Negative Horsepower

[wrench459]

My goodness how long does the test last?
While playing around this weekend, I thought is was setup properly only to bale out way to early. Rookie mistake I supose.
From the info on this site I should see a 12-15% driveline loss?

[opelspyder]

Depends on the dyno and the operator, some compensate up to 25% loss. When you say negative horsepower, its not really negative is it. When you back off the speed on a Dyno, it shows a negative number-but that doesn't mean your not showing power, thats just in the computer slowing down. I have read several peoples explanation of how much horsepower will drop in a drivetrain-its across the board
Keith

[wrench459]

Thanks Keith
I'm walking a fine line due to professional courtesy.
The dyno in question is a "dynojet 248" and the operator can be a jerk!

[opelspyder]

Dynojets are notorious to show higher numbers. We have a Land and Sea Dynomite, more comparable to a Mustang Dyno I guess you could say. We have the option to change whatever readings we want, you may find they will figure in less to show you big numbers. Just remember the numbers do not matter until you change something and try again on the same dyno on the same weather conditions-or inside. Also doing the test in third gear will show better results with "clihimm-clears throat" lower horsepower cars. I do not think there is a such thing though as Negative Horsepower on a Dyno unless they are using a water brake or brake...still isn't negative but road force load. Basically like climbing a hill and making the engine work.
Keith

[wrench459]

Lets agree to disagree and debate this in a private setting.

[hrcollinsjr]

Lets agree to disagree and debate this in a private setting.

So you're going to send the rest of us to another room while you grown ups discuss this, huh?

Dan, I think you'll find different drivetrain losses for various combinations. I would think different transmissions, two piece driveshafts, driveline angle, RWD, FWD, AWD, etc. are going to vary in efficiency. You know this, so as Keith said, percentages can vary greatly. Now as to whose Dyno is the most accurate, it's probably like a lot of things, the best can probably be screwed up by incompetent operators and good operators can probably get excellent results from mediocre equipment. I personally try to use the best that I can so if there is any fault it has to lie with me.

No dog in this but always up for a learning experience.

Harold

[RallyBob]

Dynos are like fingerprints, no two are alike.

There are a lot of factors which will affect the outcome, so really it's just a tool for development. Tire size, type and weight makes a difference, transmission type makes a difference (4-speed/5-speed/auto), gear oil types make a difference, tire pressures make a difference, etc. Then there are the SAE smoothing factors, the gear you choose to dyno in, the altitude, the barometric pressure, the air temperature, the cooling (or lack of it) to the radiator and air inlet to simulate road speed, and the inputted information such as vehicle weight and gear ratios.

Anyway, just some things to think about.

[newman27]

I never bothered to post this because I find the results somewhat suspect and the Dyno operator never emailed me the completed graphs I asked for but since it applies to this topic...

Last month I took the GT to a Dyno here in Atlanta for three pulls (right after my CAI was installed). They have a Land and Sea brand with front and rear rollers for AWD cars sunk into a cement floor. I believe the operator told me that the Dyno (with installation) cost over $200K (I mention that because I think it indicates we are talking about a very sophisticated unit here). The three pulls showed a high of ~96 bhp with no allowance for drive-train loss (i.e., that field had 0% in it). I know I gave the operator the right bore / stroke / etc. because I called Keith that night to get the numbers specific to my car as the operator keyed them into the PC. This is a roughly 50% increase over the HP measured in 2007 at the Tennessee Dyno Days meet. I know the car is stronger for sure because of some things that have been tweaked and added (like the CAI) but not so sure that number is "right". Just thought I would post now as an example of the variance that can occur between Dynos...

[wrench459]

Matt
The dyno is just a tool. Just like say a screw driver that hopefully tightens and loosens screws. I'm just as guilty of falling into the HP trap.
If you have the print outs take a look at the curves.
Heres how I'm planning my method of attack.
Three pulls to see consistency of the pulls then average them together to get a baseline. Then the fun starts "tuning" changing something be it a carb,intake,cam timing... and then another set of pulls to see hopefully increases in the planned spots.
BTW I still cant get the negative numbers the X#@@%^&*#*@ dyno keeps slamming on the brakes after two minutes of coast down.

[hrcollinsjr]

BTW I still cant get the negative numbers the X#@@%^&*#*@ dyno keeps slamming on the brakes after two minutes of coast down.

What's actually happening when it's doing this?

Harold

[wrench459]

Harold
I'm not sure but I've probably misconfigured the software somewhere. Or are you asking about drivetrain loss?

[hrcollinsjr]

Harold
I'm not sure but I've probably misconfigured the software somewhere.

This may answer my question. Garbage in garbage out. It would be nice if the software was more user friendly I'll bet.

Keep posting!

