ZeeOsix....i think you and I beat our heads up against brick walls the last time this thread came up. I have been out all week traveling, so luckily I missed the vast majority of this one. I don't think anyone will ever change their minds unless they have hundreds of data points where the engine is dyno'd in and out of the car.....good luck..

 

But the title of the thread is "True HorsePower", not "HP best guess estimation based on opinions" or "Close but no cigar HP estimations"

Despite all the debate here, it is actually pretty simple, fact is, you can not get "True HorsePower" from a chassis dyno.

 

To all involved,thank you for the intellectually stimulating post,bright indivudals,making valid points with real world examples. Makes for a very interesting read , although I admit like said in a previous my head hurts ,but only a little.

 

Dynos and the numbers they give should be used for testing only, not just making the big number. Here is a thread about a mag article that we did on the new Z06. This test we didn't make any money on. We actually lost money on the testing but that is part of R and D work. There is never going to be two dynos that have the same amount of loss as the horsepower goes up. Dyno load the engine differently and the tunes do change also, because of this. If you go for the gusto on the enigne dyno tune, the engine will not live a long time on the road-track. Experience can get one close to a good car tune on the engine dyno. But also should be checked in the car also because things do change. After this forum member pointed out this, we have been watching the differences in losses. They are following the same trend as what was pointed out. No big concern to us, because it shows increases and decreases as we change parts. I got asked one time why I don't post dyno numbers on the forum. My responds is, "If I had the dyno up the road from us, I would post them all the time"

http://forums.corvetteforum.com/show...light=drm+rwhp

Randy
PS I have never seen two dynos at the tree, going down main street, coming out of turn 10, going up the hill at RA.

 

You forgot leaving the parking brake on.

I'm assuming you are referring specifically to the HP number the dyno "calculates". If so then yes ... an inertial dyno does not measure torque directly. The unit of HP in general is a derived unit invented by Mr. Watt while trying to determine how much avg work a horse could do all day long.

This is what happened when they were worked too much --->

 

I hear you ... but the new caviet in this discussioin is that Tony has done just that (engine and chassis dyno tests) and he is using the date to pitch the "driveline loss is a constant value no matter how much HP you put through it" theory. I think the dyno is masking what is really going on or else there just isn't enough range in the tests to get beyond the normal dyno scatter.

All I know is that there is no physically possible way that the drivetrain always losses 75 HP regardless if 100 HP or 1000 HP is going through it.

 

... but these discussions always turn into "drivetrain HP loss" debates. For the time being, I guess it will have to be "close but no cigar HP guestimations".

I think we all know that dynos are just good estimates, and that a dyno's real primary use is for tuning and estimating the effects of modifications on output power -- assuming the same dyno is used all the time.

 

Guys,

The quote above by ZeeOsix is addressing a portion of an earlier post I made where I stated "With close to 400 at the crank and 300 at the ground they are losing close to 25%" which was me referencing how a stock Vette with the least power (compared to a modded Vette) shoots the biggest hole in the percent theory because low power means low percent loss and the stock Vette's have just the opposite....they have the highest pecent loss at close to 25% (once again assuming that is the theory you subscribe to which I obviously do not).

Zee, IMO this clearly shows that you dont have a complete understanding of the dynamics involved (between chassis and flyweel dyno's) yet you are relentless to defend your position as if it was your field of expertise.

Factory published HP figures are not even close to real world engine flywheel dyno numbers (published HP ratings are much more conservative). One of the main reasons why is the OEM's rate their engine outputs "net" and have been doing so for 20+ years, meaning they are quoting HP numbers including the losses from all the factory accessories bolted to the engine. Engine/flywheel dyno's usually have zero accessories involved and even the water pump is usually electric so that loss doesnt factor into the mix (some shops run the mechanical pump but most use an electric).

In fact the accessory losses are a decent chunk of the loss you see when comparing flywheel dyno results with rear wheel numbers. Also, the factory rates the power output in SAE where its been my experience most engine/flywheel numbers are usually posted using the STP correction factor (which will read close to 4% higher). GM is also notorious for underrating the power outputs of their high performance offerings and its not uncommon at all to see them produce significantly more power than they are rated, especially when you see the numbers without all the power robbing accessories (water pump, power steering, air conditioner, etc.).

Long story short a stock LS1 engine using an STP correction will make right around 395-400 HP BONESTOCK on a flywheel dyno....add headers and you will see right around 420-430 HP. A stock LS6 engine will make closer to 450 bonestock and also see about the same gains with the addition of headers. A stock Z06 (C6) rated at 505 from the General will put up approximately 550 at the flywheel (no accessories using the STP correction factor) losing about 95-100 thru the driveline....with 450-460 RWHP very common. Once again another point of reference backing my "close to fixed loss" theory. If the C6Z06 had a lighter clutch and lighter smaller C5 rear tires, it would also lose 80-ish HP from engine dyno to chassis numbers (with close to 100 being the right number with the heavier clutch flywheel and bigger tires).

