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Discussion Starter · #1 ·
After a long year (mainly last year) where I had to replace the diff after it exploded, replaced the gearbox after it lost some teeth, replaced the clutch... may aswel, and then finally i replaced the entire engine as the old girl had enough.

When I had the engine made, its got, new pistones etc, port polish and stage 2 crow cam, valve springs and port the manifold. So she is practiacally a new engine.


Got it dynoed yesterday, it made 119kw and 401 nm at the rear wheels.

Happy with that as its a beautiful car to drive...
 

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Discussion Starter · #4 ·
I'm difinatly happy with the results, but I do realise that if i dynoed it somewhere else might get a different result..... but till that day, those will be my power figures... lol
 

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IV SEEN 4 XR6T DYNO RUNS ON THREE DIFFERENT DYNOS AND ALL GOT JUST OVER 1000Nm of torque. it seems for some unknown reason that dynos double the flywheel torque at the wheels..they have 500Nm standard. must just be one of those things..
 

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Nice figures! From what I have been told rear wheel figures can vary, depending on diff ratio and tyre size, anyone confirm this?
Also, you shouldn't compare one dyno to another, as they can be way different. Watch out for operators that fudge figures by putting in ridiculous values for the temp and barometric pressure of the day.
If you wanna compare 2 cars, dont use a dyno, use a dragstrip.
 

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Discussion Starter · #10 ·
smally351 said:
Nice figures! From what I have been told rear wheel figures can vary, depending on diff ratio and tyre size, anyone confirm this?
Also, you shouldn't compare one dyno to another, as they can be way different. Watch out for operators that fudge figures by putting in ridiculous values for the temp and barometric pressure of the day.
If you wanna compare 2 cars, dont use a dyno, use a dragstrip.


Agree with the dragstrip! As for the diff, its a 3.45 and 235 rear tyres on 17's, whether that has any bearing or not, iono.
 

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Look... torque figures will depend on what gear the car was in when it got dyno'd. Everyone thinks that power will change with gears, but this is a common misconception. Apart from different frictional losses in each gear, the power figure will stay the same plus or minus a few Kw. Two things, however, will change: Torque and wheel rpm. A gearbox is either a speed multiplier or torque multiplier. In most 5 speeds, 1st-3rd are the torque multipliers. 4th won't multiply anything (1:1) and 5th will be a speed multiplier (overdrive). Diffs are torque multipliers.
A gear ratio of 2.39:1 (1st in the falcon autos) means that the velocity ratio of input to output is 2.39:1- for every 2.39 revs of the input, output does 1 rev. This also means that at the output shaft there is 2.39 times as much torque.
Now power is a result of torque x angular velocity. If a gear halves the torque but doubles angular velocity (rpm essentially) compared to the previous one then the power figure must stay the same. Thus power figures are the same through every gear. Torque, on the other hand, will vary depending on what gear the car is in, what diff ratio and the diameter of the tyres.
The ONLY reasonable way to get an idea of torque at the flywheel is to use an engine dyno and trying to quote engine torque figures from anything else is pretty much useless and misguiding.
Sorry...don't mean to be harsh- just sick of the all the stupid hype you read in magazines.
 

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I understand what you're saying and totally agree about magazine hype.

Would be interesting to see what my mates ute would do on the dyno if we changed from 4.56 diff gears to 2.75. In theory it wouldn't change much.

You hear a lot of theories about power losses thru' the drivetrain too. Most of em seem to be a percentage. But that means the more power you make, the more it takes to drive the trans and diff!! I read somewhere a figure of about 90HP loss thru' a c4 and a 9inch. God I hate rear wheel figures.

At the end of the day, a dyno is a tuning tool. You don't race dyno's, you race cars.
 

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madmelon said:
Look... torque figures will depend on what gear the car was in when it got dyno'd. Everyone thinks that power will change with gears, but this is a common misconception. Apart from different frictional losses in each gear, the power figure will stay the same plus or minus a few Kw. Two things, however, will change: Torque and wheel rpm. A gearbox is either a speed multiplier or torque multiplier. In most 5 speeds, 1st-3rd are the torque multipliers. 4th won't multiply anything (1:1) and 5th will be a speed multiplier (overdrive). Diffs are torque multipliers.
A gear ratio of 2.39:1 (1st in the falcon autos) means that the velocity ratio of input to output is 2.39:1- for every 2.39 revs of the input, output does 1 rev. This also means that at the output shaft there is 2.39 times as much torque.
Now power is a result of torque x angular velocity. If a gear halves the torque but doubles angular velocity (rpm essentially) compared to the previous one then the power figure must stay the same. Thus power figures are the same through every gear. Torque, on the other hand, will vary depending on what gear the car is in, what diff ratio and the diameter of the tyres.
The ONLY reasonable way to get an idea of torque at the flywheel is to use an engine dyno and trying to quote engine torque figures from anything else is pretty much useless and misguiding.
Sorry...don't mean to be harsh- just sick of the all the stupid hype you read in magazines.
what he said :hy: spot on... I would have written that if I could have been bothered hehe
 

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Dynos are good for tuning... Ive ran 180rwkw-160 rwkw and 150 rwkw all with the same motor just differnt dynoes and transmissions. THe 150rwkw was the tune that the car went its quickest....
Not bad power from the old 2v any hows :>
 

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Reply to Tza.

From what madmelon posted about the gearbox and diff being a torque multiplier you would probably need to know the gear ratio for 3rd gear to be accurate.

Otherwise, 726 / 3.44 = 211Nm at the output of your gearbox.

Rule of thumb for naturally aspirated 2-valve engines is approx 1 bhp and 1 lbft for every cubic inch.

2 litres = 120 cubic inches, approx 120 lbft, somewhere around 160Nm.

211 / 160 = 1.31:1 ratio for 3rd gear.

Higher revving 4-valve per cylinder engines will tend to produce a higher horsepower figure than the rule of thumb numbers because they can breathe more efficiently, and the torque peak is generally higher in the rev range.

Also, BHP = Torque x revs / 5252, so at 5252rpm, BHP = Torque (lbft).
If your engine makes 200bhp at the flywheel at 5252rpm, it must be making 200lbft at the flywheel at the same revs.
 

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Craig is spot on with the: POWER = TORQUE x (RPM / 5252)
which is the same as: TORQUE = POWER / (RPM / 5252)

where POWER = Horsepower
TORQUE = lbs/ft
RPM = RPM where maximum power is achieved.

It can all be worked out from these equations.
 
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