Dyno Jet vs. REAL world horsepower Part 1

[Cali_KR]

Don't want to spoil your day/evening. But here are numbers from my pulls today on my stock 2008 GT500.

 

If you search google, you'll see many articles on why these loaded dynos vs. inertia (Dyno Jet) are a truer number....

 

Here are todays results, I'll be adding CAI, Pulley & SCT tune when I return from Europe in a few weeks,

 

to be continued.....see part 2 for your reading pleasure...

 

Let the hate mail begin....

 

Don't get me wrong, I flippin' love this car, and would NOT trade it for anything, except a Ford GT...

[Cali_KR]

Here is Part 2 for your reading pleasure...

 

I found this on google, not sure who the author was, but much other info substantiates this...

 

I was totally shocked at my numbers, when I explained to the dyno operator what numbers I had seen on this forum. He immediately said, those must have been on a Dynojet, and with a few key strokes, he was able to pull up on his screen what the number would have been reading on a Dynojet, and it was 434HP.

 

**cut and pasted from an online search for information and education purposes only**

This discussion revolves around chassis dynamometer's and is intended to be informative and thought provoking. There are two types of chassis dynamometers on the market, inertia and loading. An inertia dynamometer (such as DynoJet) does not measure torque, but measures acceleration. A loading dynamometer applies resistance that is measured (using some type of strain gauge.)

 

The most often heard discussion is that what factor can be applied to rear wheel horsepower to reflect crankshaft horsepower. This is where we need to understand how the rear wheel horsepower number was derived. Since the DynoJet seems to be widely used and numbers quoted are those from a DynoJet, we are going to use them as our inertia dynamometer example.

 

First it is important to have an understanding of how DynoJet gets their horsepower numbers. Power in mechanical terms is the ability to accomplish a specified amount of work in a given amount of time. By definition, one horsepower is equal to applying a 550 pound force through a distance of 1 foot in one second. In real terms, it would take 1 HP to raise a 550 pound weight up 1 foot in 1 second. So to measure horsepower, we need to know force (in pounds) and velocity (in feet per second). Dynojet's inertial dynamometer measures power according to the terms just described. It measures velocity directly by measuring the time it takes to rotate two heavy steel drums one turn. It measures force at the surface of the drum by indirectly measuring it's acceleration. Acceleration is simply the difference in velocity at the surface of the drums from one revolution to the next. The force applied to the drums is calculated from acceleration using Newton's 2nd law, Force = Mass * Acceleration. Since the mass of the drums is know and acceleration has been measured, Power (horsepower) can now be calculated. Torque is then calculated using the horsepower number: Torque = Horsepower * 5252 / RPM.

 

Once they have these numbers a series of correction factors are applied, some made public, some hidden as proprietary secrets. The public correction factor is the SAE correction factor. This formula assumes a mechanical efficiency of 85%. The formula used is: Where: CF= 1.18 * (29.22/Bdo) * ((Square Root(To+460)/537)) – 0.18. To = Intake air temperature in degrees F, Bdo = Dry ambient absolute barometric pressure. This correction factor is meant to predict output in varying atmospheric conditions and is a +/- 7%. The proprietary correction factor is supposed to reflect the loss of power from the crankshaft to the rear wheels.

 

A Loading Dynamometer applies resistance to the dyne's roller(s) , typically using either a water brake or a current eddy brake. In either case, the amount of force is measure using a strain gauge. The measured force is torque which is a real, indisputable measurement of the actual output at the wheel. Horsepower than can be calculated: Hp = Trq * 5252 / RPM.

 

A Dynamometer can only measure actual power at the output location. Actual power produced AND delivered by an engine will be highest if measured at the crankshaft, lower at the transmission output shaft and even lower, but more meaningful, still, at the rear wheels. The power that you use is the power at the rear wheels. Some Dynamometer companies add to measured rear wheel power readings a factor that is based on ESTIMATED rear wheel power losses (under what power conditions? 3.0 ltr.? 5.0 ltr.? Under coasting conditions? with a 185/70/15 radial tire? a 335/35/18 radial tire? New heavy radial tire vs. worn old, light, racing tire? Who knows?) In short, there is NO meaningful "average" tire to get a correct rear tire power transmission loss measurement for all cars - so obviously, unless they actually measure the power lost in the rear tires, under driven load conditions, NO dyno company should BE ADDING incorrect power figures into the measured power. It's simply wrong. The fact that they add varying amounts of power to the actual, "true" amount of power delivered and measured to the surface of the drive roller creates a situation that makes it an onerous task to compare power figures from different brands of dynamometer systems. On simple inertial dynamometers, some (most) companies use an average for the inertial mass value of the engine, transmission, driveshaft, axles and rear wheels. This is saying that a 4 cylinder, 2.0 ltr. Porsche 914 has the same rotating mass and same rear wheels as a 8 cylinder, 5.0 ltr. Porsche 928 S+4. This simply is not so and wrong.

