WHAT KIND OF GAINS FROM MODS?
11-02-2005, 12:39 AM
#21
2nd Gear Member
Join Date: Jun 2005
Location: No. Virginia
Posts: 186
RE: WHAT KIND OF GAINS FROM MODS?
ORIGINAL: INTERCEPTOR498
So Mac10chap, if your running about 314HP with those mods, what do you think these cars are pushing for HP stock at the wheels? I'm assuming the factory "300" horsepower rating is at the flywheel?
So Mac10chap, if your running about 314HP with those mods, what do you think these cars are pushing for HP stock at the wheels? I'm assuming the factory "300" horsepower rating is at the flywheel?
there are too many anomalies to factor in when rating the RWHP.
fine print...
unless otherwise stated: rear / front wheel horsepower
757GT, I have heard of some a bit higher but gould be bad dyno results, Mine pulled 254 RWHP Stock (Temp 84, high humid). With CAI, UD pullies, Charge Motion plates, and SCT Tune it's at 292 RWHP (Temp 62, low humid)
looking at getting these before spring ( 62mm TB, Plasma Booster, Aluminum Drive shaft, TCI Torque converter, 3.73 gears, xpipe + High flow cats)
11-02-2005, 01:05 AM
#22
2nd Gear Member
Join Date: Jun 2005
Location: No. Virginia
Posts: 186
RE: WHAT KIND OF GAINS FROM MODS?
Dyno Thoughts and HP Losses
After reading various posts and publications on dynos and horsepower, I feel I should put forth a few observations:
Chassis dynos are great tuning aids but they only give a approximation of power output as some of the important variables are not accurately controlled. Certain magazines seem to think that results obtained from chassis dynos are the gospel. They are not. In one recent independent test, hp figures varied by 11% simply by doing the runs in different gears and in another test, results varied by almost 4 % by doing the runs with a different wheel/tire combination. Tire alignment has been shown to affect results up to 3% as well. Note that Engine hp DID NOT change here yet the dyno recorded an increase in hp at the wheels. A change in wheels/tires also does not affect true, wheel hp either, only the rate of change on the rollers and the vehicle acceleration on the road. One can only conclude that inaccurate moments of inertia and correction factors are being used.
On intercooled, turbo cars, there is usually insufficient airflow to ensure accurate results due to charge temperature variation which can be substantial. Even coolant temperatures may not stay down during the run which can affect power outputs considerably. The rate of acceleration is also important on turbo cars to be sure that the boost is not lagging the engine rpm. With RPM climbing too quickly, the boost has not reached a peak value so the hp figure is again inaccurate. Turbo cars should therefore be tested in top gear.
Without proper temperature stability and accurate moments of inertia on the rotating components, there CANNOT be accurate results as the scientific method is no longer being applied.
When all things are kept the same between runs and you get a tangible gain, it is a gain at least. How much, is open for discussion. It is important to note that as the oil temperatures in the engine, transmission and differential increase, friction usually decreases. This manifests itself as an increase in power at the rollers on each subsequent test. This factor should be accounted for when doing back to back runs. It may look like you are gaining some power on each run by making other changes when in fact this is due to reduced oil viscosity. When using a chassis dyno, always use the same gear and tires and wheels and start the runs from the same speed or RPM. Re-baseline periodically to see what temperature increases have done to power output.
Chassis dynos are quick and easy to hook up but have many of the above failings. They do not possess the accuracy of a properly calibrated engine dyno which has a more carefully controlled environment and condition set. Obviously, most non-professionals don't want to be yanking engines to use an engine flywheel dyno so chassis dynos do have their place.
Flywheel vs. Wheel HP
As most people know, there are power losses through the drivetrain so wheel hp is always lower than flywheel hp. Front wheel drive cars with transverse engines tend to be more efficient than most rear drive configurations due to the layout of components. However most publications overestimate these losses considerably.
Most rear drive cars have a 1 to 1, 4th gear which means that the power path goes directly through the mainshaft of the transmission. The only losses here are bearing drag which is less than 0.5% and the viscous drag of the gears running through the oil which is about 1% with hot oil. Indeed, published data indicates a transmission efficiency of 98 to 98.5% for conventional transmissions in 4th gear.
Additionally, automatic transmissions can account for about 10% loss, over the manual trans
Losses within the driveshaft account for about 0.5% if they are properly aligned, balanced and with fresh U-joints.
Differential losses in the commonly used Hypoid type gearset is in the order of 6 to 10%.
Tire pressure and wheel alignment can have very significant effects on losses at the rollers. Tire pressures should be set the same between each test. Tire rolling resistance varies inversely with speed, another factor not taken into account by most chassis dynos when applying phantom flywheel hp formulas.
