dojj

iTrader: (3)

i've been comparing graphs and need either confermation or some sort of explanation as to why it isn't the way i think it is, and why petrol turbo's seem to be different

the graphs i'm comparing are for turbo dieseasals and non turbo petrols, plus a few i've seen that are turbo petrols (athough i've not seen a factory turbo petrol graph for a recent car)

the normal graphs look like you would expect, power goes up and torque comes in with peaks a lot softer
looking at the td graphs they all peaked really low down when the over boost facility kicked in and then the torque dropped away afterwards, not massivly, but a good 30% in most case and it kept dropping for the rest of the rev range, but the power graphed as normal
then my auto, which graphed the same as a td, and span the wheels (because every time he put the foot down it would drop a gear and the figures would look really peaky at the lower range and every time he lifted off it would go up a gear and the power would drop off)
obviuosly i couldn't get it powered up in first only as it would just spin the wheels, and i couldn't get it run up as a manual car

so, how "should" automatics be set up on the rollers?

how do you prevent td's overboosting very low down (as they are designed to do from the factory) and then not doing normal numbers afterwards?

not that i want to open up a can of worms here or am casting any doubts on the operators methods, i just want to know if anyone else has had experiences like these and what methods have been employed to recreate "normal" graphs

thanks

Christian and Beccy

iTrader: (14)

The only cars that we find hard to run successfully are Auto's. Unless you can lock it in a gear, the run is unlikely to be successful and accurate IMO.

Regarding the diesel thing. If you use a fast ramp rate, the dyno is likely to have trouble keeping the car in control. The boost will spike high and drop off fast. Diesels make all their torque very low down anyway and after that its a constant drop-off.

Have you got the graphs in question that you can post?

M-Tech Automotive

Agreed, I hate dynoning autos. I usually reun them up to top gear and I do explain the graph may be messy due to kick down and such, but yes, autos=pain

Diesels always produc torque low down, thats just how the engine behaves. Low down torque=increase bhp at the bottom end, a motorbike has very little torque but becuase it has it at 15k RPM it has a resonable power figure....

Matt

dojj

iTrader: (3)

they should have been posted over the weekend, let me find the thread on the other forum and i'll link it across

mine i can scan and put up

dojj

iTrader: (3)

right then, still not got the graphs but i'll get some pics as the scanners broke

can you give me a simplified explanation of what the IT's and AT's are and why them being higher/lower will affect the calculated figures

for example, mine were:
it - 10
at - 7

does this mean that the air being picked up by the engine was hotter than the air outside?

and if so, why would this be happening?

thanks

Christian and Beccy

iTrader: (14)

Dojj, AT is Ambient Temperature measured by the weather station that is communicating with the Dyno. You'll also notice RH, which is relative humidity and BP, which is Barometric Pressure.

IT is Intake Temperature. It is a temperature probe attached to the end of a fly lead. Dyno Dynamics intended it to be placed in the Air Filter of the car, so as to measure air entering the engine and thereby make a compensation to the power figure according to how hot the air going in is.

However, we and many other dyno operators have seen that this is flawed, so infact we place the sensor in the vicinity of the car. Air is processed into the engine fast enough so that a compensation here isn't really needed.

It is generally regarded that a difference between AT and IT of 10° maximum is acceptable, so your temps are nothing to worry about. Some crazy DD operators put that probe near the radiator or manifold to create a high temperature differential and a subsequent large upward power compensation.

Hope this helps!!

dojj

iTrader: (3)

got the scans so tell me what you think

one was from years ago and one was from last week

Christian and Beccy

iTrader: (14)

Dojj, in a nutshell, what is your beef with those graphs?

dojj

iTrader: (3)

i don't have any beef what so ever

i'm just trying to work out why the torque comes in early and then drops off in one and not in the other

i understand that auto's don't work in the same ways, but the graphs were doing the same thing with the td's as well as their overboosts kicked in right at the bottom and then the torque dropped off again

from what i can understand, the rollers won't be able to be set up for real road conditions unless you disable this overboost facility, which sort of deafeats the purpouse of having it on the rollers

so is there a method to coutner this?

same as when he was testing my car and put his foot down, the box would drop down a cog and spin up, and doing it in first wasn't really going to give me realistical figures as this was causing most of the spinning in the frist palce

video here