 

It's expensive to measure frictional losses in the engine and drivetrain, requiring the dyno to be able to drive the vehicle with engine off. Add the cost of a 50+hp electric motor, controlled power supply, etc. It's just not likely that $20,000 dyno will be equipped with that equipment. It is also common for dynamometer companies to add to the power readings by adding transmission and driveshaft losses back into the measured power readings. Some companies make a concerted effort try to measure frictional losses and, optionally, add the power to the measured readings. Other companies - some that would surprise you - say that it's not important and give a blanket, single factor for frictional losses in every engine. Some simply say that there is a meaningful "average" for every car,( 4 stroke/ 4 cylinder/ 4 speed transmission, 4 stroke/ 8 cylinder/ automatic transmission) and apply it to every car and that it is not a significant difference. Blanket estimates of "average" losses and corrections are, quite simply, incorrect. At the upper levels of the industry, (we are talking about $150,000 - $500,000 AC or DC 4 quadrant dynamometers) it is not tolerated - shouldn't be - and needn't be. There is a dyno company that actually has different versions of software that displays their own identical data files as different amounts of power depending on whether you use the DOS version or the Windows version of their software!!

 

True, rear wheel horsepower is the standard of measuring the power that is actually delivered to the rear wheels. It is honest, true, fair and duplicable. It is the ONLY standard that can be duplicated by the entire industry - regardless of the dyno manufacturer. From my experience and that of many others, when comparing True, rear wheel horsepower to DJHP you must apply a factor. It appears that this is a sliding scale based on horsepower but the best estimate is 1.05 to 1.21 (maybe higher). What this means is that for those of you trying to calculate what your crankshaft horsepower is based on DJHP, and are adding 15%, the most common number I hear, you are actually doubling (at least) the factor. Why? Because DJHP already has a puff number added into their DJHP. Lets say DJHP shows 200 hp and you add 15%, you get 230 hp crankshaft horsepower. In reality DJ has already added in 15 or 20% to their 200 DJHP number. How does this help us.? It does not, and is fact harmful to the many dynamometer test facilities that report only what the dyno actually measured. I can not tell you of the many discussions that we have had as to why the horsepower numbers we recorded lower than that of DJ. For those manufacturers that use DJHP as proof of their claims, can you imagine the shock your customers get when the horsepower number of a vehicle tested on a load bearing dyno do not come close to their claim.

 

Proper tuning, especially on highly modified engines greatly affect the power difference. Due to the fact that the DJ dyno's sweep so quickly on sweep hp tests, there is no way to properly tune a fuel map. What you get is the acceleration and full throttle maps both triggered during the test, ending up over-rich, affecting the horsepower. The other factor that needs to be taken into account is that DJ dynos assume that every vehicle has the same rotating mass - they don't - and that disregard is another reason why the hp conversion figures are different. The most accurate measurement of rear wheel horsepower is in Steady State Mode (inertia is not a factor in power equation.) The inertial mass changes on each car affects the DJ power, but not the true, rear wheel horsepower. There's another message in the above example, besides the average true, rear wheel horsepower to DJHP conversion factor - It's up to the more experienced reader to figure it out.

 

Chassis dyne HP, What is it? What to call it? DynoJet = "DJHP". It's not really proper to call "DJHP" "rwhp", as neither the Mustang, DynoJet, Fuchs, Superflow or Land and Sea will necessarily produce the same numbers as a DJ dyno, except by luck - and the whole idea of true, rear wheel horsepower is that EVERY dyno manufacturer HAS the capability to provide those numbers! The Superflow chassis dynes, the Mustang, Land and Sea are all capable of measuring power in steady state mode and producing the same numbers - they all measure torque. Torque x rpm / 5252 = horsepower. We've not diddled with physics! The only factor that is added to the measured reading, in true, rear wheel horsepower, is the additional energy (dyne parasitics) required to spin the dyno(s) roller to whatever speed the roller is turning at - logical, proper and required for any measuring instrument, torque x rpm / 5252 = horsepower + parasitic power = true, rear wheel horsepower.