Comparing the Numbers
Many novices are quick to compare hp numbers between chassis and engine dynos and come up with all sorts of wild conclusions about drivetrain losses. These comparisons are essentially meaningless. Inertial dynos are based on the sound scientific priciple of accelerating a certain mass with a known moment(distance) over a given time. The rate of acceleration of that mass and moment is a result of the force applied (torque). If the RPM is known, HP can be calculated. On an inertial chassis dyno, it is virtually impossible to calculate the the moment of inertia of every tire, wheel, gear, joint , axle and shaft in the power train between the crankshaft and roller, therefore its results cannot offer an accurate HP figure. Even with coastdown drag measurements, these cannot be accurately calculated as different factors are affected in different ways. Some are proportional, some are inverse squared functions etc. Inertial engine dynos offer a very accurate figure if properly calibrated as only the flywheel's moment of inertia needs to be calculated and added to that of the billet. Water brake or eddy current dynos generally measure force (torque) directly through a ram or strain gauge so moments of inertia are not important on these in fully loaded tests.
Concluding that there was a 25% drivetrain loss by comparing HP achieved on an inertial chassis dyno and that obtained on an engine dyno is fundamentally flawed in that the chassis dyno numbers are highly suspect in the first place.
Other things to watch are correction factors applied for altitude, barometric pressure and temperature. These factors are NOT the same for atmo and turbo engines. Using atmo factors inflates the true, corrected HP figures on a turbo engine. In fact, look at the correction factor applied on your dyno sheets and see if they make sense. Many shady dyno operators simply enter a phantom correction factor to make the customer happy. This is a case where the dyno sheet DOES lie. Chassis dynos are essentially for tuning purposes, they are not well suited to giving an accurate hp figure.
After reading various posts and publications on dynos and horsepower, I feel I should put forth a few observations:
Chassis dynos are great tuning aids but they only give a approximation of power output as some of the important variables are not accurately controlled. Certain magazines seem to think that results obtained from chassis dynos are the gospel. They are not. In one recent independent test, hp figures varied by 11% simply by doing the runs in different gears and in another test, results varied by almost 4 % by doing the runs with a different wheel/tire combination. Tire alignment has been shown to affect results up to 3% as well. Note that Engine hp DID NOT change here yet the dyno recorded an increase in hp at the wheels. A change in wheels/tires also does not affect true, wheel hp either, only the rate of change on the rollers and the vehicle acceleration on the road. One can only conclude that inaccurate moments of inertia and correction factors are being used.
On intercooled, turbo cars, there is usually insufficient airflow to ensure accurate results due to charge temperature variation which can be substantial. Even coolant temperatures may not stay down during the run which can affect power outputs considerably. The rate of acceleration is also important on turbo cars to be sure that the boost is not lagging the engine rpm. With RPM climbing too quickly, the boost has not reached a peak value so the hp figure is again inaccurate. Turbo cars should therefore be tested in top gear.
Without proper temperature stability and accurate moments of inertia on the rotating components, there CANNOT be accurate results as the scientific method is no longer being applied.
When all things are kept the same between runs and you get a tangible gain, it is a gain at least. How much, is open for discussion. It is important to note that as the oil temperatures in the engine, transmission and differential increase, friction usually decreases. This manifests itself as an increase in power at the rollers on each subsequent test. This factor should be accounted for when doing back to back runs. It may look like you are gaining some power on each run by making other changes when in fact this is due to reduced oil viscosity. When using a chassis dyno, always use the same gear and tires and wheels and start the runs from the same speed or RPM. Re-baseline periodically to see what temperature increases have done to power output.
Chassis dynos are quick and easy to hook up but have many of the above failings. They do not possess the accuracy of a properly calibrated engine dyno which has a more carefully controlled environment and condition set. Obviously, most non-professionals don't want to be yanking engines to use an engine flywheel dyno so chassis dynos do have their place.
Flywheel vs. Wheel HP
As most people know, there are power losses through the drivetrain so wheel hp is always lower than flywheel hp. Front wheel drive cars with transverse engines tend to be more efficient than most rear drive configurations due to the layout of components. However most publications overestimate these losses considerably.
Most rear drive cars have a 1 to 1, 4th gear which means that the power path goes directly through the mainshaft of the transmission. The only losses here are bearing drag which is less than 0.5% and the viscous drag of the gears running through the oil which is about 1% with hot oil. Indeed, published data indicates a transmission efficiency of 98 to 98.5% for conventional transmissions in 4th gear.
Additionally, automatic transmissions can account for about 10% loss, over the manual trans
Losses within the driveshaft account for about 0.5% if they are properly aligned, balanced and with fresh U-joints.
