Reckless

iTrader: (9)

Found some interesting info on the web page from my local shop:

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">A BIG BLOCK CHEVY WAS INSTALLED ON A SUPERFLOW ENGINE DYNO THIS ENGINE PRODUCED 685 HP AT THE FLYWHEEL. THAT NIGHT, THE ENGINE WAS INSTALLED IN A 3000 POUND CAR THAT RAN AN AVERAGE ET OR 10.15 AT 5800 FT. ELEVATION. THE DRAG RACING CHASSIS AND DRIVE TRAIN (equipped with a race converter) CONSUMED ABOUT 180HP, DROPPING FROM 685HP AT THE FLYWHEEL, TO 504HP AT THE TIRE PITCH.

AN IMCA CAR WAS INSTALLED ON THE CHASSIS DYNO AND TESTED THE NIGHT BEFORE.

THE IMCA CAR LOST 93 CHP (calculated) TO THE DRIVE TRAIN WHICH IS 24%. THE DRAG CAR LOST 180 CHP (measured) WHICH IS 26.5%. SO MUCH FOR THE FIXED PERCENTAGE LOSSES THAT SOME HAVE USED IN ELEVATION OF CHASSIS AND ENGINE COMBINATIONS. WITH THE CAPABILITY OF READING ENGINE RPM, TIRE RPM, AND ROLL SPEED, THE AUTODYNO CAN SHOW HOW MUCH SLIP OCCURS IN THE DRIVE TRAIN AT THE TIRE OR AS IN THIS CASE, AT THE CONVERTER.</font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">The info is from http://kammerracing.com/kmr/pages/superflowchassis.htm

<small>[ September 10, 2002, 08:00 AM: Message edited by: Reckless ]</small>

CHRISPY

I have seen tests on T56 equipped cars that came off the engine dyno onto the chassis dyno. RWHP loss for T56 equipped LS1's is right around 45-55RWHP when using a stock rear and stock DS. (Also depends on flywheel type/weight as well)
This was also determined to be the case with the larger higher power motors and the smaller HCI cars as well. is: the same 45-55RWHP loss.
The T56 is one efficient tranny <img border="0" title="" alt="[Smile]" src="gr_stretch.gif" />
Chris

383ss

iTrader: (14)

finally some good info on the subject. Thanks.

ShiznityZ28

iTrader: (11)

i wounder what a th400 loss % is compared to the 4l60

J-Rod

Well, also you have to look at how loose the converter was. There are alot of converters that will slip on the big end.

As for the IMCA car, was that a car with a 'glide and a valve doing a direct drive or what?

Reckless

iTrader: (9)

Can't answer that...just found the info on their site.
Todd

dug

iTrader: (10)

From what I have seen it looks like there is 5% loss through axle assembly. Another 5% with t56 and 10%through a locked A4 (has a pump to turn).

Bode

I knew a guy named Reckless once, he was also called "Hacksaw" at times. <img border="0" alt="[cheers]" title="" src="graemlins/gr_cheers.gif" />

gator's 99TA

iTrader: (2)

ok, my feel on this is that there is NO SET PERCENTAGE. it might be a nice rule of thumb for smaller applications, but take a look at bigger HP motors. are you telling me it takes hundreds of HP to turn the same drivetrane as it does a stock motor? no way. if your motor makes 700 RWHP, it doesnt take 105HP to turn your rear, tranny, etc (assuming 15% loss). i say there is a limit or around 50 some odd rwhp - but hey it gives us some BS to talk about <img border="0" title="" alt="[Wink]" src="gr_images/icons/wink.gif" />

ArcticFormula

I agree Gator, but I guess the convertor that race car was using might be a wildcard, sucking away the horses. Plus I didn't understand the mentioning of the altitude in the post. Was bhp measured at sealevel and then the car ran at 5800ft?
Regards,

racer7088

Well.........engine dynos are usually knobbed a little to keep up with the joneses for the most part and they read in STP rather than SAE so you already lose some hp to the SAE correction which is more accurate. If you correct your engine dyno to SAE like we did at SAM and got 716 for a big block chevy engine at one point and then took it to MTI on their SAE corrected dynojet where it made around 100 hp less or 615 at the wheels through a powerglide that was lightened up but still hooked to a 6000+ stall converter. So it only lost 14% through that drivetrain in SAE corrected form.

