Competition Parasitic losses on torque numbers?

[HillCountrykid]

Are there parasitic losses on torque numbers when dynoing? No one I've asked know's the answer, and I figured one of you guys would know. Thanks.



Brian

 

[Don M]

very very little.



Don~



did I say very little? Oh yeah, very little

 

[HillCountrykid]

Dang that was quick!

 

[docdyno]

I hope I am interperating your question right- Yes there are parasitic losses. On a chassis dyno (rollers for rear wheels) there is considerable loss in the transmission, U-joints, rear end, wheel bearings, etc. The mass of the driveshaft spinning even adds to the loss. They all add a load which the engine must overcome. There have been lots of numbers tossed around as to how much that is ranging from 20 to 45%. Many seem to think that a logical average might be about ~30% HP loss for all driveline components totalled together. (really just a guestimate) Every application will vary with wear, gear clearences, bearing friction, etc. Temperature and lubricity of the gearbox fluids will also cause notable variances.

On an engine dyno (bolt the engine and directly couple to dyno) all but a small driveshaft are eliminated. Additionally some engine dynos can "motor" the engine. A big electric motor drives the engine. With this set-up you can actually measure the parasitic losses of the engine components. i. e. friction caused by the piston rings, bearings, etc. On a 400 HP gas engine for example, it can take almost ~70 HP to overcome the parasitic losses of friction. Sorry I don't have any hard factual numbers for you here. I hope this was the information you were looking for.

 

[HillCountrykid]

Sorry docdyno, I was asking about torque numbers, not HP. I know they are losses for HP, and was wondering if it is the same for torque.



Brian

 

[docdyno]

A braking dyno actually MEASURES torque. HP is simply a calculation based on that torque measurement. Formula is:

HP = torque X lever arm. So torque will proportionally be effected, although it is not a direct relationship. IMHO torque will also suffer from parasitic losses. I wish I had some actual diesel engine measurements to share, but I don't at this time. You might want to refer to "Engine Testing Theory & Practice" by Plint & Martyr. Let me know if you need additional info or if I havn't addressed your question.

Doc

 

[HillCountrykid]

Thanks for the help Doc. I'll have to look it up sometime.



My truck dynoed at 255/650. If you use 20% hp loss, it's right around 300 at the flywheel. Cummins has a 300 hp version with 660 ft. lb. of torque. I was'nt sure if this was a coincidense, or with the defueling and limited boost taken care of with the COMP, it is set up close to the 300 hp version.



Brian

 

[nascar mark]

Hi, HillCountryKidd.



Your boost #'s will give you a close hp rateing at flywheel with single turbo.

1st gens. . 1lb of boost=10hp

2nd gens. . 1lb of boost=12hp

Hope this helps.



mark

 

[MCummings]

Originally posted by nascar mark

Hi, HillCountryKidd.



Your boost #'s will give you a close hp rateing at flywheel with single turbo.

1st gens. . 1lb of boost=10hp

2nd gens. . 1lb of boost=12hp

Hope this helps.



mark

Well, How about that,,



With my HX-35, I saw 38 pounds of Boost. pulling,

and an easy 35 pounds driving unloaded. (36-37 drag racing)



Wow, I guessed 375RWHP, but my calculator is saying,

38 * 12 = 456

and in town,, drag racing etc.

36 * 12 = 432



20% drivetrain loss...

432 * 80% = 345. 6



Oh man,, that was a roller coaster post...

First, Wow, lots O Power. . then, Bam, *only* 345 RWHP. I was hoping for 375RWHP



Oh well. I have a cure for this BOMBitis. (it's More power)



Thanks for the info Mark,



Merrick Cummings Jr

 

[HillCountrykid]

Empty, I made it hit 31 pounds one time and 30 or so most of the time.

I was just wondering if the the 650 ft lb I dynoed is what's at the flywheel, or if there is any lost through the drivtrain.



Brian

 

[LSMITH]

Your 650 is at the rear wheels, and does not reflect the final drive gear ratio. The flywheel number if you took the engine out and dyno'ed it on an engine dyno would likely be in the high 700's. Multiply your 650 by the final drive ratio and you get what the dyno actually recorded for torque. The torque is definately affected by the parasitic losses.

 

[nascar mark]

MCummings,



20% loss thru drive line is a base line. Also matters what gear the truck is dyno'd in. Also matters in what gear you are make the boost in. As with seeing higher boost numbers when pulling because the engine has to work harder. I see a 4# difference from 35#'s in D to 39#'s in O. D..... O. D. being higher at 39#'s in my 1st gen unloaded, I thought I would have dyno'd at close to 315hp at the rear wheels lately at BD's Dyno days.

Guess whatthe paper read out said 271hp and 698. 1ftlb's. Could not believe my eyes. So I asked whats up with that? I found out they dyno'd in drive. So my 35#'s = 350hp at the flywheel=271hp at the rear wheels=22% loss through drive line.

I know I run thicker gear oil every were, from the engine back as I like the max protection I can get.



So keep in mind your losses can be higher depending on a lot of factors. Even tires make a difference as I run bigger tires and more aggressive tread. Like you said just add more power to get the numbers