Harold

[wrench459]

Your very right Harold
Thats why I try to back up any claims using different methods.
[ame=http://s250.photobucket.com/albums/gg246/wrench459/performance/?action=view&current=Opelmafrun.flv]performance :: Opelmafrun.flv video by wrench459 - Photobucket[/ame]
This is not a dyno pull this is pure scope
You'll need these numbers
Ford Voltage to Mass Air Flow Conversion Table 1995
Grams/Sec Grams/Sec Grams/Sec Grams/Sec Grams/Sec
Volts 2.3l Ranger 3.0l Aerostar 3.0l Windstar Mustang Crown Victoria/Gran Marquis Town Car 3.8l Windstar 4.0l Ranger Continental Thunderbird Cougar
4.60 139.24 229.08 231.79 299.37 243.49
4.47 133.41 219.64 222.35 289.93 234.05
4.35 127.59 210.21 212.92 280.50 224.62
4.22 121.76 200.77 203.48 271.06 215.18
4.10 115.94 191.34 194.05 261.63 205.75
3.97 110.11 181.90 184.61 252.19 196.31
3.85 104.29 172.47 175.18 242.76 186.88
3.72 98.46 163.03 165.74 233.32 177.44
3.59 92.63 153.60 156.31 223.89 168.01
3.47 86.81 144.16 146.87 214.45 158.57
3.34 80.98 134.73 137.44 205.02 149.14
3.22 75.16 125.29 128.00 195.58 139.70
3.09 69.33 115.86 118.57 186.15 130.27
2.97 63.51 106.42 109.13 176.71 120.83
2.84 57.68 96.99 99.70 167.28 111.40
2.71 51.85 87.55 90.26 157.84 101.96
2.59 46.03 78.12 80.83 148.41 92.53
2.46 40.20 68.68 71.39 138.97 83.09
2.34 34.38 59.25 61.96 129.54 73.66
2.21 28.55 49.81 52.52 120.10 64.22
2.09 22.73 40.38 43.09 110.67 54.79
1.96 16.90 30.94 33.65 101.23 45.35
1.77 14.49 26.67 28.32 82.67 37.96
1.58 12.07 22.39 22.99 64.12 30.57
1.38 9.66 18.12 17.65 45.56 23.17
1.19 7.24 13.84 12.32 27.01 15.78
1.00 4.83 9.57 6.99 8.45 8.39
0.92 4.17 8.32 6.03 7.27 7.24
0.84 3.52 7.07 5.08 6.10 6.10
0.76 2.86 5.82 4.12 4.92 4.95
0.68 2.21 4.57 3.17 3.75 3.81
0.60 1.55 3.32 2.21 2.57 2.66
0.56 1.41 3.11 2.05 2.38 2.47
0.52 1.27 2.90 1.89 2.18 2.29
0.47 1.13 2.70 1.72 1.99 2.10
0.43 0.99 2.49 1.56 1.79 1.92
0.39 0.85 2.28 1.40 1.60 1.73
0.38 0.83 2.22 1.36 1.56 1.69
0.37 0.81 2.16 1.33 1.52 1.64
0.36 0.78 2.11 1.29 1.47 1.60
0.35 0.76 2.05 1.26 1.43 1.55
0.34 0.74 1.99 1.22 1.39 1.51

Yes they dont look right go figure welcome to my life.

[hrcollinsjr]

Alright Dan, that's cool as heck. What was I watching? I'm assuming it's some type of oscilloscope pattern and since everything appeared to be uniform that everything is good! Educate me! What a coincidence, I have two Sun oscilloscope books coming in the mail tomorrow, I hope.

Oops. I watched the video and didn't read your explanation down below until after I posted this. At least it looks like I had a clue.

Harold

[wrench459]

Its a real run going down the road.. thru three gears.
Come on Harold you want me to tell all?
Just think of it as the tip of the iceburg from here on in it gets heavy.

[hrcollinsjr]

Its a real run going down the road.. thru three gears.

So you're (A) running an A/T, (B) Opel 3 spd. from Vega, (C) being cautious in first gear, or (D) you've already destroyed one gear with this awesome power

Come on Harold you want me to tell all?
Just think of it as the tip of the iceburg from here on in it gets heavy.

You can just tell me, I CAN HANDLE the truth, just ask Jack N.!

Harold

[wrench459]

I need to amended post 9
First retard the high rpm ignition timing into a safe range.
Set the A/F ratio to the appropriate spot.
Slowly add back timing till torque drops off then subtract two degrees just for some headroom.

THEN

Three pulls to see consistency of the pulls then average them together to get a baseline.

Then the fun starts changing something be it a carb,intake,cam timing...

Then start all over..some steps could be skipped its up to you.
And No she's not a "Dyno Queen" by any means.

Humm what did I forget?
Harold its a four speed manual for now.

[wrench459]

I'm planing on using the step method of tuning.
Thats why the need for powertrain loss numbers. I'm going to use 15% for now but I believe its closer to 12%. This is a work in progress so they will change more than likely.
So lets get to it.
My little street ride makes approx. 100 rwhp. So lets place a 15 percent load on her with the eddy current dyno and run her through 500 rpm "steps" all the while noting the numbers.
Before we go any further I need feedback with the above technique!
And no the aero numbers are not included yet.

[wrench459]

Finally the five watt light bulb came on. In order to get loss I needed to plot against time duhhh

[GTJIM]

When the engine drives the dyno the power absorbed by the dyno is engine power minus drive train losses.

On the over-run the dyno 'drives' the engine, and measures the amount of power required. This is the 'minus' horsepower actually measured by the dyno and gives a pretty good idea of drive train/engine friction losses. It is shown as 'minus' so that it can be regarded as the 'power loss' due to the drive train and added to power measured in a 'pull' to get and idea of 'total engine power'.

There are always 'conversion factors' to bring measured power to that at standard conditions - as the dyno guy next to me says to his customers: "What conversion factor do you want me to use to get the computed horsepower as high as possible?" Any reading is dependant on the 'factor' used - so only 'pulls' on the same dyno under the same conditions with the same 'conversion factor' have any relevance to each other.

Fiddling with the 'conversion factor' just adjusts bragging rights!