The dynojet also sees all the inertial loss that the drivetrain imparts plus the smaller and more constant frictional losses. That's what is nice about the dynojet. You can see how much more power can escape to the wheels where it matters when you lighten things up or do different converters or wheels and tires etc. The engine dyno accelerates at a CONSTANT SPEED against a varying load to come up with the power while the dynojet lets the engine accelerate at whatever rate it wants to against a CONSTANT LOAD of the roller's inertial resistance. So the engine dyno doesn't reward and penalize the power as much as it really should based on the rotating inertia of it's own parts. The dynojet measures the actual power at the wheels minus all these inertial losses in the engine and drivetrain.

If you step the engine dyno at a faster acceleration rate the power will fall also just like the dynojet when you test in a lower gear so it's just a different way to measure and more representative of what it will do in that car with the real exhaust and intake systems etc.

Dom

iTrader: (2)

That makes alot of sense now that I think about it. It takes a certain amount of torque to move the drivetrain, not a percent of total power. So does anyone know how much power it takes to turn 4L60E and a 10 bolt? How does one compare dyno with 4.10s to that of 3.42s or just gears in general?

SStrokerAce

iTrader: (2)

Check this out:

http://www.ls1.com/forums/showthread...hreadid=159239

Old SStroker
LS1.COM Member

This was done at one of the Advanced Engine Technology Conferences (AETC) held annually at Colorado Springs, CO. I was there and observed what was reported. Yes, those were the numbers I remember.

A couple of interesting observations: the BBC drag car had a slicks, a high stall converter, as mentioned, and a Powerglide, I believe. It was important not only to measure engine rpm, but also rear wheel speed to detect tire slip, tire growth and driveline slippage. They had made previous AutoDyn (chassis dyno) runs on this combination, and had developed an approximate correction factor for this driveline. I believe they had not previously tested the engine on the 901 dyno, at least not recently.

When the engine dyno curves were overlaid on the chassis dyno curves which were corrected for drive line losses...in other words, corrected back to the flywheel, the curves agreed within something like 1%!

You must realize that in order to get this kind of correlation, you must measure exact atmospheric test conditions and correct for them, as well as tire slip.

The AutoDyn has the ability to control the acceleration rate of the rolls or even run step tests, because the inertia roll also has eddy current absorbers in series with it. Interestingly enough, the BBC owner only allowed an inertia run which lasted roughly 10 seconds, about his normal et.

I think it's intuitive that different drivelines absorb different amounts of power. Loose converters and big soft, deflecting tires heat up during dyno runs or on track runs more than manual trans and non-drag tires. That heat is from the power absorbed (or lost) thru the driveline.

A 450 hp Viper, run during the same session, used a much smaller correction factor for FWHP from RWHP because it was run in top (or 5th) gear with stock tires; of course it was spinning the rolls at 203 mph at hp peak! It showed right at 450 corrected FWHP. Standing a few feet away from that is impressive.

Last edited by Old SStroker on 09-10-2002 at 09:17 AM

Reckless

iTrader: (9)

Hey Bode...wussup? Guess you finally got back online?

WeatherGuy

Here's a little difference I found switching from an M6 to an A4 on my car. Both figures were SAE corrected and measured on MTI's dynojet:

Best m6 power/torque: 495/489 RWHP/RWTQ

Best a4 power: 469 RWHP (converter unlocked; torque reading not accurate unlocked)

Both runs were through a 3.73 geared 12-bolt spinning 315 nitto drags. The A4 is a built 200-4R transmission using a custom Yank converter (basically a PY3400E). The driveshaft for the A4 pull was a much heavier Inland compared to an ACPT CF driveshaft for the M6 pulls.

Even with probably the most efficient A4 out there, there was still a power loss over the M6, though probably 10-12 RWHP of that was unlocked converter.

Red2000SS

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by Dom:
<strong>That makes alot of sense now that I think about it. It takes a certain amount of torque to move the drivetrain, not a percent of total power... </strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">A lot of people think this, and intuitively this does sort of make sense - it seems logical that a certain fixed amount of power would be required to move the drivetrain at a certain rpm.