 

Chassis dyne HP, What can inflate HP readings on a dyno, but not really make more engine power in the real world? A few things can affect HP when using inertia dynos (not a dyne in Steady State Mode) to measure power (what else would you do??:-): Changing to light, worn race rear tires will improve power output on an inertia dyno, but, not improve real world top speed. A heavier (brand new street) tire that replaced the above, light, worn tire, will decrease measured power on an inertia dyno, but not decrease real world top speed. Lighter wheels are a good thing! Better acceleration in lower gears, especially 1st and 2nd (accelerating less inertial mass!). Better handling is possible, too! Driving hard on worn, light tires is foolish and is not being recommended.

 

Problems with Inertia dyno test procedure and fuel injected vehicles: A Sweep Test (hold throttle wide open and sweep from low rpm to high rpm) will often trigger the Acceleration Fuel Map, along with the Main Fuel Map, causing the fuel mixture readings to indicate dyno operator that the motor is overly rich. This would cause the tuner to lean out the main fuel map. Of course, in the real world, upper gears, the acceleration rate of the engine is much slower than what they tested, doesn't trigger the Acceleration Fuel Map, and the engine ends up a lot leaner in reality in top gear. It's not that common of a problem, since most people never drive that fast for that long to cause engine damage. Work around: Tune full throttle fueling in real world usage at dragstrip (to best trap speed) or in Steady State Mode on different dyno.

 

You can optimize tuning for a DJ dyno and make big numbers - and you can tune the engine to make the best power under load on a load bearing dyno and blow off the big DJ dyno numbers. Can a tuner cheat and make a load bearing dyno read higher? The only way that could happen is in a Sweep Test - Sweep Tests are the least reliable of all tests, period. There is NO question about that. Since the Rotating Mass is a variable in a Sweep Test (NOT a Steady State Test!), the actual inertia factor entered affects the final HP figure - Tell the software that the vehicle has a lot of rotating mass to accelerate, and the HP number increases. (torque, rpm, acceleration rate and mass are the factors) - just like DJ dyno ignoring the difference in mass of all cars - So - true HP, again - Steady State Test - No acceleration, mass makes no difference, anymore. Torque, RPM and dyne parasitics. Period. True. Can you make a Steady State Test read higher? Really hard to do - The software will NOT take data unless speed and load are completely stable - eliminating cheating. As far as atmospheric conditions making a +/- 10% difference? Unless you REALLY mess with the barometric pressure (and you can look at every atmospheric factor on the test report sheet - it's hard coded to display - and not an option), it is simply, absolutely impossible to do without obvious evidence. Are final tuning optimal dyno settings different on an Inertia dyno vs. a load bearing dyno? For many reasons, final tune settings are different - and, since most load bearing dyno's will do both , there is a choice of tests - from a DJ style Sweep Test to Steady State. Having a choice of those types of tests to do and seeing what the results on the track are, most tuners will choose the Steady State Test over a Sweep Test. Without a doubt - the Steady State test Mode is the most consistently superior method of tuning - anybody who has the capability to do it will echo that sentiment - it's only an arguable point with those who can't do it properly. One of the reasons why the load bearing dyno will provide settings that work better in the real world is that combustion chamber temperatures are more in line with the actual operating temperatures that the engine.

 

Does altitude make any difference at all in horsepower? The engine couldn't give 2 hoots at what altitude it is tested at - it only cares what the air pressure, temperature and humidity is. Sea level at 28.02 inches baro is exactly the same as 4000 ft at 28.02 inches, as far as the engine is concerned. When tested at 5000 ft, we get virtually exactly the same power (corrected to atmospheric conditions, of course) as we do at sea level - It's just about 24%-25% less on the track! I am confused why some dyno operators insist on putting altitude on their charts and swear that it's a factor.

 

Crankshaft horsepower vs. true rear wheel horsepower. That's a tough one. As each vehicle is different, the best way is to dyno the engine and then dyno the vehicle to see exactly what the loss is. The best estimate I can give you based on experience and research is take crankshaft horsepower, subtract 14.5% ( search SAE ), take that, and subtract around 10% to 15% and you'll get about true horsepower at the rear wheels. The actual formula contains a curve for power loss through gears and there's another curve for power lost in a tire. Remember, too - that unless you dyno your engine you are only likely to get a crankshaft number from the manufacturer and that's probably a "good" one that the marketing department is providing.

