what is the correct gear for a power run on a dyno please. now i thought it supposed to be 4 as thats the closest 1:1 ratio but most of the sheets state 3rd gear run.

 

now with modern dynos i assume it doesnt matter as it calculate the loss through the drivetrain on the deceleration stage? im sooooo confused as i have been comparing dyno printouts on some cars and there are some interesting findings

Manual 4th gear is 1:1

Auto 3rd gear is 1:1

Manual 4th gear is 1:1

Auto 3rd gear is 1:1

 

but does it actually matter? as the dyno calculate the fly hp via the rundown after the load?

 

a lot of the cars on here being manuals are run in 3rd? my z was run in 3rd on the rr days i have been on and it seems common across the range on dyno days.

so assume it dont matter as the dyno is cleverer then we think

The power run must be done in a 1 to 1 gear or you have to apply a correction factor to calculate the horsepower figures. A dyno run in first gear will give you huge torque and horsepower figures. Do it in 5th and it will look very sad. The calculation it does on run down is a drive train loss calculation, therefore allowing you to determine flywheel horsepower

ok so say both cars are MANUAL Z32

 

car A.... was run in 4th gear (1:1)

189 hp at the wheels and calculated back to 243 at the fly

 

210 ft lbs of torque

 

car B..... was run in 3rd gear

 

193 hp at the wheels and calculated back to 240 hp at the fly

217 ft lbs of torque

car B..... was run in 3rd gear

193 hp at the wheels and calculated back to 240 hp at the fly

217 ft lbs of torque

They either took the gearbox and diff ratios into account or Car B needs a really good tune up :)

it is 4th gear that should be used on man. tr ..

Gaz, when my zed has been on the dyno at Surrey, it ws done in 3rd and 4th.

Dont know if it makes a difference, all i know is when they do it, i turn away and just listen.

As its scares the **** out of me, thinking is it going to bang..................

here is some interesting info i have found....

 

 

the reason for the dyno in the 1:1 gear ratio is due to the Dynojet. Dynojet mathematically creates a horsepower number based on mass (which is the known weight of the rollers) and accleration (how fast the car is accelerating the known weight).

 

F=ma

 

From force (F), we can calculate horsepower.

 

Dyno the car in 2nd gear, and acceleration (a) goes way up, causing force (F) to go way up.

 

So by dynoing the car in the gear closest to the 1:1 gear ratio, we eliminate any acceleration advantage or disadvantage caused by the transmission, which gives us unskewed whp numbers (even though Dynojet has a fudge factor in there which makes them skewed anyways and read high).

 

As for other dynos out there (i.e. Mustang and Dyno Dynamics) - they use a load cell to measure roll force (the amount of force the tire is placing on the roller). Based on roll force and the radius arm going to the load cell, we get roll torque. Based on roll torque and roll speed, we can get vehicle horsepower. Vehicle horsepower and vehicle RPM gives vehicle torque. It doesn't matter what gear you run in on load cell style dynos as they are measuring force, not acceleration. Force does not change from gear to gear.

im getting welkl confused there loads of conflicting info on here http://forums.nasioc.com/forums/showthread.php?t=1478091&page=2

Just to confuse things further..... does it matter which diff you are running with ?

 

I've got an NA manual box with a TT diff on a TT car What effect will the diff have to the 1:1 ratio ?

It doesn't matter what gear you run in on load cell style dynos as they are measuring force, not acceleration. Force does not change from gear to gear

. That's like saying my car should accelerate in forth gear the same as it does in first. A lower gear will alway generate more force, that's why we have gears. The only difference is, is in the way it's measured, one using force or exerted pressure, the other using acceleration.

does it matter which diff you are running with

Yes. Using a shorter ratio diff is like using a lower gear. Quite common for a TT with an NA diff to get huge figures, but they are not right. The Dyno operator needs to put the right diff ratio into his machine (usually selected with the type of vehicle)

Just to confuse things further..... does it matter which diff you are running with ?

 

I've got an NA manual box with a TT diff on a TT car What effect will the diff have to the 1:1 ratio ?

 

In your case, no difference. Na manual box is same as TT manual box (other than the bellhousing thickness).

 

The only difference between TT and NA ratios, is the rear diff.

surly when going through the gears the power produced stays the same

 

as power = torque x rpm ie in a higher gear you have less torque but you still have the same power as the rpm has increased.

 

if a dyno calculates the torque being applied to the roller and knows what rpm they are going at the it can calculate the power at the rollers. This torque must be being applied by the car.

 

basically once you know the power produced at the wheels you can then calculate the torque

 

Power in HP = (Torque in lb-ft) ´ RPM / 5253.5

 

ie it dont matter

This is true for wheel power but for flywheel the gearbox and diff ratios must be included in the calculation. One of the problems using a lower gear on a dyno is that the engine doesn't ever get to "real operating" conditions and skews the numbers somewhat. An engine can make more horsepower on a short dyno run as the cylinder temps are lower. Give it a more real world situation and the numbers become more reliable. A taller gear reduces wheel slip as well.

what i dont understand is that car A has a lower wheel hp then car B but has a higher engine hp then car B

 

surely if the gears were artificially causing an upped power figure surely the wheel hp and fly hp would be consistantly increased too?

So by dynoing the car in the gear closest to the 1:1 gear ratio, we eliminate any acceleration advantage or disadvantage caused by the transmission, which gives us unskewed whp numbers

Think you answered that earlier. A lower gear will give more drag on the dyno and may indicate a lossier transmission therefore upsetting the flywheel numbers

Usually you have to consider two things really:

1) Too low a gear and you keep getting wheel slip.