This simplified view does not take into account the amount of torque being transmitted through the drive train. The force of friction is determined by the coefficient of friction between the to rubbing surfaces (which is constant) AND the normal force (basically the amount of force applied perpendicular to the plane of the rubbing surfaces). The result of this is that as you use more torque to turn a heavier load the normal forces that are applied to gear teeth, bearings, etc. actually goes up, thus the losses due to friction go up!

The losses due to friction in the drivetrain that occur when you spin it at a certain rpm ARE different when when you have the rear end jacked up and just spinning the tires in the air vs. spinning the tires at the exact same rpm on a dyno providing a significant load.

While this may seem suprising, it is simple physics. The losses due to friction are linear - increase the load by a factor of 2 and the frictional losses go up by a factor of 2.

To provide an anology that might be easier to see. Suppose you had a 2' by 2' piece of plywood loaded with 100lbs of weight and you dragged this across a parking lot at a constant speed - this would require a certain amount of force.

If you instead loaded it up with 200lbs of weight, it would require twice as much force to drag it at the same rate. The same principle applies in the rotational case of our drivetrain, but it is harder to comprehend.

Determining the true losses through the drivetrain is more complicated than just considering friction losses, especially in the case of an A4 in which you are slinging a lot of fluid around and the drag of an object moving through a fluid is proportional to the velocity squared.

The only real way to determine the losses due to the drivetrain is to dyno the engine on an engine dyno and then dyno the car on a regular dyno operating under the exact same conditions.

The results will not be linear across the rpm range either, because of the drag in a fluid issue, but at at a certain rpm using loads that are close, the losses should be similar.

The rule of thumb that I have seen is 15% for M6's and 20% for A4's. This is probably close for an engine turning at an rpm close to its max HP against a significant load i.e. a dyno. The losses would be MUCH less if you ran the same rpm while free wheeling the back tires - but nobody measures this.

Bode

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by Reckless:
<strong>Hey Bode...wussup? Guess you finally got back online?</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">No, not really, just using the laptop to come check on you. <img border="0" title="" alt="[Big Grin]" src="gr_grin.gif" />

niphilli

There are a few other things to consider about the engine dyno Like:

1. Did they use open Headers?
2. Were the accessories hooked up?
3. Correction factors?

I am sure there are a few more. These also show the differences in the new Net HP ratings versus old methods. Old methods were to dyno with open headers and no accessories to get an engines HP rating.

-Nick

Old SStroker

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by niphilli:
<strong>There are a few other things to consider about the engine dyno Like:

1. Did they use open Headers?
2. Were the accessories hooked up?
3. Correction factors?

I am sure there are a few more. These also show the differences in the new Net HP ratings versus old methods. Old methods were to dyno with open headers and no accessories to get an engines HP rating.

-Nick</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">In the original BBC drag car example in this thread, open headers, accessories, etc. were identical during the engine only run on a 901 dyno and the AutoDyn (chassis) run.
Both runs were corrected to the same standard conditions. Corection is extremely important to compare apples and apples, especially at an altitude of 6000 feet or so like C'Springs, CO.

By the way, with an inertia-only chassis dyno like a Dynojet, the acceleration (mph per second) is determined by the power being put down and the inertia (mass)of the rolls; 800 hp engines accelerate it faster than do 300 hp engines. This acceleration rate, say 300 rpm per second or 600 rpm per second can be matched on the engine dyno to account for inertia effects.

Realize also the OEM torque and hp figures are measured on engine dynos using step tests so inertia doesn't reduce the measured output. EOM figures are also corrected to a higher temp (77 F) than most aftermarket tests which use 60F, as well as slightly different baro pressures. The lower the temp correction factor, the more the corrected torque and hp. They are run just as installed in the vehicle with exhaust, accessiores, intake pipes, etc.

It's a far cry from the pre '71 era when OEM's advertised "gross" hp which indeed was measured with open exhaust, no accessories, and more importantly, best fuel and spark at each step. This was done by adjusting mixture and timing while the engine was running at each rpm step! A test took many minutes to run, unlike the typical 15-20 second 300 rpm per second test with today's computerized dynos.

Listen to Red2000SS. He put things very well.