Here is a link to some early testing I was involved in where we baselined a stock LS1 on the engine dyno (with headers in this particular test)

http://www.airflowresearch.com/ls1_dyno.php

The stock dyno curve is in red, versus the blue curve with our 205 heads...

Also, you had questioned "different ways to test on a chassis dyno" in another former post....there are no different ways to test. A chassis dyno is a relatively simple device and there are only two ways that a chassis dyno operates. A conventional less expensive "inertia" style dyno has a known fixed mass (the drum) and it measures how quickly the engine can spin that drum essentially measuring horsepower and converting those figures into torque based on the RPM and the mathematical relationship between the two. A more expensive load cell dyno usually works inverse of that actually measuring the torque and then converting to horsepower once again using the mathematical equation (HP equals TQ X RPM divided by 5250)

Zee, no offense but it seems to me that you have spent little time around the actual instruments we are discussing (engine dyno's and chassis dyno's). On the other hand I have dedicated most of my life to this hobby and this is also how I make my living (designing cylinder heads, building engines, and R&D directly and indirectly related to what we are discussing). I have spent countless hours around engine dyno's and chassis dyno's so I just might have a better vantage point than you understanding how all of this works. Does that make my opinion on this topic the right one?....no...because everyone is entitled to their own, it just makes me a little more informed when I'm actually formulating one.

Not to mention the basis of my opinons have been formed from real world hands on testing on multiple combinations with alot of engine and chassis dyno experience to draw from (not from theories not directly related to what we are discussing).

-Tony

 

Show me the data where a M6 Vette with 400 fwhp is only putting down 300 rwhp on the dyno. If that data point is something you saw, then I have 3 responses: a) the dyno data is junk or b) something was very wrong with that car, or c) both of the above.

OK ... this sounds like the start of a pissing contest. I haven't attacked your knowlege if this subject, but frankley since you mentioned it, I also believe you are missing something here. I have a very good understanding of how both an engine and chassis dyno works and what it is measuring.

Understanding that the HP lost is 98% due to the friction in the system and that heat is the result, it is very easy to understand the the drivetrain loss can never be a constant number as the levels of HP increases in the drivetrain.

Look, the manufactures these day rate the engine's fwhp as "SAE Certified". What you said in red above is how it should be, as you don't drive a street car around without the accessories on the engine ... So right there is probably a reason why your "engine dyno" and "chassis dyno" numbers are skewed. If you test an engine with no accessories on it, then throw it into the car with all the accesories back on you are comparing apples to oranges. The lack of the accessories on the engine dyno is showing more HP for the engine out of the car then in the car. How in the hell can you even make the claim of what the lost HP is between crank and wheels if there is stuff missing in one of the tests?



Hummm ... I see two different ways right there. That's what I was refering to. There are other types of dynos in the world besides "intertial drum" types.

I'm going to skip the rest here because frankly I don't have the time to disect every comment you've make here ...

 

When you disect this data you can see that the delta is 75 HP on both combos. But, if you look at the % loss you have:

13.1% for 550 fwhp --> 475 rwhp
12.2% for 615 rwhp --> 541 rwhp

The delta in % loss is basically 1%, which you could say the "error" in the measurements are +/- 0.5%. The accuracy or running dynos on different days, etc can fall easily into this error range.

Plus, if you are running those engines on the engine dyno without accessories, etc then that puts even less confidance in the numbers.

Sorry, but your arguements are slippy away quicley IMO.

 

I have decided this thread is a fruitless exercise and I have already invested waaaay to much time....

I hope I have given some of you reading (and perhaps not posting) some things to think about.

Zee....your on your own...I'm outta here

 

I see a trend here, which I had mentioned in another thread.

As fwhp is increased, the loss as a percentage of available fwhp is decreasing.
So it may be that actual loss is increasing by a small amount, but it is not enough to actually put a good figure on at these hp levels.

I'd like to see the results of a solid 750-800 fwhp engine in there.

It may take greater fwhp levels to see a more clear example of the additional loss being generated.


ZeeOSix,

I certainly agree that the dyno results of stock engines without accessories is a test I would place less faith in.

However, when Tony tests his particular vehicle, I will guess he is reinstalling the engine with the same accessory system he had dynoed with previously, which would minimize differences during these tests.
Tony, can you comment on that?

Of course weather conditions would come into play, but that is what SAE correction is for.

I find his tests of his car to be of interest, and his continued testing will give him and us more data to consider.

 

He has already stipulated that the engine dyno tests do NOT have all the same accessories on the engine as if the engine was in the car. I would assume 99.9% of all shops that do engine dyno tests use the same test methods. How can that be good if people are comparing engine dyno fwhp to chassis rwhp and then saying there is X amount of drivetrain HP loss (or X% loss) when there is a different configuration between the two tests? That is sloppy data that just confuses the whole issue IMO.

 

I'd like to see these other testing facilities engine vs chassis dyno results. But again, if they are not testing the engine out of the car with exactly the same accessories, etc as it has while in the car then this data is virtually worthless IMO.