Differential losses in the commonly used Hypoid type gearset is in the order of 6 to 10%.
Tire pressure and wheel alignment can have very significant effects on losses at the rollers. Tire pressures should be set the same between each test. Tire rolling resistance varies inversely with speed, another factor not taken into account by most chassis dynos when applying phantom flywheel hp formulas.
Comparing the Numbers
Many novices are quick to compare hp numbers between chassis and engine dynos and come up with all sorts of wild conclusions about drivetrain losses. These comparisons are essentially meaningless. Inertial dynos are based on the sound scientific priciple of accelerating a certain mass with a known moment(distance) over a given time. The rate of acceleration of that mass and moment is a result of the force applied (torque). If the RPM is known, HP can be calculated. On an inertial chassis dyno, it is virtually impossible to calculate the the moment of inertia of every tire, wheel, gear, joint , axle and shaft in the power train between the crankshaft and roller, therefore its results cannot offer an accurate HP figure. Even with coastdown drag measurements, these cannot be accurately calculated as different factors are affected in different ways. Some are proportional, some are inverse squared functions etc. Inertial engine dynos offer a very accurate figure if properly calibrated as only the flywheel's moment of inertia needs to be calculated and added to that of the billet. Water brake or eddy current dynos generally measure force (torque) directly through a ram or strain gauge so moments of inertia are not important on these in fully loaded tests.
Concluding that there was a 25% drivetrain loss by comparing HP achieved on an inertial chassis dyno and that obtained on an engine dyno is fundamentally flawed in that the chassis dyno numbers are highly suspect in the first place.
Other things to watch are correction factors applied for altitude, barometric pressure and temperature. These factors are NOT the same for atmo and turbo engines. Using atmo factors inflates the true, corrected HP figures on a turbo engine. In fact, look at the correction factor applied on your dyno sheets and see if they make sense. Many shady dyno operators simply enter a phantom correction factor to make the customer happy. This is a case where the dyno sheet DOES lie. Chassis dynos are essentially for tuning purposes, they are not well suited to giving an accurate hp figure.
11-02-2005, 01:27 AM
#23
3rd Gear Member
Join Date: Aug 2005
Location: New Orleans, La
Posts: 740
RE: WHAT KIND OF GAINS FROM MODS?
Accurate post[sm=closed.gif] Your research is pretty on the dot.
But next time add divide it into chapters. I had to take a coffee break before I could finish it.
[sm=icon_blah.gif]
But next time add divide it into chapters. I had to take a coffee break before I could finish it.
[sm=icon_blah.gif]
11-02-2005, 03:06 PM
#27
2nd Gear Member
Join Date: Jun 2005
Location: No. Virginia
Posts: 186
RE: WHAT KIND OF GAINS FROM MODS?
ORIGINAL: 757GT
SWIEDUWI, is yours an auto?
SWIEDUWI, is yours an auto?
[sm=interesting.gif]Here Is a great Artical on the 5R55S Auto Trans. Explans in detail why this is a good Drag Trans.[sm=insomnia.gif]
ORIGINAL: INTERCEPTOR498
That was some good information. I'm just disgusted with the stock numbers.
That was some good information. I'm just disgusted with the stock numbers.
11-02-2005, 04:20 PM
#29
4th Gear Member
Join Date: Oct 2005
Location:
Posts: 1,189
RE: WHAT KIND OF GAINS FROM MODS?
your the the voice of reason! i've long told my friends not to pay attention to advertised hp gains from products. if they were true almost every 5.0 on the street would make 450hp! do your research and talk to as many people as you can that have the mod you are thinking about.
11-02-2005, 08:27 PM
#30
2nd Gear Member
Join Date: Jun 2005
Location: No. Virginia
Posts: 186
RE: WHAT KIND OF GAINS FROM MODS?
757GT -
Mine Is Mineral Grey
Check out my website
spyder7724,
True True, Remember Mods are 20% Actual HP and 80% HP in our Minds. We Want to beleive that the advertisment is true
but if it makes us happy, then don't fight it, Just do it and have fun. thats what these cars are all about - right..... Having Fun..
don't forget to add some [sm=bling.gif] too, that always adds a few +Mental HP + [sm=groupwave.gif]
Mine Is Mineral Grey
Check out my website
spyder7724,
True True, Remember Mods are 20% Actual HP and 80% HP in our Minds. We Want to beleive that the advertisment is true
but if it makes us happy, then don't fight it, Just do it and have fun. thats what these cars are all about - right..... Having Fun..
don't forget to add some [sm=bling.gif] too, that always adds a few +Mental HP + [sm=groupwave.gif]