2) Too high a gear and you may exceed the dyno's max speed or the max speed of the tyres (had one explode on me - not funny!)

 

If you're using a rolling road type dyno then if its a modern one the rundown should be pretty accurate so from a results point of view it doesn't really matter.

 

What you will see which makes a mockery of the whole RWHP thing is that even with no slip if you just measure power at the wheels you get very different results for each gear due to higher frictional losses in higher gears. Its why I always quote flywheel HP, RWHP is meaningless. Had some results somewhere from an escort we did in each gear and it makes interesting reading, will see if I can dig them out.

Usually you have to consider two things really:

1) Too low a gear and you keep getting wheel slip.

2) Too high a gear and you may exceed the dyno's max speed or the max speed of the tyres (had one explode on me - not funny!)

 

If you're using a rolling road type dyno then if its a modern one the rundown should be pretty accurate so from a results point of view it doesn't really matter.

 

What you will see which makes a mockery of the whole RWHP thing is that even with no slip if you just measure power at the wheels you get very different results for each gear due to higher frictional losses in higher gears. Its why I always quote flywheel HP, RWHP is meaningless. Had some results somewhere from an escort we did in each gear and it makes interesting reading, will see if I can dig them out.

The problem there is that FWHP is still just a guess with rundown measurement as the drivetrain is not under load, and friction is increased with load. Different vehicles will react differently to varying loads.

 

If you stick to the same gear for measuring vehicles (the one that gives a 1:1 ratio, or closest) and use RWHP then you have a more reliable comparison imo.

Edited February 1, 201015 yr by Yowser

ok we are getting some good info now. the thing is every rolling road day i have been on the car has been run in 3rd!!!

 

surrrey rolling road (dyno dynamics machine)

 

triton motorsport (dyno dynamics machine)

 

read performance (sport dyno v3.3)

The problem there is that FWHP is still just a guess with rundown measurement as the drivetrain is not under load, and friction is increased with load. Different vehicles will react differently to varying loads.

 

If you stick to the same gear for measuring vehicles (the one that gives a 1:1 ratio, or closest) and use RWHP then you have a more reliable comparison imo.

 

It's under some load, all be it in the other direction (braking the rollers) but yes, friction will be increased with more load on it. The main culprit for losses is the tyres themselves rather than the transmission and the losses through them come mainly through deformation of the contact patch so not hugely affected by load. A good manual box has very little loss something in the order of 1-2% I belive for a good one.

Point is that using this method still gives figures close to the same engine run up on an engine dyno then stuck in the car.

 

RWHP falls over again with things like tyre size, tyre inflation, transmission temp. Lots of things affect it. Same car, two runs with the wheel/tyre size changed will give different results. Changing the diff on mine from visc to plate changed the RWHP byover 20bhp but obviously the actual power being produced by the engine was the same.

I'll get some figures next time I'm playing with mine on the dyno maybe do some stuff like change tyre pressures, run in different gears etc.

It's under some load, all be it in the other direction (braking the rollers) but yes, friction will be increased with more load on it. The main culprit for losses is the tyres themselves rather than the transmission and the losses through them come mainly through deformation of the contact patch so not hugely affected by load. A good manual box has very little loss something in the order of 1-2% I belive for a good one.

Point is that using this method still gives figures close to the same engine run up on an engine dyno then stuck in the car.

 

RWHP falls over again with things like tyre size, tyre inflation, transmission temp. Lots of things affect it. Same car, two runs with the wheel/tyre size changed will give different results. Changing the diff on mine from visc to plate changed the RWHP byover 20bhp but obviously the actual power being produced by the engine was the same.

I'll get some figures next time I'm playing with mine on the dyno maybe do some stuff like change tyre pressures, run in different gears etc.

that would be good john:yes:

 

i just want a good comparison between my cars output compared to another na with similar mods. the only comparison i could find gave me the figures i quoted thats why i was concerned with the gears mine being in 3rd and the other car in 4th

 

comparing my dynos tho when i first got it was (all run in 3rd)

 

210 FWHP and 187 FT LBS of torque(mods just air filter)

 

after some maintaince eg new oil,s service and cat back pipes 1 year later

216 FWHP and 189 FT LBS of torque

 

modifying it with decat pipes, st/steel tubular manifolds , chipped ecu,lightweight flywheel.

241 FWHP and 217.73 FT LBS of torque

 

im aiming for 200 whp before i consider other means of power eg nos.

 

have on the way full lightweight underdrive pulley set which will hopefully release some ponies ;)

you wont get any more power from a light weight pulley. less inertia so the engine will rev more freely though

you wont get any more power from a light weight pulley. less inertia so the engine will rev more freely though

only going from what I read from unorthodox themselves. "Unorthodox Racing pulley sets on average can provide gains of 8 to 15 HP and 6 to 10 lbs.ft. on normally aspirated engines and 10 to 18 HP and 10 to 20 lbs.ft. on forced induction engines. Higher gains can be realized on vehicles that are modified. Power gains are obtained through weight loss on all our pulleys. An average of 2.7 HP is gained from every pound lost off the crank shaft. 85% of our gains are from weight loss. In most models we introduce underdriving for additional gains. With the lighter accessory pulleys, as much as 15% to 20% more power can be found. Underdrive Series (Ultra SS) Our Underdrive Series of pulley sets provide power gains through weight loss and through the underdriving of all the accessories (which accounts for about 15% additional gain). "