 

I understood that Tony engine dynos with no accessories, but when he chassis dynos the car, each time the same accessories are in place.

Of course, there is additional loss with the accessories back in place, but it will still show whether the trend is for hp loss to increase to the wheels as fwhp increases substantially.

It would stand to reason that as the accessories are spun quicker, there may be a bit of additional loss associated with it, just as in the drivetrain.

Let's say his previous results showed a 75hp difference from engine to chassis.

Now he bumps hp to 750fw, and he loses 90hp to the wheels.

I'm interested in the trend that develops.

 

That's some good info there - thanks for the info. Now that's what makes sense based on real world experience and physics. And this is doing engine vs. chassis dyno testing -- so why do some people still believe that the drivetrain loss is a constant amount of HP regardless of the amount of power put through it. There have been about a dozen examples of why it can't be.

 

Only kidding!
The right way to figure horsepower is not with 0.85 or with 1.15. the equation is:

Rwhp + (Bhp x 0.15) = Bhp

this is algebra

if you add 15% of your rwhp you are not adding enough, because 15% of your rwhp is less than 15% of your hp at the crank. This would be an underestimate of your horsepower!

so you actually have a little more than you thought!

 

Humm ... it comes out the same way. Equations can be written different ways and give the same results.

The consensus is that the general rule of thumb is 15% drivetrain loss for M6 C5/C6 Vette.

This means if the fwhp was 405 HP, the loss is 405 x 0.15 = 60.75 HP. That would mean the rwhp would be 405 - 60.75 = 344.25 HP.

The same result can be achieved by saying the rwhp is 405 x (1-0.15), which is the same a saying 405 x 0.85 = 344.25 HP.

Using your equation above would yield: 344.25 + (405 x 0.15) = 405.

They are mathematically the same.

The simplest formulas for a 15% drivetrain loss are:

rwhp = fwhp x 0.85

fwhp = rwhp / 0.85

The factor 1.15 never comes into play.
rwhp x 1.15 is not the same result as rwhp / 0.85

 

So, I am curious.

If Tony has data which correlates his position, why is it so easy to dismiss him as being wrong? I understand it upsets the applecart of folks who want to bank on a fixed percentage. But, in the posts I have read, folks are not even willing to conceed it as being possible. "It just can't happen because I would be wrong, and I can't be wrong". If there is anything I've learned its that I don't know everything. Even if I don't agree with something I will listen. I may be 100% against it, but I will at least listen to a well thought out argument, and if I'm wrong I will admit it, and move on. But, I'm not so sure the same can be said here.

But, I've seen the same thing on this an similar forums when it comes to air intakes, headers, head and cam packages, cylinder heads, etc... People want to defend their purchasing decisions to everyone on the forum, and get "religious" about how part X has to be better than part Y (because they bought it).

Now, I have a question. Its been mentioned here as well. It is proven that if you swap out your stock wheels for some really heavy replacements you loose horsepower. If you swap out an Ls7 clutch with a cast iron flywheel to a a Exedy twin disc you will pick up HP. In short mass in the driveline accounts for additional loss/gain. Those affect that percentage.

You have plenty of slung mass to change that fixed percentage going car to car. but, in Tony's car you have a static driveline combination that gets run on the same engine dyno and chassis dyno and it repeats consistently.

Although you may not agree with his results, you cannot deny the data. I will be very interested in Tony's next dyno. If he see the numbers he's predicted, then I would say that three controlled data points will provide a pretty credible basis to support his static loss assertion.

 

There is no denying that if you change the mass of the driveline components that you will also change the amount of HP that is lost due to accelerating that mass.

I think you might be confusing the real issue in this discussion. Tony is claiming that the lost HP is a constant value no matter how much HP is put into the drivetrain. He is basically saying that the drivetrain loses 75~100 HP regardless if the engine is putting 100 HP or 1500 HP into the drivetrain.

The reason most people shoot down that theory is because any real world example simply shows that can not happen from a mechanical system or thermal viewpoint. I can give a dozen real world examples that show the amount of HP lost in the drivetrain increases when the HP input increases ... which follows closely to a fixed % loss where rwhp = fwhp x (% drivetrain loss factor). As HP input increases, so does the torque, load and stress on all the parts which will cause added friction, heat and HP loss. That's how any mechanical system works when transferring power.

There are also other members posting in this thread that have done engine vs. chassis dyno HP comparisons (see Post #64) and their data shows that the drivetrain loss correlates closely to the "% loss theory" rather than the "constant value HP loss theory". Plus, Tony's engine fwhp deltas do not have a very large difference test 1 to test 2 whicm makes it hard to see any real differences in drivetrain loss. The error factor comes out around +/- 0.5%, which could easily be masked due to typical dyno testing error. Also, his engine dyno numbers are without the same accessories, etc as when the engine is in the car ... more discrepancies that skew what's really happening IMO.