[1fastford]

Wow that was a really nice read. No hate mail here. I fully agree with most of it.

 

I just don't want people to misunderstand something. Dynojet does make many load bearing Dynamometer's with a Eddy Current Load Absorption Unit which measures torque quit well. I no this because I have one. I think your post suggests dynojet dyno's are not load bearing. I just want to clarify that for people reading this post. The numbers are different from the Eddy Current dynojet dyno's than they are from thier enertia dynojet's. I don't believe any dyno should be that far off on their numbers. Thay are usually only slightly off on the overall numbers. Like maybe 20 hp at the most. Other wise I feel the dyno should be calibrated or something.

 

I have been tuning and building racing engines for 15 years. My main field is building racing heads for motorcycles with many racing world championships. I have worked in both fields with Yoshimura, Ford Cosworth, Bmw, Honda, Kawasaki, Suzuki, Ktm, Edelbrock, hendrick, Porsche and even ferrari. Heads are where all the tq and hp are made. The rest of the motor just has to hold up to the power. I am not saying it's not a combined package but heads are where its at. I mean I am talking about little stuff like valve angles, tulip angles, margin angles, valve seat angles, radius', titanium valves, ampco seats, copper-beryllium seats and much more. I could go way deeper but it just doesn't matter.

 

Dynos are only a tool for us tuners I dont care what the numbers are. We (tuners) don't even care about the numbers. We only care about air fuel, timing, Load, and rpm. I read all this stuff and people talk about hp numbers all the time. If your going to talk about a number then talk about the TQ number. TQ is everything just like you said in your post. I just feel a dyno is for tuning and it doesn't matter what numbers it spits out. Dynojet dyno's are fine for tuning. Most every tuner takes into account thier dyno for tuning. If you are a fifth gear wide open type of person then tell the tuner and make sure you are on the rich side of a tune. If you are a drag racer then tell the tuner and he will probably set you up on the lean side a bit.

 

I really like your post and I hope people read it and enjoy it as much a I did.

[Tucker]

3 things

1) don't read too much into what one dyno reads Vs. another. We have a Dyno Dynamics here local and NO GT500 has ever got numbers like that. I'm sorry to say this, but your numbers ARE very low. To find out if it's that dyno or your car I would check with another dyno.

2) you can not use a math formula to see what your Dyno Dynamics, Mustang, Superflo or any numbers "would be" if it was a dynojet.

3) this forum is full of results on Dynojets, Dyno Dynamics, Superflo and Mustang dynos, not just dynojets. For your dyno operators first reaction to make excuses throws a red flag. It says he has heard this before from other locals and blames Dyno jet for the low numbers on his dyno. Think about it, if his dyno reads 40 RWHP less then all other dynos in the area he's going to lose business.

 

I'm a firm believer a dyno if for testing, not "mine is bigger then yours", but what you also need to know is if the dyno your using is accurate. Ask for other graphs of GT500's, Cobras, GT's or any car you can find that is close to the average, they have done.

 

For instance, we use a dynojet and have a very good friend with a Dyno Dynamics. Wehave had the same car on each dyno countless times with very close numbers, like 5-10, not 40-50.

 

Please don't take my post personal. My 08 pulled 444 as have tons of others and some on my local Dyno Dynamics. If you want to use this dyno shop, fine, but for your own piece of mind to see if your car is off, go to another dyno. $75 is cheap insurance before you add all those parts.

 

Good luck and don't let this turn into a back and forth dyno numbers thread.

 

Jay

[Master Yoda]

This article/author seems to go to long extremes to explain the Dyno Jet & how it works & the faults of it but not the other way around.

 

Also when he (the author) makes the statement of "Does altitude make any difference at all in horsepower?" & then replies with "The engine couldn't give 2 hoots at what altitude it is tested at." All I'll say is ask any NHRA engine tuner why it's harder to tune a motor in Colorado then Gainsville, FL & he'll say the air is thinner (less oxygen) at a higher altitude & makes less HP.

 

The GT500 motors are tested in Romeo & are rated at 511 to 517 Flywheel HP off the line, so now add that into your math

[KCMO-GT500]

I guess I would be more impressed by that lengthy explanation if it did not read so much like a defense or publicity column. I'll admit I'm not an experienced engine guy, but I do have a couple of engineering degrees and have a decent ability to cut through to the heart of things. None of us are trying to come up with crank hp anyway, so half of that column really doesn't seem to be needed here. I also fail to see much solid information to back the claims, or even to allow someone to check on the claims.

