gearing vs torque
I have fuzzy eyebrows
Joined: Oct 2001
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Bitemark46...going from 4.10 to 4.56 will still affect the dyno...however it may be only 3-4 hp max. Its tough to see that small a diff on a dyno from day to day unless you do alot of runs and avg them out. You say you lost 1-3 mph? The 3mph seems a bit high. There may be other things besides the things we discussed above. Like being a little farther out of you powerband in 4th gear as you go through the traps with the 4.56s. Not sure where your car likes to be shifted. Like I said before...everything is a tradeoff. You could put the 4.10s back in and do more work on your suspension to try and eqaul your 60 foots with the 4.56s.
28" tires may be an option....although changing tire height is the same as changing final gear ratios. 4.56s with 28" tall tires may eqaul out in final drive to 26" tires and 4.10s...however that combo of taller tire with more sidewall/contact patch may give you the launch you need as well as the MPH on the big end. I am really just guessing though...hellifino its a damn mustang!
28" tires may be an option....although changing tire height is the same as changing final gear ratios. 4.56s with 28" tall tires may eqaul out in final drive to 26" tires and 4.10s...however that combo of taller tire with more sidewall/contact patch may give you the launch you need as well as the MPH on the big end. I am really just guessing though...hellifino its a damn mustang!
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if it's cheap & reliable, it ain't fast, if it's fast & cheap, it ain't reliable, if it's fast & reliable, it ain't cheap
if it's cheap & reliable, it ain't fast, if it's fast & cheap, it ain't reliable, if it's fast & reliable, it ain't cheap
The H N I C
Joined: May 2002
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How about this, Dyno numbers are bull shit. Only good for one thing and that's a/f.......Other then that, all that matters is the time slip at the track.
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I have fuzzy eyebrows
Joined: Oct 2001
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How about this, Chet asked a question he wanted an answer to so I attempted to answer it! Nice input to the discussion..Thanks! 
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if it's cheap & reliable, it ain't fast, if it's fast & cheap, it ain't reliable, if it's fast & reliable, it ain't cheap
if it's cheap & reliable, it ain't fast, if it's fast & cheap, it ain't reliable, if it's fast & reliable, it ain't cheap
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Originally posted by "speed_daemon1"
as goofy as this sounds, I have personaly whitnessed it.
If you take the tach signal out, the dynojet will still give you hp numbers but no torque, if it truly measured torque and calculates hp, how does it pull that off?
My best guess is the dynojet software measures acceleration over time to calculate hp and then calculates torque from that using the tach signal.
as goofy as this sounds, I have personaly whitnessed it.
If you take the tach signal out, the dynojet will still give you hp numbers but no torque, if it truly measured torque and calculates hp, how does it pull that off?
My best guess is the dynojet software measures acceleration over time to calculate hp and then calculates torque from that using the tach signal.
Measuring Horsepower
If you want to know the horsepower of an engine, you hook the engine up to a dynamometer. Horsepower is pure theory--it's an arbitrary number. A dynamometer places a load on the engine and measures the amount of TORQUE that the engine can produce against the load. Some dynamometers measure the acceleration rate of a known mass at a given rate of speed--like a DynoJet. The basic formula used is:
Force (ft/lbs) = MASS (lbs) X ACCELERATION (ft/second)
Since the MASS of the roller is known, and the ACCELERATION rate can be measured with simple sensors, the Force exerted on the roller in "ft/lbs" is then measured. With in input from the engine such as RPM--we then input the data and make up "horsepower". There are other correction inputs like atmospheric pressure, humidity, etc...but we won't go into that here. The formula most widely accepted becomes:
Here's more info on this:
http://www.eidnet.org/local/westers_garage/horsepower.htm
Wherever I may roam...
Joined: Mar 2001
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Originally posted by "The^Thief"
This should help claify that Dyno's don't meausre HP they measure torque and use that to create a HP curve.
Measuring Horsepower
If you want to know the horsepower of an engine, you hook the engine up to a dynamometer. Horsepower is pure theory--it's an arbitrary number. A dynamometer places a load on the engine and measures the amount of TORQUE that the engine can produce against the load. Some dynamometers measure the acceleration rate of a known mass at a given rate of speed--like a DynoJet. The basic formula used is:
Force (ft/lbs) = MASS (lbs) X ACCELERATION (ft/second)
Since the MASS of the roller is known, and the ACCELERATION rate can be measured with simple sensors, the Force exerted on the roller in "ft/lbs" is then measured. With in input from the engine such as RPM--we then input the data and make up "horsepower". There are other correction inputs like atmospheric pressure, humidity, etc...but we won't go into that here. The formula most widely accepted becomes:
Here's more info on this:
http://www.eidnet.org/local/westers_garage/horsepower.htm
Originally Posted by speed_daemon1
as goofy as this sounds, I have personaly whitnessed it.
If you take the tach signal out, the dynojet will still give you hp numbers but no torque, if it truly measured torque and calculates hp, how does it pull that off?
My best guess is the dynojet software measures acceleration over time to calculate hp and then calculates torque from that using the tach signal.
If you take the tach signal out, the dynojet will still give you hp numbers but no torque, if it truly measured torque and calculates hp, how does it pull that off?
My best guess is the dynojet software measures acceleration over time to calculate hp and then calculates torque from that using the tach signal.
Measuring Horsepower
If you want to know the horsepower of an engine, you hook the engine up to a dynamometer. Horsepower is pure theory--it's an arbitrary number. A dynamometer places a load on the engine and measures the amount of TORQUE that the engine can produce against the load. Some dynamometers measure the acceleration rate of a known mass at a given rate of speed--like a DynoJet. The basic formula used is:
Force (ft/lbs) = MASS (lbs) X ACCELERATION (ft/second)
Since the MASS of the roller is known, and the ACCELERATION rate can be measured with simple sensors, the Force exerted on the roller in "ft/lbs" is then measured. With in input from the engine such as RPM--we then input the data and make up "horsepower". There are other correction inputs like atmospheric pressure, humidity, etc...but we won't go into that here. The formula most widely accepted becomes:
Here's more info on this:
http://www.eidnet.org/local/westers_garage/horsepower.htm
Obviously it doesn't reference the curve against rpm, it does it against mph.
However I have seen dyno charts against rpm where the tq curve has spots where it completely dissapears, John says that happens when the inductive pickup isn't reading any spark, but the hp curve continues on a normal path.
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hmmm, well, HP is TQ over time, so if it knows the rollers weigh 5k lbs and it takes 10 seconds to accelerate them to a known speed (known by the computer) then it knows how much HP it produced. But it may not know where in the powerband the motor was accelerating the rollers more or less, and thus cannot find a torque curve. Just a guess.
