

You're defining engine power as power produced by the engine without any drivetrain losses. And that's fine, you can define it that way, most people do. But your definition then makes it impossible to describe the torque figure the dyno is showing.

I was really just trying to illustrate how gearing is used to raise torque and lower rpm, and how the act of gearing something deeper does not change horsepower because the definition of horsepower is a combination of torque and rpm without regard for the makeup. 600 lb-ft and 3000 rpm at the engine can be run through a 4.10 axle, after which it becomes 2460 lb-ft and 731 rpm, but on both sides of that axle it's still 343hp, and both sides see any drivetrain losses that may exist.

If that Ford really only has 630 lb-ft at the rear wheels, then a VW Beetle will out tow it any day of the week.

630 lb-ft after running through a 4.10 axle means it only had 154 lb-ft coming out of the transmission. Assuming they did the dyno pull in the 1:1 gear (whichever gear that is on a Ford), that means a whopping 154 lb-ft at the engine. Somehow I don't think so ;)

No, what their dyno is doing is exactly what my Dynojet does. It measures rear wheel horsepower, and then if it also knows engine rpm, it calculates torque at the crank. And yes, you're right, the torque figure it gives will reflect drivetrain losses, of course. But it's still torque at the crank. If it was torque at the rear wheels, the number would be 4.10 times bigger.

You don't have to believe all that, but if you don't, then explain something to me. I'm sure you agree that horsepower = (torque x rpm) / 5252, right? Common, well known formula. Okay, now look at any dyno sheet that shows horsepower and/or torque versus rpm. Is it plotted against engine rpm or rear wheel rpm?

It's plotted against engine rpm, right? And yet the formula relating the horsepower and the torque are still valid, right? I mean, you can pick any point on the torque curve, multiply the torque at that point by the rpm, divide by 5252, and come up with the horsepower at that rpm, right?

So if it's rear wheel torque, howcome you can multiply it by engine rpm and divide by 5252 and get the horsepower? Shouldn't you have to do the calculation with rear wheel rpm?

The answer is obvious: it's crank torque, i.e. on the upstream side of the gearing. So engine rpm is the right number to combine it with.

OK this does make sense, and you obviously know more about dyno's than I do... I do believe there is one more piece to add into the equation though... your final gearing ratio and it's relation to the tire size. Wouldn't this in turn drop your torque number way down? I can't remember the exact calculations.. it would take a bit of thinking, but it should lower the actual torque output.. The torque if measured at the wheels would not be tq*4.10... it would start there, then be significantly reduced by the tire size.

A 2008 f250 with 20's has a tire diameter of 34"...

So you have a twisting force pushing a lever with a distance of ~17 inches....

So on a dyno (I've never actually been strapped to one), You don't input any gearing info? No tire diameter or rear gear ratio?