 

I guess I am actually agreeing with the posted comments. Dynos (the same one on the same day) are a good way to check the results of modifications. I also trust Jay's experience since he really has a lot of experience with these engines, and I have never known him to mislead someone.

 

For the original poster, there are some easy ways to screw up a dyno reading on these engines, so it is helpful to use a dyno operator who has some experience with them. Good luck with your future mods, but I would certainly recommend same day before and after results. You also need to ask yourself if crank hp from factory is over 500 (and I hope no one is claiming that the factory numbers are false) and dyno results are 120 - 130 less than that, is it realistic to say that is due to drivetrain inefficiency, or is something else in play?

 

John

[shel-b001]

Great topic , I`am & probably alot others are on a learning curve when comes to Dyno`s. This is what makes this forum the `BEST` as we have so many knowledgeable people . Thanks very interesting reading.

[rsfdiver]

When it pops wheelies then it is enough...?

[VNMOUS1]

I've got 50 bucks that says they didn't have a strong ISOLATED lead on the car. I had my car on a couple of different dynos and had sub-400 readings on both. THEN I spoke to someone that knew what they were doing. Mine immediately popped to 445 on one of the same dynos. The leads have to be split and isolated and the coilpack covers have to be back on good and tight so as to keep the packs from "rattling". You'll get poor readings otherwise....PLUS heat is a killer on this car. You'll easily lose 10-30 rwhp due to heat soak. Cars that just got to the dyno after being in traffic or back-to-back runs will always show this.

 

As Jay said, go get another look at a baseline before you start playing around with it. Dyno to dyno numbers mean squat, except for the fact that you have hundreds of them that have all baselined at 420-445 and that should be your litmus test. Once you know that you're in the ballpark, have fun. Then, measure your performance with your butt, ETs and trap speeds.

 

 

bj

[BanditSRT8]

Don't want to spoil your day/evening. But here are numbers from my pulls today on my stock 2008 GT500.

 

If you search google, you'll see many articles on why these loaded dynos vs. inertia (Dyno Jet) are a truer number....

 

Here are todays results, I'll be adding CAI, Pulley & SCT tune when I return from Europe in a few weeks,

 

to be continued.....see part 2 for your reading pleasure...

 

Let the hate mail begin....

 

Don't get me wrong, I flippin' love this car, and would NOT trade it for anything, except a Ford GT...

 

 

I feel your pain. Mine dynod on a Mustang dyno today at a measly 379rwhp.

[DDT]

Ford stands behind advertised 500+ Flyweel HP on our engines...........

 

With a 15% power reduction;

 

The rear weel HP #s need to be at least 425, no matter what dyno is used??????????????

[Tucker]

Ford stands behind advertised 500+ Flyweel HP on our engines...........

 

They do?

[RUFDRAFT]

[DDT]

 

They do?

 

Maybe "Stand Behind " is missleading???????????

 

I guess correct phrase is "ADVERTISED"...........

 

 

Feel better now???????????????

[Justin00Stang]

I can load my Dynojet and slow down a pull by a few percent, or double the time it takes, or totally bring the car to its knees. Is my DJ still inferior?

 

My big problem with other dynos, like DD, MD, SF, is they can be adjusted to read whatever the operator wants them to read. This is probably why several have reported DDs that read "normal" and your DD read low. The DJ software does not all the operator to tweak the roller mass and greatly effect the power numbers, like other dyno's software let you do. This is what really matters to me, because I see way too many off brand dynos that read funny.

[srk1959]

I like the Dynojet #s because them seem to be pretty close to what Ford figures for crankshaft hp after driveline loss. A lot of the others seem to be way low or way high which would mean to me that Fords numbers are off, which I think they are accurate.....just my opinion I admit I am not a dyno expert.

[68fastback]

Under "standard" SAE conditions (which I think is something like 70*F, sea-level, 0% humidity, 29.someting baro, etc) the GT500 motor consistently makes 511-517 at the crank. That's 440-something at the wheels.

 

Heat (ambient and soak), low barometric pressure (both weather-caused and altitude-based), humidity/water-grains will all reduce power and does so quite equitably for everyone. Still that seems very low, imo ...worthwhile trying another place/dyno on the outside chance there's some issue with the engine vs the dyno/operator.

 

Good luck! Let us know what you find out ...

 

Dan